Tophat Thien Baffle How To

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Forum topic by atlas posted 02-01-2016 09:45 PM 813 views 7 times favorited 4 replies Add to Favorites Watch
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4 posts in 538 days

02-01-2016 09:45 PM

I wanted to build a top hat thien baffle, and had a hard time finding a single place with clear instructions, so i am hoping to develop that here. I do not intend to over explain (example – i will say fasten boards together vs. drill holes, drill countersink hole, apply glue, then screw) with the belief that if you are on this page you can put the details together yourself. DISCLAIMER: I am pretty new to woodworking, so i am certain to call something by the wrong name or you may know an easier way to do something (if so, please post in comments) but this is how I did it. It will help if you have a rough idea of how the baffles work and how most of them look – youtube is a great reference. Ghostes has a series of 5 videos that is very helpful and served as a base for my design.

-Two 2’x2’ pieces of flat, 0.75” plywood. I bought baltic birch at lowes for 10$ a piece; i had intended to buy one sheet of pine but everything they had in stock looked like a potato chip, and i had concerns that wavy plywood would not seal to a garbage can.

-one garbage can – i bought the lowe’s brand 32 gallon for half price of the rubbermaid brute. One thing i would consider if i were to do it again would be the metal can because it is perfectly round. NONE of the plastic ones were – this caused some small problems when routing the bottom of the baffle to accept the trash can but nothing major. Routing the bottom of the baffle may be unnecessary – i have heard of people using pipe foam insulation and their DC sucking the top hat onto the trash can creating an air tight seal.

-lexan (or clear plastic material) – 6” x 68”. Clear because what good is a dust tornado in your shop if you can’t see it. I bought a sheet 24” x 48” and joined two pieces together (see details below) to achieve the 68”

-three 3/8×8” hex headed bolts with two washers and one nut each
-an inlet to attach ducting to (i purchased from woodcraft for $6 or so)
-an outlet (i used metal ductwork – you could use PVC, a fitting, depends on how you plan to connect the baffle to your DC)
- caulk

- router with 0.75” bit and 1/8” bit. NOTE: the only 1/8” bit i found had a 0.25” shank, so your router will have to accept this size. roundover and chamfer bits
- circle cutting jig. I made my own by removing base plate from router and attaching router to a scrap piece of wood and used a nail as center pin on which the router rotated.
-rotozip (or dremel) with circle cutting guide for smaller circle for outlet
-plastic cutting knife (next to lexan at lowes)

The most difficult part about this is getting started. You will need to spend some time sketching out all your cuts, dados, etc before you ever turn on the first piece of equipment. Mistakes are much easier to fix with an eraser. Plus you don’t want to be almost finished and realize that two cuts foul out so you have to throw your work piece away and start over. So step one is to lay everything out (NOTE – as i am writing this, it is confusing even to me. For most of you, just look at my picture and make that):

-take one piece of 2×2 plywood to use as your baffle (bottom) of the tophat. Locate the center of your baffle WHICH IS NOT THE CENTER OF THE PLYWOOD. You will want the intake to be on the far left hand side of the plywood to allow the max length of intake. to achieve this your 22” circle (see below) will need to be 0.5” from left edge of plywood, and 0.5” from the rear of the plywood. So for me, with a 22” +/- trash can lid, i measured over 11.5” from left side of plywood and 11.5” from back of plywood and made my center point to be used as reference for baffle.

draw onto the plywood a circle 22” in diameter from center point above, then a second circle 21.25” in diameter. This circle represents the dado you will cut in the bottom of the baffle to accept the top of the trash can. Note the inside circle represents the inside of the trash can.

come off your center point 90 degrees to the left and mark this point on the 21.25” circle. Draw a straight line from this point to the bottom of the plywood. This represents your intake. make a second line over 0.75” to the outside of the baffle and make a line that connects to the 22” circle. this represents roughly where your 0.75” plywood intake will sit.

Using the inside intake line as a reference, mark a second line over 4” +/- from the outside of the plywood to the 21.25” circle mark. I used the intake fitting that i purchased, layed it on top of the outside line (because it fastens into that plywood), and made my mark for the second piece of intake plywood. move inside 0.75” and make a second line to represent your plywood.

This all sounds confusing until you look at my attached pictures, and then i think it will make more sense.

