Thread protector

[Riesel]

OK, I got a one inch diameter cold roll steel chucked up in my three jaw chuck. I center drilled the end to run a live center and turned it down to true round and the size I wanted, knurled, drilled and threaded it. Cut it off to the size I wanted and all is well. Now the question, if I mark a spot on the steel and a corresponding spot on the chuck, when I chuck it up again and align it with my my reference marks will it run true? I still have a center hole on the end I cut off.

 

[Dusty Stevens]

A 3 jaw scroll chuck will not. Theoretically you would think so but no. Bore, cut the threads all that in one setup and its no problem. Dont matter then if youre using a 3 jaw as youll be done with it

 

[geo.ulrich]

Excuse the question, but why would you need a thread protector to run true?

 

[Riesel]

That's a good question. More for the knurling tool than anything else. Really can't be to make sure it is centered to the bore as those holes are not all that centered anyway.

 

[X Ring Accuracy]

Dustys reply was more from a machining stand point, good practice. But yes it is no problem for a thread protector. Problem with us machinists, we get picky and weird over the littlest things : )

 

[paperpuncher]

If I understand the question correctly I would say it depends. If you were using turned ground and polished stock the chances would be better it would return to 0. Depends on the quality of the chuck as well clapped out chucks generally dont repeat a good quality chuck in good condition will repeat fairly well

 

[carlsbad]

So you made one and now you want to make another? You'll not notice the small amount your chuck is off. Go for it.

But if you want to get your threads better centered, put it in the chuck and put a dial indicator on it. If it is more than .002 or so off, then loosen the chuck, rotate it, retighten it, repeat until you get it within .001 or .002.

For things under 1", I often use a collet which is close enough for most jobs.

 

[geo.ulrich]

That's a good question. More for the knurling tool than anything else. Really can't be to make sure it is centered to the bore as those holes are not all that centered anyway.

Then knurl first then drill,bore and thread then part off....

 

[Riesel]

Then knurl first then drill,bore and thread then part off....

That is the sequence that I used. I also left a center drill hole in the end of the original piece and found when I used my live center and reference marks on chuck and cold roll I was very close to original.
Thanks for the comments and information.

 

[tobnpr]

As mentioned, precision isn't needed for the second operation work you're doing.
Collet, or set-tru type scroll chuck, or four jaw once the material has been removed if concentricity were critical (I don't even own a three jaw chuck).

Your center drilled hole will not be precise but doesn't need to be, for this. If you needed a precisely located center, you'd face off the existing one and recut it.

 

[Riesel]

Agreed ^^^^^

 

[ntsqd]

It's all relative. A concentricity tolerance of .0005" on a part that will both function and look good with a .005" tolerance is just extra work for no good reason other than pleasing yourself. My nearly new 3 jaw holds under .007" and that is fine for most of the parts that I make on it. If I need better I either start out with larger stock & design so that the second op features won't be affected or I switch to the collet closer.