Steel Finishing Insert (Lathe)?

[#Rekd™]

Hi,

 

Got a small job machining some 1018 CRS. It is 7/8 dia and I have to turn about 3.5" down to .6255. I am roughing it first and finishing with a VNMG tool. The finish is not great.

 

Is there something better? Sharper insert?

 

Any suggestions would be welcome!

 

Thank you in advance!

[jeff]

What are your RPM's capped at?

Which insert are you using? what is the radius on the insert? What feedrate?

Can you use a tailstock?

We use VNMG all day long here for finishing 1018,4140,4150HT,4340 etc...

[#Rekd™]

Jeff,

 

4500 rpm max. I can not use the tail stock. I tried the following inserts: VNMG-331, 1/64 tip rad grade C5, and VNMG 331 1/64 tip rad grade WP25CT. I also tried a positive Sandvik tool 55 degree insert TR-DC1304-F.

 

I have tried various feed rates and depth of cuts. The best finish was 1000rpm and 0.002"/rev. I also tried cooltool 2 to see if that helped and there was no change. It is chattering on the end if I go to fast and will not cut straight.

 

Thanks for any advice.

[crazy^millman]

Hum, I was always able to get a great finished on 1018, but you need the SFM to get it. You might also try leaving 2 times and radius for the finish pass. It take a little bit of testing, but once you dial in the amount of stock to leave to get the size you are shooting for them it becomes pretty straight forward. Also might trying some cutting oil to finish with verses coolant. If you got a skimmer then good to go, if not throw a catch pan in the bottom to catch as much oil as possible.

 

HTH

[Mr. M]

Leave at least the nose radius per side stock and feed it faster

It is chattering on the end if I go to fast and will not cut straight.

Ahh, have fun

[kh012]

on long shafts like that we have good luck with a vngp-330 insert .007 rad.

depending on how the fin. looks after the rough tool you may have to do a rough and fin. pass

with the small rad. insert.

to get rid of the chatter the rpms might have to be slow like you ended up (s1000 f.002).

when that doesn't get it some times we will rough and finish the shaft in sections from the front

to the back.

 

the chatter will determine the rpm. you can almost never get it into the correct sfpm for the insert

 

good luck

Ken

[#Rekd™]

Hi Ken,

 

Do you use the VNMG holder for that insert (vngp-330)?

 

Thanks

[crazy^millman]

Ken another idea is to leave the part long for a center that can be removed after you have done all your work. We did this for years on long small diameter shafts and helped us to achieve our SFM and keep the shatter down. Yes another operation cutting off the false center, but in the long run much quicker and easier than fighting them without one.

[kh012]

Hi Ken,

 

Do you use the VNMG holder for that insert (vngp-330)?

 

Thanks

 

yes it will load in a vnmg holder. the holder is for any 35 deg insert regardles of the rad. on the insert

 

HTH Ken

[kh012]

Ken another idea is to leave the part long for a center that can be removed after you have done all your work. We did this for years on long small diameter shafts and helped us to achieve our SFM and keep the shatter down. Yes another operation cutting off the false center, but in the long run much quicker and easier than fighting them without one.

 

we also do this alot when the part allows a sacraficial end to be removed later.

thanks

 

Ken