Another lathe hint.

[mcostello]

If You are lucky enough to have a collet setup, and need to bore out some parts then You could rough drill them all.Then get Your boring bar set to the size You need and just swap out parts with out changing the setting on the boring bar. Old Pro's may already know this, but the newbies might not.

[SteveM]

I find that my drill is much better at drilling than my lathe, so this approach would be a time saver for me.

If you don't have collets, use soft jaws.

Steve

[Ray Wangler]

I think I'm right here (a problem when I'm really wrong!!) However, if concentricity is not critical, but diameter is, you can be exact on the diameter on any 3 jaw chuck with that technique. correct away if necessary

Good thread.
Ray

[Ironman1]

Ray, if you use the 3 jaw chuck, you will be within 2-3 thou and the next part will be off maybe 2 thou, a scroll chuck is all over the map, even new.
A collet chuck is dead accurate to the spindle of the lathe. Every single time.

[Harold_V]

A collet chuck is dead accurate to the spindle of the lathe. Every single time.

That's a matter of degree, isn't it?
Nothing is dead accurate, including collets. The chief difference, at least in most cases, is that the degree of error is small, generally too small to be seen by the human eye. Put a good indicator on any revolving item and, generally, that will become quite obvious.

It is not reasonable for anyone to expect collets to yield better than half thou accuracy. Yes, some do, but some don't. There's simply too many places for error to be introduced.

You want "dead" accuracy? That's what 4 jaw chucks are made for, but without a very good indicator, even they may not perform to expectations.

H

[Ironman1]

You are right, chasing the elusive 4th decimal place is foolish, but people do it. For most home applications 1 thou is great. I often think of when I used to do driveshafts and busted a gut to get under 10 thou. Then I read the specs and factory runout is 25 thou....yep, for something turning 2500-3000rpm.

Of course, driveshafts on cars are becoming a thing of the past, too.

[Jawn]

Of course, driveshafts on cars are becoming a thing of the past, too.

Not completely. RWD has made a bit of a comeback in some segments, and AWD stuff is a lot more common than it once was.

[Harold_V]

You are right, chasing the elusive 4th decimal place is foolish, but people do it.

Absolutely true, and it may not be foolish. A reasonable percentage of the work I pursued was well within the 4th decimal point---and sometimes even closer.

Even the home shop type can be in the position to require high quality work, assuming they have hopes of the given piece performing to expectations, and having a viable lifespan. Keeping diameters concentric and of proper size goes a long ways towards that goal.

I just didn't want readers to get the impression that collets are a panacea, the solution to concentricity. They're not, depending on the collet, as well as the application for which it might be employed. I certainly wouldn't want to trust a collet for turning bearing fits when the piece had to be flipped end to end. You'd open the door to all manner of discrepancies, yielding questionable results, although the outcome may appear perfectly functional.

You want dead concentricity? Pretty hard to beat precision grinding, accomplished on dead centers, with the centers of the work piece lapped properly.

H

[Ironman1]

Yes, I have to go to the 4th when doing a press fit bearing holder, and I wish I had a grinding setup, but the paydirt isn't in it. The majority of my work is horrifying stuff. Shafts made by John Deere to fit bearings private labeled to JD with 15 thou clearance, and the owner wonders why the bearing spun on the shaft. Anything like a sliding fit is better than that. I got good at weld buildup and turn, or sleeving shafts. I do take pride in a job well done but the only response from a customer on a precise fit is 'that took too long.'
I understand where they are coming from, the throw away mentality has a good grip on farm equipment now.

[Harold_V]

Chuckle! I hear you, and feel your pain.
A few months ago I rebuilt a portion of the feed control (for lack of better definition) of a hay rake for a neighbor. Spent a lot of time getting it "right", which was a considerable improvement over the factory fits. Turned out great, and he was exceedingly pleased. For him, it was a "freebie", for which he has more than repaid my wife and me with fresh pressed apple juice, as well as a crate of fresh cut asparagus, a favorite of ours. He's the kind of neighbor who appreciates a favor, and keeps you in mind, even when he doesn't need anything. A great guy to know.

I've always taken great pride in doing a job well. It was something instilled in me by my father, and deeply entrenched when I was in the first year of my machining apprenticeship. Working in a missile facility changes how you see things, for which I will be eternally grateful.

H

[JackF]

Harold, they may be calling you back to work at the missile factory if this North Korea thing gets any hotter.


Jack.

[Harold_V]

Heh! Not much need for dinosaurs like me anymore---but I certainly agree with the current world situation(s).

H