The Thien baffle

As I mentioned in my interview with George London, I have too many hobbies. Long-time readers of this blog know that I started a second blog, Fabulous Adventures in Casting, because I was building a backyard foundry to learn how to cast aluminum.  Starting a new job on top of everything else was too much and so I decided to put that hobby on hold for a year or so, but I’ve started up again recently. And since this is not just my MSDN-hosted work blog anymore, I’m going to gradually move that content over here and occasionally post about stuff I’m doing that does not involve C#, like casting and woodworking. (UPDATE: As promised, those posts have been integrated into this blog; see the Foundry category.)

I’ve been frustrated in the past by the amount of dust in my shop, and also by how vexing it is to deal with shop vac bags. If you don’t use a bag then the filter gets clogged and it’s a real mess to clean it. But the bags are expensive and difficult to handle when full. I did some research online and discovered[1. Or in a sense rediscovered; I first found this page back in my UW days.] Matthias Wandel’s fabulous woodworking site, where he describes how to build your own shop vac, which led me to Phil Thien’s site about his famous baffle device for separating sawdust from air without a filter. I knew I had to build one posthaste, and I had all the parts already lying around the shop. I had some scraps of 3/4 and 1/8th inch MDF hardboard; the former I cut into a 10 3/4 inch diameter circle. The latter I cut into one third of an 11 inch circle concentric with a 9 inch diameter circle. I then made a sort of grommet to hold the shop-vac hose ends. There seems to be a great variation in shop vac hose end sizes so I cut a slot in the end so that if I need to force something slightly too large into either hole I can. I then painted them with some leftover paint from another project and added a coat of finish leftover from when I had my floors redone a few year ago.

Here are the parts: (click for larger images)


The holes in the grommet are sized to fit shop vac hoses. The center hole in the large disk is slightly undersized so that the hose doesn’t go all the way into the body. The other hole in the disk is sized to fit a pipe elbow that I happened to have lying around. Here I’ve attached the disk to the lid and the pipe elbow to the disk. The hole is sized so that the elbow stays in with friction. If it were too loose I suppose I could glue it.


And then the baffle attaches to that:


And the whole thing put together looks like this:


The center hose attaches to the shop vac, which still has a bag and a filter. That produces suction in the bucket; the only place the air can come from is the other hose. That effectively creates a wind inside the top of the bucket which blows the dusty air towards the side of the bucket. Centrifugal force keeps the denser dust particles against the outside of the bucket where they fall through the gap; the baffle then prevents any air currents from lifting the dust already in the bucket back into the airstream. Only the very finest dust gets to the shop vac, which then filters it out. (I hope.)

This was a fun little project that didn’t take very long but will undoubtedly pay dividends in making it easier to collect dust in the shop. I think I might make a wheeled dolly for the bucket as well so that I can pull it around the shop by the hose.

9 thoughts on “The Thien baffle

  1. Mechanical separation of particulates using velocity would seem like a simple concept, though from a practical standpoint it would seem (literally) like what’s commonly called “rocket science” [though should perhaps more accurately be called “rocket engineering”]. I’ve sometimes wondered whether clothes dryers could use a similar principle for handling lint, though its lower density would probably make it harder to separate than sawdust.

  2. I’ve been wanting to do something like this for my power carving station. All the gadgets I’ve seen have been way too expensive or looked too hard to build. This one looks easy enough that even somebody with my meager woodworking skills can pull it off. Thanks, Eric!

    • At least here in Sweden you can find similar devices for $30 at cheap hardware stores.
      Primarily marketed for clearing ashes from the fire place.

      But building your own is of course much more fun!

  3. You may want to consider grounding protection. The static charges that can build up in plastic dust collection systems can be fatal.

    Search for “dust collection grounding”.

  4. I have read your blog on and off for as long I can remember but never knew you were into woodworking and backyard foundry! That’s just awesome.

    I am a programmer myself but just not a celebrity one 🙂 I am also a woodworker and a man of too many hobbies. My woodworking took a turn for the better the day I realized that hobby woodworking is not about tools and jigs and dust! I don’t know if you have heard of Paul Sellers. After reading his blog and watching his videos, I discovered my true path in woodworking., Now I really am proud of my woodworking efforts!

    Just a thought I wanted to share with you. YMMV of course!

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