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Old 04-13-2005, 08:46 AM   #1
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Default motor - comm truing issue?

I've noticed that I can't seem to true my comms as smoothly as the came when new.

They come out kinda "rippled" - not as smooth as they come from the factory or builder.

I'm using a HUDY lathe, w/ a carbide bit.

Am I doing something wrong (probably)? Tell I don't have to buy a diamond bit...... please!

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Old 04-13-2005, 08:50 AM   #2
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is the carbide bit still sharp??? that might be the problem. carbide bit cant last.
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Old 04-13-2005, 08:51 AM   #3
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Your carbide bit is probably dull. the good news is it can be resharpend with a diamond file. Just don't change the angles of the bit. See Big Jim's forum for more information about bit sharpening.
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Old 04-13-2005, 08:53 AM   #4
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I had that issue with my Orion lathe. It turns out I was running the slave motor backwards. Check to see if it's running backwards.

As far as needing a diamond bit. I checked with tool and dye workers and they say that diamond bits are overkill when it comes to cutting something as soft as copper. The only requirement of a carbide bit is that you run the slave motor at higher revs in order to get a good cut.

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Old 04-13-2005, 08:54 AM   #5
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How many volts are you using when running your lathe?

How old is the Carbide bit? Has it been dropped?

Is your lathe turning the motor to be cut in the correct direction?

Are you using cutting fluid or a Sharpe pen on the comm?
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Old 04-13-2005, 09:03 AM   #6
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Don't bother with a diamond bit, they are overkill. Go to www.mscdirect.com and search for brazed carbide. You'll have to compare your bit to get the right one, but they should only be $3 or so. Also try slowing your lathe down, be sure there is no chip buildup on the tool, and always oil the comm-any oil is better than no oil. Carbide is a sintered metal, meaning compressed, and by nature is brittle. It doesn't like interrupted cuts or low rpm. Look closely for a broken tool, sometimes it is hard to see the broken tool. On all good lathes, there is an adjustment on the guideways, called gibs. Tighten them to your feel, as they help take out backlash. They shold also be oiled regularly.
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Old 04-13-2005, 09:03 AM   #7
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which hudy lathe do you have? motor lathe rotation makes a difference.
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Old 04-13-2005, 09:07 AM   #8
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Dr.X,
Sounds like your cutting out of round. Make sure the bit is also shimmed correctly. Try cutting at 2-2.5 volts to avoid bounce.
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Old 04-13-2005, 10:14 AM   #9
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I can only cut about 5 motors on a fresh bit before the quality of the cut starts to deteriorate enough for me to swap bits. I have a few extras that I keep sharp. Just get a diamond file and a couple of swipes and your good to go. Just dont touch the bottom edge of the bit, just the sides.

Machinists always say that diamond is overkill for copper but they dont understand how "work hardened" our comms get and how precise of a cut we need.
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Old 04-13-2005, 10:48 AM   #10
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which way does the motor need to turn?

ive got this lathe
http://www.hudy.net/xhudy/show.php?i...7cb790dc20f80b

and i just hook up the positive to the positive and the negative to the negative on my pulsar, and my comms look like crap
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Old 04-13-2005, 10:53 AM   #11
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I use/do the following and I get perfectly polished comms that are sometimes better than from the factory:

* Cobra comm lathe with diamond bit
* 3.5v to slave motor
* use one comm cutting drop for each cut
* Pre-mark comm with permanent marker
* I only cut the comm from right to left and I back off the bit before moving the comm back to the start position. I've seen others move the comm back with the bit still in the same cutting position and I noticed the comm had waves in it afterwards.
* initially each cut I make is half a "tick" mark on the lathe until most of the marker is shaved off the comm and the only marker visible is on the lips of the grooves.
* last cut (or two, until all marker is completely gone) is only a quarter a "tick" on the lathe wheel. This smooths out the surface better.
* clean the groves carefully with a very small flat head screwdriver or blunt back side of hobby knife blade
* use a standard ball point pen and run it down the groves twice to round off the edges
* clean the groves carefully again with a small screwdriver
* spray off the comm with motor cleaner and blow dry completely
* put the comm back on the lathe, start it back up (with the bit backed way off) and use a 1/5/10/20 dollar bill to polish it to a mirror shine!

If you've put on new brushes and the comm has been previously trued by yourself, I suggest you break the new brushes in partially before cutting the comm for the next run. Since you can trust yourself, you shouldn't have to shave much off the comm and your brushes will not take long to seat now that they have been halfway broken in to the approx curve of your comm. I only suggest this because when you use the steps above to cut your comm, it will be almost too smooth to break in the brushes and you will have to break them in at <1 volt for 30+ minutes (been there).
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Old 04-13-2005, 11:18 AM   #12
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primus,
make sure the comm is turning up to the bit.
i would think hudy already wired it correctly. but check to make sure.
as the comm is turning use a sharpie marker to coat the comm. this acts as a lubericant for the bit. i myself use WD-40 just a dab.
make your final cut you only skim the surface. very light cut.
what voltage are you using??
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Old 04-13-2005, 11:29 AM   #13
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i was doing 3.5 i think
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Old 04-13-2005, 11:44 AM   #14
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did you put anything on the comm for the final cut. or did you cut it dry??
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Old 04-13-2005, 11:46 AM   #15
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i used a sharpie on the first and last pass
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