Lathe Inserts for Stainless

For some unknown reason, I have taken on a ton of stainless turning work.... not my strong suit. It is predominantly 304, 316 and a bit of 440C.

I usually use WCMX (trigon) inserts for roughing, and DCGX style inserts for finishing tight areas. I also use some CCMT inserts for my boring bars. I'm thinking that now would be a good time to order some SS specific inserts, rather than just picking randomly from MSC.

I don't have a tooling rep, and don't use enough inserts (thank God) to have the carbide people send me free samples.

I am running these parts on a CNC machine I built out of old pallets, a blender and an InkJet printer... just kidding, Haas turning center.

After trying a few other brands, at the old day job we ended up back with Sandvik (that's who I started with, but whatever LOL). We did a lot of 304 and 416 work with their 1025 and 1145 grades. The 1025 was for when we could run higher SFM (like 600-800 in 304 stainless) but if we couldn't (bar vibration, main and sub phasing issues, etc.) then the 1125 grade worked well and got good life. We used their CCMT and 1.5-3mm cutoff inserts mostly, and then sometimes an 85* (VNMT?) for back turning on the Swiss. The geometry on the inserts we were using was actually the same as for aluminum in some cases, with a different grade and coating. So we actually did use them for aluminum as well to save having to have a whole drawer full of slightly different inserts.

Find your local Sandvik guy and get him in to help you. You might not be a big place but they still have an account to have you try a few out before buying. Our guy (Matt F) was great and we weren't exactly spending a fortune on inserts right off the bat.

I like Mitsubishi WNMG432MA MP7035, from Curtis. He may have a new favorite by now, but awhile ago this was his recommendation.

Regards.

Mike

Finegrain said:

I like Mitsubishi WNMG432MA MP7035, from Curtis. He may have a new favorite by now, but awhile ago this was his recommendation.

Regards.

Mike

Click to expand...

I forgot about Curtis. He is usually a wealth of information, easy to deal with, and has pretty good prices. I'll give him a call in the morning. Thanks

Honestly, I don't even pay attention. I use negative geometry. I want the roughing chips to come off just like running an Engine Lathe, hot and gold colored.

But I'm only cutting about 1/2 the time. If I were cutting 125 hours a week, I'm sure I'd pay more mind. But at 15-20 hours a week, I just try to not use Aluminum specific inserts and go to town.

R

For stainless, either Sandvik 1125 or Mitsubishi VP10RT (Or VP15TF if the VP10RT isn't available in the size/shape you want)

Our shop runs 300 series stainless all day every day.

Most important is the grade of the insert. Don't worry about the shape just yet.

We use Kennametal KCM25 & KCM35 or Iscar IC6015/25, IC808/807 & IC908.

Typical SFM is ~600. It stays true for any of the grades.

You need spindle torque. If you have a ST-10 or ST-15 then you likely won't have the torque for maintaining 600sfm for parts above 8".
In this case, you will need to use positive rake inserts to lower the spindle load, at the cost of your insert life.

As usual, make sure your DOC is at least 2/3rd tip radius, ideally more than the tip radius.
Feed you will have to play with in order to ensure proper chip breaking.

My goto for medium boring is ISCAR TCMT IC807, depth 0.040, feed 0.008, 620sfm. Chip breaking on SS316 & 304 is perfect. Finishing at feed <0.006"

For boring/roughing I use ISCAR CNMX-432 IC6015 at doc 0.070, 0.009-0.011 feed, 660sfm. (my feed is actually too low per Iscar recommendation, but I don't have the torque to go much higher).