Automatic nut-hobbing device
October 17, 2012 01:43PM

This device automatically carve a brass nut to make a filament driving wheel for DIY extruders. Just install the nut, switch it on and it works by itself.

The carving tool is a simple stainless steel M4 threaded rod / hardened steel M4 screw shaped with a dremel to make the teeth :

The electronics is build around an NE555, it generates the step pulses for the stepper driver.

Stl files, scketchup assembly and electronic schematic are avalaible on the heavy_mendel wiki page : []
open | download - Hobbing_tool_1.JPG (156.3 KB)
Re: Automatic nut-hobbing device
October 18, 2012 04:09AM
Excellent work ! And thank you for sharing the sources, will help people adapt it to other sizes of nut, etc.

Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.
Re: Automatic nut-hobbing device
January 16, 2013 03:06PM
I improved the design, now it uses a real tap, it carve the teeth better and more quickly :

The device now split in two parts by a 1/4 turn mechanism te release the bobbed nut.
Result on a round steel nut :

Re: Automatic nut-hobbing device
January 20, 2013 03:40AM
What driver board are you using? I'm looking for a way to forward/reverse speed control a 1:56 geared bi-polar stepper for a filament extruder I'm working on.

Is the circuit schematic correct at SW2 with the step connecting to ground?

Is pin 1 on the 555 grounded, and pin 8 5v+?

Edited 1 time(s). Last edit at 01/20/2013 04:27AM by Dirty Steve.
Re: Automatic nut-hobbing device
January 20, 2013 09:09AM
I am using a salvaged bipolar stepper driver, it works at 1/4 steps.
SW2 connects the step input of the driver to the output of the NE555 that generate the pulses or to the ground, so no pulses = brake.
Yep pin 1 is GND an pin 8 is +5V
Re: Automatic nut-hobbing device
January 21, 2013 04:57PM
What chip is your stepper driver? I can get a pulse with a 555 at various speeds and I'm trying to hook it to a ULN2003. I'm getting motor current but no rotation on bipolar or unipolar motors. The ULN2003 circuits I can find are 4 input, but it looks like I need to find a 2 input circuit.
Re: Automatic nut-hobbing device
January 22, 2013 01:09PM
The driver I use is composed of 2 H-bridges circuits and a programmable circuit.

The ULN2003 is just a darlington array it only amplifies the current. It needs a circuit that convert the step and dir signals to phase signals.
So you need to add an L297 to your ULN2003, like this : [].
Re: Automatic nut-hobbing device
January 22, 2013 03:36PM
Thanks Petrus, that will get me headed in the right direction.
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