G0602 10x22 LATHE 3 STEP CNC CONVERSION

[BillTodd]

The rattle appears to be once per rev of the lead screw, is that how it sounds there? It also seems to vary with position.

Are you using the lathe's original half-nuts? (Sorry, I have been following your build but my memory isn't what it used to be... )

I have just viewed your early video of the Z axis driven by a battery drill. The rattle isn't apparent, so something has either come loose, or it has to do with the stepper motor end.


[edit] Ah! what's happening at the gearbox end - could the original dog-clutch(?) or gears be catching somehow?

[Crevice Reamer]

The rattle appears to be once per rev of the lead screw, is that how it sounds there? It also seems to vary with position.

Yes and yes. Rattle seems concentrated worse in center area of screw.

Are you using the lathe's original half-nuts? (Sorry, I have been following your build but my memory isn't what it used to be... )

Yes, original half nut, locked down tight as possible.

I have just viewed your early video of the Z axis driven by a battery drill. The rattle isn't apparent, so something has either come loose, or it has to do with the stepper motor end.

Drill ran much slower. If I run the axis at half-speed, rattle is barely noticeable. Drill also ran the very same coupler--And it was DEFINITELY misaligned with drill.

It almost seems like the screw is whipping, although I can't imagine that 3/4 inch screw flexing that much. Maybe it IS whipping in the looseness of the half-nut, but I can't see or feel it. The half nut feels really solid.

CR.

[BillTodd]

Might be worth dialing the lead screw with a DTI to check for straightness (it could be slightly warped, if it was hardened at the factory - a small warp would not have caused a problem while surfacing or screw cutting, so they may not be a super high spec' component)

[Crevice Reamer]

Might be worth dialing the lead screw with a DTI to check for straightness (it could be slightly warped, if it was hardened at the factory - a small warp would not have caused a problem while surfacing or screw cutting, so they may not be a super high spec' component)

That explanation makes a lot of sense to me. Just a slight enough warp to not be noticed at low RPM, but obvious at 1315 RPM. It also explains why the rattle is most evident in center of shaft.

I think you've solved it Bill! Thanks!

Nothing I can do about it then. When I remove it for stage 2, I'll check it for warp. I'll just have to live with it for this stage. Now I wonder what the 5/8 inch Acme screw will sound like? We'll see--or hear.

CR.

[Crevice Reamer]

Well, Bill called it:



Nice troubleshooting Bill!

CR.

[Crevice Reamer]

Let's test for backlash:

Jog has been set to single step. Each step moves the carriage 0.001 inch. On the DTI, each step is 0.001 inch.

I will move the carriage ten steps, then reverse. The number of Mach3 pulses, (Or clunks) before DTI starts moving again, will indicate the backlash in thousandths. You will have to listen and count the non-movement clunks.



Looks to be slightly less than 0.008. I'll call it 0.00775. That's a lot, but not nearly as horrendous as I had feared. Mach3 Backlash Compensation should take care of it.

CR.

[BillTodd]

Well, Bill called it:



Nice troubleshooting Bill!

CR.

You really need a large flat head on the DTI, or a piece of shim steel between the end and the screw, just to ensure the pointer doesn't dip as it crosses the thread.

[Crevice Reamer]

The fat tip on that DTI does not dip much, but just in the interest of science I removed the tip. That gives a nice flat surface:


Then repeated the test:



I believe that lead screw is either warped or out of round--Or both.

CR.

[BillTodd]

I believe that lead screw is either warped or out of round--Or both.

Unlikely to be far out of round. It might just be worth checking it in a few different places along its length; Turn the lead-screw by hand and note displacement and the radial position. That will give you an idea of the shape of the warp - If it's only a single arc between the two ends (and not an S shape) you might be able to improve things with a little careful leverage or by removing the screw and finding someone with press who knows how to straighten things

Bill

[Starleper1]

You could also find someone with a shaft straightener. We have one, its basically a set of V-Blocks with a hydraulic bottle jack that is movable to the position where it needs straightened. They are a beautiful thing to have when you need it.

~Scott

[BillTodd]

You could also find someone with a shaft straightener. We have one, its basically a set of V-Blocks with a hydraulic bottle jack that is movable to the position where it needs straightened. They are a beautiful thing to have when you need it.

~Scott

Ah ha! The man "with a press who knows how to straighten things" has just arrived

[Crevice Reamer]

Unlikely to be far out of round. It might just be worth checking it in a few different places along its length; Turn the lead-screw by hand and note displacement and the radial position. That will give you an idea of the shape of the warp - If it's only a single arc between the two ends (and not an S shape) you might be able to improve things with a little careful leverage or by removing the screw and finding someone with press who knows how to straighten things

Bill

Thanks Bill. The rattle does not appear to affect performance any. If I were going to use the lathe with stock screws for a considerable time, I would persue it further, but I will use this only temporarily. It will have to serve as-is for now.

CR.