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Stepper Tilted Axis.

Posted by MRGiacalone2005 
Stepper Tilted Axis.
May 16, 2014 11:13PM
I am in the process of setting up a Delta Printer. We just noticed that one of our steppers has a tilted axis causing it to run eccentric (Motors: Tilted Axis). Besides buying a new stepper, does anyone have any ideas of the problems it may cause and how to fix it?


Marcelo R G
Re: Stepper Tilted Axis.
May 17, 2014 11:10AM
I know you said "besides buying a new stepper", but what about returning it since it is defective? I don't know what kind of problems it will cause, but it will cause problems and you'll probably spend more money on excedrin/alcohol than you would on just buying a new stepper.
Re: Stepper Tilted Axis.
May 17, 2014 07:28PM
Good advice. They were sent from Hong Kong though but I'll contact the supplier to see if they will send me a new one in the following order.

The subject may still be of importance for some looking for a quick fix, perhaps even one involving printed parts.
Re: Stepper Tilted Axis.
May 17, 2014 11:20PM
Machinists call it "runout", and it was probably caused by dropping the stepper and bending the shaft. You can unbend shafts somewhat by finding the high side and bending it back with a press or a hammer, but you can't reliably eliminate all the runout that way. The common way that machinists fix runout is by turning the shaft down to a smaller diameter. You'd then have the problem of an undersized shaft, which might still work if you could use a printed or custom-drilled pulley, or a bushing. If you could take put your rotating setup on a surface grinder, you could easily run the stepper while grinding a little off until it is true.

With a reprap strong enough to hold a Dremel tool, it might work as a surface grinder for a light-duty job like this.
Re: Stepper Tilted Axis.
May 20, 2014 11:10AM
Thanks for the useful info.

That is possible. I'm sure we didn't drop it, and if it was dropped by someone during shipping, I would have guessed that it should have a small dent or something - no sign of that. Still, even without the dent it is possible that it was dropped.

Anyway, the supplier agreed to send a new one with the next order. We are still going to set up the machine with the defective stepper until we get the replacement, and to the useful documentation found in this forum, we will post our findings. First some things to consider: (please provide your comments on these issues). The first thing we have to decide is where it would be wiser to test the stepper (i.e. X,Y,Z, or E).

- Testing it in the extruder needs extra attention because the cold end has gears that may be damaged by the additional movement.
- Using it in any axes, either X, Y, or Z will probably have the same effect on precision. However, before we test it here we have to do the initial testing and calibration with all the good working order steppers in the X, Y, and Z.

Anything else we might have missed?
Re: Stepper Tilted Axis.
May 20, 2014 03:17PM
You can bend steel things without denting by using a softer material -- search for 'non-marring hammer' for examples.

You might measure the extent of the runout (http://www.precisebits.com/tutorials/spindle_runout.htm, and compare it to your good motors) and then consider how much that effect could throw off your machine. Probably a wave in the positioning with a magnitude of the size of the runout and a wavelength of the circumference of the pulley, both modified in the vertical direction by cos(leg angle from vertical) and both modified in the horizontal by sin() for a delta.

If it were me, I'd try bending it back some--you've already got a spare on the way, and you have a good chance to improve it. Or, if you have an extra pulley, you could drill it out bigger by about the size of the runout and put the grub screws on the low side to pull the pulley toward center..

I'd try it on one of the delta axes rather than the extruder, since it would be stretching/loosening a belt rather than messing with the spacing between the gears.
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