Variable “H” Version of retired2’s Top Hat Build.

[BernardNaish]

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:

[galerdude]

Your kidding about the copyright infringement, right?

[alan m]

it should work. the only issue i forsee is sealing between the spacer rings

[BernardNaish]

galerdude. Of course I am not joking. Would I ever! Woodworkers never joke.......Do they?

Alan,

I think leaking might be a problem. My guess is that MDF plates are so consistently flat that there may be minimal leaks between them. I made the bottom plate thicker partly to keep the whole lot flat. I left in the ribs so that the threaded rods are less likely to distort the plates. The nuts would need to be tightened progressively.

It would be possible to seal the outer edges of the bottom block with a smear of silicone caulk, duct tape might also work.

Otherwise "O" rings or gaskets would have to be fitted.

[BernardNaish]

I have changed this design to make it less likely to leak. The threaded steel rods now pass through the vertical spacers. Nuts are locked onto the bottom ends of the rods and buried into the bottom plate under the baffle and secured with epoxy resin. In retired2's design there are three ribs and the remaining "corner" of the square is spaced by the inlet rectangle support structure. Rods should pass through these points and in the spaces between them giving a total of eight rods. Clearly the retaining rings cannot be clamped in place by nuts and washers where the rod passes through a rib but must be elsewhere.

These changes ensure that the clamping force is evenly spread over the clamping surfaces.

Drawing here:

[Latham]

What are you planning on using for the seal that shows in your sketch? Between the seperator and the container.

L

[BernardNaish]

The seal is usually the closed cell foam rubber used to seal doors and windows from draughts. Use the thickest you can get and not the very thin stuff. Dress it down carefully so it sits tight against the walls of the bin groove. As I said I am mostly a hand tool woodworker these days so unlikely to ever build one. Just using my design experience. Having said that my curiosity might yet get the better of me. My colleagues in our shared workshop might also insist I make one if they get wind of this site.