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]

.... 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