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# the use of threaded rods for cnc miller and cnc 3d printers Answered

I got some threaded rods today. They look straight. 16 threads per inch.  The tag on one of the shorter ones says 3/8" - 16x36", course threads, zinc plated 1700lb.

I was planning to use these for the x,y,z control for a 3d miller/printer. I realize it may be slow. Someone mentioned that the McWire repstrap uses a 4 1/20 (the only part I understand is 20 threads per inch) was really slow, but someone made it work with 2 1/16.

I did not really have plans to attempt position verification because I think the resistance vs torque should be minimal for a threaded rod setup. I figure I could get away with just sending it specific pulses for a specific amount of time.

Could I have some feedback on this?

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Would assume that is 1/4"-20 so there are 20 threads per inch.... so to to move the axis 1" the stepper has to spin 20 times... if you are micro stepping at 1/4 step typically there are 200 steps for 1 revolution of the stepper but microstepping at 1/4 make that 800 so for 1" of the 1/4"-20 that would be 16,000 steps... thread pitch X # of steps per revolution.

So for every revolution of the 1/4"-20 threaded rod the axis would move 1/20th of an inch and every microstep is 1/800th of 1/20th of 1"

1/20th of an inch = .05"
.05" / 800 is .0000625"

Is bigger CNC there are threaded rods with multiple starts to make movement faster

Real CNCs use ballscrews, not threaded rods - 10mm /rev is pretty common.

3/8"-16 for mine. It takes 16 rotations to go 1 inch.

I was told that I would get alot of resonance, but I think I decided on a way to avoid that. Here are two options that I came up with.

A: Spin a threaded sprocket or pulley that is on a stationary thread.

B: Have the thread spin as most would expect, but have there be 2 points per side where the work arm (the piece that will hold the X and the Z) connects with the thread an have the majority of the work be done near the center of the device.

For both options, I will probably use a spring loaded nut combo to greatly reduce backlash.