Still planning my tophat?

[tvman44]

I want to make a top-hat and thinking about using 3/4" plywood for the top and bottom and cutting the slot in the bottom larger (like 280 degrees and 2"wide) then putting a piece of 1/8" hardboard over the bottom and cutting the proper size slot in the hard board (240 degrees and 3/4" wide) for very fine dust from my scroll saw.  My reason for wanting to do like this is to use the 3/4" to support the 1/8" so it does not sag, I would glue the 1/8" to the 3/4".  By making the slot in the 3/4 larger than the slot in the 1/8" my thinking is I will get the support I want for the 1/8" without the thickness of the 3/4" effecting the separation (slot will only be 1/8" thick.   Also I would be able to route a slot underneath the bottom 3/4" to seal to the barrel.  Is my thinking flawed or do you'll think this should work good?  Also I plan to use Formica for the side walls since I have it already, I would use the slick top side for the inside of the wall?  8)

[jdon]

I had a similar question in a recent thread, which was addressed by retired2; see this thread: http://www.jpthien.com/smf/index.php?topic=1046.msg5639#msg5639.

Like your plan, I'm planning using a ring beneath the baffle, with a goove to seal the waste can. I thought of extending a "tongue" of the ring beneath the baffle- like yours, but with a essentially a really wide slot. Anyway, check retired2's comments. I've followed his threads, and he sounds pretty smart. Nonetheless, I might try my idea regardless. Something about fools rushing in, I guess.

Good luck with your top hat. I just need more time to get mine underway.

[Bulldog8]

It worked for me. I used a piece of sheet metal for my baffle. I didn't want to have support rods in the chamber, so I made a  "support baffle" out of 3/4" material keeping it smaller than my metal baffle and then laid my sheet metal baffle on top of it. I did put a couple of flat head screws through the sheet metal into the support baffle to ensure that it stayed where it belonged.

Realizing that there is still an amount of spinning air below the baffle, I chamfered the edge of the support baffle to mitigate any effect that the support may have. It works well in my situation, and really seems to get the fines. I don't have anything in the shop that produces large chips or stringy material. My planer and jointer have Byrd cutter heads. When I had straight knives on my planer, I would get some long strings of wood from poplar and soft maple. They were tough to get through the duct work and would cause some separation problems.

[tvman44]

Bulldog8, how wide is your slot?  I am thinking about a 3/4" wide slot.

[BradD]

Hey, TVMan. Looks like you're trying to answer the same question I had. I just went ahead and did it. I was quite happy with the results. My build may not be (probably isn't) the ultimate in fines removal, but I'm not going to complain. I have a 4 inch gap between the window/wall and the edge of my baffle plate support, with the "peninsula" falling under the 120* no-gap area. As I mentioned in my write-up, I would move that area about 30* clockwise. If you're using 3/4" ply for the base, then it would also be good to narrow the peninsula a bit, too. Take the extra meat off on the side where the duststream is about to meet the intake.

I noticed some dust buildup on the peninsula at the end of the exit slot (1.125" wide), indicating to me that the peninsula was interfering with air flow. I took a wood rasp to the end of the slot and created a downward ramp. I ass-ume this made some small performance improvement. At least now, the dust stream hits a ramp instead of a wall.

Bulldog8, how wide is your slot?  I am thinking about a 3/4" wide slot.

The brains behind this contraption seem to think a 1-1/8" slot is optimum. I don't know if that dimension is scientific or not, but I say go with it.

I get much more (subjectively) air flow than I did thru my old separator, and the dust removal is phenomenally better. I say give your ideas a try. What could go wrong?  ;D

BTW, did you find a program to read my DXF file?

Brad

[tvman44]

I found a on-line converter and converted it to .pdf.

[Bulldog8]

Bulldog8, how wide is your slot?  I am thinking about a 3/4" wide slot.

I don't remember what my slot width is, but its somewhere between 3/4"-7/8" my original tophat had a wider slot, but in this build I was trying to maximize fine separation. My planer and jointer have helical cutter heads so the chips are very fine. Back when I had a straight blade planer, I needed a wider slot to accommodate the shavings.