Hi,
After reading through a large number of threads, I feel time is right to start making one of these wonderful contraptions. In my introduction, made just a few hours ago, I mentioned that I am into composites and it is these skills that I wish to use in my construction. Unfortunately, probably due to an age thing, I cannot remember which of the many threads I have read that mentioned the possibility of a curved inlet, the idea of which was to force the particles against the outside of the inlet before entering the separator. One of the problems mentioned was the construction of such an item. Using composite techniques, this is not a problem and I have drawn up such an inlet as shown in the attached.
My question would be; does anyone know or can guess at a reasonable radius for such a curved inlet? Incidentally, I will also be making a composite bell mouth for the outlet.
A word of warning - I am not the speediest of workers so don't expect too much too soon :)
Mike
Sounds as though you probably already know how to generate an elliptical former for your bell mouth but if not see here:
http://www.jpthien.com/smf/index.php?topic=1098.0
Please let us know how you get on and measure if you can. GOOD LUCK.
Mike, you might be referring to what is called a scrolled inlet. There have been a couple of discussions about this, but I don't know if "search" can find them.
In any case, a scroll design is not just a curved inlet pipe, as I recall the design effects the shape of the separator chamber, it is no longer a true circle - it becomes eccentric. Not sure if anyone has ever really built one because it complicates the construction task. And if anyone has built one, I don't ever recall any test data to see if it improves performance.
These are all the links I could find to scroll inlets.
http://www.jpthien.com/smf/index.php?topic=492.msg2625#msg2625
http://www.jpthien.com/smf/index.php?topic=1085.msg5880#msg5880
http://www.jpthien.com/smf/index.php?topic=492.msg2920#msg2920
Bill Penz also talks about a curved inlet pipe but you will have to plough through his rather complex site here:
http://billpentz.com/woodworking/Cyclone/Index.cfm
Hi guys,
Thanks for responding.
Retired; I am pretty sure it was in one of your threads or replies that the curved entry was mentioned but I cannot find the reference. It was discussing how to ensure the particles were as close to the wall as possible on entry and it was postulated that if the flow were directed to the outside of the entry, by forcing the air to travel in an arc, this may help. I know what you mean about the scrolled inlet and this was not quite the same thing but was trying to achieve something similar.
Bernard; Yes, the elliptical bell mouth is very easy to achieve using composites but the procedure is not everybody's cup of tea. I would use male formers/plugs for making the laminates for both the bell mouth and the entry as this will give me a very smooth inner surface. I remember trying to plough through Bill Pentz' site some time ago but I will re-visit for a refresher.
It's past midnight here so that's it for today. I'll do some more CAD work tomorrow and maybe start cutting plugs/patterns soon. If no one can answer the question of radius, I will just have to suck it and see. The problem with the composite solution is that there is a little more work to do for each iteration. The beauty is that once there, you can produce as many identical pieces as you or others wish.
Cheers,
Mike
Maybe this is the discussion you were remembering:
http://www.jpthien.com/smf/index.php?topic=536.msg2813#msg2813
I believe Phil raised the issue of a curved entry and the benefits it would offer in encouraging particles to move towards the side before entering the central ring. Makes sense to me. Seems you would get some of the benefit of a scroll inlet without the complicated construction. This is also related to the issue of an off-center outlet that both Retired2 and Phil have mentioned. In the CFD thread, replies #16 and 17 show why an off-center outlet should improve separation - you are moving the outlet away from the region where particle-laden air is entering the ring and has yet to be forced to the side. Perhaps a curved inlet transition from round to rectangular, combined with an off-center outlet, would be a good combination.
Regarding the OP question of dimensions, I'm not sure about the the radius of the curve, but I would think the piece needs to mate with a 20" diameter top hat. The 32 gallon Brute has an inner diameter of 20" and is commonly used.
The image below shows a curved inlet on the left and a typical straight inlet on the right. Might as well curve it!
Mike, I would imagine, if you are thinking of retailing your round to rectangle adapter, that an outside radius would need to be similar to a 32 gallon garbage can. That seems to be what the majority of the forum top hat users use. Myself using an even smaller collection container would be interested in an adapter as you have proposed. Have any idea at this time what one might be able to purchase one for? I have some other ideas for a new Thien top hat separator and this would certainly make it easier to incorporate those ideas.
Thanks for posting!
I can confirm that a curved inlet does force the particles to the outside of the separator.
I haven't tired to photograph it, but the intersection of the particle flows looks like a "merging traffic" sign and no apparent turbulence where the flows meet.
Andy
Retired; you are correct, that was the thread I read about the idea and, Schreck, it was Phil who posed the question.
My application would be fitted to a standard, British dustbin of 460mm (18inch), internal diameter so the dimensions will not be too far away from your standard 20inch drum. I will re-draw the inlet and make sure the curve meets the wall tangentially while giving enough clearance at the circular end. I will also try and model the whole thing and post the result here for criticism.
Galerdude; I have no intention of retailing the inlets or bell mouths but am prepared to make a few as long as my costs are covered and if they are wanted/needed/prove to make a difference. However, I will not be inclined to make lots of different models for different diameters of drum or inlet. We will have to see how it goes. If I document my progress here then other folk with some composite know how could easily pick up the cudgel. Early days yet but I do need to get this thing made as I have some huge moulds to make that will create oodles of dust and chips and I don't want to start without this system in place. I will try and take some shots of my current DC to show how inefficient it is at trapping the sort of debris I am creating.
Thanks Andy for confirming this is worth continuing with. I don't recall seeing a thread where anybody has tried this. Did you document your build? If so could you give me a link to it?
