CNC Lathe : OD threading turning = thread entry burr problem

[ghettosled]

7/8-14 od thread

G76 canned cycle w/ iscar 14un thread insert.

having a burr on the entry / start of the thread.. The first 3/8" of the rolled thread (not the depth in z) basically where it turns from smooth solid into a formed thread. Material is super thin (like tin foil) and looks very wavy and brittle. The result is a sharp and partially chipped thread. It cleans up with scotch brite to the point where it feels smooth, but you can still visually see it and i'm trying to avoid manual labor.

have tried everything from spindle rpm changes, to the start location of the thread, add more material in x prior to thread cycle, more spring passes etc..

other then the initial burr, overall the threads looks PERFECT all the way through!

any help would be greatly appreciated.

[Geof]

It is practically impossible to avoid any burr and it is impossible to avoid the thread tapering down to a thin feather as it reaches the end of the stock.

To reduce the burr as much as possible you need a chamfer the end at the same angle as the thread flank.

You can chamfer before cutting the thread but you will still get some burr, however if you go back and re-chamfer and then take another final pass down the thread you can minimise this.

One way to do it without tool changes is to use the threading tool to chamfer and make the tool path go down the chamfer starting at the largest diameter.

If you really want to get rid of the wavy edge altogether you need to find out about a 'Higbee' cut. This completely removes the wavy edge by using a straight tool to cut off the thin part of the start and then pull out very quickly leaving an abrupt start to the thread. Try doing a search for Higbee and you should find something.

[ghettosled]

thank you for your help. ran the thread tool down the lead in taper, then ran two more spring passes and it cleaned up very nice!!