J. Phil Thien's Projects

This is an idea for a way to make a slightly modified version of retired2's top hat build so that spacers can be added under the inlet rectangle to make it into a double height (2H) version, or more, or anything in between. The only functional difference is that the baffle is a ¼" below the bottom of the inlet rectangle in the 1H situation. It also allows easy access to the baffle if you want to play with it. I have not tried to make one of these as I work mostly with hand tools these days but I have no reason to believe it will not work. I have included an improved taper lead in to the bin seal as retired2 has mentioned he would change. The top end of the threaded steel rod can take the springs that retired2 mentions. His build is here:

http://www.jpthien.com/smf/index.php?topic=563.msg3024#msg3024

This proposed build is exactly the same except:

1.   The outside diameter of the plates and rings is increased to 22 ¼"
2.    Make two "bottom plates" one in 1" MDF and the other in ¼" MDF.
3.   On the underside of the 1" plate route the groove to take the bin seal. Route the outside wall of this groove at a 45 degree angle to help guide the bin into place. Round over the inside bottom edge of this groove with a ¼" radius cutter as there is not enough meat there to use a 45 degree chamfer on this vulnerable inside edge. This is the bottom plate.
4.   Glue the baffle to the top of the bottom plate.
5.   The ¼" plate is exactly the same as the bottom plate but without a bin seal on the underside. It forms the bottom of the chamber directly under the retaining ring in place of the bottom plate as in retired2's build. Let's call this the chamber bottom.
6.   The spacers are stacked up between the bottom plate and the chamber bottom.
7.   Make spacers of any thickness and in any quantity you want. They are exactly as the bottom plate but without the bin seal.
8.   Use the vertical spacer ribs and the threaded steel rod, nuts and washers. 
9.   To make the chamber walls use polycarbonate sheet (Lexan, Makrolon) instead of acrylic (Perspex, Lucite, Plexiglass) because acrylic is notoriously brittle. Thin galvanised steel can also be used.

Please feel free to comment or propose changes or better still a wholly different solution.

Here is a sketch with apologies to retired2 whose copyright I have infringed:

Over the last few days we have had very unusual atmospheric conditions in England that have caused sand from the Sahara desert to be blown our way. Taking out the waste bins for collection this morning I noticed a fine layer of dust on my cars windscreen

This was fine sand but it got me thinking about how I dispose of the waste collected by my DC and shop vacuum cleaners. I have composted bags of it but there is only so much compost my small garden can take. I have also given a lot to a colleague who uses it as litter for his chickens; they apparently love pecking around in it. When soiled he composts it and the combination of wood and chicken droppings breaks down very fast but his garden is much larger than mine. I do not like the environmental damage caused by landfill disposal that is made worse by me putting shavings in the household waste (trash) bags. I do not know the answer perhaps it could be used in wood burning stoves or made into liquid slurry? I would like to hear ideas from other contributors.

I also thought about taking the filter off the DC and discharging outside. After seeing sand on my car that has travelled hundreds of miles from the Sahara I wonder if this is wise or responsible?  What is your view?

It occurred to me that if anyone wanted to experiment with top hat designs perhaps they could make one like this.

Make a Top Hat the same way, or as close as you can get to retired2:

http://www.jpthien.com/smf/index.php?topic=563.0

Leave the top, bottom and retaining ring plates square, instead of cutting their outside edges into circles. Fit spacers between the top plate and the retaining plate and seal them to the walls with silicone caulk. The baffle; bottom plate and the retaining plate can now be bolted together without glue and the outside edges of the plates sealed with tape.

The bottom plate can be removed at any time to get at the baffle & play with changes to the slot. You can add spacer plates between the baffle plate and the retainer plate and bolt them together again. The spacer plates can be made from different thickness's of MDF sheets and stacked up to give ¼" increases in height as tall as you like but perhaps 6" is enough as this gives a double height chamber.

You can now adjust the chamber height, slot characteristics and the distance of the bell end from the baffle. Perhaps you could measure motor amps, air flow, noise level and collection efficiency. This means the difference between the weight of input debris and the weight of debris recovered from the drop bin. Electronic kitchen scales should be sensitive enough even if the test dust has to be weighed in batches to get enough to show the difference.

