Pompf Coring Jig

Note: This is a work in progress!! There are still a few tweaks I need to make before it's actually a good design. ex: more stiffness, embedded nuts, ability to tune center, etc. (lwk im not sure if I will do that because it's usable rn and I'm busy, but if you want to make quality of  life improvements, the source .f3d files are included. have at it).

Relatedly, the irl photos are outdated - check the cad. I replaced the bushings with sets of bearings based on the MPCNC style and what I had lying around.

The stl contains all the printed parts you'll need. If you want to use a 1/2" tube instead of a 7/16" tube, you can swap the bearing mounts with the other stl. Some notes on printing and post processing:

• cut the little strips at the bottom of the spacers before using them. They're just to prevent distortion and peeling during printing by taking the hoop stress near the bed.

• shave/sand any elephant's foot off any parts that interface with the v-slot extrusion. The interface there is important to get precise.

Also needed are: 

• 6 M4 bolts at least like 10-12mm long

• 6x 625 bearings

• 10x M3x10mm bolts 

• 10x M3 T-slot nuts

• 3x binder clips (to clamp the foam)

• a 7/16" OD tube (for the cutting). I use mcmaster 8859K331.

  • if you want to use a different OD, you can open the .f3d file and change the user parameter tube_od. If you want 1/2" there's also an stl for the one part you need to change.

• a piece of V-slot extrusion at least 140cm long (sadly Openbuilds has closed, but you can still get it off amazon or a number of other places. If you want to use T-slot, like standard 8020, you'll have to open the CAD and adjust the profile of the parts so they register to the T-slot profile nicely).

All the COTS parts except the V-slot are listed in the file as mcmaster parts so you can just order from there.

Usage

• heat the tip of the brass tube with a heat gun. Don't use a flame; for some reason it rapidly accelerates the buildup of plastic on the tube. I think it must char the outer layer a bit, which then makes it build up.

  • I just set my amazon heat gun to 100% and it's about the right temperature.

• When pushing the tube into the foam, make sure you're not holding your finger over the end (or blocking the tube in any other way). If there isn't a way for air to get out, the tube will get clogged with plastic and will rapidly become unworkable.

  • if this does happen, wait for it to cool, then cut 2-3cm off the end of the tube. Behind that, the plastic shouldn't be bonded to the tube, and you can push/pull it out.

• Use binder clips to clip the plastic bits around the foam. If you have a smaller diameter noodle, use the spacers (tape them in place if you're doing a lot; it helps make it easier to take things in and out). 

  • If you don't clip it shut, the hole won't be on center.

  • if you need a significantly different diameter, you'll need to just edit the CAD.

• Core one side, then take the noodle out, flip it around, and core the other. This is tedious, but it's much better than just using a longer tube, since the deflection of the tube will quadruple if you double the length of the cantilever.

• Try to limit the amount of time foam stays inside the heated tube. Don't let it bond to the side of the tube. When you finish coring the second side of a blade, pull out the long spaghetti offcut so that when you retract the tube, it doesn't take the offcut with it.