Cheers,
Mike
Hi fellow Brit. You may have already considerd this but it has just occured to me that you might want to wait a short while to see if this produces some usefull results:
http://www.jpthien.com/smf/index.php?topic=1105.0
We have not had a post on this link for a while which is a pity as it looked as though the model work could be usefull if it got close to retired2's data:
By the way what make of dustbin are you going to use? Presumably you also found that the usual Brute bin costs an arm a leg here!
Regards.
Build thread:
http://www.jpthien.com/smf/index.php?topic=1085.msg5880#msg5880
I too would like to see how these variations affected the computer model,
Andy
Hi Bernard,
I have been watching that particular thread with a lot of interest but it strikes me that there are just too many wanted variables for Supertrucker to model, despite trying to tie him down to a specific model. If we now throw in a few different inlet variations, he may blow the proverbial gasket :)
I have a bin that is very similar to the American Brute and it's been in my garden for many many years and I have no idea how it got there. It has a bit of garden rubbish in it at the moment but nothing that cannot be cleaned up.
Attached are some more CAD presentations, for criticism, drawn up in lieu of the previous replies. One of them shows the projected circular, internal diameter of the bin and the proposed entry trajectory. It now has a cuff on the inlet side to accept 100mm duct.
Andy; thanks for the link.
Cheers,
Mike
Hi Mike, I had not thought to make the modelling more complex. I believe that ithat nteresting work should stick to modeling retired2's build until it gives results similar to his. THEN we can try out lots of lovely ideas. I too hope we have not put superptrucker in a bad position. I think we all got so excited with the possibilities that we may have overloaded him.
Mike,
That last picture is very similar to mine. Except your round-to-rectangle transition is more graceful.
BernardNaish: I definitely agree to get the current CFD model to where we understand it before we start making changes like eccentric shapes, chamber heights, and inlet angles.
I hope we didn't run off superptrucker........
Andy
QuoteThat last picture is very similar to mine.
Yes, not surprising really, I looked at your thread before drawing this version and took some inspiration from it :)
Bernard; I absolutely agree. The CFD analysis will be invaluable once we have an existing unit modelled precisely and can compare theory to practice. Retired's version would appear to be ideal for analysis.
Incidentally, I see references to 1H and 2H systems but am a little confused. At first I thought the H referred to the distance between the top and the baffle being the same distance as the diameter of the inlet but then I realised this cannot be the case as you cannot have a 1H version if the inlet ends in a rectangular form, where the H would then have to refer to the depth of the rectangle. So, my question is; what does the H actually refer to?
Cheers,
Mike
Hi Mike, I think retired2 coined the term. A one "D" is a Thien top hat where the top plate and the baffel are spaced by a distance equal to the height of the rectangular inlet just as in retired2's build. A 2D is twice the height of the rectangular inlet. It has been suggested that this will help separate fine dust by reducing turbulence from circulating air and debris hitting the air coming into the chamber. retired2 has suggested it may not need to be 2D but perhaps 1 1/2 D or less and I think this certainly makes sense with regard to debris because the videos show it hitting the inlet point about two thirds or three quarters down its height. Ain't this great fun. I think it brings out the creativity and the development engineer in us all. I hope one day an easily built TTH will equal or surpasse the best cyclones. Cheers B.
Hi Bernard,
Thanks for the explanation. Reading through lots of the threads would suggest that a 2H (D - not sure which) should be better than 1H and as I have the room, I may as well go at least 1.5H. It makes sense that the outlet be lower, if possible, than the inlet in order to minimise the bypass.
As promised, though I am very embarrassed, here is a shot of my DC in a sorry state. The problem I have is that the materials I am machining create an awful lot of dust, rather than chips, and this dust clogs the filter very quickly and once blocked, the dust find any nook and cranny it can escape from. With the DC being sited in the garage, the other side of a brick wall from my workshop, I don't always get to see the problem as it occurs.
I am sincerely hoping the separator will help with the bulk of the problem.
Cheers,
Mike
Yes I see what you mean Mike. I had quite a bit of very fine dust escaping from the plastic bag on my DC today. The bag seal is rubbish as many are. I sealed it up with duct tape and as I believe it will take well over a year for it to fill I can live with the need to clean off the tape glue. That is with a crude Thien separator before the fan. I also emptied my bin today and I have a natural airflow between two building that draws away the dust when I empty the bin into a plastic bag. Even then there is a lot of fine dust and this without sanders just a band saw making fine dust. With your ultra fine resin dust how do you handle this emptying? Regards, B
Actually, I think it was Phil who first used the 1D and 2D shorthand for top hat chamber heights, and I think it was in a conversation I was having with him so that might be how it got attributed to me.
I don't think the shorthand nomenclature is intended to mean strict dimensions. I think they are just approximations, but Bernard's explanation is still correct.
Now with regard to which is best, that is what I was hoping superptrucker could help us with. In fact, height was the first variation of the standard build that I suggested he simulate. I really don't have an opinion about which is best. Intuitively, it would seem like a deeper chamber would be better, but without testing with instruments we can't really be sure. In fact, someone would have to built two separators, identical except for height, and then test both.
I have been thinking the same thing retired2 and have drawn up a design that would allow extra chamber height to be added to a version of your build. Hence no need to make two and they would be identical except for the chamber height.
I keep having to remind myself that I am really a hand tool wood worker and that I want to make furniture but my fascination with innovation keeps pulling me back to this forum.
