If you have invested in a commutator lathe to keep your electric motors in top condition, you may be a little intimidated before your "first cut". After setting up your lathe per manufacturer's instructions, you may be able to use the following tips.

Before attempting your first cut using a comm lathe gather these tools.




A spring post nut driver
stock lathe (Trinity makes a nice one).
A Sharpie permanent marker pen (Wet type not a dry marker).
3 in 1 oil or the equivalent.
An Exacto blade knife or jeweler’s screwdriver.
An old pinion gear.
A small paint brush.
90% of the time it takes to make a good cut it the set up. If you don't take your time and do it right you will not make a good cut. Even worse you could ruin your arm, bit, lathe and or your eyesight. Follow the these steps to insure a good cut and always ware eye protection.

Be sure the lathe is in good shape. No loose parts, alignment is good.

Insure the motor will turn the arm in the proper direction. This will vary per make and model of lathe.

Move the bit as far away from were the arm will be mounted as possible. You don't want to damage the bit.

Put a drop of bushing oil on the U or V grooves the arm will lay in.

Mount the arm and attach the belt between the drive motor and the arm.

Mount that old pinion gear to the arm in such a way that you remove lateral movement but the arm still spins freely.

Set the travel limiter / stop so the bit will not contact the end of the arm were the wires are connected. This would tear up your bit if they touched while spinning.

Move the bit to a position so it will touch the comm 1/64 of an inch in from the end opposite the wire end when you start to cut. DO NOT TOUCH THE BIT TO THE COMM YET.

[IMG-LEFT]http://www.hobbytalk.com/bbs1/attachment.php?attachmentid=12973[/IMG-LEFT] With the bit away from the comm. Turn the motor on. While it is spinning use your sharpie to mark the comm. Use a "Sharpie" type of pen for visual effects. It helps to see and lubricates but take very small cuts. While the commutator is spinning hold the tip of the Sharpie to it. This will give you a good visual reference as to where you have not cut.

Start your cut by slowly bringing the bit in using the in and out adjustment until you see a thin copper line in the sharpie marked comm.

[IMG-LEFT]http://www.hobbytalk.com/bbs1/attachment.php?attachmentid=12974[/IMG-LEFT] Using the left to right adjustment move the bit off the end of the comm and then back across the comm to the stop sit in step 7. If you encounter a comm that is badly burned you are going to be making a lot of small, shallow cuts. Use very light oil, 3 in 1 oil, or any light machine oil, will do and apply it with a small paintbrush. As far as the bit is concerned, carbide will leave a shinier (glossy smooth), finish where the diamond will have a dull satin smooth finish.

Using the left to right adjustment move the bit back across the comm and off the end

Stop the motor and inspect the comm if it is clean and no sharpie marking remains your done if not you will need to continue.

While the bit is still off the comm use the in/out adjustment to bring the bit in one half mark or less. The less you cut each pass the better the cut and the longer your bit will last.

Use a small paint brush to apply a drop of 3 in 1 or bushing oil to the comm.

Start the motor again and make your next pass. Repeat steps 13 through 16 until all sharpie markings are gone

[IMG-LEFT]http://www.hobbytalk.com/bbs1/attachment.php?attachmentid=12975[/IMG-LEFT] To remove the sharp edge created by the cut, use the cap of a "Bic" pen to scrape the sharp edges of the grooves. I will sometimes finish by applying a comm pen to the spinning comm to smooth it and remove any remaining residue.

As for a Diamond or carbide bit, get used to the lathe using the standard carbide first. Practice on your worst motor. A junker is best to get the feel of the lathe before you cut into your best racing motor. If you have a machine shop near you might be able to get carbide bits by the dozen for about $50. That's almost half the price of one diamond bit and would last just as long (all 12) if not longer.

Watch the video on how to cut a comm (http://www.hobbytalk.com/bbs1/attachment.php?attachmentid=23110)




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There is also a video at http://photos.hobbytalk.com/showphoto.php/photo/7869/cat/552

good article hankster!

carterdiamond.com for sharpening diamond bits. $26.50

I also take a hobby knife and clean between the segments in the com. and clean w/ motor spray to get off any shavings

I do not recomend the bic pen down the segments part... Do it some time then take a magnifyer and look at the segments.. You change the distance between them.. your folding the sharp edge over..

If you have a good lathe, you should never need to do anything after the cut..
since ive stopped doing the pen thing i have noticed my motors are slightly more consistent,

also if you want the most perfect finish use a light oil on the comm instead of a marker.. cutting oil works very well. just make sure you spray it off after..It not only saves the bit, but makes the comm look better..a carbide bit and a light oil will shine.. works even better with a dimond..

If you read the article is says to use the "cap" of the BIC pen... you know the part that sticks down to clip it on your shirt. I know a lot of people would actually use the "writing" part of a BIC pen to remove the "burrs"... not good! I like using the cap because it gets down in the grooves to clean out any chips and if you happen to slip the plastic will not scratch the surface of the comm.

I read it worng.. but the picture in the lower left shows a bic pen tip being used on the comm. so that is what i thought was being said...