Jun 27 2008

Building the 5-Gallon Thien Separator for your Shop Vacuum.

Published by at 3:51 am under Dust Collection Strategies,Power Tools

Adapting the Thien Separator Baffle to a 5-gallon bucket isn’t hard, and overall; it is going to reduce a lot of the suction clogging dust that gets to the filter of any shop vac. I feel it is a worthy addition to the shop vac portion of your dust collection system, so here is what you need to know.


This may seem a little over detailed for some readers and I apologize, but there was some engineering involved regarding the measuring and layout, so I will detail my approach, and leave you to decide your own approach. You are welcome to blaze your own trail or follow mine. For my part, I am very happy I did it, and feel it can benefit anyone who is inclined to make one, so I am sharing how to with you.

I am glad you are interested in Shop Vacuum dust collection and cleaning. I am too! I have continued to pursue the improvement of dust collection and general cleaning with the Shop Vacuum. Please have a look at a recent article I’ve written about this by following this link right here.

First you will need to obtain a 5-gallon bucket, which is available from most any hardware store, and the Woodcraft Mini Dust Collection Separator Lid. (part# 143868), which is of course available from Woodcraft. Once you have those; please take not of the following critical measurements, and double check them for yourself.

The bucket will not be perfectly round, but on average, at the rim, it will be 11-1/16th in diameter, at the least if the bucket is held to nominal roundness. If you find the bucket is deformed beyond this roundness, I would reject it, and get a different one. This is easy to check with something like a telescopic pointer, or magnet, if you have one. Those handle inside measurements really well, and then simply compare them to a steel ruler or tape measure.

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Now back to the article.

The lid and baffle has to seal on the bucket lip, and side. The lid will come with open cell foam on the under side of the lid to seal the separator, and it will work to seal up the device just fine.

From the rim of the bucket, the Thien baffle will protrude down 4-3/8ths inches. I concluded this by measuring the inner dimensions of the lid, the rim ledges, and the inlet pipe protrusion, left a touch of space and added the thickness of the material, which the baffle plate is made from. With the protrusion into the bucket figured out, and the offsets molded into the lid itself, the length of the stand off dowels that connect the baffle plate to the cyclone lid can be found.

For the visual idea, I measured down 4-3/8ths inches from the top of the bucket and made a dashed mark, just to see how much space the device really protrudes. I can say that there is such a thing as a 6-gallon bucket, and it is the same as a five in every way, except taller, and is a viable capacity enhancing alternative.

To make the spacer stand offs, the dowels that connect the baffle to the lid, I selected 3/4 inch hardwood dowels and cut three of them 4-3/4 inches long. Please note, yes, I did say 4-3/4 inches long, because this compensated for the offsets in the lid. Find the center of each end of the dowel with a center finder, center punch this, and drill a 3/32nds inch holes into both ends of each dowel. I clamped the dowels in a small wooden hand screw and drilled them on the drill press approximately 1-1/4 inch deep. This hole size is the appropriate size for use with fine thread drywall screws, fine threads grip better in hardwood, and we need this to be a 1-1/4 inch screw because we are screwing into end grain, and want to elongate the area where we stress the long grain connection. When you are finished, coat these with Teak Oil and Wax

The baffle plate will be made in the same shape as the Thien design. Remember the dashed lines you drew on the bucket at 4-3/8ths inches below the rim? Grab your telescopic pointer and verify that you have a 10-7/8th inch nominal diameter at that point. I did, so that was the major diameter of my baffle circle. This dimension compensates for the taper in the sides of the bucket.


Laying out for the baffle plate is not too hard, let’s go over it. Cut a square of 1/4 inch MDF 11-7/8 inches by 11-7/8 inches on the table saw. Don’t cut it a foot, because you want to have scraps that will be 1 foot by 1 foot and 1 foot by 2 feet, as they are handier sized scraps.

Take your MDF Square and using a steel ruler, find the exact center of this and mark it for a compass radius point. Set your compass for exactly 5-7/16ths inches, set it in the radius point and mark your circle. If you do not have a compass that will swing this radius, small holes drilled on the same hole centers in scrap-anything will do.