Bernard; Emptying the bag and cleaning the filter is a messy job. The bag is relatively easy - once I have shaken as much dust out of the filter as possible (whilst holding my breath) I remove the collection bag and place it upright on the floor. I then get a plastic, bin liner and place it over the collection bag and then invert the whole lot. Raising the collection bag then fills the bin liner while vacating the collection bag. This process creates no extra dust and is dead easy to do.
The biggest problem is cleaning the filter bag. Just the action of removing it from the machine creates quite a lot of fine dust. On removal, I carefully take it outside and shake it into the wheelie bin before reaching inside and turning it inside out. Once inside out it gets put in the washing machine for a quick cycle. I have found that the filter bag has lost some of its effectiveness over the years and could do with replacing but I cannot find a replacement anywhere. It appears that this particular, Rexon model is no longer available :(
With regards the height of the unit, like Bernard, I would like to make my design capable of being easily altered by simply replacing the chamber wall. We will have to wait and see if this will be as easy as it seems.
Mike
Mike,
If you know all this I will shut up. I tend to be an interfering know-all so please do not be offended.
I am deeply concerned that you may be exposing yoursel to a lot of very dangerous dust. If I understand correctly you fabricate with composites using fibres and resin. The fumes from the resins are bad enough but the dust generated by machining the resins is lethal. I suggest you should be wearing a full face respirator when machining and certainly when you empty the bag or even going into the DC room.
I will try to get a sketch and a construction method posted of a design for a top hat that can be grown in height by adding spacer rings. This has the advantage that you can play easily and the basic TH is exactly the same each time. Thus comparisons are easy and hopefully comparative measurements can be made that would be so helpfull to everyone here.
Mike,
If these people don't have the filter bag you need they will make it, and they will make it larger for better performance. Don't know about cost.
http://www.americanfabricfilter.com/facts.php
Hi Bernard, not offended at all, I appreciate your concern. The only time I am exposed to much of this dust is when I clean out the system. One of the beauties of CNC machining is that you can walk away from the machine :) Some of the programs can take up to twelve hours to run! I also have a very good, brushed hood around the spindle that does a really good job of taking all the chips away. The worst machine for dust not being extracted efficiently is my bandsaw. There was a thread here somewhere, may have been one of yours, that documented an alteration to a bandsaw to make extraction better and I may have to do something similar. Incidentally, none of the materials I machine have fibre in them and I make a point of not machining glass or carbon fibre. It's definitely a no no.
I look forward to seeing your sketch for the adjustable height version.
Retired; thanks very much for the link. I did a search for something similar in the UK and came up with a couple of hits. I will be contacting them after the May Day bank holiday,
Now a question - what, if any, difference will I see if the internal diameter of the separator is smaller than the drop box? You can see my intended drop box in the photo but it would make installation easier if the separator were 400mm (15 3/4 inches) to 425mm (16 3/4 inches) The drop box is 460mm (18 inches).
Cheers,
Mike
The fact that the separator is smaller than the drum will make no difference. However, within reason a larger diameter separator will probably perform a little better than a small one.
This may be the bandsaw modification you were referring to:
http://www.jpthien.com/smf/index.php?topic=537.msg2846#msg2846
However, the final chapter was never added to the post. After some use and testing, I finally concluded the 2" connection around the blade wasn't doing much for me other than weakening the draw on the large port that was doing most of the work. I removed the 2" pipe, covered the slot in the door with a piece of painted aluminum and it works even better.
Bernard, I must apologise. Re-reading my reply to your concerns about my health made me realise it seemed rather trite. It wasn't meant to be. Having been a teacher of Design Technology for thirty odd years before my retirement, due to my wife's ill health, I am acutely aware of the health risks of dust and airborne debris. When I retired I no longer had access to the school's workshop facilities and decided to extend my existing workshop. Right from the start of this exercise I installed ducting to all my machines and installed a decent sized extractor. It has worked very well indeed but the DC does have its shortcomings hence the desire for better separation to alleviate the need for such often cleaning of the filter bag.
I don't know if anyone on this forum machines acrylic foams but I was wondering how effective the separator is with very lightweight particles? A lot of the model aircraft work I do involves 3D profiling of foam blanks before they are put into moulds. The dust from this foam is particularly good at clogging the filter bag and if the Thien Separator can solve this little problem, my prayers will be answered. The particles are not particularly small but they are very light in weight.
Cheers,
Mike
Mike, Not trite at all. Never know if hobby workers are as aware as you. I had too many years in labs where one of my jobs was Departmental Safety Officer.
Back to the important stuff. Regarding your floating dust. I suspect that most of us here are thinking that the Thien baffle can remove a lot, if not all of the very fine dust as well as the large shavings. If this fine dust is separated then why not your tiny bits of foam? Usualy a narrower drop slot is used to remove the fine dust but I suppose your particles are relatively low density hence larger than most dust particles so the slot may need to be a little wider. How do we know. We just have to try it out.
My build (see link and photos below) uses a cheap dust bin, a cheap bucket, a length of pipe and some MDF. Ignore all the guff about brackets because I threw these out within a few days. Just wedge the baffle into the dustbin with a bit of 3/4 inch dowel so that it sits just below the rectangular inlet. In under an hour you can have an experimental lash up working. Mine worked so well that I have not bothered to change it.........yet. You can now play with slot width, slot edge profile, depth of baffle below inlet etc. My guess is that you will find a set of dims that work well. Please let us know.
http://www.jpthien.com/smf/index.php?topic=857.msg4947#msg4947
Bernard, yes, I have read your build and although I could do a quick lash-up, I fear that it would remain a 'lash-up' even if it worked only 70% effectively. As I have the wherewithal to produce a reasonably well made unit in probably just as little time as it would take me to do a 'lash-up', I am tempted to go that route. My design background tends to get in the way sometimes :)
Attached are some renderings of my proposed unit for criticism. One question I have is of the baffle. I see most baffles seem to be made from thin material, presumably to aid separation and reduce turbulence at the interface between separator and drop bin. In my design I have made the baffle and base out of 18mm MDF but have chamfered the bottom edge to minimise turbulence somewhat. I can re-do the design to make the baffle as a separate item but is this necessary?
