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Old 10-19-2004, 06:25 PM   #1
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Default Help with my Twister Lathe

I bought a used twister lathe a week or so ago and today it finally arrived in the mail. Everything looks to be in good shape and it came with nearly everything I could want, including a brand new diamond bit. So far, I only have one problem. Although it came with a bunch of instructions on how to cut a comm, there's nothing that tells me how to properly mount the bit. I know once its mounted I'll need to mess with shims in order to properly align the bit but, I can't even figure out how to place the bit in the first place.

The lathe also came with an older carbide bit which I l=plan to use first just to get the hang of the thing. The bit itself is a piece of square metal with a blade on the end but, I could put the bit into the lathe on any of the 4 sides of the bit. Its obvious to me that it matter which way its installed but I can;t begin to guess which way is correct.

Can anybody help me figure out how to install the bit?
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Old 10-19-2004, 06:37 PM   #2
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hi i have a cobra lathe and it says the bit should contact the middle of the com i shimed it up with a small piece of lexan as far as witch way the bit goes in the part that cuts the comm should be facing down towards the base for additional help i would ask someone at your track who has one or try to find pics of one correctly setup
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Old 10-19-2004, 06:50 PM   #3
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Here's a picture of the bit that came with the lathe:

http://www.carterdiamond.com/RC-com_...html&mainFrame

Mine is the S-2907 bit.

Do I just install it with the S-2907 part facing out?

My LHS is closed for the next week so, I'm kind of on my own here unless I just wait for them to reopen in a week.
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Old 10-19-2004, 06:51 PM   #4
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It's been a while since I had my Twister lathe, I use a Cobra now but there are a couple things they all have in common.

1) The armature (and commutator) must rotate into the cutting edge. So the direction of travel has to be set up correctly first.

2) The bit should not "scrape" the metal off the comm, it should cut it. The leading edge of the bit will only be a few thousandths above the horizontal line going through the center of the comm. Work with the carbide bit until it cuts old comms fairly well then be very careful with the diamond.

You'll have to experiment a little with the speed of rotation and the bit position, mine likes to be a little bit at an angle to the comm surface. I use an old stock motor running on 4 volts from a power supply, you certainly don't need more than 4.8 volts from a four cell pack.

Good Luck
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Old 10-19-2004, 07:49 PM   #5
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In the link you posted, it states the top one is for the twister lathe. This is correct. The picture however, has the bits upside down. The top in the picture is actually the bottom of the bit for our lathes. Most convetional lathes have the work spin down. Since our lathes have just an oring to hold the armature in the grooves, the armature must spin up into the bit to keep it planted it the v-grooves. As Javen 13 said, the cutting point on the bit should be just a hair higher than the centerline of the comm.

Once you get your bit heigth set, start the thing up with a four or three cell pack. Make sure the armature is spinning in the right direction. Use a sharpie and blacken the whole comm. Aim the bit just a little into the copper from the top of the comm. Turn the bit into the comm until it just touches. Stop the lathe. Align the bit with one of the gooves and turn it back to the top of the comm. Restart the lathe. Turn the dial to draw the bit from left to right slowly and smoothly. Stop when you get to the raised up part of the copper. Turn off the lathe motor. Align the bit with a groove and spin it back up to the top. Turn the bit in one notch. Start the lathe up again and re-sharpie the comm. Turn the dial again to the bottom of the comm. Repeat until no sharpie ink is left after a pass.
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Old 10-20-2004, 08:00 PM   #6
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Still having problems and I'm almost certain its because the bit is dull but, just to make certain: Is this the correct way for the bit to be mounted?
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Old 10-20-2004, 08:00 PM   #7
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Another shot
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Old 10-20-2004, 08:16 PM   #8
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Quote:
Originally posted by tr6_guy
Still having problems and I'm almost certain its because the bit is dull but, just to make certain: Is this the correct way for the bit to be mounted?
it looks right but do yourself a favor get a diamond bit here is the link for the one on e bay I got one and it works fantastic
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Old 10-20-2004, 08:19 PM   #9
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Yeah, that is mounted right. Did you ship it up at all? It has to be parallel or slightly above the centerline of the comm.
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Old 10-21-2004, 07:09 AM   #10
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I haven't really messed around with the height of the bit much yet. Like I said, the bit itself doesn't look very new so, I think I need to sharpen it before I'm going to get decent results.

Thanks again for the help.
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Old 01-21-2005, 04:54 PM   #11
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Guys, I hope no one minds me tacking my question on this thread.

I got a twister lathe a few days ago and it cuts great.

My problem is that it didn't come with the set screw that prevents the bit going too far to the right and hitting the comm tabs. Does anyone know what size the screw is?

Thanks,
Jason
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Old 01-22-2005, 08:01 AM   #12
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Dont try to sharpen a carbide bit by yourself you need a diamond faced grinding wheel talk to a machine shop about doing it for you
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Old 01-22-2005, 08:09 AM   #13
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check here about lathes...

http://www.rccars.com/forums/showthr...=&threadid=374

Lots of stuff there that will save you money and headaches
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