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Old 04-04-2005, 11:19 AM   #1
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Unhappy Trinity Tru Lathe Setup Problems

Ok I've been having a lot of problems rebuilding stock motors and I've narrowed it down to my lathe. Here is the problem...any help would be much appreciated.

I take a poorly performing Stock motor after about 10 runs on it, check it on the GFX and it is pulling 6 Amps @ 2 Volts. I cut the comm, replace the brushes, clean the motor out completely, reshim etc...now the motor is pulling 4 Amps @ 2 Volts. I am convinced that it is the poor cut I"m getting with my lathe.

I have my trinity lathe being powered by a blue endbell handout stock motor. I cut the comm at 2 volts, not sure if that is fast enough! I use a carbide bit, I have many spares. I cut both ways, left to right and back. I thinkI have the bit height set properly. The comm doesn't look as nice as it does when its cut on other lathes.

Help?!?
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Old 04-04-2005, 11:39 AM   #2
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Change your bit, set the voltage for 4.5 volts so you get more RPM. Check to make sure your holders aren't worn.
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Old 04-04-2005, 12:17 PM   #3
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Thanks John...I'm going to try that right now. Best part of working from home....I can wrench while I'm working LOL.
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Old 04-04-2005, 12:21 PM   #4
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Default Re: Trinity Tru Lathe Setup Problems

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Originally posted by tminus3
Ok I've been having a lot of problems rebuilding stock motors and I've narrowed it down to my lathe. Here is the problem...any help would be much appreciated.

I take a poorly performing Stock motor after about 10 runs on it, check it on the GFX and it is pulling 6 Amps @ 2 Volts. I cut the comm, replace the brushes, clean the motor out completely, reshim etc...now the motor is pulling 4 Amps @ 2 Volts. I am convinced that it is the poor cut I"m getting with my lathe.

I have my trinity lathe being powered by a blue endbell handout stock motor. I cut the comm at 2 volts, not sure if that is fast enough! I use a carbide bit, I have many spares. I cut both ways, left to right and back. I thinkI have the bit height set properly. The comm doesn't look as nice as it does when its cut on other lathes.

Help?!?
even the worst cut will improve a motor with 10 runs on it. its something else...
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Old 04-04-2005, 12:23 PM   #5
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i got a hudy lathe from my gf for christmas, cut a few motors, with brand new bits, and they look like crap, nothing like when i let people at the track cut my comms.

i dunno if i got them shimmed bad, or im running too few or to many volts, or if my bits are crap(they dont look bad)

i cut some at 3 volts some at 4 and some at 4.5 and not one turned out good, they made loud noises, and the cuts are pretty rough, i thought maybe i was taking too much off, but i dont think i can take off any less
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Old 04-04-2005, 12:28 PM   #6
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comm must have been bad with 10 runs, how much did you take off? did you break in the brushes? its got to be the brushes...
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Old 04-04-2005, 12:35 PM   #7
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Not positive about the Trinity but I know the cobra uses a directional bit. Can't cut in both directions or you muck it all up. If the Trinity is that way and you are cutting both directions that could be your problem there. Good call on asking if the brushes are broken in fully also.
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Old 04-04-2005, 12:36 PM   #8
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Quote:
I have a fever, and the only prescription is more cowbell!
oh man thats hilarious, that skit was awesome
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Old 04-04-2005, 12:40 PM   #9
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Bit height is very important. If your bit is lower then the dead center of the comm then you will get a crap cut. The bit must be either dead center or a touch higher to get a good cut. I always oil both the comm and the blocks. Carbide bits will fall off after a few cuts so either re-finish them or change them often. Also make sure your lathe blocks are aligned properly so you get a true cut and not a cone cut.
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Old 04-04-2005, 12:48 PM   #10
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Carbide loves high rpm, so the faster the better. I'm a machinist, so I know the noise you are having. Reshim the tool, and try again.
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Old 04-04-2005, 12:49 PM   #11
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Ok I tried cutting at 4.5v, it didn't cut any better. The armature was spinning REALLY fast.

Right now I'm guessing the problem is between improper bit height and possibly directional bit.

Any tips on setting the bit height? I've been setting it up by eyeballing it.

Also the brushes I think are broken in pretty well. I at the motor at 3v for 120 seconds with a fan.
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Old 04-04-2005, 12:52 PM   #12
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btw, I also made sure I was turning the armature the right way. Away from the tip.
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Old 04-04-2005, 12:55 PM   #13
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I forgot-feed one direction only. Cutting tools have a relief to them, usually 8 to 10 degrees, that side should be the trailing side, and the part should turn against the large flat side. When you get to the end of your cut, back out and return to the start point, then start over.
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Old 04-04-2005, 12:59 PM   #14
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Originally posted by tminus3
Any tips on setting the bit height? I've been setting it up by eyeballing it.

Use a small, thin strip of metal, hold it gently between the tool and the part by feeding the tool into it, and if it is perpendicular, then the tool is close to correct. Be sure there are no chips built up on the tool, and that the tool is not damaged-carbide damages easily.
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Old 04-04-2005, 01:10 PM   #15
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To me it sounds like the motor (slave) is spinning the wrong direction. On my Cobra lathe, you have to run the motor backwards.

Think of it this way, looking at the comm side of the motor, the arm (Being cut) should be spinning clockwise if the bits cutting surface is down. It most likely is this way so that when there is cutting force, the arm is forced down into the guide ways or bearings supporting the arm. If you spin the wrong direction, first of all you'll break the carbide, or chip it. You might not be able to see it unless you use a jewelers loop. Secondly the arm will try to rise away from the tool, causing bounce and chatter.

At any rate, I have found that the carbide bits just suck for turning armatures. The diamond bits work MUCH better, and last much longer and make cleaner cuts.

I cut my arm at 2 volts with a 19t slave motor set at 0degrees of timing. works great.

Higher RPM can be an enemy here because as you increase RPM, you decrease chip load. With a slightly dull cutter this will lead to more chatter and a crappier finish. PLus, the higher rpm with such a low chip load, (turning .001 off) will shorten life of cutter because of heat and friction(chiping).

Yea, I am a machinist too. Did the 4 year apprenticeship.
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