Cheers,
Mike
Possibly the most beautiful top hat renderings ever!
The design represents the current thinking for a 1 1/2 H top hat. The recent thread on CFD raised some interesting ideas, however, and Phil's follow-up questions/thoughts pointed the way to what may prove to be a better design.
The first idea is that there is a benefit to moving the inlet away from the top of the top hat. CFD modeling showed that particles were slowed when the inlet was tight to the top, and that separation improved when the inlet was lowered slightly from the top. Phil speculated that it may be best to have the inlet closer to, but not tight to, the baffle rather than at the top. Since we want the particles to end up at the bottom, why not introduce them closer to the bottom? Air is more agile and will find its way out.
The second idea is that the outlet may perform better if it is flush with the top of the top hat. CFD modeling (with a high inlet) showed there was less pressure drop with a flush outlet. The modeling held airflow constant, but in our systems, less pressure drop means higher airflow rates and higher velocity, so separation should improve. Would lowering the inlet diminish the benefit of a flush outlet? I doubt it, but CFD could answer that question. (hint, hint)
Combining these two ideas could be the foundation for the next generation of top hats.
Aaaaargh, thanks Schreck, too many variables to play with. I desperately need to build one of these things right now. I will put the inlet and outlet wherever the consensus says, if there is such a consensus. Without knowing much about the theory, I would have thought the entry at the top would be most effective as the velocity of air entering the chamber would keep the particles against the wall. If there were 'dead' air above the inlet, would this not cause more turbulence with more chance of particles being held in the chamber longer than necessary?
I think I may keep the inlet at the top for now but it will be very easy to play around with the outlet position by simply pulling or pushing the outlet pipe lower or higher in the chamber.
Rendering CAD models does make it look good but the real test will be if the actual product looks anything like the rendered model :) It shouldn't be too far out as the CAD model is used to generate the toolpaths for the CNC mill.
Mike
"I would have thought the entry at the top would be most effective as the velocity of air entering the chamber would keep the particles against the wall. If there were 'dead' air above the inlet, would this not cause more turbulence with more chance of particles being held in the chamber longer than necessary? "
The CFD model showed particles were slowed down by the top when the inlet was tight to the top. Slower particles are more likely to be pulled into the outlet airstream. Air is probably better (more slippery) than a hard surface. Less friction means higher velocity.
I don't think there is any "dead" air in a top hat - it is all spinning around. The slowest spinning air is that which is up against a surface. At the side walls and the baffle, this helps dust to drop.
I've never tested in 2H unit with the inlet shifted LOW, towards the baffle. I've made a couple of them now and each one of them has had the inlet HIGH, towards the top. The primary reason for the 2H unit with the inlet ABOVE the outlet pipe was to prevent bypass.
In at least a couple of ways the simulations don't seem to closely follow my own observations. I do not know why.
Personally, though, I would hold the inlet towards the ceiling of the separator, rather than down low.
Mike, I agree with Phil. The computer models did not fit the observations that have been measured. I think it unwise to go along with any conclusion drawn from them. In the long run it may be that the model will show the direction we could look but it is not yet consistent with other work yet. I hope we get some more results from the model.
Hope your build goes well. Look forward to hearing your results particularly the fluffy outcome. Regards, B
Thanks for all the input guys. I will continue with the project, as is, pending any revelations within the next few days. In the end analysis, if something does come of the CFD analysis, it is not beyond the whit of man to re-design and implement any changes. Judging from all the units already made, and documented here, anything even half resembling the best practice will be far better than what I have at the moment.
I will attempt to keep this thread alive with my progress. The plugs are already drawn up for the curved inlet and I am working on the toolpaths. With any luck and a prevailing wind, I may be able to start machining the plugs this weekend.
All the best,
Mike
Quote from: phil (admin) on May 08, 2014, 12:26:50 PM
I've never tested in 2H unit with the inlet shifted LOW, towards the baffle. I've made a couple of them now and each one of them has had the inlet HIGH, towards the top. The primary reason for the 2H unit with the inlet ABOVE the outlet pipe was to prevent bypass.
In at least a couple of ways the simulations don't seem to closely follow my own observations. I do not know why.
Personally, though, I would hold the inlet towards the ceiling of the separator, rather than down low.
Phil,
Any thoughts about the drop slot with a 2H unit? It would seem the start and stop positions have less significance with the taller unit. In fact, there was an earlier question about a continuous slot that seems like a good question for 2H units. Of course that brings construction issues! Since the slot would most likely have to be bridged at two or three locations.
My first drop can had a round tangential inlet pipe and a "baffle wall" that extended down from the top plate. This worked very well but when I switched over from a shop vac to a DC the scrubbing became very bad. I think the effective drop slot width was too wide. I installed a Thien baffle and a rectangular inlet with a 1 1/2 inch width and I was back to or better than I was before. I left the "baffle wall" in place only cutting it down in height to match the outlet pipe projection that was the usual 1/2D.
It would be interesting to try this floating baffle but what of the cheese grater slicing effect (I think Phil called it that)? Such a baffle plate could be suspended by four thin steel rods from the top plate much as retired2 used to stiffen his baffle.
