Filament twist

I think that this is more of a general hardware topic but I don’t have that option for starting a new thread.

I think that many, if not all of you, have experienced the occasional clog/jam that is accompanied by the hobbed bolt chewing a bite out of the filament which then prevents any more filament from being pushed into the hot end.

Over the past few months I have been working with a number of different filament types and have developed a hypothesis that I would like your input on.

I believe that the hobbed bolts are twisting the filament due to their construction and this causes the filament in the transfer tube to bind and cause excessive drag leading to the hobbed both chewing through the filament.

I suspect that hobbed bolt as the culprit due to the “standard” method of manufacture: Using a threading tap to create the hobbing. The use of the tap introduces a slant to the hobbing which in turn will cause the filament to twist.

My data:

  • I first noted this twisting when I started using NinjaFlex. The NinjaFlex is “slippery” enough that it doesn’t bind in the tube, rather it twists itself into a knot between the spool and the tube.

This weekend I had a large nylon (alloy 910) print start to fail with less than 1mm left in the print. This resulted in a very rough finish of that part and a refusal to start printing a new part until I removed and reinserted the nylon filament. When I removed the filament from the transfer tube I noticed that it had much more resistance to being pulled than normal, but after I took it out and allowed the nylon to relax, reinsertion was at normal resistance.

I normally use ABS and HIPS which are much less flexible than NinjaFlex or nylon. While I have not been able to detect the suspected twisting, I believe that this is because I have not noticed the increased resistance until the “bite” has been taken out of the filament which requires removal of the filament from the extruder with the resultant release of the twist.

The way to “fix” that would be to use a gear cutter in a mill and create a hobbed bolt with straight (perpendicular?) hobbing. The downside is that would drastically increase the cost of the hobbed bolt.

Do your experiences correlate to my observations? Is there a better explanation available?

Well instead of a TAZ I now own a MakerGear M2. They just use a standard straight cut gear mounted directly on the gear reduction box output shaft to drive the filament. That gearbox is coupled directly to the extruder stepper motor. The M2 units have very few jamming issues, I just had my second one in just about 3 months. They also use a physical gap as a way to prevent heat creep into the extruder body and that is the second part of the no jam design.