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Replacing Old Lead Screws Today

Posted by Roberts_Clif 
Replacing Old Lead Screws Today
August 01, 2017 10:09AM
Today I finally replaced my Hictop All thread lead screws with some T8-2 Trapezoidal lead screws. "8MM with a 2mm pitch per turn"

#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 1600, 94.4962144 }

The job took less than a hour to complete including updating the firmware for the new lead screws.
I do not tighten the main screws until all is in-place as that little bit of slack is sometimes all you need.
when tightened you get the perfect tension on the lead screws leaving you with a smooth inter-action between the parts.

And of course during the testing determined that my Z-Axis still had the 2560 so could only get about 118mm on the Z-Axis.
I know that I had changed the Firmware correctly looked in Controller Menu under Control, Motion and ZSteps/mm and It still had 2560, tried to reset EEProms to firmware would not work from controller.

As it had been quite a while since my initial configuration it took me awhile to remembered, with firmware changes you have to reload firmware defaults into EEProms. This was accomplished by using Cura and the M502 to reload firmware defaults and M500 to save the changes back to EEProms.
Re: Replacing Old Lead Screws Today
August 01, 2017 09:28PM
Just be careful with lead screw calculation, the pitch is different to the lead. Yes the pitch of the thread is 2mm but if you have 4 starts (number of threads there are spiralling around the shaft of the screw) then your lead would be 8mm (lead = pitch * starts). The lead should be used in the calculation and not the pitch. You can see the number of starts you have by looking at the end, most common are 1, 2 and 4

You might already know this, just putting it here for others who might upgrade to lead screws and wonder why their steps / mm are off
Re: Replacing Old Lead Screws Today
August 02, 2017 11:39PM
Thank you! I Have the the T8-2 Trapezoidal single start lead screws this is not the 4-Start, though I have that lead screw on my 2nd Printer.

By using the lower 2mm pitch in lieu of the 8mm pitch. A single start lead screw with the tightest pitch possible is generally your best bet for the z-axis
The T8-4 start is a more aggressive lead screw and will require more torque to drive.

Using the T8-2 single start lead screws on this printer with smaller stepper motors will place less stress on the stepper motors.
And a 2 mm pitch with a 1.8° stepper gives you 0.01 mm vertical movement for a full step.

Edited 2 time(s). Last edit at 08/02/2017 11:42PM by Roberts_Clif.
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