Multi start threads

[nickbe10]

Hey Folks,

The guys down in our Gundrill dept. just had a whoopsie and destroyed a 4 start thread on one of our Drill Tubes on a BTA STS (Single Tube System).

The lathe manger has asked me to see if we can program a new thread if we cut back the tube to "fresh metal". This is something I have yet to try in MC. Can someone point me in the right direction? Is it even possible? We have a Mori NLX single turret with C and Y.

Thanks for any help.....

[gcode]

back up the Z  value start point the pitch of the thread

say you're doing an 4 pitch double lead thread

the first thread would stat at Z.1 the second at Z.35

I would try it on a piece of scrap stock first just to be safe

[crazy^millman]

Yes possible, but the question is do you have to match existing threads or just new threads? If Matching existing threads you better pack a lunch using a lot of xxxxm and be extremely patience. I did this on manual lathes 20 years ago and it would take a better part of a day to fix some of the old parts the paper mills would tear up. With a CNC is becomes more tricky as you cannot change the rpms once you get started. Commit to a RPM and stick with it. Adjust your Z until you get the pitch matched and then just take your time sneaking up of the diameter. I have made molds and then went to the optical comparator to see what each .001 adjustment was doing sometimes. Now if not matching just a matter of programming the number of leads in Mastercam and it will give you code needed to help you get it done. Not sure about the Mori, but other machines have canned cycles that will do Multi-Lead threads with a Value as part of the threading cycles.

[nickbe10]

Thanks guys, that will get me started......

[Mike@Lustre]

Thinking out loud , with a C axis one would think you could keep the same Z zero position and index the spindle 90 deg for each lead .

 

12 TPI for example would be a 3 tpi thread .

1st start  would be a C "0"

2nd start would be  C "90"

3rd start would be C "180"

4th start would be C "270"

[Orvie]

"Q" is the value that you would use to shift the start angle.

This does not have to be used with a canned cycle, G32 will also work.

Also, Your 1st start must include a Q value. I don't think that Q zero is assumed by the control.

Also, I used to home my C-axis before doing this even though I wasn't threading in milling mode.

G76X_Z_I_K_D_F_A_P_Q_;
I : Difference of radiuses at threads
K : Height of thread crest (radius)
D : Depth of the first cut (radius)
A : Angle of the tool tip (angle of ridges)
P : Method of cutting
Q: Shift angle of thread cutting start angle

[Matthew Hajicek - Singularity]

I'd put it in a mill and threadmill it.  Excellent control over multi-starts.