T8-8 vs T8-2 Lead-screws

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T8-8 vs T8-2 Lead-screws

Post by Roberts_Clif » December 5th, 2017, 6:43 pm

Today's post is my opinion of the Z-Axis lead screws for use on Hictop Reprap Prusa i3 3D Printers.

I have read what I believe is a lot of bad advise about what kind of lead screws to use. So this post starts with me putting my 2 cents in.
It has been suggested to use a Z-Axis lead screw with the following specifications.
Trapezoidal T8-8 as a newbie to the 3D Printer innovation went with the suggested.

The suggestion that this lead screw should be a must have purchase was a T8 Trapezoidal 2mm pitch 4 start, (8mm per turn pitch) 3D Printer Z-Axis Lead Screw. This lead screw has a thread form that is profiled with trapezoidal outlines. They are designed for high strength, ease of manufacture and are designed for high torque with its trapezoidal thread design. Making it perfectly suited for CNC machining.

This lead screw design with its 8mm shaft (4 start, 8mm per turn pitch) has one major flaw. Using the lead screw for over a year now, I find that the 8mm per turn pitch is highly wrong for the Z-Axis when using a Prusa style 3D Printer design. It seems that I am constantly crashing into the bed as the lead screws do not maintain its alignment very well. I find that if the Z-Axis is just aligned to perfection and the 3D Printer is turned off, and if you have a second 3D Printer sitting on the bench next to the first. This vibration can cause the 3D Printer to need to be re-aligned. Now this is just from the vibrations, causing the printers Z-Axis to spin unevenly downwards. Normally this may not be a problem though the Z-Axis on the Prusa i3 designed 3D Printers causes one of the Z-Axis lead screws to turn more than the other causing the Z-Axis to become out of alignment.

As I have two 3D Printers one was equipped with the T8 Trapezoidal 2mm pitch (4 start, 8mm per turn pitch) and the other is equipped with a T8 Trapezoidal 2mm pitch (single start, 2mm per turn pitch) lead screw. This is the lead screw that will be suggested by me from this date forward. It is identical to the T8-8 with only one difference. This lead screw has a T8-2 (single start, 2mm per turn pitch), and does not loose the position like the T8-8 (4 start, 8mm per turn pitch).

Take a T8 Trapezoidal 2mm pitch (4 start, 8mm per turn pitch) install the nut, turn vertically the nut will spin to the other end, What is this some kind of an expensive fidget by Adding the lead screw to a 3D Printer is just asking for alignment issues. And when any downward pressure is applied to the 3D Printer X-axis this will cause the Z-Axis rods to spin. If they would only spin equally this would be not problem, but this truly is not the case.

So Needing Lead Screws save yourself a major headache and buy this one T8-2 Trapezoidal (single start, 2mm per turn pitch) Lead Screw.
Electronics Technician / Computer Programmer

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Re: T8-8 vs T8-2 Lead-screws

Post by Chaco » December 20th, 2017, 1:40 pm

interesting info... will sure give it some tought...
im lately interested on ball leadscrew s

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