Thein Baffle for Shop Vacum

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Forum topic by BGST posted 09-27-2016 12:50 PM 503 views 0 times favorited 3 replies Add to Favorites Watch
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24 posts in 928 days

09-27-2016 12:50 PM

Hi Every one,
Not sure this is the right forum to ask this and thought anyone who checked this out might have an idea to help me out. I just built a Thein Baffle using PVC pipe fittings for the intake and out-take portions of the separator but the 2.5” hoses do not fit tightly. For the time being I used masking tape to make the hoses fit but cannot find anything that I could replace the tape with for a permanent fix. Hope some one has an idea for me. Thanks

-- Barry, Edmonton, Alberta, Canada

3 replies so far

View clin's profile


929 posts in 1143 days

#1 posted 09-27-2016 06:49 PM

First off, I think you’d get more help if you titled your thread something like “Matching shop vac hose to PVC”, the Thein baffle really has nothing to do with your question.

There seem to be a lot of slight variations in shop vac hose sizes. And there are differences in plastic pipe fittings. I suggest taking your shop vac hose (or at least the mating fitting) with you to a plumbing supply store and find what works. Don’t restrict yourself to some preconceived idea of the fitting you need. You may find your vac hose fits over the outside of a fitting meant to accept a pipe internally. Be sure to look at both PVC and ABS fittings.

Maybe your hose fits over or inside a pipe size that you can then use. Or if there is something it almost fits over, but not quite. You can sand down the diameter of the pipe or fitting. This can even be helpful to get a really good fit if you put a slight taper on it.

Still other things to look at are those rubber sleeve fittings. These have some give in them and can work to go between slightly different sizes.

Now, you mention that your existing setup doesn’t fit tightly. If it is just loose, but not large gaps, a hose clamp may do it. And it might be helpful to cut some slits in the vac hose fitting to allow it to be squeezed down.

All in all, it is a pain that shop vac fittings, even when described as being a given size, just aren’t the same. And of course, there is no reason these should match plumbing fittings. So in the end, you just have to look at what your options are and play around. It is a puzzle to be solved. But fortunately, not a very complex puzzle.

-- Clin

View Cooler's profile


299 posts in 990 days

#2 posted 09-27-2016 07:13 PM

I ran hose through a wall (sheetrock). I cut the hole and “screwed it in”, as the hose ribs were in a helix. If your is a helix, then correctly sized 1/4” thick ply should “screw in”.

-- This post is a hand-crafted natural product. Slight variations in spelling and grammar should not be viewed as flaws or defects, but rather as an integral characteristic of the creative process.

View JBrow's profile


1366 posts in 1067 days

#3 posted 09-27-2016 10:57 PM


If unable to find a suitable solution to make the transition, then an option would be to re-size the PVC pipe and make your own custom transition. This is done by heating the PVC pipe with a heat gun until it softens. Once softened, the pipe can be slipped over a die or into a mold and the PVC pipe allowed to cool. The PVC pipe will hold is new size after it is cool.

If the PVC used to build to the Thein Baffle cannot be removed, a separate 2-1/2” PVC pipe can be re-sized and married to the Thein Baffle inlet with a straight coupling and PVC glue.

Enlarging the inside diameter (ID) of PVC is easier than to shrinking its outside diameter (OD), but both can be done. The die for enlarging the ID of PVC pipe is a round plug whose walls are smooth with an outside diameter that will result in a just right fit. Multiple layers of MDF can be used for the die. The layers are glued and screwed together. Waxing the walls of the die makes releasing the PVC from the die easier. Chamfering the die makes it easier to engage and press the softened PVC onto the die. An end of a piece of PCV that is long enough to handle is heated with a heat gun until the end is uniformly softened around the perimeter. The heated PVC is worked back and forth over and onto the die until the die is fully seated inside the pipe. The pipe is allowed to cool. A stick dropped into the pipe allows a hammer to knock the die loose from the cooled PVC pipe. The most difficult part of this method is making a die to just the right size.

Compressing PVC pipe to reduce its OD can be done with a two part mold, a mating die, and some clamps. The multiple layers of MDF glued and screwed together are cut to leave a hole whose walls are then smoothed. The diameter of the hole matches the OD you want. This is then cut in half forming two part mold consisting of semi-circles. The round plug from cutting the hole in the mold is reduced in diameter to the diameter of the hole cut in the mold MINUS 2 TIMES the thickness of the PVC walls.

One half of the MDF mold is screwed to a ¾” plywood backer. Both halves of the mold and the edges of the die are waxed. The heated PVC pipe is placed over the die and between the two halves of the mold. Loosely fitting cauls or clamps are placed on the shoulders of the free half of the mold to keep it from rising off the plywood backer when the pipe clamps squeeze the PVC pipe in the mold to its new and smaller OD. After the pipe has cooled in the mold, the clamps are removed and using a stick and hammer the inner die is taped free.

The photo shows the setup for shrinking the outside diameter of PVC pipe.

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