CMS tragedy ;(

[chopnhack]

My beloved 10" GMC sliding cms decided to release its magic smoke today. It was only ~6 years old and I am really p.o.'d about it. As I type this, I am taking a break from unwinding the field coil, which is what cooked. 50 turns yielded about 455", untold thousands to go.... It always seems to happen that way, right in the middle of a project, something decides to jump up and bite you in the arse. Any tips on field coils anyone?

[Richard in Smithville]

. It was only ~6 years old

Isn't that around 56 in CMS years?

[chopnhack]

May the Daleks and cybermen pay you a visit Rich :P

So all told, 46 turns of 18G and 60 turns of 24G per side of the field coil. I guess I will try and find magnetic wire locally as I only need about 80' of each.

Any idea why a fairly young saw would crap out? The brushes were still near full thickness, the inside of the motor had very little dust. I have never misused the saw. The most recent thing I did aside from crosscutting some 2x4 today, was make a few small dados by repeated chops.

Does anyone think that the saw being on for too long might have caused it to overheat?
Should I be thinking of upsizing the wiring?
Are there any other components I should be testing before rebuilding and testing out again?

The two windings of different gauge I can only assume, the smaller gauge was the start winding with the larger being the run winding. It seemed like the smaller gauge showed all the heat damage.

Thanks!

[LCHIEN]

Failure of motors is usually due to insulation failure causing windings to short out.

The wiring of the coils in a motor is usually enameled copper wire. Because copper has the best electrical properties for the money and enamel has higher dielectric strength and smaller sizer than other wire insulation types so it packs smaller.

Most probably Failure of the insulation is either due to (1) excessive heat, (2) mechanical vibration or (3) simple breakdown of the insulation.

(1) is caused by motor overheating. sustained Excessive loads where the work load exceeds the rated load of the motor and the wire heats from excessive IR loss or more likely, the magnetics are saturated and the excess current becomes heat loss in the core; either way the heat goes up and the insulation breaks down smells bad and shorts. Another failure cause is high load and low voltage (low line OR perhaps too long and small gauge of extension cord).

(2) Improperly tied down or fixed wires can vibrate with motor vibration and literally rub thru the insulation. Most motor cores are covered with epoxy or more enamel after winding to hold them in place so they won't rub.

(3) Simply poor quality control can make wires insulation failure. If the enamel is too thin or has pinholes or is substandard material-wise this can lead to breakdown over time exacerbated by otherwise acceptable heat.


considering GMC is a inexpensive tool maker, it might be 2 or 3 and not overloading that killed your saw after 5 years.

[dbhost]

For what it's worth, Harbor Freight has the 12" slider on sale this weekend for $109.99, and of course there is a 20% off coupon you can use with that...

[cabinetman]

For what it's worth, Harbor Freight has the 12" slider on sale this weekend for $109.99, and of course there is a 20% off coupon you can use with that...

A friend of mine bought the 10" and doesn't like it.
.

[chopnhack]

Thanks for the info guys.

Loring, from the information I have seen on magnet wire, the manufacturers I have seen say they use polyurethane as their coatings. Do you know if this is a special poly, or can I get a can of minwax after rewinding and glob it on

Thanks Db, I checked out the saw online and though the general construction looks similar, and it would be an upgrade both in size and tilt, it lacks a depth stop which my old saw had and frankly I doubt that for $100 the saw would last more than a few years. No offense, I buy harbor freight tools on occasion, but I stay away from their electrical items because of my experience with them in person (looking at them in the store).

[LCHIEN]

i'm not reaslly super up on the materials they use for this application now.
I would imagine its formulated for high temperature operation and not just ordinary PU varnish. But I don't know for sure.

http://en.wikipedia.org/wiki/Magnet_wire says:

Modern magnet wire typically uses one to three layers of polymer film insulation, often of two different compositions, to provide a tough, continuous insulating layer. Magnet wire insulating films use (in order of increasing temperature range) polyurethane, polyamide, polyester, polyester-polyimide, polyamide-polyimide (or amide-imide), and polyimide. Polyimide insulated magnet wire is capable of operation at up to 250°C. The insulation of thicker square or rectangular magnet wire is often augmented by wrapping it with a high-temperature polyimide or fiberglass tape, and completed windings are often vacuum impregnated with an insulating varnish to improve insulation strength and long-term reliability of the winding.

[chopnhack]

.... Any thoughts on what to do with nearly 40lbs of cast aluminum?

[BobSch]

You might want to keep the rails and sliders for some future project.

[chopnhack]

Loring, how did you modify my post with your reply? LOL

"I see (maybe not the most current prices) cast aluminum scrap somewhere around $0.80 per pound at any scrap metal or aluminum can recycling center....
That would be $20 to $30. "

[luteman]

Some time ago, I posted my bad experience with owning a GMC cms piece of crap. To recap, it was shipped to me missing one of the outboard rail slider bearings not to mention one of the laser units was defective and the other was totally misaligned. I tried in vain to get help from GMC so-called "customer service". Was told to ship the saw back to Amazon. I would never,ever buy a tool made by this company again!!!!

[woodturner]

I buy harbor freight tools on occasion, but I stay away from their electrical items because of my experience with them in person (looking at them in the store).

FWIW, I have an HF hammer drill that has outlasted three Makitas (but not the Bosch). I prefer their 4.5" $10 angle grinders - none of them have failed after 10 years of heavy use.

Many brands are made in the same factory. From my perspective, GMC is a lower quality brand than HF.

I'm sure HF tools must fail eventually, I just haven't had that experience in many years.

[LCHIEN]

.... Any thoughts on what to do with nearly 40lbs of cast aluminum?

I see (maybe not the most current prices) cast aluminum scrap somewhere around $0.80 per pound at any scrap metal or aluminum can recycling center....
That would be $20 to $30.

[LCHIEN]

Loring, how did you modify my post with your reply? LOL

"I see (maybe not the most current prices) cast aluminum scrap somewhere around $0.80 per pound at any scrap metal or aluminum can recycling center....
That would be $20 to $30. "

WHOOPS. Sorry. Inexperienced moderator here. Actually the second time I did it.
The new (to me) moderator functions gives me an edit button where my reply button used to be, I hit the edit button instead of reply and did not notice I did so. I think i cleaned it up now.