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First Attempt at hobbing a 8mm bolt

Posted by randyf1965 
First Attempt at hobbing a 8mm bolt
March 02, 2014 04:03PM
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.

Edited 1 time(s). Last edit at 03/02/2014 04:07PM by randyf1965.
Attachments:
open | download - hobbed bolt.jpg (94.7 KB)
Re: First Attempt at hobbing a 8mm bolt
March 02, 2014 07:21PM
way better than i could do I am sure, but it looks like a bit to deep on the groove and I think you have about 30% too many teeth
Re: First Attempt at hobbing a 8mm bolt
March 02, 2014 08:07PM
It's similar to the hobbed bolts I make except 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.


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Waitaki 3D Printer
Re: First Attempt at hobbing a 8mm bolt
March 02, 2014 08:40PM
I agree w/ n9jcv. You might want to use a little bigger tap like M6. Also, I'm not sure of your extruder design, but the hobbing is pretty close to the bolt head. That won't work on something like a wade's.
Re: First Attempt at hobbing a 8mm bolt
March 02, 2014 09:40PM
it is a 50mm bolt and I found it works better with the nut on the pulley side since the hob section would be on the taper going to the threads the other way around.

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.
Re: First Attempt at hobbing a 8mm bolt
March 02, 2014 10:34PM
Tried to hob a harden steel bolt.

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
Re: First Attempt at hobbing a 8mm bolt
March 02, 2014 10:39PM
To get perfect placement of the hobbed bolt I turned the inside of the head down until it centered the groove on the opening for the extruder.

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.
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