Brushless foam cutter

I found this really interesting design on thingiverse for a foam cutter that uses a very fast reciprocating needle to cut dollar tree foam board (and probably some other things as well). The design was by dkj4linux. I took his design and modified it to fit in my DW660 mount. Attached are a couple of pictures of it so far. I still need to attach the cutting wire to the bearing on the flywheel, and balance it so that it doesn’t shake itself apart at 10,000 RPM.

Check out the design, details, and video of the cutter in action here:

Thanks dkj4linux for sharing your design - can’t wait to get mine going!

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Thanks, Karl, for starting this thread. I love your adapter… it’ll be so much simpler to add/remove to the MPCNC. You gonna put it out on Thingiverse?

I’ll definitely put it up on thingiverse once I get it all hooked up and running, just to make sure there are no problems.

Blue-cor, $tree foam board, and the cardboard box it came in… I’ve even tried Coroplast but with very limited success (it’s very tough on needles but I wasn’t turning as many RPM’s then and had to do a lot of Xacto work… maybe a multipass approach is in order?)

Something to consider… the inflation needle guide can get pretty hot when the foam cutter is run at high speed (8000-10000 rpm?) for the time it takes to cut a sheet of foam board. If it gets hot enough it will soften the guide needle “threads” in the PLA and allow the needle point to drift away from where it should be.

To be honest, I normally run with no lubrication at all on the needle or in the guide. The high-quality spring steel of the music-wire needle and the brass(?) guide needle seem suited to the task, especially at lower rpms. At any rate, I consider the needle a “consumable” as it is easily fabricated and replaced. Though I’ve not had a music-wire needle work-harden and break to date, I have had a needle guide start “wallowing” in its plastic threads. It could be that a proper lubricant would help…but everything I’ve tried so far – light machine oil, vaseline – either blackened and crusted up and/or migrated down the needle and stained the work piece. Possibly white lithium grease or other non-migrating lube might be a better choice?

A better approach IMO is to “heat sink” the guide needle and spread/lessen the heat build-up so that it doesn’t soften the PLA plastic. Two approaches I’ve considered so far…

  1. a 8mm BW tube motor mount can be mounted directly under the 5/16" hole through the foam cutter platform and the guide needle then simply mounted in the motor mount with setscrews… or better (if you have a metal lathe and suitable tiny drill bits),

  2. a 5/16" x 2" carriage bolt can be bored through its center – very similar to a 3d printer nozzle. I start with a 0.040"-0.050" hole bored through the head for a depth of 1/2" or so, then flip the bolt end-for-end and center-drill to form a conical opening, followed by a 3/16" bore through the center of the bolt, to finally meet the “nozzle” hole bored through the bolt head.

I recognize the carriage bolt approach is not something many are likely to take on but I suspect a “poor man’s approach” to accomplishing a similar result is to simply purchase a real all-metal 3d printer hot-end and enlarge the nozzle opening to 0.040" or so (~1 mm).

Here’s where I am with my current foam cutter. I’ve incorporated Karl’s foam cutter mount for HicWic’s MPCNC universal mounting system and Thurmond Moore’s MIG-tip needle guide. I used a spare flywheel, bored out to 1/4" to make a needle guide holder that allows adjustment for varying material thickness, up to the full stroke length.

Looking great, David! Very ingenious way of having an adjustable cutting depth!

I was just getting ready to modify my cutter mount to accommodate the welder bit, but now I think I’ll follow your lead and just print another flywheel.


Would it take much effort to modify the needle cutter to cut through 1" pink foam? I assume slowing it down and perhaps increasing the diameter of the wheel and just a longer needle… I could also see just using the spindle, but needle will be SO SO SO much cleaner.

I don’t know of anyone who has built one for 1" foam but it has been mentioned a time or two off-hand. I should think it pretty straight-forward as the entire cutter is a pretty simple build anyway. All my cutters so far have been used for cutting sheet foam of 1/4" or less and, with my printed flywheels and bearing offset of 6mm, the stroke is just shy of 1/2" (12mm).

You would need to offset the flywheel bearing by a bit more than 1/2" to get a full 1" cut. Balancing the flywheel might be a bit trickier but should still be doable. The needle flex would be greater so it would probably be best to increase the distance (height) between the flywheel and the needle guides to keep the flex and friction manageable. This increased distance would also require a longer needle, of course, and possibly an increase in the needle’s diameter for stiffness. With just the changes to the flywheel/offset and the cutter height, I think everything else should work fine,

After a couple of years of inactivity there’s a renewed discussion going on over in the RCGroups forum, focusing on KISS aspects of the needle cutter right now. Several rather crude but very effective cutters have been built and demo-ed – one in just the past couple of days – that demonstrate just how simply a cutter can be fashioned.

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Take a look, starting about here, for the most current discussion…

Please keep us up to date on your progress… and feel free to join in the discussion(s) going on in the FliteTest and RCGroups forums.

Good luck.

– David





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Great stuff guys! I feel like I had read about this technique a while back on the Flite Test Forum and had completely forgotten until now. I was trying to figure out what would be the best way to cut foam board for plane parts but now I might try this out instead. How do you both like this system of foam cutting compared to other methods? My main goal would be to knock out FT Plane parts so any insight would be awesome!