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Old 04-29-2004, 08:52 PM   #1
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Default Lathe Tips?

Is there any tips people have on cutting the comm.
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Old 04-29-2004, 08:58 PM   #2
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general machining tip - use some sort of cutting fluid while cutting. Wear safety glasses, if you go to far the comm will split and become a projectile. Just take your time and go slow. Dont try to get it all in one cut. Practice moving both the x and y axis before you get a arm on the lathe so your familiar with which direction to turn the wheels.......
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Old 04-29-2004, 09:39 PM   #3
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ok sounds good. anyone else?
(i plan to use an old arm first, one i dont need)
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Old 04-29-2004, 09:46 PM   #4
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VERY slow, VERY steady feed on the X axis.
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Old 04-29-2004, 10:10 PM   #5
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make sure the rotor is spinning towards the bit and that the bit is just over the center of the arm.
marking the arm black would also help get the low spots.
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Old 04-29-2004, 10:13 PM   #6
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these are good, any others
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Old 04-29-2004, 10:24 PM   #7
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The best I can advise is to only cut ONE way....don't move the bit back and forth over the comm....all it will do is put the wrong type of finish on it and more than likely cut it out of round. Lathe bits are meant to cut in one direction, not two....

Some people will argue this, but watch any of the top motor builders like reedy, dieter or big jim.....and they will all cut in only one direction.....

Other tips including making sure you lathe is cutting the comms round by checking the alignments of the bits all the moving parts of the lathe.....

I use carbide bits and just resharpen them.....diamond bits can cut great, but they are pricey and if they become dull or damaged....they will still give the appearance of a good cut, when in fact its out of round.....

Use a sharpie for lube.....and use a decent oil on the guides of the armature shape to prevent scoring and uneccessary wear on your lathe....

Never take more than .030 off a comm.....small comms start at .300, so you can go to .270.....large comms start at .350, so .320....anything less your playing with fire....get a decent set of calipers to measure with.

And remember, you can ALWAYS cut off more.....but you can never put it back on.

Hope that helps....

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Old 04-30-2004, 01:30 AM   #8
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Hello!

I need a picture of the bit...

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Old 04-30-2004, 06:17 AM   #9
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I contacted associated about the limit for there mid comm ( 9mm , or .350 ) and they said you can safely cut it down to .300 . I have done this and never had a problem.

you pretty much got good info here, if you need a diamond sharpening tool try and get about 200 grit. I usually use 180 and then 260 ( thats what I had ) and it works quite well.

Anyone know if the color of the sharpie you use makes a difference in the quality of the cut?
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Old 04-30-2004, 11:16 AM   #10
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I was told the same thing........I cut one down to about .310 and the comm plates exploded.....had another do it at .317....

Also, if you cut it all the way down to .300.....its not really a LARGE comm anymore......motor sure will act different. Stick with .320 and be safe....


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Old 04-30-2004, 02:21 PM   #11
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It seems to me black sharpie works better than red. Don't know why, maybe more ink coveage with black, because you can see it better and get more on.
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Old 04-30-2004, 04:32 PM   #12
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may be the actual ink. I picked up a black one and will test.

EddieO thats strange that happened. I went down basically that low and it ran fine. I am on a new motor so I will keep that in mind.
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Old 04-30-2004, 04:44 PM   #13
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Keep in mind, I am not saying you cannot get it to work that low....I am just saying your playing with fire.....sure would suck to be winning the A main with 20 seconds to go and have a comm plate explode.

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Old 05-03-2004, 08:52 AM   #14
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Im having a hard time with people saying to use a sharpie as lube...... I work in a shop with both a lathe and mill. And I personally run a CNC router everyday. On brass,aluminum,copper, I always use cutting fluid. So I know the importance of using some sort of coolant while cutting. But a sharpie?? How can that provide any real sort of lube........I do realize that its good to use a sharpie on the comm so you can see your progress but not as a lube. So just buy some comm cutting fluid.................
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Old 05-03-2004, 09:33 AM   #15
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A Sharpie does nothing for lubrication. It simply makes it easier to see the high/low spots. This way it is easier to see when the comm is 100% clean.
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