Using a protractor, you need to mark the edges of the circle with a tick mark at 120-degree spacings, just as if it were a Mercedes Benz Logo. One at the top and eh, one around 4 O’clock, and 8 O’clock positions. Set a pencil on the radius point in the center of the circle and set your steel rule against it, and locate the opposite end of the rule on the tick marks on the circumference. Measure in 1-1/8th inch from the circumference and draw a line from there to the edge of the circumference in the 4 and 8 O’clock locations.

Reset your compass from 5-7/16ths inches to 4-5/16ths inches, replace it in the radius and position the lead at the 8 O’clock position. Draw a line from the 8 O’clock (240 degree radian) clockwise through the 12 O’clock (360 degree radian) to the 4 O’clock (120 degree radian) and stop. Mark a few “x” marks in the 240-degree area you just drew, as you will be cutting it off.

Using a band saw, or a jig saw, even a scroll saw will work if you have one, carefully and smoothly as possible cut out the baffle plate. Once you have it cut out, carefully smooth the edges with a mill file. If you have only sandpaper, hand sand with a block.

Test fit this baffle at the dotted line you marked in the bucket earlier; it should fit with close tolerance along the 120-degree portion left proud. If you like, sand this with 180 grit and coat it with Teak Oil and Wax, or wait until you are about ready for final assembly.


Now we begin the lid alterations. The lid requires a little fabrication on it, but it isn’t too drastic. However if you choose not to, the Thien baffle is not going to work effectively at all. The lid as supplied will allow the shop vac to suck most of the debris straight through the device. Baffle or no. The problem is that the 5-gallon bucket only has about 18 inches of circumference to decelerate particulate matter in the air steam before the stock lid inlet/outlet arrangement allows the vac to suck the air out. If the inlet and outlet are in line with each other, and they are, then this is not much time to gain on cleaning the waste from the air stream. We need to help buy it a little more time. This is why we need to modify the air inlet and outlet locations and add the baffle.

Turn the lid over and pull the elbow pipe loose. It is just a compression fit. Set it aside. Remover the two screws which hold the handle on the lid. The handle will not be reused, however it is leaving two vacuum leaks in the lid. The simple fix is to get a tube of Amazing Goop Adhesive from the hardware store, and glue a dime in each hole. Yes, a dime is a perfect fit. It adds value to the project too, A lid that was not worth a dime, is now worth at least two!

In the location where the handle was, there is a circular indentation in the center of the lid. Using a 2-1/2 inch diameter hole saw without a center drill, preferably chucked in your drill press, drill this center indentation out. Do not use a center drill. Once you have drilled this out, do not damage the blank that came out.

Using that mill file we used to dress the MDF earlier, clean up the edges of the plastic disc you just made and set it into the top of one of the molded-in vacuum fittings on the lid. See how it rests on the landing in there? Nice eh?

Grab the Amazing Goop, and lay a thin bead on that land, place the disc over that and press, then lay a thin bead of RTV silicone on the top side of the disc along the edge after the goop cures up enough. It will be sealed up nice.


Now that you have prepared the lid, for the new exhaust air outlet, center the Woodcraft 2-1/2 inch Router Fence Dust Extraction Fittings (part# 85O13) over the new 2-1/2 inch hole you just drilled in the lid and mark the hole locations for mounting the outlet with a sharpie marker, just the hole centers is fine. Then, using a center punch, mark them. You can choose to drill these free hand or on the DP, whichever is most convenient. Make the holes 3/16th for 10-24 hardware. De-burr the holes, test fit dry, then spread a thin coat of amazing goop to the underside of this outlet, position it and bolt in on. Set aside the lid and allow the goop to kick, the off gassing fumes during cure are not fun to breathe.


The balancing act, or assembling the baffle went something like this. Why am I detailing this? Well I fooled with it 2 hours before I was happy with the process. I want to share what I learned in hope of reducing your frustration, because, it will be an exercise in patience.


On the underside of the lid, there are two plastic runners cast into the lid, which run perpendicular to the lid as braces, and are parallel to each other on both sides of the center part where the air inlets and outlets are cast. It is best to position the dowels next to the outside surfaces of these runners. You have three dowels, so you need to balance the lid on a tripod. While positioning both the lid and the runner against the dowels, and the dowels on the baffle as best you can. What I felt was the best positioning, looks like the assembled Thien baffle photo I have supplied for study here.


