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Help with drive belt setup

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15 Apr 2024 21:04 - 24 Apr 2024 16:22 #298312 by MDP
I have created my own homemade CNC router. I have kind of a "hybrid" setup where my Z and X axes are screw driving while the Y is belt driven. Everything is up and running fine but I'm having a difficult time dialing in the Y axis (the one that is belt driven). I'm unsure of what values to use in the "Pulley teeth: (Motor Leadscrew)" field and the "Leadscrew Pitch" field. I currently have "Pulley teeth..." set to 1.0:1.0 and 0.635 in the "Leadscrew Pitch" field. I arrived at that number by measuring the diameter of the belt pulley, converting that to a circumference and then dividing by one. The result was really far off so I have tweaked the value little by little. So when I cut out a part, the dimensions in X and Z are spot on but the Y measured value is slightly larger than it should be...about 1/64 of an inch on a 4 inch part. Not bad but I would like to get it better. So my question is this....What is the correct method to mathematically arrive at the values I should enter?

UPDATE: So...I found the issue. Cheap router bits / adapter. I was using some cheap 1/8 bits and a 1/4 adapter. Got a high quality 1/4 spiral bit and everything works perfect now. I'm within +/-0.008" on a 6 inch part which is more than accurate enough for my needs. Lesson learned!

Oh and the correct way to calculate the value I needed appears to be: (# of Pulley teeth X tooth pitch) / 25.4 to convert to inches per revolution. Then 1 / the number you get above. That is the value to enter for Leadscrew Pitch.

So in my case (20 X 2) / 25.4 = 1.5748
1 / 1.5748 = .6350 (which just happened to be the value I worked out thru trail and error)

If I'm wrong about that someone please correct me!!
Last edit: 24 Apr 2024 16:22 by MDP.

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16 Apr 2024 00:47 #298321 by tommylight
Example:
motor steps per rev 200 (this is almost always true for steppers 2 phase)
drive microstepping multiplied by above, say 1/8 micro makes 1600 steps per rev
motor pulley teeth multiplied by teeth pitch, so GT2 20 tooth is 40mm of motion for one rev
then 1600/40 makes 40 steps per mm.
You gave us no info at all about what you are actually using on Y.

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16 Apr 2024 03:35 #298337 by MDP
Replied by MDP on topic Help with drive belt setup
You actually guessed all my details...GT2 belt with 20 tooth pulley, 1600 steps

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16 Apr 2024 08:18 #298345 by tommylight
No reduction?
Using metric or inch?

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16 Apr 2024 19:30 #298398 by MDP
Replied by MDP on topic Help with drive belt setup
No sort of reduction is being used. I'm running in inches.

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16 Apr 2024 22:28 #298407 by tommylight
Ok that is 40 steps per mm times 25.4 for inches = 1016 steps per inch.

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