What if the outlet pipe had a thick wall with the difference between its outside diameter and the wall of the chamber made equal to the width of the inlet rectangle? My build with a "wall baffle" plus the Thien baffle is very similar.
Quote from: retired2 on May 09, 2014, 06:12:05 AM
Quote from: phil (admin) on May 08, 2014, 12:26:50 PM
I've never tested in 2H unit with the inlet shifted LOW, towards the baffle. I've made a couple of them now and each one of them has had the inlet HIGH, towards the top. The primary reason for the 2H unit with the inlet ABOVE the outlet pipe was to prevent bypass.
In at least a couple of ways the simulations don't seem to closely follow my own observations. I do not know why.
Personally, though, I would hold the inlet towards the ceiling of the separator, rather than down low.
Phil,
Any thoughts about the drop slot with a 2H unit? It would seem the start and stop positions have less significance with the taller unit. In fact, there was an earlier question about a continuous slot that seems like a good question for 2H units. Of course that brings construction issues! Since the slot would most likely have to be bridged at two or three locations.
A continuous drop slots turns into a problem as the bottom drum fills. When sawdust approaches the level of the baffle, a continuous slot really increases scrubbing something awful.
For a 2H unit I don't think the positioning of the baffle relative to the inlet is less important, just harder. The incoming airstream is going to bounce of the walls and ceiling of the separator and then want to dig down into the drum and if the drum is full, it is going to resuspend debris. Introducing a handful or two of bright chalk dust into a new separator should give one a good idea of where to position the baffle. Just don't do the chalk with the filters installed as it might blind them.
Phil, my proposed design is a 1.5H unit and I can see your point about the positioning of the baffle. From the inlet, in my design, there is a small shelf that gets narrower the further it goes round the wall. This continues for approximately ninety degrees. This might suggest that I move the baffle round ninety degrees as the shelf will keep most, probably not all, particles high until the shelf runs out. Does this sound reasonably logical?
Mike
QuoteIntroducing a handful or two of bright chalk dust into a new separator should give one a good idea of where to position the baffle.
Maybe you could elaborate on the positioning? Assuming that the chalk makes a spiral pattern along the wall, is it correct to say that the solid portion of the baffle (i.e., no slot) should begin where the chalk spiral intersects with the baffle? That is, should there be a 120 degree landing zone ("runway") on the baffle for the air path to take before it hits the slot.
In my mind, the alternative is that the spiraling air path would shoot straight through the baffle slot into the waste container, which would create a lot of turbulence, and stir up collected dust. Of course, my mental image of what's going on has often been in error ???, so I appreciate any clarification.
jdon, you're thinking about it correctly. If the chalk demonstrates a fan or splayed pattern, you want to align the baffle such that the debris below the baffle is protected from a sudden widening airstream above the baffle.
Another question, if I may. I read somewhere on the forum that the outlet should be 10% larger than the inlet. When I was drawing up the 'curved inlet' I assumed this meant the inlet and outlet of the inlet itself and now I am questioning my belief and am wondering whether it was the outlet, from the top of the separator that should be 10% bigger. My curved inlet, from circular to rectangular, does have the rectangular section with 10% more area that the circular end.
I am about to start machining the plugs and thought I had better check first.
Thanks, Mike
retired2 suggests that the cross sectional area of the inlet rectangle should be 10% greater than the cross sectional area of the pipe from which it morphs. This to reduce losses caused by turbulence in rectangular compared with circular ducts. So you first assumption was correct. It is not that the outlet of the chamber should be 10% larger than the inlet to the chamber.
Bernard, thanks for the verification.
I've just made a couple of small modifications to the inlet so I can make better use of the materials I have to hand for making the plugs. Getting closer to some actual construction and the 2mm polycarbonate sheet should be arriving later this week. All the toolpaths are now complete and, barring any unscheduled shopping trips, I can start machining tomorrow.
Quote from: Mike F on May 12, 2014, 12:50:44 PM
Bernard, thanks for the verification.
I've just made a couple of small modifications to the inlet so I can make better use of the materials I have to hand for making the plugs. Getting closer to some actual construction and the 2mm polycarbonate sheet should be arriving later this week. All the toolpaths are now complete and, barring any unscheduled shopping trips, I can start machining tomorrow.
Mike,
Bernard is correct, I suggested making the rectangular end of the round to rectangular transition 10% larger. However, let me qualify that statement. The HVAC industry is the source of that recommendation. Whether it is applicable here or not is uncertain, but my thoughts are it can do no harm.
Thanks Retired, that gives me the go ahead to start machining tomorrow ;D Really looking forward to seeing how it performs in my system.
Having just finished a (non-curved) round to rectangular fiberless inlet using the lost foam method, I'll be very curious to see how you construct yours.
L
Latham; As I have access to a CNC milling/routing machine that I made some time ago, making a curved inlet was always going to be relatively easy. The way I have decided to make it was to do a male mould or plug so that the internal walls of the inlet would be smooth. This means I have to make the inlet in two halves and then join them - no big deal when working with composites. I have just finished machining the plugs and have attached photos. These had to be made in two pieces each as the overall depth was greater than my machine could cope with. The photos show one half already glued together and the other still in two pieces. They are also posed in their finished state to give an impression of the size. This is designed for 100mm ducting.
Cheers,
Mike
Mike:
Good grief, you set a high bar. Makes my mold plug look like a baling wire/duct tape contraption. :'(
Please keep posting.
L
QuoteGood grief, you set a high bar.
