Thein Baffle Cyclone Separator

CNC is awesome, it makes it easy for a guy that spent more time in computer classes than woodshop to make cool things.  One thing my experience with CNC used for wood or plastic is that they create a hell of a mess.  Since I don't like cleaning up after myself on a regular basis, I will be attaching a vacuum to my CNC to clean up as it goes.
Since CNC jobs can run for quite some time and I don't want to listen to a vacuum for that whole time, I will be enclosing the vacuum in some sort of sound-deadening cabinet.  I did not want to dedicate an expensive shop vac to my CNC table, all locked up in a sound-deadening cabinet so I purchased one of these cheapies;

It's a simple topper for a five gallon bucket that turns it into a shop vac.The problem with this type of vacuum, as well as other shop vacs is the filter, they clog with all the dust and chips created from a CNC router.  The solution? A cyclone separator that dumps most of the solid material into a pre-container before it reaches the vacuum and clogs the filter. Three key factors to this build; it must be effective, it must be reasonably small to fit in the prescribed sound-deadening cabinet, it must be cheap.  Well, five gallon buckets work for vacuums, why not the separator too?  It dawned on me that I have had hell when buckets are stacked together and don't want to come apart, sounds like a formula for an airtight seal.  My separator will be made from the top of one bucket and stacked into another. The parts will consist of two five gallon buckets, a lid, a couple of 45 degree PVC connectors, a straight PVC connector, a PVC coupler, some 2x4 scrap, some screws and caulk.

My design is based on the Thien Baffle Separator, a variation of a cyclone separator that adds a baffle to reduce the possibility of reintroducing captured material back into the airflow that goes to the vacuum. I needed a smaller, cheaper version.

Let's start with the lid.  With a hole saw, cut two holes just large enough to accept the PVC fittings. The first is spot on in the middle, this will be the straight fitting that will create a return duct to the vacuum. The second will be as close to the edge as possible and will accept the 45 degree fitting, this will connect to the vacuum hose that will be run to the CNC machine.

Fit the two 45 degree PVC fittings in an "S" formation through the outer hole.  The "S" is an attempt to maintain as much velocity as possible with the solids, this is important.  The inside fitting should be angled so that items coming out will be flung along the outside of the bucket in a spiral pattern creating our cyclone action.

Next, to create the body of our separator, cut the top off of one of the buckets just longer than the depth the lower 45 degree PVC fitting will hang down.

Go ahead and cut the bottom out of the same bucket, we will be using this later.

Attach the straight PVC adapter to the coupling through the center hole in the lid. Use the caulk on the inner ring of the lid and attach it permanently with an airtight seal to the top of the bucket we cut off. attach the 2x4 blocks around the center hole with screws (sheet rock screws worked great).  You could use other material than 2x4s for the standoffs, but I feel the weight of the 2x4s adds to the stability of the separator's connection to the waste bucket.

Finally, screw the bucket bottom we cut of earlier to the 2x4s with screws.  Make sure to leave a gap around the edge, this is where our solids will fall.


Shown here is the separator leaned cockeyed on the waste bucket for clarity.  In use the separator will simply stack into the waste bucket like five gallon buckets are meant to stack.

Ready to go. It should be noted that PVC fittings are rarely a perfect match for vacuum hoses.  Always purchase slightly larger fittings and you can simply wrap duct tape a few times around the hose to make it a snug fit.  Also, depending on the buckets you chose, you may need to add a wrap or two of duct tape around the separator to make sure it has a solid fit to the waste bucket.  Some buckets fit tighter than others.

The vacuum is attached to the cyclone, the cyclone is attached to the hose, may the separation begin.

The next stop? Time to build that sound deadening cabinet.

As seen on Hackaday


  1. So do you want the 2x4 standoffs to be of a length to hold bottom of the bucket you cut out against the bottom of the S bend couplers? I'm just trying to get a feel for how long the 2x4 standoffs need to be. I'm guessing there will be more space between the cutoff lid and the coupler in the center than there will be between the S bend couplers and the cutoff lid.

    Thanks for a nice write-up.

  2. Thanks Ron. The 2x4 standoffs are just a bit longer than the coupler. The material should have a pretty clean shot from the coupler to the lower bucket. As a note, I should add that right after I published this article I had to cut a small section of the baffle (the bucket bottom attached to the 2x4s) to allow just a bit more flow where the waste material is shot down. If the baffle gets too much in the way you will notice material getting in the space above the baffle. Just snip away a bit of the baffle until you get a direct line-of-sight into the bottom coupler.

  3. How is the airflow with the separator compared to without? Is much flow/volume lost?

    1. Airflow is essentially the same as long as you don't have any leaks. Over time, your airflow with the separator will actually be higher than the same time w/o since your filter on the vacuum won't clog nearly as fast.