CNC Lathe Cutting Small Threads

[jbhill]

We are trying to cut a 3/8-16 thread 1-1/4" long in 1018 steel using an Iscar insert and a Mazak QT-10 lathe. We can only go to 95 SFM without a program error (not enough acceleration distance) but that is really leaving a terrible surface finish. We tried a number of things, even making up to 20 passes but it always yields the same results. Does anyone have any suggestions?

Thank you,
Jason

[mrainey]

Sometimes a cermet insert will cut cleaner on gummy steel.

[wjbzone]

Have you checked your insert alignment? (is it on center, is the helix angle correct .) Do those inserts require an anvil?

Bill.

[HuFlungDung]

Using a positive rake insert will help a lot, I do not know what the Iscaar thread tool looks like.

What kind of approach are you taking? A simple 90 degree plunge is not a good method, because of the excessive chip width, especailly when your SFM is low.

Brushing on a good threadcutting oil might also help improve things a bit.

I suppose you are right out of room to increase the start distance in front of the thread, so that you could run faster and not get the error?

[jbhill]

I wish we could afford cermet! The insert is on center and I'm not sure about the helix angle, these inserts fit in the grooving holders so no anvil is required. We are approaching at 29-1/2 degrees (59 in the program of course). We found out that there is a parameter in this control (T-1 plus, ancient) that will allow us to increase the accelaration distance. We did that and ran to 200 sfm. Still low but it is more than 2000 rpm, probably enough for this old machine. The threads look much better but there is still chatter for the first 1/2" of the part. I guess with no tailstock and this length of part we might be better off using something like a floating die holder... Thanks for all of the help.

Jason

[oldjohn]

G'day
Have you considered rolling threads?