A request for information on your mill or lathe

[nova_robotics]

New idea. What about static guard spray for clothes? It lays down a slightly conductive layer to dissipate static charges. I've used it on some strange projects in the past and it worked well. What about giving your workpiece a coat of static guard to protect your spindle bearings?

[DSTP]

1952 Logan 920: 0.9 ohms first time, 0.9 ohms after a few rotations.

[rgsparber]

Whatcha doin'? Making a touch probe?

I’m assessing how many people could use my least sensitive version. I’d say all of them which is a big surprise.

Rick

[nova_robotics]

I’m assessing how many people could use my least sensitive version. I’d say all of them which is a big surprise.

Rick

How are you handling the spindles that are isolated?

[rgsparber]

How are you handling the spindles that are isolated?

Resistances greater than 1 ohm aren’t a problem. When we get below 0.2 ohms, my edge finders can’t reliably detect touchdown.

Rick

[Toolmaker51]

I’m assessing how many people could use my least sensitive version. I’d say all of them which is a big surprise.

Rick

We like the legacy version Rick, just the way you are.

Some had our fill of sensitivity several months ago, many even longer; much longer. IYKWIM, LOL.


It interests me still, but have to postpone collecting readings. There are a couple with serious mass between spindle and table.

[nova_robotics]

Resistances greater than 1 ohm aren’t a problem. When we get below 0.2 ohms, my edge finders can’t reliably detect touchdown.

Rick

Okay but I have two machines that are open between the spindle and chassis/table. No electrical connection.

[Frank S]

A little disappointed in my Fluke 81438 multimeter. I use it mostly for reading VAC or VDC and HZ hardly ever for any ohm readings if I want of think I need to know the true resistance since it has no zeroing adjustment. I had removed the batteries from both my Simson 260 multimeters since I rarely need to use them I don't want the batteries available today to develop a leak in them.
I checked my LaBlond 17inch lathe today with the flake, "sorry" the Fluke, I hadn't used the lathe in about a week so the first test reading came out to be .8 ohms. but when I put the ends of both leads together instead of getting a reading of o,oo I had a reading of 0.2 ohms Huh? so I removed the red lead and touched the black lead to the red lead socket , o.1ohms, same for the red lead when I touched it. Checked from the chuck to the bed again and the reading was 0.8 ohms. SO I'm going to call that one 0.6 phms allowing for the 0.2 of the leads. I did a 1/4 rotation same reading half rotation no change full rotation still no change.
Since I never start my lathe after it has been sitting unused for a full day or more I filled the oil cups the turned it on for a few seconds the took readings again 8.2ohms I decided to switch it on at a low RPM and hold the probe to the outer edge of the chuck while it was turning and the bed. Nothing no continuity reading at all OK at the highest reading nothing. wondering about whether there was a possibility of the chuck generating voltage I set to DCv at low RPM touching the chuck and the bed nothing. High RPM . 0.001VDC I will get some new batteries for my Simson meters the next time I think about it and check with them

[rgsparber]

Whatcha doin'? Making a touch probe?

I've already developed a family of Electronic Edge Finders that cover a wide range of spindle resistances. They all compare the spindle to machine body resistance before and after touchdown. My simplest one works down to a spindle resistance of 1 ohm. My most complex ones go down to 0.1 ohms.

Rick

[rgsparber]

Bet this turns out interesting. Two variations that come to mind immediately are direct spindles vs driven spindles, and the bearing packs. A lightweight drill press gets away with just two. A tough mill often has three or four. Other machines are completely isolated.
Don't know the exact term, but there is an issue where stray current erodes contact areas of bearing components and races. IIRC, VFD rated motors have additional frame grounding to bypass the bearings.

My lathe and mill use belts so the motor is electrically isolated from the spindle.

I've seen large variations in electrical resistance between the spindle and machine body on my mill. I can't explain it, but when I raise or lower the quill, the resistance drops below 1 ohm. Turning the spindle by hand a few degrees brings it above 1 ohm. The quill to machine body resistance is always below 0.05 ohms.

I know you can get ceramic ball bearings for motors. That would permit a large voltage to build up on the rotor and cause arcing if not, as you mention, grounding of the rotor is not present. This arcing is identical to EDM so would easily eat steel ball bearings.

Rick