Yes, unfortunately, I am a bit anal when it comes to making things but, I have always said that it takes very little extra time to do things accurately than to do a half hearted attempt. As I have said previously, if I was to make a lash-up I would never get round to making a proper job - unlike many on this forum. Before I get flamed, I must also add that I am in admiration of those people who can assemble working models very quickly, by whatever means and, if it were not for people like that and this forum, I would have no starting point and nothing would ever get built. In the end, we all work slightly differently and as long as everyone contributes, the end result and the progress will be so much better and quicker.
Now we need to see some photos of your finished build. My thoughts were with you when you were dissolving the foam with the acetone. I have made plenty of things that way and it can be soooo messy with liquid styrene everywhere and if you let the solution dry, it takes some getting rid of - makes a pretty good varnish though :)
Cheers,
Mike
Mike:
Dissolving the foam wasn't too big of a mess. I screwed a piece of plywood to the dowel. Set the whole thinig on the same large garbage bag I'd used to cover the lathe. I was a bit concerened the goo would disolve the garbage bag but it didn't. At least when you dissolve the foam, you don't end up with much mass.
I'll certainly upload build photos when I've got them. There's another project or two stacked in front of this top hat.
L
Bit of an update - no fibreglass laid up yet but the plugs are now lacquered, rubbed down, polished and have the release agent on them. Just need to add the false base and ends before the glassing starts. I have also managed to machine the MDF top, bottom and entry mount, get those lacquered and rubbed down and also laser cut the polycarbonate to the right shape. Attached is a photo of the almost completed body of the separator.
Still have to make the small floor for the inlet air where the two radii meet and do the machining for the bell mouth. After the reminder about the air straighteners, I also need to fabricate those.
Shouldn't be too long now before I can give it a whirl, so to speak :)
Mike
Some more progress. Managed to get the plugs laid up last night and released this afternoon. I am very pleased with the outcome and the two shells just need trimming before joining them. They have a pretty good finish on the inside so shouldn't trip up the air flow too much.
The polycarbonate is giving me a bit of a headache where the two ends are joined. I think I have a solution and will post here if it works out okay. I am glad I went with the recommendation of using polycarbonate as I know for sure that had I used acrylic, it would not have withstood the abuse this has already taken!
Cheers,
Mike
Great looking pieces.
I'm wonderng how you got the cloth to lay on your plugs. It doesn't look like they were vacuum bagged. Did you use a mat cloth?
Thanks,
L
p.s. I've got my seperator up and running. It works great. I need to put a coat of poly on the outside and then I'll post a pic or two on a new thread.
Hi Latham; No, they weren't vac bagged though I had considered it. The glass was laid on in just one piece, although there were three layers. The plugs were first gel coated and left to go tacky before the first, thin, 50g cloth was applied. The second layer was one of 600g glass cloth and the final layer was one of 75g glass cloth. The secret of getting the glass around compound curves is to use twill weave. A standard, plain weave cloth just would never go round the complex shape but the twill weave allows the warp and weft to move and the material can be coaxed and persuaded round relatively easily. All three layers of glass were applied in one operation with the flanges having an extra layer of 600g to beef them up.
I am hoping to get the flanges trimmed and the two shells joined this evening - all being well. I have just drawn up the bell mouth plug and am currently doing the toolpaths. I have decided that the bell mouth will be easier to manufacture by glassing it straight onto the ducting. The plug will be made to accept the duct then the plug and the end of the ducting will be glassed over. I'll post some pictures of the procedure.
Mike
Interesting, I'v never used a twill weave fabric. Had to Google it. I bias cut some strips to lay over my 90ยบ edges and still struggled with that.
Thanks,
L
Yes, twill is great for going round compound curves.
Didn't get the shells joined this evening but got the outlet plug made instead :) Still have to rub it down and lacquer it before laying it up but, it's another job out of the way.
Wow, some of these builds are way over the top!
Love watching the progress.
Quote from: phil (admin) on May 27, 2014, 06:39:30 AM
Wow, some of these builds are way over the top!
Love watching the progress.
Wait till I get my 3D printer!!
Quote from: retired2 on May 27, 2014, 04:31:47 PM
Quote from: phil (admin) on May 27, 2014, 06:39:30 AM
Wow, some of these builds are way over the top!
Love watching the progress.
Wait till I get my 3D printer!!
Says the guy that started the insanity!
Quote from: phil (admin) on May 27, 2014, 06:40:09 PM
Quote from: retired2 on May 27, 2014, 04:31:47 PM
Quote from: phil (admin) on May 27, 2014, 06:39:30 AM
Wow, some of these builds are way over the top!
Love watching the progress.
Wait till I get my 3D printer!!
Says the guy that started the insanity!
Thanks for the compliment, but I think we would have to go back a little farther in this evolution to find the winner of that award! :)
I don't know who started it but all I can say is thank goodness the development was done by a guy savvy enough to put this forum together so that others may learn and help the development - thanks Phil.
Quotesome of these builds are way over the top!
I don't know about that, it's just the way I happen to work and know. You guys like manipulating wood, I like making moulds and plugs. In the end, both methods get the job done.
Retired2; I like your comment about the 3D printer because it so happens I have one on the way!
Bell mouth is now laid up - just waiting for the resin to cure before attaching the duct.
Mike
Quote from: Mike F on May 28, 2014, 08:55:23 AM
Retired2; I like your comment about the 3D printer because it so happens I have one on the way!
I've thought a 3D printer may be a good way to make a tangential inlet that would fit standard 30 and 55-gallon drums. I just wonder how long it may take one to be printed, and what kind of cost would be involved if we did develop some models that people could download and provide to a friend/business w/ a 3D printer.
