I recently completed a Prusa i3 build and had purchased a hobbed bolt but wanted to try my hand at it. I used a triangle needle file to groove the bolt chucked in my drill press then used a small round needle file to make a round groove roughly the size of a 4mm tap. Used my drill press vise to hold a hand drill with the tap in the chuck and took the belt off the drill press. Running the hand drill about 1/4 speed stopping to oil the tap and bolt all told took maybe 5 minutes. Unfortunately I am now waiting on a Stepstick replacement for my extruder since somehow I killed it (too high of current). I was using heatsinks and I thought the thermal shutdown would have stopped it but it is dead. https://reprap.org/forum/read.php?1,318696,318696#msg-318696 Thu, 11 Jun 2026 06:00:07 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?1,318696,318836#msg-318836 https://reprap.org/forum/read.php?1,318696,318836#msg-318836
Now I can insert the filament in the top and it feeds straight to the hole. Before I had to loosen the tension roller and feed it in manually.]]> randyf1965 General Sun, 02 Mar 2014 22:39:16 -0500 https://reprap.org/forum/read.php?1,318696,318835#msg-318835 https://reprap.org/forum/read.php?1,318696,318835#msg-318835
Will have to build a jig to hold the bolt and tap then SLOWLY turn tap.

Too hard to do by hand and keep it steady]]> randyf1965 General Sun, 02 Mar 2014 22:34:38 -0500 https://reprap.org/forum/read.php?1,318696,318828#msg-318828 https://reprap.org/forum/read.php?1,318696,318828#msg-318828
The hobbed bolt I bought has almost flat teeth, my curved teeth fit the 3mm filament I am using less than 50% of the circumference.
Manually turning the pulley it grips way better than my purchased bolt.
But I won't know until I get a new Stepstick to be sure.
Bolts are cheap.]]> randyf1965 General Sun, 02 Mar 2014 21:40:39 -0500 https://reprap.org/forum/read.php?1,318696,318818#msg-318818 https://reprap.org/forum/read.php?1,318696,318818#msg-318818 iquizzle General Sun, 02 Mar 2014 20:40:58 -0500 https://reprap.org/forum/read.php?1,318696,318811#msg-318811 https://reprap.org/forum/read.php?1,318696,318811#msg-318811 you have rounded the groove after filing it. I do not do that as I find it grips better with a fairly deep V groove (just like a VCR mechanism which uses a round rubber belt ("filament") running in a 60 degree V pulley) - I hob it after making the groove. I have never needed to change it, still grips perfectly good. And yes, you need to run the tap very slowly in the cordless drill.]]> waitaki General Sun, 02 Mar 2014 20:07:30 -0500 https://reprap.org/forum/read.php?1,318696,318799#msg-318799 https://reprap.org/forum/read.php?1,318696,318799#msg-318799 n9jcv General Sun, 02 Mar 2014 19:21:28 -0500 https://reprap.org/forum/read.php?1,318696,318696#msg-318696 https://reprap.org/forum/read.php?1,318696,318696#msg-318696
I used a triangle needle file to groove the bolt chucked in my drill press then used a small round needle file to make a round groove roughly the size of a 4mm tap.

Used my drill press vise to hold a hand drill with the tap in the chuck and took the belt off the drill press.
Running the hand drill about 1/4 speed stopping to oil the tap and bolt all told took maybe 5 minutes.

Unfortunately I am now waiting on a Stepstick replacement for my extruder since somehow I killed it (too high of current).
I was using heatsinks and I thought the thermal shutdown would have stopped it but it is dead.]]> randyf1965 General Sun, 02 Mar 2014 16:03:54 -0500