Quality carbide inserts for turning stainless?

[Munty Scruntfundle]

Hi folks.

Over the last few months I've purchased a few different tips advertised as being for stainless, but I'm not getting the life out of them I would expect. Turning to a shoulder seems to be where most have struggled, which I guess makes sense. My feeds and speeds are in the ball park and when working I'm getting a glorious finish, they just don't last long.

So, does anyone have any recommendations for CNMG 120408 for stainless? I kind of need the 04 for shoulder detail so I can't go to a larger radius.

Many thanks.

 

[ChaiLatte]

...does anyone have any recommendations for CNMG 120408 for stainless? I kind of need the 04 for shoulder detail so I can't go to a larger radius.

Your post contradicts itself. You quote an ISO code for an 08 radius insert and then say you need an 04 radius.

Please give an example of the insert you have purchased, including the brand and complete code from the box (i.e. make sure it includes the insert grade). For stainless, you need an 'M'. See:

https://www.cutwel.co.uk/blog/how-to-select-the-best-turning-insert-grade-for-your-job

 

[Lorenzl]

We used to use a high top rake PVD coated tip for aluminium on our CNC lathes and it worked great for stainless. Found out by accident as the user once forgot to change it when changing over from an aluminium job to a stainless one.

 

[Dalboy]

Just for reference this may help for future use

 

[Sideways]

We used to use a high top rake PVD coated tip for aluminium on our CNC lathes and it worked great for stainless. Found out by accident as the user once forgot to change it when changing over from an aluminium job to a stainless one.

If those were for ally, they would have been positive rake, yes ?
I use high +ve rake, highly polished inserts from Taegutec for aluminium. They do well in an old lathe that doesn't have the RPM to use indexable tooling properly. I hadn't thought to try them on stainless. Even if they don't last it would be useful to have the option. Thanks for the hint.

 

[ChaiLatte]

I use high +ve rake, highly polished inserts from Taegutec for aluminium.

Many of the highly polished ones are 00 radius (i.e. a sharp point). It is also possible to buy the non-ferrous (aluminium) inserts in 02 radius. With even that very small corner radius, they will have a longer life in tougher stainless.

 

[kinverkid]

I would like to thank everyone above for the advice too. I'm new to metalworking and also struggle to get a good finish. I do have carbide insert tooling but I'm trying to shape my own tool steel tooling which isn't as daunting as I thought it would be.

 

[Lorenzl]

When I was an apprentice most of the tools were HSS and hand ground. As you say not that hard to grind and once the original shaping is done it does not take long to maintain them.
Getting the top rake and clearances correct helps.

 

[Lorenzl]

If you want a sharp corner and only have a radiused tool you can dig the tool in at the shoulder to produce an undercut.

A chamfer on the tip works just as well as a radius and is easier to produce.