KNRLR - a tool for making knurled bolts which are actually spiky

by chopmeister, published

KNRLR - a tool for making knurled bolts which are actually spiky by chopmeister Apr 21, 2012

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This nice thing attaches to your Dremel and lets you make your own M8 knurled bolts for your extruder. Technically speaking it's a "spiked" bolt, not a knurled one, but it's close enough. :) And yes, the name is supercheesy, but I like it anyway.

I made this because the standard Ultimaker knurled bolt doesn't fit the extruder I'm currently designing.

It's modelled in 3dsmax, so no openscad files, sorry :( If anybody wants to make a parametric version be my guest.


Print all the parts. I sliced mine with Cura, 0.2 layers, 25% infill.

You'll need:
2x M3x8 screws
1x M3x20 or longer screw
1x M8 nut (NOT a locking nut)

To prepare:

  1. Use two M3x8 screws to attach part B to part A.
  2. Use one M3x20 screw and attach the Dremel mount to part B. (do not overtighten to ensure a smooth motion of the mount)
  3. Remove the rubber cap from the tip of your Dremel 300(should work with other Dremels too).
  4. Gently screw on the hexagonal part to the top of the Dremel tool.
  5. Attach a thin cutting disc to the Dremel.(I sincerely recommend original Dremel discs, the Chinese knockoffs tend to shatter and get spent to quickly so you have an inconsistent cutting radius, also due to that they produce a cloud of nasty metal dust - very bad to inhale).
  6. Place a M8 bolt you intend to cut through the round hole on part A
  7. Screw in the 17 tooth gear to the bolt, being careful that the bottom layer you printed is turned toward the tip of the bolt. (That's for a better fit to part A, cause the first layers tend to be a bit wider than the rest of the part).
  8. Place the gear in its slot on part A and screw the bolt to the correct position for cutting.
  9. Screw on the M8 nut to secure the gear in position.

To cut:

  1. Turn on the Dremel to max speed.
  2. Holding the Dremel in one hand, use your other hand to push the bolt towards the cutting disc (it's good to keep your thumb on the M8 nut, to secure the bolt in place).
  3. Make a quick precise cut.
  4. Pull it away from the disc and rotate the bolt one tooth in your preferred direction to prepare for a new cut.

Repeat until done. Easy ain't it?

In reality it's done in a minute but I wanted to leave detailed instructions so nobody misses something or hurts himself (please use hand/eye protection).

It makes bolts which grip like the devil. Haven't tested them though because I'm still working on my extruder. Hopefully it will be done soon.

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The only issue with such tools for me is that the diameter of the cutting wheel reduces quickly when I use them, so the attack angle changes with time, defeating the purpose of the tool. May be I should look for better cutting wheels though.

Still I should have used your tool or a variant to make my own (new) kind of hobbed bolt. I wrote about it here http://betterprinter.blogspot.fr/2013/03/which-hobbed-bolt-for-filament-feeder.htmlhttp://betterprinter.blogspot....

This works great, thanks a lot!! :)

hi! this looks like an awesome tool! Could you post some pictures of the hobbed bolts? If you have some around :)

thnx! :D

Using the threaded part of a bolt will cause the problem that it will try to twist the filament as it progresses. (Beeen there.... :) )

Yes you get a great grip. Thats why my bolts now have also a tiny groove in the middle. That helps center the filament and also creates the "spikes"

What kind of groove? Is it circumferential? How does it keep the filament from twisting?

Hi, thanks for the comment. You are right. I tested the bolts and they work good, but the filament does try to twist. Could you post a pic somewhere how you solved the problem?

I think he means to not use this bold design at all, but to use the 'standard' Wade's bolt with an added middle groove. I've sketched a picture of what I think it would look like http://cl.ly/Gc6Fhttp://cl.ly/Gc6F

Okay, I'm apparently an idiot and can't visualize how this works. Do you have a video of it in use by any chance? DONT_KNOW

I didn't have one, but I made one for you: http://youtu.be/T7cabOkz2DEhttp://youtu.be/T7cabOkz2DE

Enjoy. :)

Thanks. I couldn't figure out how the gearing made the Dremel go up and down. It's for registering the cuts (nothing to do with the Dremel) and the fixture just pivots the cutting wheel into the bolt. I see now! Duh! =-X

This a very nice dersign. Prints well and is a good test of overhangs.

Is just my printer or is the hole within the gear too large? I'll just wrap some tape around the ind of the bolt to let it friction fit.

Well, it could be the printer. I made mine from the exact same STL and it's a pretty tight fit.

"I'll just wrap some tape around the ind of the bolt to let it friction fit" too... Printed on Makerbot ToM. Nice tool, thanks.