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Old 02-14-2002, 04:43 PM   #1
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Default motor lathe bit installation?

I'm using a trinity lathe with a carbide bit.
I want to know what the proper way to install the bit and the correct height and shimming or way to shim is.
what do you look for?
I'm pretty sure the bit is worn. I can see 2 reflections on the tip. I think this means it's worn out but i'm not sure.

Please help
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Old 02-14-2002, 05:24 PM   #2
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Just make sure your bit is at or above the centerline of the com. If it is too low it will really cut badly.
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Old 02-15-2002, 03:46 PM   #3
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how do you tell if a bit is bad?
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Old 02-15-2002, 04:53 PM   #4
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If its suspect you just sharpen it. You can't sharpen carbide on any grinding wheel though, carbide requires a special sharpening stone that is a seafoam green color.

Most machine shops dont even bother, carbide bits cost arround $1 each when you buy them in quantity. You can find them for arround $3 each at www.mcmaster.com or www.grainger.com
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Old 02-16-2002, 07:45 AM   #5
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colossus, what type of lathe are you using i have a trinity tru lathe 2 and i have to send it back to trinity to have it looked at because it cant cut for crap, and i have only cut about 4 or 5 comms with it. after i have cut from left to right and i am coming back to the left the bit digs in real deep for some wierd reason.
let me know if you can get a good cut with yours
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Old 02-16-2002, 12:04 PM   #6
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Spaz, sounds like you have one or both of two problems. Your bit height can be too low and the vibration of the slave motor is causing the lathe's feed to move slightly. Some lathes have this problem if they are set up loose, to see if this is the problem set your cutting depth and put a small piece of masking tape on that keeps the feed from moving.
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Old 02-16-2002, 07:32 PM   #7
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I recently bought a Cobra Pro Comm 2000. I had a chance to talk to Cobra's owner who was able to give me advice on how to set the bit. Shimming to the right height is critical. For the Cobra, cutter should be .002 - .004 inches above dead center of the motor armature when it is placed in the armature holder. This happens to be about the same height as the top of the right armature support. I had to use a lot of shim -- a piece of Lexan and a piece of and old AOL CD -- to get it high enough. It works great.

Get a diamond bit. It's worth it. Cobra had a deal going for the lathe and diamond bit for under $200.
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Old 02-17-2002, 11:18 PM   #8
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an easy way to check the height of your bit is to put a scrap piece of lexan between the bit tip and the comm and gently move the bit against the comm, if the top of the lexan moves towards you then your bit is below the center of the comm, if it moves away it is above the center, you can get a feeling of how much above it is by how much it moves
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Old 02-18-2002, 10:10 AM   #9
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thx pat ill try a new slave motor
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Old 02-18-2002, 11:13 AM   #10
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The slave motor isnt the problem, all motors will cause some vibration. The problem lies in the looseness of the lathe, if this is your problem of course.
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Old 02-20-2002, 05:58 PM   #11
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THX new racer for the trick. and everybody else.
I do have that directional problem though. I forgot which way it is.
the cut is horrible, and the lathe vibrates realy badly.

Its a TruLathe 3 Pro
and I'm using the ballbearing support.

sometimes its seems to almost make a fingerprint pattern on the
comm. this is the first few times I've used a lathe. I've had help but it just seems to cut bad no matter who does it.
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Old 02-20-2002, 06:04 PM   #12
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btw how should i tighten the sliding guides for the toolbit carrier.
the ones that adjust depth and left righ position.
should i just tighten then down all the way?
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Old 02-21-2002, 10:05 AM   #13
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How long should a carbide bit last before it needs sharpening?

I recently acquired an eagle comm lathe and I'm not too impressed so far. The instructions are in japanese with odd sections that they have translated into what I presume is supposed to be English. One of the ball bearings wouldn't rotate properly as the mounting plates either side were squeezed together slightly.
The standard bit that came with the lathe needed sharpening
before it was even usable. It is an odd shape though and I won't be able to sharpen it again I don't think. I tried a cobra bit but it went blunt after about 5 skims (maybe because it was mounted 90 degrees out as my lathe cuts the opposite way to the cobra).
I have now acquired a tool with a changeable head and about 30 different heads to go on it. They are all titanium nitride or carbide but I am not sure what shape is best although I understand that the cutting angle for copper is supposed to be about 12degrees.
Any suggestions?

Finally what motor/voltage set up should I be using?
The drive system is a copy of the hudy dual belt design.
The instructions say about 7000rpm and tell you to buy some unobtainable 55t motor and run it at 7.2v.
The hudy lathe however says 15000rpm, although it may be geared differently. I am currently using a p2k at 4.8v.

Thanks
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Old 02-21-2002, 02:36 PM   #14
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Colossus you will find that if you tighten everything all the way down things just wont move. You want it to be snug but not overly tight.

DW a carbide bit should last about 10-15 cuts before it needs a little sharpening.

Is that eagle lathe the red one? I saw that one before and I just didnt like the way it looked. The bit from the cobra lathe is the wrong style bit and using it will really screw things up, there are left and right hand bits. The style bit you want is either AL-4 or AR-4 I forget which one the Cobra Lathe uses but you obviously want the other one. You can buy carbide($3), diamond ($53), or high speed steel ($8) bits at www.mcmaster.com for a very reasonable price. They offer Carbide and High Speed Steel for cutting various different materials you want the compound for non-ferous metals. Personally I like High Speed Steel over carbide because I can sharpen them myself with a hard Arkansas stone and dont need a special gringing wheel. I have one of their diamond bits and it works great and has lasted a very long time.

Speed of the lathe should be reasonably slow. I use a stock armature in a mod can with timing set to 0 and run on two cells. This is slower than alot of people run theirs but I get great cuts. You can buy that 55 turn motor from Integy or Race Prep. I plan on buying one soon so that I can run my lathe off a 6V gel cell.
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Old 02-22-2002, 01:26 AM   #15
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Default How to shim my cobra pro com lathe?

Guys
Ive just bought a second hand cobra pro com lathe and am unsure how to shim the armature to stop it moving. Any advice? Also the armature seems to bounce (vibrate) approximately 1/2 way through cut (going right to left), any ideas? Can anyone point me ion the direction of instructions for the lathe? Finally am I right in thinking the first cut should be from right to left (end of com inwards)?

TIA

Rich
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