Getting the workpiece straight in the chuck.

jlsmithseven said:
Oh so you're saying loosen the chuck jaw a little bit, run it at like 35 rpm or something and it will true it up and then just tighten the screws. Sounds simple and awesome, not sure if I will be able to do that though.
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Just run it at the lowest speed you have. It works well but don't expect to be dead on concentric this way. It will get you close enough, though, and the tool is worth making and using.
 
brino said:
I had quoted jlsmithseven who apologized for asking a question.
I want him to know that asking any question is fully encouraged here!

-brino
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Yes, there should be no need to apologize for asking any question, no matter how basic it may be; that is what this forum is for.
 
3jc it forces the stock to conform a little.
 
benmychree said:
Not always necessary to turn a blank piece to line up the steady rest; I just get it close, then put a center drill against the shaft end lightly and see what trace it leaves on the shaft end if not on center, then adjust the SR jaws until the center drill hits the shaft dead center and drill the center hole, With a bit of practice it is easy and quite accurate. There is nothing wrong with running things fast speed in the steady rest as long as the jaws are not overly tightened and a lubricant is used; way oil, center lubricant, white lead or whatever is at hand. If the jaws are roughed up, they can be re machined. I have thought of using a hand reamer in the spindle and carefully adjusting the jaws, one at a time against the rotating reamer, but have never tried it; same could be done using an end mill, the more flutes the better.
Click to expand...
The best way to dress the end of the steadyrest
Jaws is to make a leaping mandral and run the mandral with a live center in the tail stock
The bring in the jaws on the mandral with the laping
Compound on your mandral
 
The above responses are all good and will likely give a better result than simply putting that piece of bar into the chuck and cranking down on it. Of course, a 3 jaw chuck does not hold perfectly, either on center or aligned to the axis of the bed. If you pay lots of money and get a new top end chuck and then mount it correctly - it will be closer to "perfect" - but it will not be zero runout up close to the chuck and well out along the bed (assuming you have an accurate test bar).

However, very few people here would actually spend that kind of $$. It really is not necessary. Using techniques like the ones described above will get a pretty good result, with a pretty ordinary chuck (cheap or well used). Don't sweat it. I actually don't do any of the tap/bump/rolling techniques. I have been through the whole chuck mounting/tuning - and for 3 jaw work, I simply snug the stock - and go. The run out is 0.003 close to the chuck and twice that 6" out. The reason it is no big deal is because after the first couple passes it will be running as true as the machine is capable of!

I have never checked using an unsupported bar, 15-20 inches out from the chuck. I can't imagine very many situations where it would be relevant (center drilling something too big for the spindle hole, even then there are other ways to get'er done)?

Another excellent solution (not mentioned above) is to set yourself up with soft jaws: load the jaws, skim them and then the work will run very close to true.

You said that it is running way off? Take some measurements (make sure it is an accurate piece of material), and check the run out at several locations out from the chuck. Maybe there is an issue with how the machine or the chuck are set up?

Let us know how you make out. Regards, David
 
One essential use for the tap/bump roll techniques in a three jaw is to true up a part that has been previously turned.

Glenn.
 
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