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Bolt filament feeder

by gringer, published

Bolt filament feeder by gringer Dec 9, 2012

Description

Alternative filament feeder that uses a bolt directly attached to the stepper to feed filament.

Recent Comments

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@ronthomp You're not really giving me a chance to see things from your point of view. Could you please confirm that the design I pointed to is the one you were referring to when you mentioned "the original Reprap design"?
That's actually a problem with my current feeder (which uses a custom knurled bolt), because the filament already wants to twist -- I wonder if the bolt was cut using some mechanism that encouraged twisting. Looking at the filament when it comes out of the threader (I bought a reprap with a bowden cable), you can clearly see that the filament is slipping when the desire to twist (or not) exceeds the insistence of the bolt to continue on straight (or twist).

I'm hoping that using the normal bolt thread will reduce this issue. In my current hand-driven tests, I've had no problem so far with slipping due to twisting.
 I didn't say it failed. I said it was abandoned, as in for better designs.

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Instructions

Download and print bolt_feeder_base.stl, then join together with 4 3mm bolts. The bolts act as a friction hold to adjust the tension on the filament. There is space left for brackets to be placed where the bolt holes are. The filament comes out of the exact centre of the model, which should make joining this with other extruder brackets a bit easier.

Still to model:

  • brackets for mounting to hot end, stepper motor
    • joiner to connect stepper motor to bolt head

I got frustrated with the extruder feeder clogging up with bits of PLA, so had a think about what other mechanisms I could use to feed the filament, preferably without the need for purchasing extra metal parts. This is my first attempt at something a little different that feeds the filament directly beside the bolt, using the bolt thread to push the filament.

Initial model:

  • M8 thread depths were taken from http://www.newmantools.com/tech/threadm.htm Update 1:
  • added 0.25mm to circle radiuses to account for extrusion width Update 2:
  • modified enclosure (hopefully a near-final design) to hold full length of bolt and support brackets

The openSCAD file has variables for almost all the things you might want to adjust. In particular, bolt/screw length, bolt/screw diameter, and filament diameter.

Screw threads are intended to have blunt peaks.  I might try cutting a sharp threaded screw on a lathe so you get better bite into the filament with less force.  Is there a problem with the filament wanting to twist?
That's actually a problem with my current feeder (which uses a custom knurled bolt), because the filament already wants to twist -- I wonder if the bolt was cut using some mechanism that encouraged twisting. Looking at the filament when it comes out of the threader (I bought a reprap with a bowden cable), you can clearly see that the filament is slipping when the desire to twist (or not) exceeds the insistence of the bolt to continue on straight (or twist).

I'm hoping that using the normal bolt thread will reduce this issue. In my current hand-driven tests, I've had no problem so far with slipping due to twisting.
Although it was abandoned this idea looks a little different. I say go for it and see how it works.
Another option is to increase the diameter of the drive wheel like the solastruder design thingiverse.com/thing:17783
I have been using one for about 9months and it is a great design.  
solastruder
This is like the original Reprap design. Research that and see why it was abandoned.
 You mean the darwin one (e.g. reprap.org/wiki/ThermoplastExtruder_2_0)? I'm not sure what you're suggesting is the 'failed' design.

My intended design will use no gears. The wheel you see on my sketches is just a free-wheeling pressure hold (a flat cylinder with an indentation in the edge). The filament is driven directly using the thread of the bolt, rather than any gear teeth.

Regardless, failure at this project will only give me more insight into how fickle the filament thread is.
@ronthomp You're not really giving me a chance to see things from your point of view. Could you please confirm that the design I pointed to is the one you were referring to when you mentioned "the original Reprap design"?
 I didn't say it failed. I said it was abandoned, as in for better designs.
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