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published: Sunday 22 September 2019
modified: Sunday 22 September 2019
author: Hales
markup: textile

Small Thien baffle dust separator

For years I have not been able to understand how people can survive without a bandsaw and a drill press in their bedroom. Now I don’t know how people survive without a dust separation system too:

On the right is my new toy, a vacuum cleaner with a thien-baffle separator ontop. This spins out the dust without having the build complexity of traditional cyclonic separator designs.

It’s possible, but difficult, to use a vacuum cleaner directly as a dust extractor. Vacuum cleaners get clogged fast. My Noo-noo doesn’t have that problem.

The baffle itself is a single sheet of material cut into a design that looks a bit like a partly-eaten pie. In my design I used some thin ply-wood, and to seal the top of the unit I used some leftover acrylic (clear plastic, expensive!) so that I can see what is happening inside:

Dust and air enter via the hose on the top of the image. The air spins around the inside of the bucket, slowly dropping the solid materials down the partial-gap around the Thien baffle. Eventually the air makes its way to the center and flows through the exit pipe to the vacuum cleaner.

Bagless vacuum cleaners tend to have mini-cyclonic separators (of dubious efficacy) built into them. As such I thought it made a bit more sense to use a bagged vacuum cleaner as the vacuum supply (especially since the bags shouldn’t need changing too often).

Other design notes:

Experiences using it

I am now able to bandsaw MDF without dust going everywhere. MDF. You do not know how exciting this has been.

Generally: being able to use my bandsaw without a thin layer of dust coating every surface in my room has been a godsend. That and not having to worry about breathing protection.

Baffle rotation

Using a clear material for the top of the separator has been useful. Rotating the plywood baffle a bit allows you to tune the separation-performance, but accidentally operating the vacuum cleaner with the baffle in completely the wrong rotational position kicks up the contents of the bucket sucks it into the vacuum cleaner (bad).

Self-imploding bucket

If you block suction too much, or run the vacuum cleaner too high (most cheap vacuum cleaners have a power control somewhere): the bucket buckles inwards and breaks its seal to the top plate. This generates an audible noise.

During such events the ability of the device to separate dust is probably getting destroyed (as the cyclone now has to operate in a much less ideal environment), but it has not been a game-breaker.

Bandsaw adaption

My bandsaw has a port for vacuum, but it’s not perfect. It ended up sealing quite a bit around the lower door.

Some sawdust still gets carried by the blade all of the way around the machine and gets dumped back out on top of where I am cutting, but it’s a small amount. I plan to add an internal brush to try and remove it from the blade.

Cleaning & efficacy

Well above 95, probably above 99.

Inside the cardboard bag from inside the vacuum cleaner:

You can see a lot of fines have reached here. They appear somewhat wood-coloured, but this might just be the lighting.

Now for the filter after the bag and before the motor:

Eep. These are not wood coloured. I’m glad the vacuum cleaner has trapped them.

The cyclonic separator is really effective at removing large, heavy particles; and very ineffective at removing smaller ones. I presume that running a higher airflow rate (and therefore a higher cyclone speed) might improve this, as would making a bigger and more streamlined separator, but I’m still very happy with what I have here.

Build one! I wish I had made mine years earlier. Also have a look at Woodgears.ca’s article on Thien baffles, he has lots of nice photos and videos.

Clifford Heath - Thursday 5 December 2019

The visible dust isn't the dangerous stuff. It's the sub-micron stuff that doesn't disrupt light that is long-term harmful. Sometimes it sort-of shimmers in the light, but mostly it's invisible. You should exhaust your filtered air outside your room!

I built a large thickness sander (750mm wide, 2HP motor) that could take a 4mm full-width cut in pine at a fair rate. It was connected in the garage to the house ducted vacuum. Within a minute of starting it, the garage air was filled with invisible dust that made me cough for a couple of weeks. After fitting an external exhaust... no further problems.

Hales - (site author) - Friday 6 December 2019


I know that the "workshop" vacs sold at Bunnings tend not to have anything more than a single, primary filter stage; and these things shoot out a lot of dust. The household ones are supposed to have up to a certain stage of HEPA filtering, but I will have a look at mine and see if it claims anything numeric.

Exhausting out my window isn't an easy option without modifying windows or walls. This is a bedroom, not a garage.

I might have to do some experiments to try and quantify dust output from the vacuum cleaner exhaust. Chimney sweep is not a profession I am aiming for.

Clifford Heath - Friday 6 December 2019

If you have a sash window, you can raise it to fit a timber strip with an exit port. The true HEPA standard requires 99.97% efficiency at 0.3um, which is great... but the 100nm size stuff walks right through the filter, and also through your skin.

A former colleague in the IT industry was there because he had to give up his trade as a harpsichord maker. No available filtration could prevent his allergy caused by exposure to some of Australia's wonderful hardwoods (myrtle/beech, acacia, etc). Even wearing a positive pressure suit wasn't enough for him, he was so sensitised.

Be safe!

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