A request for information on your mill or lathe

[bi11hudson]

A strange request.
I have a Craftsman 101.27440 (12X36) and a Grizzly G-1550 (Taiwan 9X19). Both machines have roller bearings in the headstock. I have NEVER welded any stock in the Grizzly, and pretty sure the Craftsman never has, the bearings are too "smooth".
I don't have any resistance readings, I strongly disapprove of any device that passes ANY (even micro-amps) current through the spindle bearings. Background: Industrial electrician with 50 plus years experience, Wang Field Engineer, BSEE, and a handful of other accolades.
Bill Hudson

[Toolmaker51]

IF the spindle and motor are direct [couplers, gears], that's a potential conductive electrical path to ground, as many jig bores & drill presses.
Lathes and other rubber belt-driven machines such as mills, have potential static conducted to table via spindle, and of course to ground.
I'd wager that static is marginal compared to what amounts to a short from armature to shaft, through bearings into motor frame. Recent bearing diagnosis charts added that form of pitting soon after those electronic motor controls came to market.

There is no reason to NOT flood most plastics, if nothing else to clear the flutes or cutter tip. Cutting and static electricity [in correct atmospheric condition] makes that s**t stick. Coolant or leastwise mist, dissipate static and heat, the film releases plastic chips. Thermo-plastics a greater offender than thermo-sets. All in all, if drilling any significant depth, coolant is de' rigueur. Milling slots or pockets though, I try a cold air gun first. Easier clean up!

A dry HSS endmill will blue readily at excess RPM in Teflon, Delrin, UHMW and phenolics. Schedule 40 & 80 PVC machines like a dream at slow RPM and moderate FPM rates, the threshold gets miserable fast bumping either past that line.

nova_robotics mentions grounding straps; IIRC it's more common to use a brush, like fine stranded wire that just needs to drag around. I'd say such wire stripped longer on one end, other short crimped/ soldered to a ring terminal, leaving a little ferrule of insulation will suffice.

Bearings, satellites and space in one sentence? Ask me sometime about 1" reel to reel tape decks, custom built for satellites, space shuttles, and likely some other high flying stuff. Maybe the most epic work I'd (we've) ever done.

[Tonyg]

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.

SKF have an interesting article on current through bearings. I have come across it on some large plasma and oxy/fuel machines with a potential difference between the gantry and the rail where you can see it sparking and the bearing gets very hot (and damaged). Caused by a poor earthing connection, a star earth to between the two generally solves the problem.

https://evolution.skf.com/en/prevent...n-in-bearings/

[Carnel]

Hi Rick,
My readings:
2 digital volt meters

DVM1 Escort 1111A
readings: test cords only: 0.2 Ohm. Lathe (AI, dutch brand, ca 1960) 0.5 Ohms between chuck en ways, but same as between chuck and tool post
drill-mill: (HBM, dutch version of HarbourFreight, ca 2000) 0.4 Ohms between quill and cross table

DVM2 Velleman DVM4200
readings: test cords 0.3 Ohms. Lathe 0.5 Ohms (same conditions as above)
drill-mill: 0.4 Ohms

So at my machines the resistance is very low, in the order of 0.1 or 0.2 Ohms. With a lot of relative uncertainty in the milliohms range.

[Toolmaker51]

SKF have an interesting article on current through bearings. I have come across it on some large plasma and oxy/fuel machines with a potential difference between the gantry and the rail where you can see it sparking and the bearing gets very hot (and damaged). Caused by a poor earthing connection, a star earth to between the two generally solves the problem.

https://evolution.skf.com/en/prevent...n-in-bearings/

Bookmarked! Worth being up at 0230.

[brianr47]

SB Heavy 10
0.5 Ohms initially, then 0.4 Ohms after 1 revolution of spindle

[Frank S]

Bookmarked! Worth being up at 0230.

When I am made aware of technical information such as this article, I often find a rabbit hole to chase. However a lot of the time right at the moment time for chasing may not avail itself to me. yes bookmarking is a favorite tool of mine, but for me a more useful tool at my disposal is the right click and print feature. I then save the data as a PDF to my computer, this way I'll always have it even when offline. I can also open the file and print hard copy of any portion or the complete file should I so choose

[Hans Pearson]

Interesting thought.
Myford ML7 with plain white metal bearing and unused for 5 days - 6 Ohms
Chuck turned ¼ turn - 3.3 Ohms
Oil drip feeds opened and about 4 drops dispensed form each feed, chuck turned about 3 turns - 2.5 Ohms.
As others said above, one thing that never enters your head, and I have been associated with this old machine for over 50 years.

[Toolmaker51]

Same here. I bookmark some first, like tech data needing some more digging. I've a vast trove of PDF's awaiting printout that are more like manuals, part lists, select black & white shop photos, etc.
Likely will open each first page in Paint or Word beforehand, noting particulars like acquisition date, serial, model, spindle taper, weight, cubic footprint; all depending on item. Sure do miss how Word used to contain ready access to write and print Barcode 39, though still have operative scanner pens. QR codes are not so compact, and read slower, prefer google not cut in to my work.

No 'best procedure' is a leader, just consistent file & folder naming precedents. Another trait bestowed on us by Uncle Sam.

[Toolmaker51]

Interesting thought.
Myford ML7 with plain white metal bearing and unused for 5 days - 6 Ohms
Chuck turned ¼ turn - 3.3 Ohms
Oil drip feeds opened and about 4 drops dispensed form each feed, chuck turned about 3 turns - 2.5 Ohms.
As others said above, one thing that never enters your head, and I have been associated with this old machine for over 50 years.

Rather conclusive test, we may allow a machine to warm up first then, lube. This says turn over un-powered a bit first. Anyone have results where 3 phase differs from single?
Is there a non-conductive container to get result on clean oil alone? Judging that compared to pure water not being conductive, minerals make it so.

Every bearing has clearance. Gravity pulls horizontal shaft "through" the oil film as it drains away, contacting bearing. Intuition says that be more conductive than a couple rotations spreading lube. Unconnected to oil, but what travels to ground when power is off? Does this justify practice in big plants, each machine [esp CNC] having individual or share adjacent ground rods?

My building stored 55 gallon steel drums of printing inks and solvents, many many dozens of them stacked up. A bare *12 copper encircled the perimeter, with multiple jumpers and clips for the barrels, terminating in just one 8' ground rod at edge of building inside the drip line. I don't think forklifts entered; material set on dock with pallet jacks. 100% No smoking within ~40'. No electricity other than minimal warehouse pendants, to a single switch. Wiring just EMT, not any of sealed types.
That's a lot of fuel, with hardly any source of ignition.