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Thread: Centering stock in 3 jaw chuck
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15th Jun 2014, 06:01 PM #16Most Valued Member
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Yea, this metal working hobby is analogous to chasing rainbows. With each new machine tool purchase comes the need for the next one… and the next….. and the next…….
When I first started turning, I thought the term "self centreing" in regards to the 3 jaw meant EXACTLY that. Needless to say that I soon learnt the importance of planning your order of operations since removal from the 3 jaw lead to other "unexpected" runout errors.
PS I'd be pretty happy with 1 micron of TIR on the 4 jaw, not many jobs require that or better in the home garage….
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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15th Jun 2014, 07:08 PM #17Most Valued Member
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I was having a little trouble with the 0.001mm run out.
Thats an imp 0.001" dial gauge so one div is 0.0254mm
Stuart
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15th Jun 2014, 07:19 PM #18Most Valued Member
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15th Jun 2014, 07:29 PM #19Senior Member
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Yes, You're right, It is imperial! so the runout figures are not as impressive as once stated.
My bad.
Still, I'm not making aeroplanes, so the this level of accuracy is good for my level of experience. I'm sure with more skill those tolerances would be better.
haha, yes the milling is definitely expensive,but I think the wife prefers that I'm home in the garage!
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15th Jun 2014, 07:45 PM #20Most Valued Member
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Yes, I was still thinking that. 1 thou runout is still pretty good*
* Well, it really depends on the job and the tolerances that are called for. But 1 thou TIR would be good enough for probably 90% of jobs in the shed.
I usually make the comparison that I'm not building bridges, but aeroplanes is another suitable analogy!
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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15th Jun 2014, 07:54 PM #21Most Valued Member
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15th Jun 2014, 08:23 PM #22Most Valued Member
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Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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15th Jun 2014, 09:11 PM #23Philomath in training
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My normal limit is about 1 thou total movement on the 4 jaw - while I can get better that's the point where tail chasing starts coming into the picture. It also seems to be the point where unless I'm using ground stock that material out-of-roundness errors start becoming significant - that is, the material is not quite a uniform (constant) diameter.
Michael
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15th Jun 2014, 09:19 PM #24Most Valued Member
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Hi Simon
Well he said "I checked the runout on the 3 jaw chuck itself, and it was 0.001mm I think thats pretty good."
So yeah not runout, but
As far as runout in the 4 jaw, as others have said I doubt the stock is that round.
So oohsam if you want to practice more, you'd be better off turning the piece you have turned already and clocking on the area you have turned....Then you can play as long as you like. I wouldnt bother trying to get closer than 0.001" on unturned stock. The best you could likely do is opposite jaws the same.
If you're going to be doing this sort of set up often you might want to make a bump center.... I've never bothered myself so I cant say how well they work. I do like my wiggler though.
http://www.gadgetbuilder.com/CenterFinder.html
scroll down
Stuart
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15th Jun 2014, 09:54 PM #25
Lots of ideas being tossed around, but a couple of things become evident from the pics posted in third post.
1, as someone mentioned, mounting in a set of normal jaws rather than reverse jaws would give much better workpiece support as the jaw clamping surfaces are at significantly longer.
2, the work appears to be hard up against the front face of the jaws. Unless the end against the front face has been accurately faced perpendicular to the length of the bar, the interference between the face and jaw face, competing with the short section of jaws clamping the work would tend to pull the work out of true.
For a given chuck with all of it's inherent inaccuracies, the OP should get a better runout using a set of normal jaws, and setting the work with the chuck end slightly clear of the chuck body if it is greater diameter than the bore through the chuck and spindle.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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15th Jun 2014, 10:12 PM #26Senior Member
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Thats some interesting stuff there...cheers for the links!
See, this was my conundrum.
I had the workpiece up flat against the jaws, but you are right, i was not sure if it was flat enough as I did not face it off. I wanted to face it off, but could not get it to sit centre enough in the jaws to face it off effectively.
Once the lathe was it was really clear that it was out and was vibrating, not much, but enough for me to not be comfortable with it being mounted in there.
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16th Jun 2014, 11:17 AM #27
RUNOUT
Hi
Yesterday i was doing the exact same thing you are ! I was getting the same results . The round stock is only being held in the jaws by a short length on its end , you have to expect runout in that setup . There is probably nothing wrong with your equipment . To test the chuck runout, use a smaller diameter bar , only 20mm from the jaws . Mike
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