Cut motor burnt

[55president]

After 936 hrs I sent my still running cut motor to Carvewright to get it rebuilt as there are
no new cut motors to buy.After it came back I reinstalled it and thought it kind of sounded of wimpy
compared to before, but it worked and I figured maybe that's the way it was supposed to be.
After 80hrs on the rebuilt one, it burnt a brush and melted the plastic case.
Called Carvewright today and they say it might have been a blue spark issue - where the commuter and
stator were mismatched. I'm waiting for the new Motors, I don't have much
faith in thier rebuilds, if I just got 80 hrs out of it. Anybody with similar issues with rebuilds?

FXP

[unitedcases]

Mine did that in my primary carver yesterday. Melted the lower brush to the case and the top brush blew apart.

[55president]

was it a rebuild?

[unitedcases]

Nope. Brand new. Ran it for a little over 150. Then did a pm and changed the brushes. Ran for another 150, did the same thing. Ran for another 50 and that was it. I had over 1500 on my first motor so I am not complaining. Plud I have a back up motor plus a backup machine.

[Digitalwoodshop]

Cut Motor Brushes can hang up in the metal sleeve causing this problem. When not enough pressure is being placed on the brush to copper commutator a arc can start and be seen throught the air cooling slits. Some arcing is natural but at some point the arc creates more heat and this causes expansion of the actual carbon brush further causing the brush to lag in pressure and creating a bigger arc.... The end result is heat to the point that the plastic housing melts....

From my Navy Days of fixing Motors and Amplidyne Generators as a Gun Fire Control tech... I out of habbit take the NEW LHR brush and run all 4 sides on some very fine sandpaper reducing the size ever so slightly AND sort of polishing the sides removing any roughness that can cause the brushes to hang up in the holder... NOT too much to let the brush flop around.... I also have a plastic spray can top that is about the size of the Cut Motor Armature and I have some fine sandpaper glued to it... I Sand the Brush to match the Commutator before installing the brushes. In the Navy days with a Commutator the size of a can of Soda we placed a piece of sandpaper on the commutator and moved it back and fourth with the brush being installed to pre seat the brush. I saw the results once of someone who did not seat the brushes and only a small part of the brush was contacting the commutator. It caused arcing to the point that the Amplidyne needed to be removed from the ship and the commutator cut on a Lathe to remove the pitting.

I also run a Cotton Swab through the metal brushe holder to clean out any dust making sure not to leave any cotton...

http://en.wikipedia.org/wiki/Amplidyne I started my Navy Career in 1975 and was heavy into TUBE Driven Amplidyne Generator Equipment and Analog Gun Fire Control Computrers with Servos and Synchros... I ended my Career in 1995 with some of the latest Microprocessor Controlled Equipment. So I know motors....

I am betting that every Cut Motor that was melted had the LOWER Brush beng melted... My THEORY is that since it is on the Low side, that DUST that is sucked into the Cooling Fins ends up around the brush and ends up INSIDE the Brush Holder....

So I ASK.... Of the Burned up Motors.... 1. Was it the lower brush? and 2. Do you have Dust collection?

In Hindsight, IF I were to setup this Cut Motor. I would have the brushes at 9 and 3 O' Clock when the motor sits in the machine rather than the 12 and 6 O' Clock or top and bottom as it ended up with the Cooling and FAN outlet....

And a 3rd question.... Anyone who had a motor burn up that changed brushes and did NOT open the motor and blow out the dust? And just installed a new set of brushes....

WE might find some "Lessons" to be learned here.... Like possibly... The Motors that burned up were never opened and cleaned out? No clue on the LHR Referb Motors.... Opened or just new brushes... It would be interesting to hear.... Over time WE learned to CHANGE the Y Gearbox Bearings BEFORE they failed....... And it has made a big difference in my humble opinion....

In the pictures... from 1977 my in the big Amplydine Driven Gun Director off the coast of Japan moving the Radar Beam around and the Analog Gun Fire Control Computer... NO Keyboard... Just hand CRANKS.... my first computer...

Showing my age...

AL

FCC(SW) Retired Navy

[aokweld101]

When changing the brushes in both my units I have always taken the casing apart and blown it out with air. I don't know if it helps but it makes me feel better. all the carbon dust can't be good for the cut motor. I also use a hand brass toothbush to clean the armature.

[55president]

Al --very informative as usual. I also agree that the 3 o’clock and 9 o’clock
Positions for brushes might be better for this motor.


To answer your questions:




The brush that burnt out was in the top housing section of the motor. The brush got so hot that it melted the plastic spring retainer thingy to the housing .





I do have dust collection but I wasn’t using it because I’m carving vinyl. The vinyl dust is a lot heavier than sawdust. It tends to just fall there and not blow around.

the dust collector sucks little of this up. I usually just vacuum it all up after the job is finished.




This motor was a rebuild from carvewright. My original motor had 936 hours on it. I had changed the brushes several times without blowing out the dust in the motor with no problems. Remember this is the vinyl dust not wood dust.I blame myself because the motor was running just fine and I figured I’d get a jump on it blowing up on me by getting it rebuilt. Next time I get a good running motor I’m going to let it run until it goes out completely. What bothered me most about this motor was the magnet for the RPM sensor had fallen off. So in the beginning of a carve it couldn’t sense the RPMs and I got tired of pushing the button to proceed.





Taking into consideration your suggestions for brush replacement, I need to get a top
section of motor housing , or a complete plastic housing. Does any body have this?

FXP

[Digitalwoodshop]

Top Brush.... That is interesting....

As for the Cut Motor magnet... Early units had a Heat Shrink retainer that came off.... A plastic retainer fixed that....

See dates on pictures.

AL