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2 axis lathe - Y axis off centre on ID holders only

Rolka

Plastic
Joined
Mar 22, 2018
External tools (tool stations 1-4) cut on centre, whereas ID holders (mounted in stations 6-11) are off centre on Y axis by about .018 (.036 TIR).
How is it possible?

Some background:
Hyundai WIA L400C, 12 station turret.
Machine had major crash about 2 years ago (ID tool rapid radially into part). After that it was realigned.
It was running pretty well since then, producing not very demanding parts.

Now true test came, as I was tasked with spade drilling 11.25 deep 17/32 hole in 6061.
Drill has been beheaded at hole #4 ( first 3 holes ended up oversize but within drawing specs).

Any suggestions?
 

13engines

Hot Rolled
Joined
Jun 30, 2015
Location
Saint Paul
You could try an eccentric holder to dial out the Y error. 21+ diameter drilling is no simple task. I hope you have plenty of coolant volume. I'm told that spade drills are more interested in coolant volume than pressure. Follow the manufacturers feeds and speeds closely. Winging it on 21+ diameters isn't going to cut it... literally!
A gun drill might be the way to go too.
 

Rolka

Plastic
Joined
Mar 22, 2018
Your machine was not properly realigned after the crash. Fix the machine.
Machine was realigned properly.
It turned out that all 4 ID holders we have were not manufactured properly - ID bore is not in the middle of the holder (out by ~ .018).What is worse - it is not concentric to Z axis of machine.

Previous machine owner enlarged bore of 3 out of 4 holders from 2.0 to 2.5 DIA, but apparently he dialed out new hole position from existing bore instead of dialing it from locating slot, so Y axis error has been transferred.

We will purchase new holders, but because current job became rush - short term solution is needed with existing holders.

We skimmed .018 from 2 locating keys to lower Y axis. Now I can dial in both drill holders to within .001 on Y axis.
Unfortunately - bore is still not concentric to Z axis, so drills do not sit straight.

For short pilot drill - the difference between ID and margin is .003 per diameter.
For long drill though - it is .023.

Question: would you rather leave X geometry dialed from pocket or from drill margins? Or maybe splitting the difference would be better?
 

Bobw

Diamond
Joined
Feb 8, 2005
Location
Hatch, NM Chile capital of the WORLD
I would stuff a piece of 2.5 inch in the existing holders and then double triple quadruple
check your head stock alignment.. And then toss a boring head in the chuck and
bore them to 2".

Dead nuts, perfect, and DONE.
 








 
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