Any idea? Just for the sake of argument, take some of the curved inlets in this thread, how long do you guys think it would take to print something that size, and what kind of materials cost would you expect?
Hi Phil; a 3D printer would be perfectly capable of printing the inlet, provided there was enough build height. The only problem might be the surface finish. If you take a look on any of the 3D forums you can see examples of builds and, dependent on layer thickness, the finished article always has a corrugated surface texture. Some people have devised ways of post processing the parts by dipping them in acetone, or appropriate solvent, to give a better surface finish. I would imagine that the inlet really needs to be as smooth as possible on the inner surface. Finer finishes are achievable by using smaller layer heights. The standard layer height appears to be around 0.2mm but 0.05 is doable though this would take four times longer to manufacture!
Material costs are around 28 dollars per kilo. My finished, glass inlet weighs 330g and is heavier than an equivalent plastic one would be. I reckon 250g should be doable which would make the costs around 7 dollars per inlet. Time to print? - not a clue at present but I dare say a question on one of the forums may well get an answer.
Thanks for the details, Mike. I might sign-up at one of the forums and do some more research.
There was also a local craigslist posting for a printer building camp. Here:
http://milwaukee.craigslist.org/tls/4483878715.html
I thought it looked pretty interesting but didn't follow-up because I'm out of time.
Beware!!!! It can become addictive, especially if you are into new technologies. I am a member of this forumhttps://groups.google.com/forum/#!forum/deltabot (https://groups.google.com/forum/#!forum/deltabot) as the printer I am getting is called a Delta printer because of the way it works and this is the actual printer I have ordered via KickStarter though the production machine differs quite a bit from that in the video. https://www.kickstarter.com/projects/ttstam/openbeam-kossel-pro-a-new-type-of-3d-printer (https://www.kickstarter.com/projects/ttstam/openbeam-kossel-pro-a-new-type-of-3d-printer)
Nearly there and it's only taken one month! That's extremely good - for me.
Just have to use some silicone sealant to prevent leaks and I can soon be testing. Before I apply the silicone, I would like some feedback on the positioning of the baffle. In one of the 'Assembled' photos you can see the current position where I have placed the start of the shelf at the end of the inlet, tapered floor (where the two bits of polycarbonate meet). I have made the assumption that the air will still be travelling more or less parallel with the inlet, at this point, and will not have started to fall appreciably.
It will not be too big a job to remove the baffle and rotate it if necessary although this would mean breaking the silicone seal and re-applying it. I will go with whatever the consensus is, if there is one :)
Mike
Edit: Just remembered - I have to add the straighteners too.
Given the height of the inlet above the baffle, the current relationship between inlet and baffle shown in your fourth picture may already be about spot-on.
OK, that's good enough for me - thanks Phil.
I'll now get everything sealed up and see how it performs. Just about to laser cut the straighteners and get them installed too. Not yet sure if I have enough ducting and flexible tubing to complete the installation but if I have, I may just get it up and running tomorrow. Unfortunately, with all the machining of the plugs, I will have to dismantle and clean my filter bag again :( What a pain - still, hopefully, it may be the last time for quite some time :)
Mike
OK, initial testing has been a little disappointing :( I managed to rig the separator up enough to do some testing without being connected to my machine ducting i.e. the inlet was not connected to anything. I had removed the filter and collection bags from my DC and ensured everything was clean. Without fitting the bags to the DC, I started the extractor to see what kind of suction I was getting at the inlet. All was good, it seemed to be as good as I ever had before. I then threw some larger dust particles (very small chips) into the inlet and watched them rotate and drop obediently into the bin - so far so good and I was getting quite excited.
I then tried a cupful of the finer dust my machine produces and was horrified to see quite a lot dispelled through the DC. Watching as it entered the chamber, I noticed that once the air dropped below the entry level, the speed dropped off dramatically and the dust made its way easily to the outlet without getting anywhere near the drop slot.
This is a 1.5H design and I am wondering whether a 1H would be better in that the air is constantly re-accelerated each time it passes the inlet. Failing that, in order to keep the air velocity up and the particles attached to the wall, maybe a tapered wall, below the inlet would be needed. Is this why the cyclone type separators are tapered? An alternative may be to add a shelf, at the inlet height and to raise the outlet to just above this height. At the moment, the outlet is about 50mm from the baffle, well into the slower air region.
One positive was that the bin liner does not get sucked up toward the baffle. My liner does not have a cage but is an excellent fit over the rim of the bin. (See photo) The baffle is also an excellent fit in the top of the bin, consequently no air can get between the bin and the liner and hence it stays in place.
I have now cleaned and washed my filter bag so the next lot of testing will have the bags attached and I will try raising the outlet before thinking about attaching an internal shelf. Any thoughts would be appreciated.
Mike
What a shame that such a beautiful build isn't working. :(
A couple of thoughts that come to mind, having pored over recent threads on this site:
Phil commented in one thread that for heights over 1H, the orientation of the drop slot might need to be changed vis-a-vis the intake port- he suggested the chalk method to trace the path.
Also, can you adjust the height of the bell mouth over the baffle- maybe lowering it a bit would reduce pass through.
Just thoughts from a newbie (in the process of building my own).
I think raising the outlet & bellmouth should be your next move. The velocity at the outlet is high, so you don't want that so close to the baffle where dust has slowed down.
What do you have to lose? Nice work, BTW.
