Wednesday, December 7, 2011

Hobbed bolt redesign needed

UPDATE: this turns out to be completely wrong, the problem was a broken idler on the extruder.
I got some ABS from a new supplier last night. It looks pretty good on the spool and when extruded, but it’s a bit softer than what I’ve worked with in the past. This is generally OK but it’s slipping on my hobbed bolt, and once it starts to do that it doesn’t stop slipping on its own (not unless I notice and push on the filament) and prints get ruined. Luckily it died on a small print, I was just making a batch of electronics brackets, not something like a plate full of X ends.
I made this batch of hobbed bolts with an M4 tap, and it’s been good for UltiMachine ABS and PLA, though it HAS stripped once in a while (rarely). Tonight I’m going to make an experimental one with an M8 or M10 tap so it’s got more aggressive teeth, and try that. I’ll have to recalibrate my esteps. I’ve seen people hobbing with both M8 and M10 taps before so it’s worth a try. It’ll be closer to the spur gear that MakerGear uses in their plastidrive, and MG’s is pretty bulletproof.  People who have used M8 and M10 say they’ve had good results.
I did buy a drill press vice last week so I could try this anyway so that’s sorted, I just need to print a pair of bearing holders so I can clamp the bearings in the vice.
If this works out I’ll have to re-do the hobbed bolts that I made for the batch of kits I’ve got nearly ready to go.
It’s all good though, if it results in an improvement in the design and an overall better printer in the end I’m OK with throwing out a half dozen bolts and re-making them.

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