Just a thought. Hobbed nema shafts.

Hey, I don't post much, but something came to me.

Why don't we (use taps) to hobb the shafts of our nemas for a true direct drive extruder setup? a smaller diameter would mean more torque and more steps per unit? To me it sounds like a good idea, but people might find problems with this. The only potential problems I see possible is that if you tap too deep then the 5mm shaft would become sub 4mm which would great a weaker shaft and a potentially to small gripping area.

I would be keen to try this out, any ideas?

Stustu

Well, the first thing that comes to mind for me is that the shafts have a flat spot on them, used to key them for drive gears, at least all of the motors that I have are keyed that way, which puts paid to the idea right there. The second thing is that the shafts are actually very hard, much harder than the iron that bolts are made from, and probably about as hard as most tap and die sets are, which makes them very difficult to actually modify in this way. (They have to be very hard, or they would deform too easily when things are fastened to them.)

Besides that, the loss of adjustability would not be a good thing, increasing the needed complexity of the motor mount. If you just want to gear down the shaft, even with a regular direct drive, it's not hard if you don't mind moving the motor out. A 5mm shoulder bolt threaded into a 5mm coupler would do the job fine, give you adjustability and cheap replaceability, but if torque really is a problem, then it is so much better to go with a geared down extruder and just be done with it.

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SupraGuy
but if torque really is a problem, then it is so much better to go with a geared down extruder and just be done with it.

Because they have 8mm shafts and you need to buy a bigger hob?????

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a smaller diameter would mean more torque and more steps per unit?

Hope you are not a bridge engineer. If so, let me know which bridges you worked on...............

[en.wikipedia.org]

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stustu242
a smaller diameter would mean more torque and more steps per unit?

For a direct drive extruder, the formula is ; e_steps_per_mm = (motor_steps_per_rev * driver_microstep) / (hob_effective_diameter * pi)
So stustu242 is right : the smaller hob diameter, the more steps per millimeter. About torque, there's a missunderstanding between Force and Torque.
Torque = Force * Distance from the shaft axis. Also Force = Torque / Distance. As long as the distance from the shaft increase, you will need more torque to maintain the Force. As the torque is calculated from a distance, for a torque of 50 oz.in, the force is 50 ounces (50/1) at 1 inch of shaft distance. If the shaft distance is only 1/4" the force applied perpendicular to the shaft will be 125 ounces. The torque stays constant but the force applied increases. The force is strong with this one, on that bridge I would step

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

Try it, and let us know how it works...

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SupraGuy
so much better to go with a geared down extruder and just be done with it.

That buys you some backlash as well, but it is a well travelled route.

Wasn't there a kickstarter in the last year that had a hobbed stepper as part of their fancy new extruder? Don't remember which one, or whether it completed or worked.