The lid needs the elbow tube assembled back onto it. It is a compression fit so there is no need to glue, in fact, I would not recommend gluing it. I would position it as such so it seems to follow the radius of the bucket side a bit. Find two things about the same size and weight of block planes, (yes, even actual block planes) and have them ready. You will want to carefully set them on the lid once you have the lid up on the dowels above the baffle plate. This is because the dowels and lid will need some precision positioning and this will help stabilize things.

The measurements on mine can be different on mine than yours due to nuance differences in perception and layout. But first thing first is to position the dowels for their permanent mounting on the lid.

Refer to my photo again. See the dowel mounted next to the inlet elbow? That is dowel number one. Dowel number two is mounted at the opposite end of the same runner. The hole centers on my separator are approximately 3-5/8ths inches apart, and are not centered on the lid. They cannot be centered. Dowel number three is mounted against the back runner, and positioned so as to balance the lid. On my baffle, I found this spot to be near the corner on the vac outlet we added to the center of the lid, and on the vac inlet elbow side. When you find what feels like a solid balance for you, and this is a little tricky, carefully reach under the lid with a sharpie marker, because it shows up well, and try to circle the locations by tracing the place where the dowels meet the lid.

Ok that was fun… Right? Still with me? Hope so. Ok in the dead middle of these circles you just drew, use your center punch to mark the center on the circle and drill these for 1/8th inch and de-burr. I used drywall screws with countersink washers to mount the dowels to the lid. Go ahead and use the hardware you like, but remember if you are following these instructions, we center drilled the dowels for drywall screws.


Half done now and continuing, the next step is to position the lid over the baffle plate so as to be in the proper rotation for the air stream and the proper offset so the baffle touches the sidewall of the bucket in the wide section. Again, please refer to and study the photo. Note the position of the inlet elbow above the edge of the wide 120-degree section of the baffle. This is the position I felt would maximize the running room for the outlet, without causing decelerated turbulence in the narrow gap area of the baffle. Consider that everything you suck up has to decelerate along the wall of the bucket and fall through a 1-1/8th slot to get below the baffle. All this in 36 inches of circumference and windstorm.

That is the rotational orientation. You will want to assure that the next adjustment does not alter the rotational orientation. Now we have to tackle the offset orientation. Grab a four to six inch engineers’ square, or a square you have that is nearly equivalent. Stand it upright on the table so that the blade touches the edge of the lid in an orientation that is perpendicular to the radius of the lid and the wide 120-degree portion of the baffle plate.

Next, lay a steel ruler on the table along side the square and affirm that a 9/16ths inch offset is created from the outside edge of the outermost portion of the lid to the edge of the wide part of the baffle below. It should measure 9/16th on average along the entire arc.

How do we know this offset? The rim of the bucket is 11/32 wide. The thickness of the lip on the rim of the lid is 1/8th. The taper in the bucket, from the rim to the location 4-3/8ths inches below is 3/32nds. Add that all up you have 18/32nds of offset, or 9/16ths. Positioned as such, the baffle will touch the inside edge of the bucket circumference, exactly, with the lid on, and this is what you want for maximum efficiency. Now with a pencil, mark the dowel locations by circling them, find the center of those circles, punch and drill them for 1/8th inch diameter, de-burr, and sand the MDF baffle.

Now if you like, go ahead and apply Teak Oil and Wax to the baffle plate, if you chose to wait, or repair with the same from the de-burr and sanding, and assemble the baffle plate on the dowels.


There it is, the Thien Separator Lid for a 5 gallon bucket. this is the last time you will see it clean, and it was a lot to build in a small space, but it will be a good addition to your vac, and help develop your chops for future tougher projects.

If you wonder how this separator works out in the long haul, it has served us well. It now handles separation duties for us on a daily commercial woodworking shop basis and has for many years. We upgraded to a 7-gallon bucket, which is taller than a 5, and that seemed to help both efficiency and capacity. The separator lid remains as built. It pulls through 20 feet of hose on a daily basis. There is a seven foot connector hose between it and the Vac. We just dump it when it gets full. Our Vac pulls 130 CFM, and on some sanders, I’ve considered adding a vacuum bleed valve to help reduce suction. If you’re worried if this separator can cut it, We find that under production environment conditions, it does.

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