Heat expansion

[jwsvandr]

I have a question concerning expansion of parts due to heating when using the lathe. I made a die holder mentioned in my previous topic. The holder started life off as 2in square stock. I drilled a 9/16 hole through the center and then bored the end out to fit a 1in diam die. When I went back to the project the next day the die didn't fit. I had to re-bore about .001 to get it to fit again. Is this normal and if so how do you compensate if you want a tight fit other than waiting for it to cool.

 

[wareagle]

The best bet is to let it cool off when it has to be that accurate. Each material has different rates of expansion when heated, and IMHO it is a gamble to take off an extra .001 or .002 to compensate. Mr. Murphy resides in my shop, and he likes to throw a kink into my well laid plans every now and again. My philosophy is to not rush it when it is that critical, and will let a part cool off before making a final sizing pass.

 

[mklotz]

The coefficient of thermal expansion for carbon steel is 6.3 ppm/degF so, to get a 1" block to expand by 0.001" requires a temperature rise of only 160 degF.

However, I don't think you want your die holder to be that good a fit on the die. Most dies are split and fitted with a screw that allows them to be expanded in order to take less of a "bite" on the first threading pass, thus reducing the torque needed to turn them.

The hole in your holder should be large enough to accommodate this growth in size which would make it larger than one inch.

 

[steamboatmodel]

That is one of the reasons when CNC machines are running you can't see anything, you have the coolant on flood.
Regards,
Gerald

 

[rake60]

That is one of the reasons when CNC machines are running you can't see anything, you have the coolant on flood.
Regards,
Gerald

I HATE not being able to see inside that machine!
First indication of something going wrong, is that gut wrenching crunching sound
that you hear just before the drives overload and shut it it down.

Before I was moved to the CNC department I ran vertical boring mills.
The smaller one did have a coolant tank on it, but if you ran the pump while
cutting it would just throw the coolant all over the shop.
When there was a critical size to hit the part was roughed to within .060" then
the table was slowed down and the coolant run over it until it's temperature dropped
to 68 degrees F.

There is something to be aware of in that.
If the part is very hot, hot enough to make the coolant turn to steam, allow
it to air cool for awhile before putting the cool fluids to it.
It's very possible to case harden a piece by cooling it too quickly.

Rick

 

[kellswaterri]

Hi JWS,
Marv is right on the die holder...I had bought a set from a uk company and found that the holder was not allowing the split die to function properly...the holder and the die dimension was almost size for size...to be effective at least 3 thou'' above die diameter on the holder should be allowed for...this lets the die expand using the adjusting screw enabling it to work as it is supposed to on tougher materials.
All the best for now,
John.

 

[Mcgyver]

use coolant, atomizer bottle if not flood. when it really matters let the work cool before finishing cuts