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Old 08-24-2006, 04:23 PM   #1
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Exclamation Getting bad cut from lathe

I was cutting a comm this morning (luckily an old one) and once it was done (no deep spots), the finish looked really bad, and it had all sorts of ridges where the cutting bit had been. I think the pictures better describes what I'm talking about.


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Old 08-24-2006, 04:34 PM   #2
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It looks like your bit is either dull, to low or your way shim screws are too loose for the cradle movement.

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Old 08-24-2006, 04:38 PM   #3
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I shim the comm so it barely moves, and when it cut, the comm doesn't move. I have the bit shimmed so its in the middle of the comm.
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Old 08-24-2006, 04:40 PM   #4
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Lube the cross slide. It is binding up a little. I use a smidge (very small amount) of AE black grease on the teflon slides.
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Old 08-24-2006, 04:43 PM   #5
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Quote:
Originally Posted by Advil
Lube the cross slide. It is binding up a little. I use a smidge (very small amount) of AE black grease on the teflon slides.
Yes...this was the item I forgot. The cross slide (part that moves the bit across the comm) must be free and smooth....but it cant twist any on the base of the lathe.

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Old 08-24-2006, 04:48 PM   #6
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Thanks, that helped a lot. Now, the comm is smooth but, its not as shiny as it was before. I think its time for a new bit...does anyone know which carbide bit fits the integy auto lathe? Also, where can I get it pretty cheap?
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Old 08-24-2006, 04:50 PM   #7
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Check the speed of your cutting and lathe motor.
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Old 08-24-2006, 04:53 PM   #8
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Don't buy into the needs to be shiny or look like a mirror.....a smooth ROUND (the KEY) cut with a appearance like the bottom of a CD is what you are after.....int he end though, as long as it has no burrs or jagged edges....and is ROUND, you will be fine.

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Old 08-24-2006, 06:01 PM   #9
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Is there anyway to tell if its not cutting round? I was thinkg just go in a bit and make a pass without cutting but moving in a bit at a time intill it hits a high spot..just wanted to see if there was a standered way of doing it.

Thanks
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Old 08-24-2006, 06:31 PM   #10
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Use a caliper and check the entire comm to see if its the same diameter throughout.
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Old 08-24-2006, 06:43 PM   #11
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But the arms on the caliper would have to be thin enough to notice the change, I think it would have to be really bad to see it on a set of those. unless it was super thin.
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Old 08-24-2006, 07:54 PM   #12
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Tek Nickal,
Big Jim has been the authority on brushed motors, but even I was a little skeptical with I read Big Jim's post saying that even new carbide bits need to be sharpened!

So I followed his advice, paid $25 for a diamond hand file (220 grit) and learned how to sharpen the carbide bits. Here is how:
http://www.rccars.com/forums/attachment.php?postid=6980

Well, I used an 8X power eye magnifying glass to see what I was doing, and I got pretty good at it. Man what a difference! After sharpening the bit, the cuts look like a copper mirror. It's so easy and fast to sharpen the bits, that I do it ever as soon as 5-8 passes!

After I become proficient at it, I started putting brand new carbide bits up against my hand sharpened bits, and wouldn't you know it, Big Jim was right. The new bits definately have room for improvement and the powerful eye magnifying glass will makes it apparent.
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Old 08-24-2006, 08:17 PM   #13
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Quote:
Originally Posted by drew85
Is there anyway to tell if its not cutting round? I was thinkg just go in a bit and make a pass without cutting but moving in a bit at a time intill it hits a high spot..just wanted to see if there was a standered way of doing it.

Thanks
it is very difficult to check for round.you need to either use a dial indicator and spin the arm on the lathe slowly or use a 3 point or anvil micrometer.you need to touch at least 3 points to check for roundness accurately
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Old 08-24-2006, 08:30 PM   #14
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Quote:
Originally Posted by drew85
Is there anyway to tell if its not cutting round? I was thinkg just go in a bit and make a pass without cutting but moving in a bit at a time intill it hits a high spot..just wanted to see if there was a standered way of doing it.

Thanks

easy way is to coat the comm with a sharpie before you cut it. once all the sharpie is gone, the comm is round
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Old 08-24-2006, 08:33 PM   #15
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Quote:
Originally Posted by protc3
it is very difficult to check for round.you need to either use a dial indicator and spin the arm on the lathe slowly or use a 3 point or anvil micrometer.you need to touch at least 3 points to check for roundness accurately
What jason says is very true.

Alot of time, not so much with turning (lathe work) but grinding, especially centerless grinding you can end up with a part that is not round, but if you measure with calipers or two point measuring like a standard micrometer, you can NEVER tell it isn't round. The part ends up like a rounded triangle, and every place you measure with two contact points is the same distance across.
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