Need Help!- How do you turn a Left Hand Inside Dia. Threads

[rapidtraverse]

Hi All,

I have a call-out for left hand, Inside Diameter, 1.250-7 threads.

The machine is a sl-40 and my book has no info for the I.D. threads for a G-76.

Can I do this with Right Hand Threading Bar? What is the code for a sub-routine machining cycle in the G76.

Any light on this would be appreciated.

Thank's i advance.

Rapidtraverse

[Geof]

I think your only difference is you start at the bottom of the hole and move positive in Z.

Write a normal right hand G76 and check it in Graphics; then exchange your start and finish Z coordinates and check it in Graphics. I think you will be able to sort out what you need.

[PBMW]

Geof's got it. Start at the bottom of the hole.

[neilw20]

If you NEED to turn from the outside to the inside and have a LH thread put the tool upside down or turn on far side face with spindle running the
other way (M4). Easy on some machines. Hard on others.

[Geof]

Originally Posted by neilw20 .... or turn on far side face with spindle running the other way (M4). Easy on some machines. Hard on others.

Have you done this? Hard is an understatement! I did it on a Haas TL because I was limited in the number of tools I could fit in so I used an internal threading tool for both ID and OD threading. It took a few minutes to bend my brain around setting up the tool offsets and the coordinates. It is not intuitive at all.

[neilw20]

Actually I did right hand nuts threaded from the inside to the outside so I could start right at a face (THE CHUCK!)
I am really chicken doing high speed threading toward a solid chuck and stopping within 0.002".
Just change the sign, and follow the logic... starting at some -Z value towards Z0.
I cheated by making a full depth groove with the threading tool first , so there was no vanishing thread inside at the starting point.

[rapidtraverse]

Geof Thanks! Your wisdom prevails again.

[cnc-king]

use a left hand insert, iscar makes them, feed Z minus with the spindle running in M4 direction