Sherline lead screw

[uniphyte]

Greeting all Sherline owner, I had a mill that was use for many years since the 90s. Most of the time I had machine only small part. Recently I discovered that the y-axis pitch is not accurate when I wanted to machine over a longer distance.

I wanted to cut a piece of aluminum of 100mm length. Using a 3 mm end mill. I trim one end. So moving forward another 103mm would mean I have cut 100mm. But I had discovered that workpiece would end up 100.8mm. In the end I had to manually trim down the piece and constantly checking with vernier caliper till i have 100mm.

I did another experiment and drill 2 hole 100 mm apart. This time, the Y-axis was turn only 100 turn in one direction to achieve 100mm. The same result. It was longer than 100mm over hundred revolution.

So I had to presume the lead screw was not accurate. All backlash were kept to a minimum. I have yet to remove the lead screw to check its pitch over a hundred mm. It is important to have an accurate lead screw in order to machine our part. If the error is less that 0.1 per 100mm, that is still OK since it a hobby machine.

So I would like to ask anyone with a Sherline metric mill or lathe to test out your machine to see if there are any difference? But do remember to test over a longer distance ( at least 100 apart ) to test the accuracy of leadscrew. Thanks!

[HZM]

0.8mm is kind of big. Can I know the accuracy of your caliper first?

Mike

[Ratboy]

i think you have to move only 101.5 i/o 103
as the 3mm cutter is diameter ?


A more accurate test is to put a masking tape on the table at the edge
where there are markings
use a pen a draw a reference to the X table
then move 100 turns
and measure from the X table reference to the masking tape mark
This will measure the actual table movements
and does not take into account any cutter diameter error etc

[uniphyte]

Hi, I have recheck my mill and found out the lead screw on Y-axis in not accurate when compare to X and Z axis. The discovery came about when I tried to cut more than 100mm and it measured longer. The actual findings are it about 0.4mm longer at 100mm as oppose to the claim of 0.8 I made earlier as I mix up the 100mm and 200mm long piece I am working on. The first time I discovered it was last year but didn't pursue further as i thought it was an backlash error.

This is how I test. I took a vernier caliper and set to exactly 50mm. When I set the lower jaw against the thread, I lock down on one side with the edge touching the tip of one thread. 50mm at the other end, the thread should line up correctly. I use a high power magnifying glass to check my finding. Truly, the Y-axis right hand thread lead screw was longer by around 0.2 to 0.25mm. Without adjusting the caliper, I check against X and Z axis. The result were better. Perharp of only 0.03 of error per 50mm. That is acceptable. Luckily the X and Z axis are quite true to measurement. As it a left hand Thread. It not easy to find replacement. Except getting a replacement form Sherline.

I also test did a test with some M6 thread from stud and screw I can find. The result varies as only the good quality machine screw were fairly accurate. Those mediocre roughly made thread were either longer or shorter.

So what next, I will go hunting for a M6 thread shaft to replace the unit in my mill. Hopefully I can get a stainless steel one with less error.Little wonder When I tried to CNC a circle in a piece, the hole is always slightly elongated.

[uniphyte]

Hi everyone, been busy for a while. Finally, I have replace the old lead screw with a new one. I manage to get hold of a M6 threaded rod. A few days of machining work and I have the new part ready for my mill.

Here a comparisons of the old and new lead screw.



Since I have replaced the lead screw, I might as well replace the backlash nut too. So I took a unused connector ( PL - 259 ) and transform into the two of backlash nut.



And, the mill is ready to machine again!



So far, I only spend less than $10 to get the M6 tap for the backlash nut. And the lead screw is free! Pocket save! <br> <br>