Carbide tooling

DavidR8

DavidR8

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Hey all, I see many people using carbide tooling in their mini lathes.
I was of the understanding that carbide needed high feed rates and spindle speeds to be effective.
Can someone educate me?


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Many of the mini lathes have plenty of spindle speed for carbide. The feed rates are likewise high enough. Where they lack is in depth of cut because of a lack of horsepower. It is all about what surface finish is needed. Most hobbyists aren't needing mirror like finishes and when weighed against the extra work of grinding tools in HSS most will accept a pretty good finish over the extra time and skill needed to grind HSS.

I have gotten into a habit of roughing out with carbide and using HSS when I can to finish. To me it is the best of both worlds. But then my lathe isn't "mini" except maybe to Abom79.
 
I have both. I don't have a mini, but my 1127 is pretty small as lathes go. I reach for the HSS 90% of the time. It gives me a better finish with lower cutting forces than the inserted carbide I have. I can take deep roughing cuts or shave a few tenths off. Inserts have a minimum depth of cut to work well. Combined with the increased forces, that can cause problems for smaller machines.

That isn't to say that the inserts are useless, I occasionally work material that eats HSS. My boring bars are also carbide.

As for time and skill, a good grinder limits the time required. And if I can do it, I think most anyone can. :) it looks far more difficult than it is.
 
Carbide tools are more brittle than HSS and the edge will chip easily from chatter or other mishaps.
My adventure into carbide started with cheap brazed carbide bits which was self defeating.
You need to sharpen brazed carbide from the start.
Inserts don't need sharpening but are expensive and just as fragile.
So now I use carbide only when the hardness of the work dictates it. My 12x36 is rigid enough to run carbide successfully and I have the confidence to run the speeds and feeds high enough. But HSS cobalt and Crobalt style bits in a tangential holder are my go-to for most one off jobs on the lathe.
 
Ash been said, it comes down to horses for courses. Carbide tools certainly perform better when worked hard. The problems you have with a mini lathe is HP and rigidity. However there are times when you should use carbide and that is when you are machining a hard material. Times when the HSS just doesn't stand up to the cut, even when you slow it down. so go the carbide.

For light finishing cuts HSS will usually give you a better finish. Also when cutting softer metals like aluminium, copper, brass, even free cutting mild steel HSS is generally best. I also prefer HSS for single point thread cutting even on a larger lathe with the rigidity and HP, it's just that most thread cutting is done at a relatively low speed.

You should try everything and then use what you find suits you best.
 
Thanks gents.
As a newcomer to the hobby it’s tough to sort out the whys and wherefores!


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Dave, you've gotten some good answers but let me muddy the waters a bit more.

The problem with mini-lathes is that they lack rigidity, speed, power and size capacity. When speaking about carbide tooling, and especially inserted carbide tooling, all of these things matter. A deficiency in any one of these capabilities will impair your ability to use carbide as intended. A lot of mini-lathe guys use inserted carbide and think they work well but it isn't until you see how carbide works in a high horsepower, high speed spindle situation that you understand that there's "work" and then there's work.

Inserted carbide tools will work on your little lathe. I mean, it will cut. However, you lack all of the things above so do not expect carbide to give you all the benefits it would normally confer. I own a Sherline lathe and I've used inserted carbide, brazed carbide and HSS with it so I'm not guessing here. Inserted carbide will work for you, and you don't have to grind anything to do so. What you will also find, however, is that the cost for this tooling will be much higher vs HSS and you will not be able to cut to tight tolerances as easily. Yes, carbide works better for harder materials but you still need enough power, speed and rigidity to cut it and you may not have it ... just saying.

If you still want to try inserted carbide tooling, probably the best geometry for a small lathe will be an SCLCR tool holder with CCMT and CCGT inserts. If you go this route, ask the guys and they will guide you.

Regardless of what the Youtube guys show you, lathe work is not really about deep roughing cuts; it's more about accuracy at the small end of things. A good HSS tool will usually cut what you dial in, whereas an inserted carbide tool requires a lot more skill and experience to do the same thing. You can definitely cut accurately with a carbide tool but you have to know how to work with the insert geometry and nose radius of the tool, and there is a whole lot more to it than you might think.

If you wish to work with HSS but either cannot grind it yet or just prefer inserted tooling, look at the AR Warner line of inserted HSS tools. Their inserts are flat on top and can be easily sharpened by honing the top of the insert so the cost per insert, while high, is not bad considering how long one insert will last.

Of course, your best bet will be to learn to grind your own HSS tools. It will work better for most materials, will be easier to use and will cut more accurately on your little lathe.
 
Count my vote for HSS. I don't have a mini lathe, but it is small enough to need to understand its limits with rigidity. My impression of carbide is that it loves being ripped in RPM and driven no less than .040 DOC into the work to produce a nice result. Most of the time I cut .020-040 based on my lathe's performance, and carbide just doesn't do that well. HSS does great at any DOC, is sharpenable for a lifetime, and highly customizable. There are some really great rinds that can be employed for incredible versatility. It's cheap, with 3/8" M2 blanks costing about the same as one middle of the road import insert. I never liked the idea of paying so much for inserts that will dull or chip then be thrown away, especially when the performance drops so much as they approach that point. If I need something harder or more heat tolerant, I can use cobalt. If I'm cutting a piece of stainless that is getting feisty, then the inserts come out, but they don't see the light of day much when I have 20 or so HSS tools ground, sharpened, and ready to work. ...aaand that's worth exactly two cents.
 
Stefan Gotteswinter has a number of great videos regarding the use of carbide on small parts and lower HP machines. From my understanding carbide is typically ground/formed to a less than sharp or razor sharp edge due to it brittleness and risk of damaging/chipping of the cutting face. Stefan regrinds his inserts and solid carbide bits to sharp edges, to allow him to use carbide in less traditional ways.

His latest video is a DIY Slow Speed Carbide Grinder
 
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