Erase the 22” and 21.25” circle between your inside intake reference lines. This shows where your dust will enter the baffle.

From your center point, make a circle 21 1/8” in diameter. Draw a second circle 21” in diameter. (this is where your lexan will be). erase the circle where it fouls out with intake. Draw a straight line 1/8” off of the inside piece of plywood. In other words, your lexan will start at the intake on the left hand side (outside) of the baffle and continue around all the way until the point where the intake is. the lexan should sit about 1/8” inside of the trash can.

From the center point, draw a circle 21 7/8” in diameter (1/8” inside of lexan), and a second circle 20 3/4”. From your right hand side of the intake, erase 120 degrees of the circle (leaving 240 degrees for you auburn graduates). this 1 1/8” circle will be removed for your dust to fall into the trash can. NOTE – i used a speed square from my center point to find the 120 degrees.

Again, i cannot overstate look at my picture and it will start to make sense.

Now you are ready to do the work on the baffle:

flip the plywood over. From the center point rout a circle 0.75” x 22” outside diameter x 0.25” depth. this should fit snugly over your trash can. As mentioned above, i had to make a portion of my circle 22.75” because my trash can was not perfectly round. If you have to do the same, be sure to do this ON THE PORTION OF THE BAFFLE WHERE THE SLOT IS NOT. you have more strength on the intake side.

Flip plywood back over. From the point where your intake lexan (straight piece) meets the curved lexan, rout a circle 1/8” x 21 1/8” outside diameter x 0.25” depth. this circle will stop at your right intake piece at the inside corner of plywood (so you can later seal the lexan to this plywood. using a straight edge, continue the 1/8” dado from your starting point to the bottom of the plywood.

To cut the 1 1/8” slot, position your router bit at the starting point. transfer a pencil line from the edge of the circle guide onto the work piece and label “start”. now move the circle guide over to the end of your cut, and transfer line onto workpiece and label “stop” this will help you know where to stop and start your cuts. Using a 0.75” router bit, remove material from the 1 1/8” slot. note that you will have to reposition router to do this. You will have to make 2-3 passes at 0.25” depth each time.

there should now be 1/8” between your slot and your dado for lexan. Using a chamfer bit, reduce this dimension to 1/16”. DO NOT GET INTO THE LEXAN DADO. This eliminates a shelf for dust to sit on, and will fall cleanly into your trash can.

AESTHETICS ONLY: Using circle cutting guide and router, i trimmed corners off of baffle, making sure to leave room for hex bolts and support blocks (covered later). I rounded over all edges top and bottom other than the intake.

Mark holes for bolt locations at the top left, top right, and bottom right of baffle (bottom left will be fastened with intake plywood). lay the bottom baffle on top of the top 2’x2’ piece of plywood, and drill 1/2” holes through both pieces (this is to ensure they line up when assembled)

LEXAN – total height of my tophat baffle is 7”, 5.5” inside the chamber (this was based on the best information that i could find – have seen as tall as 16”). my lexan is 6” in height – 5.5” for the chamber, and 0.25” recessed into each top and bottom piece of plywood. To cut the lexan, i purchased an inexpensive platic cutting knife. The back of this knife has a hook, and using the hook and a straight edge i cut two pieces of lexan at 6” x 48” (full length of lexan panel – will trim to fit later). I joined these together with a 5.5” x 2” piece of scrap plywood, centered on the lexan (0.25” up from top and and bottom). i predrilled holes in lexan and wood, then applied caulk to the block (to create an air tight seal) and attached first piece of lexan onto the wood. Making the joint as tight as possible, i joined the second piece. Then i placed the lexan in the 1/8” dado (i put the long piece as the second piece) and marked where the lexan came out of the intake. using a square i made sure this was a straight line, then cut off excess with plastic cutter and straight edge. NOTE: although lexan is tough, it can chip so be careful when removing from dado that you don’t break off a corner.

Next i cut a piece of 0.75” x 10” +/- plywood to serve as my left side intake. I cut a second piece to fit on the right side, cutting one end square and the other end to match the profile of the lexan circle (apprximately 35 degrees. I applied caulk to the 35 degree side, predrilled holes in lexan, and fastened lexan to plywood. Again had 0.25” of lexan above and below plywood to fit in dado.

