Newbie here... an idea for a simple foam cutter that I borrowed from "A Foam Cutting Machine by Tom McWire" (http://www.instructables.com/id/TFsc46j ... 2snUMXxQx/). I don't have a Phlatprinter but believe that the idea could be readily adapted to almost any overhead gantry machine. I've lurked in this forum for a while and gotten lots of great info and ideas but seen little or no info on perforator-type heads for CNC machines. So in the spirit of giving back...

I've built several incarnations and construction is straight-forward. It's quiet and clean, the kerf is narrow, and well-fitted tabs and slots are easily realized. I've used it to cut foam and light cardboard primarily.

For this particular machine I've used a DC motor stripped from an HP inkjet printer, a small ball-bearing mounted eccentrically on an aluminum disk pressed onto the motor shaft, a flexible length of .025" Mig wire looped around and resting in a shallow groove ground into the outer race of the ball-bearing, and the business-end stabber guided by an inflation needle with its closed tip ground off and pressed into the bottom plate. A 12v power "brick" provides sufficient RPM's to "cut" cleanly and completely at the 24 IPM my machine. The stroke is a little over 1/2 inch.

Hopefully it'll give someone some ideas. I'll be glad to answer questions if there is any interest. Attached files

 

Reverse brake isn't required here since Z-axis is fully implemented here and I can pick the whole mechanism up. On Tom McWire's foam cutter design there is no Z-azis so he has to stop the cutter in the top-most position and clear of the foam to move to the next cut position.

The particular CNC machine shown here can carry a full-sized router and has indeed cut all the MDF parts for another machine pretty much just like it... for a friend.

 

Thanks, Mark and Trish, for the kind words. The "stabber" head is indeed relatively quiet... my CNC's axis stepper motors actually "sing" louder in operation. And there is virtually no dust while cutting. A little residue is sometimes left under the foam sheet and on top of the styrofoam sheet underneath if the needle isn't dressed to a sharpish point (it instead "punches" its way through) but it is easily cleaned up. My friend's machine is actually in a spare bedroom and his wife doesn't seem to mind too much.

While things may look a bit on the fragile side it will surprise you the force at the needle's point. And if the motor is placed even more closely to the needle guide (the needle is shortened/stiffened accordingly) it will handle heavier materials (cardboard, balsa, etc.) without bending the needle. More work is needed to determine when a blunt point might be preferred to a sharp one.

I use Sketchup8 and the Phlatboyz scripts for CAD/CAM and use 1/32" for the tool diameter with 0.025" Mig wire. This seems "close enough" and usually results in fairly nice fitting foam parts. No tabs are necessary to hold finished parts in place while cutting as there are thousands of little fingers in the kerf holding things together until it comes time to punch the parts out of the sheet.

Thanks again for your comments. I think the stabber head is a great addition to your tool box if you're into profile foamies. I'm anxious to see what you guys can do with it... especially when it comes to handling fold lines, etc.

Regards,

David Johnson, aka "dkj4linux"

 

Here are a few more pictures that highlight the stabber head's simplicity and performance. The first stabber I made simply used a discarded computer CPU fan. Ugly though it was, I simply clamped it into place on the Z-axis mount and it was highly effective, cutting "miles" of foam kerf for this plane and numerous others before it finally bit the dust. The plane parts shown here are straight out of the sheet and illustrate the clean sharp edges/corners that are formed by the thin needle. Also note that the foam is only moved/displaced by the needle... not removed... therefore little or no loose dust/debris is generated.

I also want to recognize "jnida63" for his "Small Raptor with Sharpie files" post of some time ago in this forum. The F22 in most of these pictures is based on his design and is now a part of a small "fleet" of planes that I and a friend have been developing over the past year or so. Attached files

 

Speedwise, Mark, my CNC machine is very modest (24ipm) and the stabber head has no trouble keeping up at that speed. I can vary the speed of my DC motor by varying the voltage I apply but 12 volts suffices for my current setup. Exactly how fast the needle and eccentric can be driven I haven't investigated but I am sure it is capable of quite a bit more than what I am needing right now. With variable speed and higher RPM motors (I'm intrigued by the potential of RC brushless motor drive in this application) the speed limitations of this type of mechanism will be quickly determined.

The wire needle is a slightly sloppy fit in the needle guide. It settles naturally into a "groove" and maintains that as long as it can keep up. If the feed is only slightly too fast the needle may trail slightly in the cut but neatly straightens up with a change of direction or stopping point. Going much too fast and the needle visibly drags until it eventually bends.

Assuming adequate "stabs/strokes per inch" for a given feed rate the quality of the cut is more dependent on the shape of the needle point. The cuts in my pictures are the result of using a sharp-ish needle point which only displaced the foam without removing it. A blunt point "punches" through the foam however and blows out the bottom edge... much like the exit wound a bullet makes... and generates a bit of debris. When I fashion a new needle I make it overlong and cut it on the diagonal a bit below the end of the guide when it is in the topmost position. This forms a little "harpoon" point which I then dress with a fish-hook sharpener to remove the barb.

The planes shown are just adaptations of various planes we've found here and in other forums/websites. We've made them CNC-ready for our machines, added tabs and slots to strengthen them and simplify construction, and most often adjusted their size to let us "standardize" on small 3000kv BW motors and 2-cell LIPO batteries. And having been the recipient of so much from sites such as this one we'd be happy to share what we have with those interested.

I was unsure where best to post this thread to generate interest. If you feel it would be better discussed elsewhere please feel free to move it. A retired electrical engineer, I'd love to be involved in the development of yet another useful accessory for your machine.

Thanks,
David Johnson