Newbie- SPINDLE MARK PARAMETER

[Paul Zeballos]

Hi, I have this new TOP TURN lathe with a 18iTB Fanuc control. I need to make some re threads on this machine and I need to set the spindle encoder mark to exactly match the thread cycle with the physical piece. I read someting about the parameter # 4077 and the M19 command. Please tell me how to achieve this changes on the spindle.

THANK YOU!!

[fanucman]

becareful with 4077 because that alters the m19 stop position.. if you have a c axis it might throw it off...

but anyways you should have an m-code to position the spindle dont ya?
if not call the the company that makes the machine and ask them..

[sinha_nsit]

I believe rework on threads is not possible, once it is unclamped. At least, I am not aware of any method.

If you are very desperate to do the rework, you can do the following:

1. Fill the threads with wax or a similar thing, and scrap the excess material to get a smooth cylinder with thread OD.
2. Hold it in chuck (in any position) and command G92 with a very small depth of cut (say 0.001 inch). This will just draw a thin helix on the cylinder.
3. Measure accurately the shift in the threading helix (from the original helix). Note that you would be measuring the distance between the root of the new thread and the crest of the original thread, which would be equal to half of the pitch, if the two threading helices coincide.
4. Now make the thread (rework) using G92, after shifting the Z start point of G92, by the measured shift, in the opposite direction. This would make the new helix coincide with the original helix.
5. Repeat the same process for every new part.
6. Do not shout at me if you did not like this method!

[Paul Zeballos]

Thanks Fanucman and Sinha nsit for your advise (very good idea indeed). I don't use the c axis right now, I think I may use it in a couple of months. I wrote about a re thread because is what our work looks like. See, the working piece is a 800mm diameter and 900mm long steel roll. We cut a groove over this roll using the G34 code. The groove has a round shape (3" diam).

I think the changes on the 4077 parameter will help me anytime it changes the point were the thead cycle starts. Where it stops is no a problem right now.

I will wait for your response

THANK YOU AGAIN

[Paul Zeballos]

sinha_nsit, I took your idea but since we make a variable pitch thread (G34), we cannot change the start position on the Z axis. We cannot even change the relative position of the working piece with the chuck because we have a device that holds the key of the shaft of this roll. This give us only one clamp point. Please let me know any idea.

Thank you

[sinha_nsit]

Originally Posted by Paul Zeballos ... This give us only one clamp point...

Then there is absolutely no problem.
Run the same program again, and it will follow the same helix.

[Paul Zeballos]

Yes.. you are right !. It should be no problem if the original thread was made on the same machine before. However, this new machine I got now is brand new and need to redress all the rolls that were made by other machine (farrel... allen bradley control). Even more... some times the shaft of this rolls break off and need to be changed, and in the maintenance shop the new shaft is placed on different angular position. The result: a lot of rolls has different relative position of the shaft and the roll.

I tell you now... please don't shout at me if you don't like this case....

thank you

[sinha_nsit]

Then the technique would be same as already described by me. Execute G34 with a very small depth of cut to just scratch a helix. Thereafter manipulate the start point of G34. It all depends on how accurately you are able to measure the shift in the helix. The shift would be same at all Z-positions, even in case of variable lead. So, you can measure shift amount anywhere.

You have to judge whether the part is expensive or the time/effort it would take to correct it...