Insert tooling/HSS

Stellite,Crobalt,Tantung etc are trade names for same kind of stuff.
They are softer than HSS but keep their hardnes up to red glow.
It is nice to have no cooling water mess and I feel they stand interupted cuts in stainless better.
 
Excellent discussion that's given me a lot to think about. My thanks and compliments to all.

I'm a hobby turner these days. I use HSS exclusively for one reason: screw threads. It seems I cut a lot of them. HSS tools can be touched up at the end to produce accurately sized flats at the roots and crests of fine or coarse threads. For threading tight to a shoulder, a tool with an offset grind can get you in closer. Then there are acme threads. Right and left hand acmes do seem to cut better with right and left hand tools ground to get the correct relief angles on the leading and trailing edges. Small diameter internal acme threads require an unnerving end relief angle. I'm not sure how people who use standard insert tools approach these operations, but I admit to being behind the times.

I spend a lot of time grinding thread cutting tools, and I think I do a better job at this because I get practice grinding all my lathe cutting tools. I'm well aware I couldn't earn a living working this way.
 
Thank you all for all of the responses!! And esp thank you all for keeping this a discussion!!!! With my lathe, its a 12" Clausing with flame hardened ways etc, I was thinking of getting inserts. Now I think I am going to pick up a set. Just what to pick up is now my research!!! Too many dang choices out there!!:panic:

So what I have picked up on, if your lathe can run the speed and feed that inserts need, its a good idea. But if your lathe cant, dont even try. Also, if you only need to take a 2 or 3 thousandths pass, use HSS correct?

Thanks,
Chris
 
I agree- and a very informative interchange! I am open to more info if anyone still wants to put in!


Bernie
 
That seems about right. Generally speaking, if you're working on steel stock of about 3/4" or greater and if you have speeds up to 1200-1400 RPMs, you can do OK with carbide. Of course, you can spin slower or work on smaller diameter metal but you won't get the high-gloss finish. Much smaller diameter material (say, under 1/2") also will flex more due to the higher carbide pressures -so you're limited there too. In general, for non-hardened steel, a minimum DoC w/carbide is probably closer to 8 or 10 thou. Finish really suffers when you get below 8. I find about 15-25 to be optimal. And of course, these are rough "guidelines" as it all depends on diameter, exact type of steel etc... Things improve as the carbon content increases.

For stainless, you need slower RPMs but be apprised, stainless gives carbide a run for it's money! One edge of a fresh insert is only good for 5-6 passes with a 20 thou DoC and is good for 15-20 passes at 10 thou. Since stainless is so tough, carbide works well on it down into the 3-4 thou DoC range. -And cuts on SS usually require a spring pass as the 1st pass only takes off about 73% (depending on grade of stainless) of what you dialed in (due to plasticity of the stock).


Ray


EDIT: Something worth thinking about when using carbide... At the much higher SFMs and DoCs, the swarf comes at you fast, hot and sharp. Wear goggles -and since I got a nice hot burn right inside a nostril (right on top of the last one I got in the same place) I now wear full face protection. Don't even think about touching active swarf with your bare hands. It's really no joking matter...


Tamper84 said:
Thank you all for all of the responses!! And esp thank you all for keeping this a discussion!!!! With my lathe, its a 12" Clausing with flame hardened ways etc, I was thinking of getting inserts. Now I think I am going to pick up a set. Just what to pick up is now my research!!! Too many dang choices out there!!:panic:

So what I have picked up on, if your lathe can run the speed and feed that inserts need, its a good idea. But if your lathe cant, dont even try. Also, if you only need to take a 2 or 3 thousandths pass, use HSS correct?

Thanks,
Chris
Click to expand...
 
The other reason to start with HSS (or cobalt, which is really just an advanced HSS with cobalt added for more "WOW") is that carbide is downright complicated. There are so many insert types, and holders and then you have grade type, size, thickness, relief angles, chipbreakers, coatings...wow it's a lot. There was a thread a while back that had a lot of good info on choosing an insert type.

[thread]14678[/thread]

The rule about taking fine cuts with carbide is not absolute. You can purchase "ground" inserts that have a keen cutting edge that would probably let you take real fine cuts, but they are pretty specialized, fragile, and supper $$$$$.
 
Just checking back in and it appears that this topic is getting a fair and open discussion. Thank you to all the gents who have offered their points of view and opinions. And especially thank you all for keeping this thread civil. Proves ya don't have to argue to discuss a valid question.

Bob
 
I've spent most of my life doing prototype machine work, where most everything I make is one off and the majority of it is aluminum. Consequently, most of my tooling is HSS because it creates a much better surface finish than carbide and is more flexible, both literally and figuratively. I also have a set of lathe holders that take triangular inserts like the ones Frank mentioned, and I use them for roughing out steel and stainless parts, but then I finish the parts using HSS for a better finish. I also have an assortment of carbide end mills that I mostly use for slots because of their stiffness, they range in size from .005" to .250" diameter. The smaller end mills (less than 1/32" diameter) pretty much have to be carbide, otherwise they would be too flexible to use for anything. In the case of end mills, that stiffness can also work against you. Push a HSS end mill to hard and it will bend, push a carbide end mill too hard and it'll break without warning. As I mentioned, HSS is also more flexible figuratively. If you need a special form cut on the lathe, it's easy to grind a HSS tool to suit. Just this morning I needed to cut a .075" wide O-Ring groove inside a .213" diameter hole and it literally took five minutes to grind a HSS tool to get the job done. I wouldn't know where to start looking for a carbide tool to do the same.

To be used effectively, carbide needs to pushed hard. It requires a high feed rate to generate nice thick chips to carry the heat away. This requires a machine with lots of power and rigidity, above and beyond what most hobbyists have in their basement or garage. I have a Hardinge lathe, which is plenty rigid for carbide, but it lacks power. For that reason it's easy to stall when using carbide on larger parts which will chip a carbide insert every time. That costs money, which is another reason why I prefer HSS. If I chip a carbide insert, it's done, but a HSS bit can be resharpened as needed 100's of times. I'd rather spend $8 on a HSS tool bit that will last for years than $5 on an insert that only has three cutting edges.

Tom
 
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Hmm this is giving me a lot to think about. A lot has been said about cutting stainless. Which it seems can be done with both. When using HSS for stainless, do you grind the tool differently the normal? Just use a smaller DoC correct?

Also for you all using HSS exculsively, when you encounter a harder material, or cast iron etc, what do you do with the shape of your bit?

Thanks,
Chris
 
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