Finally upgraded z-axis on p3steel, but I am having stepping issues now. Seeking help.

Hello.

So, I have a p3steel that I cobbled together a number of years ago. I have finally upgraded the z axis by installing 8mm lead screws in place of the M4 threaded rods

I am running RAMPS with DRV8825 drivers. PSU is 12 volt. The motors are Kysan Nema 17 with 1.8 degree and 1.5A per phase.
[www.kysanelectronics.com]

Both motors are running off of the one Z stepper driver and they are connected directly to the Ramps board, so in parallel.

Marlin version is 1.0.2 ( I plan on updating this but I was trying to get the old version of the firmware working first )

Previously, my default axis steps for Z in Marlin was set to 8000. This matched Prusa's calculator for 1.8, M5 with 1/32 microstepping.

Now here's my problem:
I've installed 8mm lead screws with a 2mm pitch. However, when I set Marlin to the calculated value of 3200, 10mm becomes 30mm of z movement.

Essentially, I've had to set it to 800 steps in order to get 10mm of travel from Repetier manual control. ( which the calculators suggest is only 1/8 step ) I've attempted to change the step jumpers to 1/16, but it didn't change anything.

I've also doubled the vref value on the stepper driver from .79 to 1.6, but this didn't change the stepping and distance traveled.

So what I don't understand is why 1/32 stepping was working fine before and now it seems stuck at 1/8. Is it because the motors are under powered for the lead screws?

I'm a bit stumped here. Maybe I'm missing something that's right in front of me?

Any thoughts, advice or feedback is appreciated. Thanks.

And how many starts is the 8mm rod with 2mm pitch?

A single start would be 3200, but.. I suspect its a 4 start, that divides the steps/mm by 4 giving 800 eg [www.aliexpress.com]

Ie its doing as it should.

Edited 2 time(s). Last edit at 12/30/2018 03:13AM by Dust.

That was a good choice of lead screws, though I agree with DUST your lead screw most probably is a T8-8 Trapezoidal 4 start Lead screw.

It is a Simple check to see which it is.
A single start lead screw will rise 2mm from a single 360 degree rotation ("one revolution").
A four start lead screw will rise 8mm from a single 360 degree rotation ("one revolution").

My Problems Using T8-8 Trapezoidal 4 start Lead screws

I personally chose the single start lead screw that rise 2mm from a single 360 degree rotation.
As I had the TT8-8 rapezoidal 4 start Lead screws and in my 3D Printer they caused me more headaches than they were worth.
Every time I would have one 3D Printer running next to the other that was not running the Z-Axis would have to be re-aligned before next use...
The vibrations from the working 3D Printer would cause the 3D Printer not running Z-Axis lead screws to turn at a random rate.
This was not a linear motion one lead screw would turn more than the other causing constant alignment of the Dual Stepper Z-Axis before a print.

See Video
T8-8 Trapezoidal Lead-screw Nut Dropping with Gravity
[youtu.be]

The T8-2 Trapezoidal Single Start lead screws have not shown to be prone the this problem for me.

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Computer Programmer / Electronics Technician

Thank you Dust and Roberts Cliff. I'm sure you must be right about the lead screws being "4 start".

This was my first ever lead screw purchase and I have to be honest, I didn't know about different 'start' values. The product listing I bought didn't mention start count anywhere and the calculators don't mention it, although they do mention height per revolution.

However, wouldn't changing the stepping on the driver require a value change in the firmware? I changed to 1/16 and it didn't seem to alter the distance moved. ( At least I changed the pin settings to 1/16 )

As for the alignment issue, I did get the anti-backlash nuts, so hopefully that will keep them where they stop.