Thread Rolling

[dookie2022]

Have Citizen M32 thread rolling 24UNC with several dia sizes of thread in stainless steel 303 using a Fette rolling head (Japan turn Key at Factory)
We used to get 2000 parts per set of rollers now it is less than 1000 parts per set of rollers.
There are signs of chipping at the front of the rollers where the crest of the thread form is broken away.
We use a Fuchs oil as the coolant and I believe after some use of the same oil for 12 Months its lubricant properties have broken down or the coolant has so much fine particals of metal mixed in the oil it is causing the rollers to fail or we need to change the grade of coolant oil
Your thoughts on this matter will be most apreciated

[MikeMc]

If the thread rollers are chipping out in front, then you are not leaving enough room for the die to feed forward after you rapid into position.

[dookie2022]

Thanks for the information and I will check my starting position

[Deco-Doctor]

Check your pre-roll turned diameter (effective diameter), don't try and get the thread to peak to full form. the thread should be slightly truncated otherwise the stress on the rolls will cause them to wear quickly.

[micky316]

You havnt changed the lead angle have you ? I find this makes a lot of difference

[dookie2022]

The lead angle has not been changed and it is within specification according to the thread rolling company specifications.
As for the thread diameter this is under investigation at the moment but I believe it is within tolerance.
We are also checking the high pressure coolant that is contact with the rollers that is blasting flood coolant away from the rollers and creating some sort of void that prevents sufficiant amount of coolant oil to be in contact with the rollers at all times ensuring a good lubricant and cooling for the rollers.

[PoiToi]

I would also check the chamfer on your part before thread rolling. I;ve found that rolls like to have a 30-ish degree angle (in the z direction), otherwise it puts too much stress on the first thread of the rolls and can cause your problem. let us know what you find out!