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Old 04-20-2006, 08:59 AM   #16
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How about diamond bits? How many cuts can you get out of that?(let's say Hudy) And do you also use any cutting fluids like the carbide bits?
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Old 04-20-2006, 10:08 AM   #17
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Speed and feed is the name of the game in machine tool to keep your bits in tip top shape. A carbide bit with the proper speed 2.5 to 3 volts to your slave motor on a lathe is ideal.
Feed not to fast donít hurry the bit across the surface of the comm. and donít try and take to much material off with one cut. Multiple cuts are much better than one big cut. If you have a pile of shavings that looks like dust you are cutting the comm. correctly.
Cutting fluid or oil really is not needed for cutting comms use a sharpie pen.
If you follow these simple practices your bits will last a very long time. Yes your professor is correct a thousand cuts are attainable, just not probable with a carbide bit.
A diamond bit would easily make a thousand cuts on a comm. But most people including myself will chip the bits before we will dull it.
I have seen a carbide bit make many thousands of cuts a day on automated CNC machines before the tooling is changed out. But where not robots and humans will make mistakes. Thatís my 2 cents.

Oh! and yes you can get just as good a cut with a carbide bit as you can with a diamond bit
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Old 04-20-2006, 11:48 AM   #18
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I also heard the if you put a blade under a pyramid it will stay sharp for a lifetime.. maybe his will hold true as well for the lathe bit....
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Old 04-20-2006, 11:54 AM   #19
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Quote:
Originally Posted by rc-zombies
I also heard the if you put a blade under a pyramid it will stay sharp for a lifetime.. maybe his will hold true as well for the lathe bit....
I put my lathe bit under a pyramid after very use
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Old 04-20-2006, 05:48 PM   #20
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I bought a cobra lathe in 93'.. it came with a carbide bit and NO BS,,, i used this lathe until 99 when i came across a deal on a lathe with a diamond bit. It was a shock when the brand new lathe with diamond bit didnt cut all that much, if any better.

I think if your not abusing the bit, it should last for a good ammount of time.

im now using the much more lathe W/ a diamond bit that came with a cobra i bought 2 years ago. Cuts better than any lathe i have ever used.

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Old 04-20-2006, 06:02 PM   #21
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Quote:
Originally Posted by JoeyE
How about diamond bits? How many cuts can you get out of that?(let's say Hudy) And do you also use any cutting fluids like the carbide bits?
Hey Joey,

I bought my Twister lathe with a diamond bit USED back around 1993. The guy I bought it from had it for I don't know how many years before he sold it to me. Long story short, 13 years and hundreds of motors later and i'm STILL on the same diamond bit. So with proper care and setup, I think the answer to your question is "forever"

-James
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Old 04-20-2006, 06:11 PM   #22
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But....you are using a "diamond" bit....I'm talking about getting maximum life out of a "carbide" bit.

13 years is still pretty sweet though...
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Old 04-20-2006, 06:56 PM   #23
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if we could get a bunch of people to request it, maybe they will.
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Old 04-20-2006, 07:03 PM   #24
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Is it possible that some of the bits we use arn't a true carbide? Its just hard to think that a carbide bit can last for 1000 cuts, if most only get 20 before they need to be sharpened.
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Old 04-20-2006, 07:07 PM   #25
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Quote:
Originally Posted by rcguy2477
Is it possible that some of the bits we use arn't a true carbide? Its just hard to think that a carbide bit can last for 1000 cuts, if most only get 20 before they need to be sharpened.

Not to sound condesending... but have you seen what most people do with their lathes?

I have seem people running them the wrong way.. taking off .010" at a time... jibs too loose... cut into the arm blank... ect... i cant say that i havnt been guilty of all of these things at one time or another

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Old 04-20-2006, 07:24 PM   #26
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A true carbide cutting tool will cut 1000 comms. Copper is much softer than carbide. But feed rate and comm rpm is important. Also tool set up is important. If you can only get 20 cuts on a tool. Then it was not carbide.