There are no guarantees that we would get the same results as each other for the same test conditions but we might get some ideas.

I apologise for not trying to make one of these even though I am pretty sure they would work. I just do not have the time or resources.

If you want to make a bell mouth for the outlet pipe of a top hat you will need a template to check the shape.
The diameter of the end of an elliptical bell needs to be twice the pipe diameter and the end of the bell set into the chamber by a distance equal to the pipe diameter. This needs to be balanced against the Thien requirement to set the outlet half the pipe diameter from the baffle.

The example here is for a 5" pipe (4" pipe in brackets).

Draw a rectangle 10" wide by 5" high. (8" x 4"). Divide it in half to give two 5" (4") squares.
Label the bottom right corner "A" and the lower left corner "B".
On the top line mark each half inch and number these marks from the right 0 to 20. (0 to 16)
On the right hand vertical line, mark each quarter inch and from "A" up to the top number these 0 to 20. (0 to 16)
Connect "A" to the top left corner and "B" to the top right corner. These two lines will cross in the centre and represents the inside edge of the pipe. Mark this point with a dot.
Draw a line from "B" to 19 (15) on the right vertical. Place a ruler from "A" to 19 (15) on the top line. Mark where these cross with a dot. Repeat with "B" to 18 (14) on right vertical "A" to 18  (14) on top line and "B" to 17 (14) and "A" to 17 (14)  etc. until you have 21 (17) dots.

Connect the dots with a line faired into a curve. You now have an elliptical shape in the bottom right rectangle. Glue it to stiff card and cut it out ALONG THE INSIDE OF THE CURVE and you have a template.

Hi All,

Can someone please tell me how to smoke test my extract system to detect leaks including smoke source?

While we are looking at this would it be a good idea if we listed, including links, of all the test methods that have been used.

air flow
static pressure
amps drawn by blower
any standardised methods of testing the efficiency of collection eg dust in dust out, chips in chips out etc.

I have been using a drop can with a shop vacuum cleaner with 2 ½" plastic piping for several years with considerable success. Made from a large trash can this had a round almost tangential inlet pipe set into its side towards its top.  I fixed a plastic bucket to the lid set upside down and fixed the outlet pipe in the middle. This was to preventing debris from being sucked straight out of the can.

The shop vac was replaced by a 1.5 hp dust collector a month back and the ducting increased to 4" and considerably extended. The can scrubbed out badly which it had not done previously. To overcome this problem I have made a Thien baffle from 5/16" MDF with a 240 degree 1 1/8"wide drop slot.

To avoid having anything that would create turbulence above the baffle I have fitted two steel brackets on the underside rather than spacer pillars between the bottom of the lid and the baffle. Two of these brackets fit into slots in blocks screwed to the can wall. Another block locates and supports the 120 degree un-slotted section of the baffle. The brackets are 3"long to give good clearance under the drop slot and 1 ½" away from the slot edge.

To get the inlet air stream as free of turbulent as I can I have changed the inlet pipe for one with a rectangular section.  I made the transition by hammering the round pipe down onto a 1 1/8" wooden block till I had a rectangle 1 1/8" wide and I found this quite easy to do. I have set this into the can making sure its top edge is as close to the top as I could get it and it is about 1/8" down.

I have left the bucket in place but cut it down to the same height as the outlet tube.
I have set the baffle so that its upper surface is half the height of the inlet rectangle below the bottom of the inlet. The end of the outlet pipe is set down by half the height of the inlet pipe. By this means I have divided the space between the top and the baffle into thirds.

I have a lot more work to do to improve other parts of this system and it is early days yet but so far it looks promising. Little debris is now getting into the DCs' collecting bag and the drop can has noticeably more fine dust in it than before. It is frustrating not being able to see what is going on inside and I am looking forward to making a top hat with polycarbonate walls.

I will post a sketch and some photographs soon. Feedback gratefully accepted.