Smooth Fit And Heat

[savarin]

I just thought I would post this as although I knew what the problem was I hadnt thought about it till after the event.
I was turning down a stainless shaft to a smooth no play fit in a bore.
Mic it up, spot on. Then it cooled to the same temp as the bore.
Shrunk enough that I had to make another one.
This time I let it cool before finishing to the correct size.

 

[David VanNorman]

That is true you make something warm it expands . Best let it cool go for lunch etc.

 

[silence dogood]

When I took machine shop in high school, we had to turn a cylinder and polish it to a certain size. I got mine that it was almost like a mirror. Stop the lathe, miked it and it was right on. Boy, was I proud of it. Took it to the instructor and he said he would not touch that thing till it cooled off. Yep, you guessed it, that cylinder was a few thousands under. Lesson learned.

 

[TOOLMASTER]

One reason you should always re tighten your chuck when grabbing internally..

 

[f350ca]

One reason you should always re tighten your chuck when grabbing internally..

I think metal expanding when you grab externally is what bell mouths jaws.

Greg

 

[Paul in OKC]

That's why I use coolant, especially on critical dimensions. I seem to be the strange old man in this, as at the shop the younger guys run dry, and I always insist on coolant. They usually just think it is too messy, but.........

 

[epanzella]

I've had the same problem with precision pieces when they cool off. I've also had aggressive press fits crack the outside piece upon cooling. A problem I've had with long pieces like rifle barrels on centers is that the hot part pushes the tailstock away a few thou. Then while I'm doing something else or having lunch, the part cools and I start turning a taper because the center is now a loose fit in the part. The longer the part the more often I have to check the center fit. I usually just grab the live part to see if I can stop it with light pressure.