The diamond tool is much more fragile than the carbide. I have 2 diamonds with chips from lazy use. My carbide is still going strong
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Old 04-20-2006, 07:50 PM   #27
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well....then moving to the topic of lathe speed.....if I'm using cells to run the slave motor, how many would be best? 2-3-4? at the moment I'm using 4. Should I take it down a cell?
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Old 04-20-2006, 08:19 PM   #28
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Carbide tool bits should last a very long time when setup right. The tip of the bit should be exactly at the center of the diameter of the comm. If its off center at all, it's better to be lower than too high. Copper is much softer than carbide, the problem is it's very abrasive and sticky. What happens is the copper chips heat up and stick to the tip of the carbide. This is called BUE (built up edge). Now, instead of cutting copper with carbide, your cutting copper with copper. That's why the finish comes out bad. Lubricants help to minimize this but copper is just a pain to cut. Make sure you have a radius on the tip of the bit for edge strength. Also, as I stated before, make sure the tip of the bit is exactly at the center of the diameter of the comm. Too high, and your just rubbing instead of cutting. Too low, and the comm will want to ride up on the bit and finish will suffer.

This is how I make sure the bit is at 0. Use a 6 inch steel scale available from any hardware store. Hold the scale in between the comm and the tool bit. Touch the scale with the tool bit (not to hard or the bit will chip) just enough to hold the scale suspended in the air. Look at the scale from the side. If its leaning toward the tool bit, your too low. If it's leaning toward the comm, your too high. You want the scale to be sticking straight up.

Other things that affect finish are taking too light of a cut and feeding too fast. Too light of a cut and your just rubbing instead of cutting. .002 to .003 a cut should be good with a sharp bit. Feeding too fast and your pushing the copper instead of cutting. Take your time and it will come out great.

Diamond tip bits work better because copper is abrasive and the harder tip resists wear and BUE. Diamond bits chip VERY easy because of the extremely hard tip. IMO, you don't need a diamond bit to cut a comm. I use diamond crystalline impregnated end mills for special materials such as stainless or carbide (composite), cermet, TIALN coatings and a new coated material called "Brite" (by Polkom Voha) that has incredible wear characteristics, but I still use trusty old carbide for 90% of the work I do.
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Old 04-20-2006, 08:30 PM   #29
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Let me take a turn here in this thread for a bit, (punny punny )

How does a chipped diamond bit cut differently than a perfectly new diamond bit? I realise under magnification you can see the chip, but if the chip has a constant shape, won't it continue to cut at a consistant depth unless it chips more during the process of a single pass? I believe I have read on here that a chipped diamond bit will cut out of round and you wont be able to tell because the finish will look the same as if it weren't chipped. That just doesn't see right to me. Can anyone explain?
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Old 04-20-2006, 10:37 PM   #30
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Quote:
Originally Posted by D_Ames
Carbide tool bits should last a very long time when setup right. The tip of the bit should be exactly at the center of the diameter of the comm. If its off center at all, it's better to be lower than too high. Copper is much softer than carbide, the problem is it's very abrasive and sticky. What happens is the copper chips heat up and stick to the tip of the carbide. This is called BUE (built up edge). Now, instead of cutting copper with carbide, your cutting copper with copper. That's why the finish comes out bad. Lubricants help to minimize this but copper is just a pain to cut. Make sure you have a radius on the tip of the bit for edge strength. Also, as I stated before, make sure the tip of the bit is exactly at the center of the diameter of the comm. Too high, and your just rubbing instead of cutting. Too low, and the comm will want to ride up on the bit and finish will suffer.
So do you think that people may be mistaking a dull bit for built up edge, when in actuallity the bit is perfectly fine? When you think about it, as other people have said, 1000 cuts isn't unreasonable. We're only taking off .004 inches off at a time.
-Josh
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