Do you think this will work

Do you think this will work as a " hobbed " bolt. The hobbed part seems to grab well with pressure. I just wanted to get your guys opinion. I'm making a pinched cold end. Thanks!!

If so I have 7 of them of anyone is interested.

Would need a grooved bearing or filament guide to keep the filament in proper alignment.

Edited 1 time(s). Last edit at 01/23/2013 06:43PM by Dirty Steve.

A regular hobbed bolt distributes the force more evenly across the feedstock, because if its circular groove.

So one thing you would want to recommend to users is to set the extruder motor power low enough to skip before the feedstock strips. If feedstock strips it will fill in the space between the teeth and then no longer work. If extruder motor stalls rather than grinding the feedstock, and if the teeth are deep enough then this should work ok for many people.

Another thing to consider is the ratio will be slightly different for flow rate as the circumference is larger.

Could I just use My dremal and deepen the grooves. Also I got parts for a printebot build and it came with a Wade's geared extruder. I have a bolt that fits well and is like many hobbed bolt I've seen. It is half smooth and half threaded. Is it better to hobb the bolt on the smooth part or the threaded part. Or does it even matter. Thanks.

REPRAP SQUAD Wrote:
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> Could I just use My dremal and deepen the grooves.
> Also I got parts for a printebot build and it came
> with a Wade's geared extruder. I have a bolt that
> fits well and is like many hobbed bolt I've seen.
> It is half smooth and half threaded. Is it better
> to hobb the bolt on the smooth part or the
> threaded part. Or does it even matter. Thanks.

most of them are hobbed on the smooth part somwhere around 25mm from the underside of the head, not sure how well it's going to work with a dremel, my feeling is that it won't or you'll have somthing that is "out of round"

most hobbed bolts judging from the ones i've bought off different people appear to just have rammed into a turning tap with little to no care given to roundness or quality of teeth, these days i would advise going with 1.75mm filament and using a direct drive extruder, with a decent filament drive

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If the cutting tap is centered on a lathe, and the bolt is tensioned into the cutting tap from a jig and allowed to turn until it cuts evenly, then little variation in bolt should occur. The teeth deepness varies depending on tap size. Typical tap size is 4 to 6. These sizes grip the sides of the feedstock, and because the teeth are not really that deep the extruder almost never gets stuff stuck in the teeth. They sort of self clean. so in some cases the smaller tap the better.

, but larger such as 8 or 10 tap does allow for very deep groves, but it does not work for long because when the feedstock skips the teeth fill in with plastic and no longer grip the plastic.

For now I am using a tap 10, because it bites deep, but I also have adjusted my extruder motor to skip steps if the feedstock has too much back pressure. This prevents teeth from getting plastic stuck in between the teeth.