J. Phil Thien's Projects

Hi bobgroh.

You will not do much better than follow retired2's build in its entirety.

The only thing I might do is not build a 2H version. I might however build a 1 1/2 height version or more likely I would build a 1 1/4 height top hat. I would do so only because my machinery and the way I use it tends to produce long thin shavings that may catch at the end of the slot. This has been reported several times and I believe a narrow space beneath the inlet rectangle might well solve this problem.

I would also make the inlet transition from round to rectangular rather longer, something like three times the diameter of the round pipe.

I might also make the inlet rectangle height to width ratio such that the height is a little greater and the width a little less. Perhaps the width might be something like twice the width of the separator slot.

I have not much science to support my ideas but I am quite a good hunchman .  It seems to me that if the inlet stream is closer in size to the separation slot size then we might be better off. The trade off might be that the greater top hat volume might lose too much of the suck.

I hope you let us know you get on particularly if you can take some measurements.

Hi.

I cannot pick up the picture either.

The width of the slot is set to suit the material being handled. The narrower the slot the finer the material separated and the wider the slot the coarser it may be.

Clearly if you are separating wide long strips from a thicknesses then the gap needs to be wider - on the other hand if you are separating dust from a sander only then it needs to be narrower.

Note the start and end of the slot is critical straddling the inlet rectangle (pipe). So it ends just before the inlet and starts again on the other side so leaving a "platform" spanning the space under the rectangle. The leading edge of the slot needs to be tapered down so that big shavings don't catch on it.

I hope this helps and it would be good to hear how you get on.

5" tube and fittings have less resistance than 4" so are best if you use them. Its possible to buy 4 to 5" converters and they are easy enough to make. 5" pipe and fittings are also available so why degrade performance?

I am sorry to say that you are quite wrong! The medical evidence is overwhelming that fine dust particles from machining wood are extremely dangerous and not just to those of us who have an immediate allergic reaction. No the response is not immediate but a time bomb waiting to kill you many years later.

Answer enjoy hand woodworking like me or kit up with fine filters, Thien baffles and earplugs.

I would not contemplate working in a shop without some way of keeping the air free of killer dust. Given that I need a fine filter. Given that I need a cyclone or a Thien baffle to take out most of the dust so it is not always blocking the filter. If you use a planer/thickneser then it makes a lot of mess unless you use air extraction of the debris. It throws it all over the place and takes ages to clean up.

That amount of chipping and dust will fill the usual bag very fast and it is much easier to empty the bin under a Thien. These are easy to make and will not take long if you follow retired2's design. I strongly recommend you make one.

At the huge price it is sold for it will have very few takers no matter how quiet and efficient it is.

That looks to be a very good build. Congratulations.

I might have made the transition from round to rectangular four or five times longer to reduce turbulence where it enters the top hat. I might also have tried to arrange that the outlet from the fan went straight into the filter, although that might mean that the filter was horizontal and that may be more difficult to clean. Eliminating this right angle bend would have reduced the resistance to flow and increased the air throughput.

Whether these changes would make a significant difference is debatable and could only be determined by making the changes.

You have not mentioned if long shavings get caught up at the end of the slot and I would be interested to know when you have your pipework set up. What is the width of the slot by the way? Is there any possibility that you could make some measurements?

I don't actually see the Thien baffle in your photographs, or am I missing something?

If you were to provide some sketches and photographs with a more detailed description I am sure you will get answers to your problem.

With respect that somewhat misses my point that large top hat volume hits flow performance and probably isn't needed with a one and a half or even one and a quarter top hat height.

If you are using a 6" diameter pipe and the height of your top hat is 12" then I presume you have not planned to have the inlet pipe rectangular? To my mind a rectangular inlet that encourages waste to hug the wall is more critical that the outlet bell mouth to baffle distance, or have I got it wrong?

Why are we thinking a double height top hat? This is double the height of the rectangular inlet "chute". With a 6" pipe the rectangle could be 2 " x 14" or 3" x 9" or 4" x 7". This would give 28" or 18" or 14" high top hats if they are double height. The ideal is to have the fans inlet fitted to a flow straightener directly above the top hat - all in a straight line. The height of the inlet to the top hat is set by the height of the dust (trash) bin and the raising/lowering mechanism. The ideal inlet main trunk from the collection network should be straight for the greatest distance possible.

Taking these all together we see that the bin height 28" (my guess), the raising/lowering mechanism perhaps 6", top hat 28", air straightener 12", fan say 12" all adds up to 86" or 7' 2" which is just below the height of a standard room. We have yet to add anything that may be needed to get the fans outlet into the HEPA filter/collection bag system. I conclude we need to keep the top hat height down as we are starting to run out of available workshop height. This is one reason why cyclones start to get impractical in amateur workshops.

I believe we worked out that the larger the internal volume of the top hat, the greater was the pressure (or was it flow?) loss, and this needed to be kept as small as possible. This also pointed towards a shorter top hat height.

Why has there been so much attention paid to a double height? It seemed to me that we were looking at two related factors that had been observed through plastic walls. The tendency to need more than one revolution of waste circulation for it to be forced down through the slot and the way circulating waste interfered with the flow entering the top hat. Hence giving some space below the inlet rectangle overcame the problem. I also suspect that hang ups on the end of the slot on the downstream side of the inlet may be caused by its proximity to the incoming air/waste stream.  I do not know if anyone has worked out how much is needed but it seems to me that it is probably half to a third the height of the inlet rectangle.

Of course there has also been discussion of a 6" diameter outlet pipe and a 5" diameter inlet pipe that will change all these calculations.

If I have got it wrong I know you chaps will not hesitate to tell me.

Yes a lot of parallel work. For example I made a separator using a rectangular, tangential side inlet from a dustbin (trash can) about eight years ago. This worked very well when used with a shop vac but not with a DC when we bought one. Then I did a search and found out about the Thien baffle and problem solved. I have yet to make my tophat, possibly because my lash up works well enough.

Thank you. Bit above my pay grade but I will struggle through.

It occurs to me that if the inline separator can be developed to remove a significant quantity of the finer waste without wasting very much of the DC suck, then we could put one in front of a Thien top hat.

I think this may result in an overall increase in the removal of fines with the bonus of being able to increase the Thien slot width so deducing blockages there.

I am doing less and less machine work but this whole waste/dust collection theme fascinates me.

Now that is interesting! I love it when we re-discover something when we come at it from a different direction.

Are there any on line sources of information about this?