Glue and screw longer piece of plywood onto baffle just on the outside edge of the lexan dado. As a precautionary measure, i placed a small bead of caulk inside the lexan dado to provide air tight seal. Place glue on smaller block of plywood (the one fastened to the lexan) then inserted lexan into the groove. I located the second intake plywood on my mark, clamped it, and screwed into place.

Note it is very important that you make sure that you rout your grooves in the bottom of the top piece. I made a mistake and made the two pieces mirror images – in other words i routed the top and not the bottom.

On the bottom of the second piece of 2×2 plywood, locate center hole as you did on bottom. Using this hole as a guide, route a 1/8” x 0.25” dado circle / straight line out of the intake to mirror what you did on bottom piece (using same method of drawing circle, finding intersecting point for intake, etc).

cut 3 blocks of plywood 5.5” x 1”. you will use these as spacers later when you assemble the top and bottom piece. When you tighten everything down when assembled, these spacers will insure that you do not overtighten and break the lexan.

Taking the top piece and lay it on a table bottom side up. (NOTE: it is much easier to fit the lexan into the dado on the top piece if you install it upside down like this, versus trying to put the top on top of the lexan). Fill the 1/8” lexan dado with a small bead of caulk. apply glue to the top of the intake plywood. Very carefully, fit the already assembled baffle and lexan into the top. make sure that lexan is fully seated into the dado. insert bolts through holes (through top and bottom piece) and finger tighten. insert spacers directly in front of bolts, and snug up nuts with a wrench.

apply a bead of caulk around lexan (top and bottom piece) to insure air tight seal. also apply caulk to the outside where lexan meets plywood inlet (the shorter one).

To mount my intake, i took a half inch piece of plywood and cut a +/- 4” hole in it with rotozip and circle cutting guide, then cut to fit over the mouth of the intake. i took my roundover bit and widened just a hair to make sure i did not have any foul out between the 0.5” plywood and the opening in my inlet piece. I applied caulk to mouth of inlet, at using 1” pin nails tacked the 0.5” plywood onto the tophat baffle. Then i applied caulk to the inlet piece, and installed with screws onto the half inch plywood. NOTE: my inlet piece is at the top of the inlet mouth mouth (will add photos of inlet and outlet in comments later)

I then cut a piece of four inch hole in the top piece of the tophat for outlet with rotozip, and rounded over the edge to give me a good place for a bed of caulk. I then cut a piece of 4” metal ductwork with tinsnips to 8.25”. I inserted ductwork through the top hole and left 4” above top of top piece, with 3.25” into the chamber (2” above baffle). I caulked in place and let dry.

I made all my connections and it works like a champ. I hope to re-read this later and make edits (i am sure i made mistakes) but i did want to get it out there. This is my thank you to lumberjocks community for all the help and ideas you have given me.

This project will take a good weekend, but you could do it a second time in a day. Once you have a good plan in place, it is an easy project. Shoutout to holbs and thanks for his help – a link to his design here:

4 replies so far

View fivecodys's profile


566 posts in 1057 days

#1 posted 02-01-2016 11:51 PM

Good write up. It is a lot to take in.
I would like to build one myself so I have placed this article in my ‘favorites’.
Thanks for sharing!

-- Chem, Central California

View Holbs's profile


1347 posts in 1450 days

#2 posted 02-02-2016 01:53 AM

I love Thein baffle builds :) I did the same, but went 16” tophat just as an experiment. I made mine out of MDF. Plan on doing Version 2 but with hardwood. Do you line your garbage can with anything?

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"

View atlas's profile


4 posts in 538 days

#3 posted 02-02-2016 02:37 AM

Holbs you get a shoutout at the end of my post – thanks for your help! I did not line the garbage can but plan to cut a section out and replace with scrap lean so I can see how full it is.

View Holbs's profile


1347 posts in 1450 days

#4 posted 02-02-2016 02:40 AM

oh..haha :) Just read that last part for the shout out. oh..and that’s my project! I feel silly now.

You should do a 30 second video of it running. It’s always hit & miss when it comes to height of top hat, width of chamber, height of chimney, etc. Plus… it’s relaxing watching the ‘swirl”... almost like those snow globes :)

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"

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