Jdon; I don't think the drop slot is too far out and you will have noticed that I have indeed changed the start position of the slot after Phil's suggestion. The height of the outlet is very easy to change and, I believe it needs to go higher, not lower. The testing was done at 50mm from the baffle which, I think, was Retired2's recommendation at 1/2D. However as my design is 1.5H, and the air below the inlet is moving much slower, I think it may be better positioned at 50mm above the bottom of the inlet. This will be my next move.
Schreck; thanks for the compliment - yes, moving the outlet up is going to be the easiest thing to try next.
The chalk test would be good if only I knew where to get hold of some :)
Mike
Mike-
Thanks for the clarifications- I'm always learning more from this site.
BTW, I don't know what type of chalk Phil has used, but I'm planning on using snap line chalk- it seems to be ground pretty fine, and dirt cheap.
Regards, John
Just a reminder, filters need to come off when chalk comes out. The chalk will blind a filter faster than any other material I've used.
Flexible ducting arrived today so I managed to get a test installation set up. I am feeling much happier now I have done a little more testing. I have made a short video but don't know if I can embed a YouTube video in this forum so I'll just post this link for now https://www.youtube.com/watch?v=uHVHt42zfjs (https://www.youtube.com/watch?v=uHVHt42zfjs) and hope it works. The test was done by dipping the inlet, flexible duct into a container of dust and chips collected from previous machinings. Not very scientific but useful.
I raised the outlet to approximately 50mm above the bottom of the inlet and it appears most of the finer dust is now able to fall through the drop slot. However, I did notice that quite a bit of the finer dust remains suspended at the top of the separator, circulating indefinitely until the DC is turned off. As they were very fine particles I was unable to see what then happened to them as I neither saw them fall through the slot or get drawn into the outlet. There is a trace of fine dust in the outlet, flexible duct.
What a relief that such a good looking build is working well, but what kind of wood are you working with that leaves light blue sawdust? ???
Jdon; if you look closely you will see blue, yellow and shiny silver bits :)
If you have read through the whole thread, you will realise I machine a lot of moulds and plugs for model aircraft. Most are made from epoxy board which is basically a huge block of epoxy resin that is filled with some kind of filler. I suspect it is talcum but the manufacturer will not tell me as the composition is a trade secret ??? Sometimes I will machine aluminium hence the shiny bits. It is the blue and yellow epoxy board that is giving me problems with the dust clogging the DC filter bag after just a couple of hours machining. I have some loooong, fifteen plus hours machining jobs coming up for a large scale model I am building and I needed a solution. Hopefully the separator will be the answer.
I made my CNC machine some years ago and, if you really want to send yourself to sleep, there is a very long thread on my build on the CNCZone forum http://www.cnczone.com/forums/cnc-wood-router-project-log/6840-sure-im-ready-ive-started-building.html (http://www.cnczone.com/forums/cnc-wood-router-project-log/6840-sure-im-ready-ive-started-building.html)
Phil; looking at the video, do you think the baffle could be rotated further from the inlet as the dust appears to be hitting the baffle just at the end of landing area rather than at the start? I'm not sure if the landing area is supposed to collect the dust, as it drops out, or whether the dust should be falling directly into the slot. If it is the latter, then maybe I should move the landing area back, toward the inlet.
I think if you rotate it any further you might run the risk of scrubbing once the drum starts to fill. Right now you see the incoming airstream spread out and push the debris hard against the baffle. If the slot were where, the airstream would spread right into the drum and possible suspend debris that had already been separated.
I say let it fill and watch it for a while, don't make any changes yet.
Thanks, Phil - I look forward to getting down to some serious machining and I will report back when I have a few hours completed, hopefully without having to clean the filter bag. Thanks again for the forum and the advice held here.
Mike
Time for an update with a few photos. I apologise for the quality of imagery but photography is not one of my skills.
I have done quite a bit of machining since the last message and in that time the DC has not been over taxed in terms of filter bag clogging. With the amount of machining I have done I would expect to have to clean the bag by now so, this is a big plus. However, there is a lot of the fine dust still getting through as can be seen by the evidence of dust in the outlet duct and the amount collected in the DC bag.
Also of interest is the track of dust left on the baffle. Does this indicate the drop slot is in the wrong place?
The other photo is of the dust that has collected on the outlet, above the bellmouth and a small trace of dust clinging to the top of the separator.
I am at a bit of a loss as to what to change, if anything, as the initial tests showed that a low set bellmouth allowed a lot of dust into the outlet. The thought then was to raise the outlet to near the top of the separator but the photos would suggest there is a lot of fine dust up there too. Any suggestions would be welcome.
Although it is not perfect, it is a lot better than I had before and is a great addition to my workshop - thanks again Phil and Retired.
Mike
It seems to me that the bell mouth is encouraging the air in a bigger diameter that may be dusty. I know that retired2 has tested it for CFM efficiency but I like to see a test for fine dust efficiency. And Bill Pentz does not have a bell mouth or an air straightener. Food for thought.
really like your build.
Ducky911 thanks for your reply - I think you may be right that the bellmouth is collecting the exit flow from a larger diameter than a straight outlet would. This will be pretty easy to test although I have no way of measuring its efficacy. I suppose we are hoping that the turbulent air, around the inlet of the outlet, will be of a smaller diameter than the bellmouth and therefore not encourage so much of the fine dust to enter? It may then make more sense for the outlet to be closer to the top of the chamber.
Thanks for the compliment on the build - despite its defficiencies it is still a very worthwhile addition to the workshop.
Mike
Quote from: ducky911 on July 21, 2014, 06:05:29 PM
It seems to me that the bell mouth is encouraging the air in a bigger diameter that may be dusty.
Good point. We have been using the bell mouth shapes that are available in the marketplace, but they may not be the best shapes for our application.