Aluminum hobbed bolt?

Just curious if anybody has long term experience using aluminum for the filament teeth.

I've been trying to make an easier to machine 'bolt' and so far the aluminum seems to work, but I'm somewhat concerned about it staying sharp in the long term.

Thoughts?

My repstrap extruder used teeth cut into aluminum in a brutstruder style arrangement. It successfully printed the parts for a Mendel and a large variety of other objects. To be honest I expected that it would not last very long, but it still works well. Note that I've only printed ABS with it, so I don't know if PLA would be an issue or not. On the other hand I've not really used it since it finished printing the parts for the Mendel.

My personal recommendation would be to contact someone with a metal lathe and have them knurl the bolt. Knurls come in many sizes and textures. Most of the patterns are pyramid shaped or raised lines.
Very gross information can be seen here [en.wikipedia.org]

I knurled my bolt with larger diagonal pattern resulitng in pyramid shapes with very good grip.
Aluminum will wear faster over time because plastic is abrasive.

Wade's hobbed bolt design works well because it's in contact with the filament over a large surface area. I don't think the knurled bolt would work as well since the contact area is limited like the toothed drive in Adrian's geared extruder.

It is teeth (or a pattern) on a bolt specifically for gripping. Knurling just puts a regular pattern on the bolt of your choice. There is no loss of contact area. I have not had any problems.
I realize not everyone has access to someone with a metal lathe but it is a very good option if you do.

Have you tested the knurled bolt and compared it to the results that Wade got. According to the wiki, he measured a pull of up to 16 kg with the stepper failing instead of the filament slipping.

Have not tested it with any other bolt. I am also running a Kysan 5.0 kgcm motor.
I have not measured the force to pull back on it. I know I need like a pair of plyers for leverage to pull filament back if the motor is on. The motor gives before the PLA filament slips. I would say it is solid but I cannot give you an actual quantifiable value.

Andrew Diehl Wrote:
-------------------------------------------------------
> Just curious if anybody has long term experience
> using aluminum for the filament teeth.
>
> I've been trying to make an easier to machine
> 'bolt' and so far the aluminum seems to work, but
> I'm somewhat concerned about it staying sharp in
> the long term.
>
> Thoughts?

I just made a hobbed bolt this week using zinc plated 5/16 bolts from Home Depot and i wasn't as hard as I thought it would be. I did buy a set of files that incuded a 3mm round file that helped a lot.

I did some comparative tests of knurled against hobbed some time ago: [hydraraptor.blogspot.com]

Knurling works reasonably well but is not quite as good as hobbed, particularly on softer plastics. Hobbing can vary a lot though because people choose different tap sizes and hob to different depths.

The contact area is less because you have a flat profile meeting a round filament rather than a curved profile closely matching it.

---

[www.hydraraptor.blogspot.com]

Conclusion: Aluminum does not work well. The sharp, thin edges bend after a time.

I never got knurled to work for my abs, either.

I am looking at the hobbed bolt area myself and had a thought about using a knurling machine, sadly I dont know anyone with one.
What I have come across is Knurled locking nuts, they are 5-6mm wide and could potentially do the job if some adjustment where made to the mounting?
[www.wdsltd.co.uk]
Since tests have been done is it worth trying this method out or stick with a tried and tested hobbed bolt?

EDIt not sure why my linked is mussed up ;-(
You had an = after url instead of a ]

Edited 2 time(s). Last edit at 12/22/2012 06:36AM by nophead.

I am also quite curious about this stuff since it does not seem to appear in when searched on google or other search engines. Any information will really be helpful. Thanks.