hobbed drive bolt with M6 teeth

I kept having trouble with the drive bolt on my extruder stripping out the fillament and loading all the teeth with plastic. From what I have heard, it sounds like a couple of other people have had the same problem and eventually went back to using timer pulleys.

The standard practice for making drive bolts appears to be cutting teeth with M3 taps. The fine teeth allow smooth operation, but I don't think there is enough bite to extrude ABS at reasonable speeds. It might work for PLA, but my ABS just kept jamming up unless I went so slow that it oozed out faster than it was "printing". Having run though the usual gauntlet of jammed-filament troubleshooting tips, I finally cut M6 threads on the drive bolt instead. This immediately fixed my problem.

It isn't quite as smooth as the M3 threads. You can feel the difference when cranking it by hand but I do not think that it makes a significant difference. My stepper motor still has plenty of torque to keep it moving and there is no visible pulse in the extrusion rate. I can finally extrude ABS at the same speed as in the makerbot MK4. If I used a larger step size or change the gear ratio, I can probably go faster but I don't see the need for that.

I have attached a picture that shows the difference if anyone is interested in seeing it. Hopefully this will help other people that have been having the same problem.

i had this problem at first and i think it was because the hobbed nut i recieved off ebay didn't have deep enough teeth, they were very light. So i made my own from scratch and it works much better with deeper m3 teeth. until i try and extrude when the heat is not right up by mistake then the teeth will become clogged with plastic and i have to clean.

Interesting - I haven't used ABS in years, so can't really say how well it works. Any chance you could hook up a scale of some sort and do some pull tests?

Wade

I have a similar problem, but using an aluminum drive wheel. In addition to the teeth filling up with plastic, the teeth eventually get deformed because I am using aluminum. With freshly cut teeth, I can get up to 20 pounds of pull. After they start slipping, the pull goes down.
I plan to try steel teeth next to fix the deforming problem, but have not gotten around to trying it yet. Not sure if it will help with the filling problem though.

Wade Wrote:
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> Interesting - I haven't used ABS in years, so
> can't really say how well it works. Any chance
> you could hook up a scale of some sort and do some
> pull tests?
>
> Wade

I have a couple of hanging scales on order. They will go to 40Kg. They are the cheap digital kind, but I know some people who use certified scales for food processing. I will be able to verify the scale's accuracy. I just don't have access to the kind of scale needed to measure tension at the moment.


damonb Wrote:
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> I have a similar problem, but using an aluminum
> drive wheel. In addition to the teeth filling up
> with plastic, the teeth eventually get deformed
> because I am using aluminum. With freshly cut
> teeth, I can get up to 20 pounds of pull. After
> they start slipping, the pull goes down.
> I plan to try steel teeth next to fix the
> deforming problem, but have not gotten around to
> trying it yet. Not sure if it will help with the
> filling problem though.

I was thinking of putting teeth right on the stepper shaft since this would allow me to make a smaller extruder. Maybe the extra few cm of print space isn't worth it. A $0.50 bolt is much easier to replace than a $10-30 motor. Steel should last longer than aluminum, but I did not think of plastic being able to deform the teeth. Maybe this could be another advantage to using M6 teeth? The teeth are slightly thicker and deeper, so in theory they would have to deform more before too much grip was lost. Thicker teeth might also slow down the deformation by spreading the force over a larger area -unless of course the fact that there are fewer teeth per mm causes the opposite effect.