# Problem with setting current for Chinese stepper...

• @briskspirit

With power off, can you rotate the screw(s) by hand reasonable freely? Nothing binding? If you have a heavy(ish) bed, you don't need anti-backlash nuts - gravity will do that job for you. But as long as they aren't binding, they won't do any harm. How many screws are driving the bed
and what is the belt arrangement?

I'm struggling to see how you arrive at you steps per mm. T8 x 2 usually denotes a 2 start thread in which case the lead will be twice the pitch (but Chinese manufacturers do weird things with their idea of specifications). To elaborate on that, the pitch is the distance between thread peaks, but the lead is how far a nut would travel in one revolution of the screw. Many people confuse the two, mostly because on a single start thread, the lead and pitch happen to be the same. But a 2 start thread with 2mm pitch will have lead of 4mm, a 4 start screw has lead of 8mm etc.

Assuming it is indeed a single start screw with 2mm lead, and assuming your motors are 1.8 degrees per step then 1 revolution of the screw would be 2 mm of linear movement and 200 full steps. Therefore it follows that 1mm would be 100 full steps so at 16X micro-stepping, the steps per mm should be (100x16=) 1600. If the screws are indeed 2 start, then the lead becomes 4mm so the steps per mm would be half (800). So where did 1040 in your configuration come from?

• @dc42 Yeah, I understand... But it is what it is... 2A - all is fine(but whining noise in idle state) and with 1A it will start only with higher acceleration.

@deckingman I had T8x8 which I could rotate freely but this one - I need to put force with two fingers so I fill a little pain because of threads... So you might be right that there is a binding somewhere. Will try to change Delrin anti-backlash for regular brass nut. And I am not wrong about steps, I set them at 1600 steps for my 1.8 stepper and single start 2mm screw. And screw is Texas made (1040 is for current setting, not for steps)

• Stepper is harder to turn than amy regular one(This one is with integrated screw)

• So I assume that something is wrong with the stepper... But I have no choice as it is integrated with the screw and to redo everything I need to print parts. And I still can't understand how to convert to free floating belt driven Z screw for Replicator clone? (these machines has stepper + screw and no space to switch to stepper + coupler + screw, so only belt as an option.. but how to support that screw? )

• Stepper is harder to turn than amy regular one(This one is with integrated screw)

If it's harder to turn when it is disconnected from the electronics and the leadscrew is not connected to anything, then there may be some swarf in the motor, or the rotor may not be centralised within the stator. These issues can sometimes be fixed by removing the 4 screws from the back of the motor, withdrawing the rotor, blowing out any swarf, and re-assembling the motor. You may have to adjust the exact positions a little before tightening the 4 screws again.

• And I am not wrong about steps, I set them at 1600 steps for my 1.8 stepper and single start 2mm screw. And screw is Texas made (1040 is for current setting, not for steps)

Sorry - I thought I read M92 somewhere but checking back I can see that you didn't stipulate what micro-stepping you were using (I am overdue an eye test).

• @dc42 Tried... Will try your idea to readjust with 4 screws! How long it will "leave" on Z axis with 2A current if rated for 1.5A(or 1.3A... )

• @deckingman I know that you are a Master in building 3D printers ! So maybe you could throw me an idea how to convert my printer from integrated screw to stepper+coupler+screw? Replicator 2X clone, stepper is underneath and no space at all..

• @deckingman I know that you are a Master in building 3D printers ! So maybe you could throw me an idea how to convert my printer from integrated screw to stepper+coupler+screw? Replicator 2X clone, stepper is underneath and no space at all..

Show me a picture of what you have. Better still, send me a PM with your email address. Then we can see what can be done without cluttering up this forum with non-duet related things.

• @deckingman I can't send you PM as you have restricted who can send.

• @dc42 Rotor is misaligned and has black marks on teeth where it has contact with stator teeth.

• @briskspirit There is your problem then. If you can't fix it, TBH I can't think of a cheaper alternative than to replace the motor/shaft assembly. Being a cheap Chinese stepper, I don't suppose you can get your money back? It's obviously faulty.

• @deckingman It will take too long... better imho is to convert to coupler or belt driven screw but I don't know how to do that the right way. Can you PM me your e-mail and I will send you photos of what I have got.

• @dc42 Tried... Will try your idea to readjust with 4 screws! How long it will "leave" on Z axis with 2A current if rated for 1.5A(or 1.3A... )

100% of rated current is safe. A little more is safe, because rated current is specified with both phases energised, but microstepping drivers such as those on the Duet only drive one phase at a time with the full current. 141% of rated current is unlikely to be safe unless standstill current reduction is used, because then the power dissipation is the same as if both phases were energised at full current, but depending on the motor position all of that power may be dissipated in just one of the windings instead of shared between both.

• @deckingman It will take too long... better imho is to convert to coupler or belt driven screw but I don't know how to do that the right way. Can you PM me your e-mail and I will send you photos of what I have got.

PM sent.

• @dc42 As I understand right I am already using current reduction to 30% with I30 argument , right?

• @dc42 As I understand right I am already using current reduction to 30% with I30 argument , right?

Only when all motors have been idle for 30 seconds.

• @dc42 Thank you ! Lapping stepper with oil - run for ~30min forward / ~30 min backward - towel and repeat . Noise is almost gone, turning better. Will see if I could reanimate it.

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