Insert tooling/HSS

For stainless, or any hard material just use a little less rake and clearance. The idea is the get more mass behind the cutting edge to carry heat away. Cast iron is not hard but it is abrasive, it'll still cut just fine with HSS.

Tom
 
several months ago I started a thread here about difficulty turning C I with HSS.
In the end I ended up buying a cheepo carbide set from HF then seemed to turn ok on my less than robust Atlas lathe

so I'm really interested in learning how to get my HSS tooling to work on C I
Thanks
 
I am retired,but I do a lot of custom parts for mechanical antiques. For most things,I use HSS. I even use carbon steel when I need to file in a decorative molding,harden the bit,and make a special ornamented part. I made all of the bracelet dies for pulling sterling silver into molded shapes for the bracelets that are sold in the shops in Williamsburg museum. Similarly,I made all the dies for special moldings for the PGA trophies for several years while the museum had the contract to make those in the silversmith manufacturing facility behind the scenes. For all those die blocks,I used cutters I filed from W1 or 01 steel,and hardened. They were only used for 1 die,and I ran them at low rpm in the mill. They did just fine. I still have all those cutters in a box,should any need come up for them. Plus,they're too nice to toss!

There are times when I use carbide. Sometimes I need to turn down a hardened shaft. Not what carbide was made for,but it works. I use carbide always when turning large cast iron stuff. It wears the edge off HSS too quickly. If my lathe could go slow enough,I could get by with HSS,or even carbon steel like they did for ages before better metals were invented. But,when I'm actually making money,and not just fooling around for my own enjoyment,time is money,and for difficult stuff,carbide comes out.
 
Stainless tools are shaped like any other HSS tool and differ mainly in having a lot more side rake than tools for other materials. As you know, increasing side rake improves chip ejection, which serves to reduce cutting temperatures and reduce the potential for work hardening. Increasing side rake results in lower mass at the cutting edge so relief angles are usually more conservative to maintain strength. If you use heavy cutting fluid and keep the cut moving HSS will cut stainless pretty well, at least 303; just try not to dwell and work harden the work. DOC depends on your lathe, of course, but a sharp HSS tool will cut 303 easily. Stainless is not really a hard metal but it does work harden very quickly, especially 304!

I haven't cut a lot of CI but I've done a few smaller castings. Tool shapes, relief and side rake angles are the same as for steel. Back rake is usually more conservative to reduce the tendency to dig. HSS will cut CI okay but cobalt is better suited to the abrasive nature of the material. A slightly larger nose radius (1/32") will finish CI really well.

I use HSS/cobalt almost exclusively but suggest you consider brazed carbide bits instead of or in addition to inserted carbide. I'm not talking about the 4 for a dollar Chinese stuff but quality tools from Micro 100 and others. They are relatively cost effective, can be shaped and sharpened, and a custom nose radius can be stoned on. Grades are available for almost any material and each bit will last a long time, or at least they do in a hobby shop. Since they do not have top rake I tend not to use them on stainless but they cut surprisingly well on most other materials. If I did not want to bother learning to grind tools this is the option I would choose.
 
I use carbide only, with a 7x lathe and a 12x lathe.

It has several benefits, ime.
First, its consistent.
Second, I can turn hardened, very hard, ballscrew ends without trouble.
And drill rod. And hardened bolts - which leave a great finish.

Carbide inserts dont chip easily, ime.
I use the right type of inserts, or at least they work well for me - triangular and CCMT.

I can take a 0.01 mm cut in steels, even less, with CCMT effortlessly.
But thats on my 12x lathe, I have converted it to cnc, and I use 12x more rigid cross slide with a 0.750 inch overconstrained ballscrew.

I have a better than 1 micron resolution on the x and z axis.
It may be why I can get very fine cuts on the x with (new) carbide.

I also use my lathes quite a lot, about 2000 hours in 6 years.
My costs in carbide are trivial - maybe 500 € in inserts and 500 € in toolholders, over 6-7 years.
Thats for about 200 inserts, 80% still in boxes.
And internal and external turning tools, acme inserts int/ext, thread inserts, generics and on and on. So a LOT of inserts and a lot of toolholders, including 1" thick boring bars etc. for little money.
Just steel in the same time has been at least 4000€.

My 12x lathe is also very good - its so rigid, that if I stall it cutting steel, 1/2 the time the inserts (fragile ccmt) wont chip.
It has 1.5 kW industrial motor and can fully absorb/use it.
I am now converting it to a servo indexed spindle, 2.5 kW.

So, with carbide i get faster results, better finish, more consistent, turn stainless and hard materials routinely and effortlessly.
Costs are maybe 1/20 of total costs.
I spend about 500€ month on tooling, so carbide costs are less than a blip, for me.
I dont, at the moment, make commercial parts. I may, soon. Mostly cnc kit.

From the people who have had difficulty with carbide, it seems most have not used positive rake inserts (ccmt) and or good toolholders.
I find the glanze (indian) toolholders to be very good value, and all ccmt inserts brands have worked for me, about 5-6 brands.
98% of my turning is steels.
 
Almost all the machines I used at work ran carbide insert tooling, they had the rpm and the hp to use it. At home I use hss and some carbide but only for tougher material. I don't have the rpm's on my lathes and grinding hss isn't that hard to do once you have the shape a quick touch up is all that's needed. If you need some to try I have several sizes. Send me a PM.
 
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