Motor windings insulation

I am restoring a small pillar drill circa 1940's, it has a vintage 1/3 HP motor with a cast iron case , what I'm worried about is the stator windings which are coated in a kind or black rubber or bitumen, there are a couple of bare areas, was this black stuff the insulation or did they use varnished wire like we do today ?

Does anyone know what this black stuff is and if you can buy it now days ?

Should I get the windings professionally tested before test running it ?

At least use a ohm meter on the lowest range possible to verify the windings have no shorts.

With no picture I'm going to suggest that you coat the bare areas with black TV Corona Dope.

It may be a good idea to check it for continuity and resistance of the equipment grounding conductor, and then for leakage current. I assume it has a 3 wire cord, and thus is basically "safe" in terms of the way it is set up.,

JST said:

It may be a good idea to check it for continuity and resistance of the equipment grounding conductor, and then for leakage current. I assume it has a 3 wire cord, and thus is basically "safe" in terms of the way it is set up.,

Click to expand...

A lot of small appliance motors back then were 2 wire only, no safety grounds.

Tom

TDegenhart said:

A lot of small appliance motors back then were 2 wire only, no safety grounds.

Tom

Click to expand...

Yep, I was around back then, and you are absolutely correct. Nobody thought twice about it. At my father's house recently, saw a nice metal case portable drill with.... you guessed it it.... a 2 wire cord.

With 2 wire cord and crumby insulation, well, that leakage test got more interesting as an idea.

Waterworks said:

I am restoring a small pillar drill circa 1940's, it has a vintage 1/3 HP motor with a cast iron case , what I'm worried about is the stator windings which are coated in a kind or black rubber or bitumen, there are a couple of bare areas, was this black stuff the insulation or did they use varnished wire like we do today ?

Does anyone know what this black stuff is and if you can buy it now days ?

Should I get the windings professionally tested before test running it ?

Click to expand...

Winding WOULD have been of varnished wire, first, yes. The other coating MAY (war years?) have been used as Glyptal was to be used otherwise, to impregnate the finished windings so as to fill the voids and combat the effects of movement, moisture, and/or corrosives finding a home.

Or it may be sumthin' simply BURNT black, and that's why it is flaking-off!



My Walker-Turner dates from around 1942 IIRC. OEM motor is two-toned. Machine-grey on the Cast Iron ends. Black in the center band.

"Sort of" a TENV plan, so I can't see the windings. Just now went and checked.

I don't see "restoration points" for period-correctness of a motor as worth the bother with its windings at all questionable. Band-aid approach is not wise. A proper rewind, re-varnish, and bake nowhere near cost justifiable, hardly any fractional HP single-phase of basic general-purpose plan.

1940's era to the present-day ones look about the same in any case.

Mine ever fails, I'll just fit a new one. ISTR I re-did the start switch and gifted it with a new capacitor about 30-35 years ago, so it is "overdue" already.

They were decent motors, but so are most if you but avoid the obvious junk.