Carbide inserts ~ lathe size

[JPower6210]

Newbie question- I am using HSS on my lathe and happy with it, but I would like to try out some inserts- In my reading I keep hearing that you need a big heavy lathe to effectively use carbide. So the question is: what is big/heavy? Is there a general guideline for how big for inserts? How big do you need before you can go to negative rake inserts and get the advantage of double sided inserts? More curiosity than anything. Thanks-

JP

 

[SamI]

I'm running carbide on my 13 x 40" lathe and I'm pretty happy with it. Sure, carbide can be run at much higher speeds than I feel comfortable with most of the time but I get reasonable tool life out of my inserts, as long as the correct grade of inserts is used (some coatings cause rapid build up when cutting aluminium).

If you experience any chatter on your machine this can cause the carbide to chip, and on something like mini lathe where it's not uncommon to stall the motor then chipping inserts is fairly common in my experience. That being said I used carbide on my mini lathe with great success.

Many people prefer HSS on smaller machines such as the mini lathe because it can hold a sharper edge than carbide and therefore reduce the cutting force. Some people also claim a better surface finish however I have personally not found this to be the case. That being said, while I can grind special tools for a given purpose I am not the best at grinding HSS tools - I suspect if I experimented a little I could get a better finish.

As for the negative rake, that's what I tend to go for for roughing operations as it works out much more economical. I guess it's a bit of trial and error. My only advice would be to invest in good quality inserts. I have had mixed success with Chinese inserts. One batch were OK then the next barely usable. They're not that much more cheaper than the high end ones and the life of the insert seems much higher so it probably works out about even and at least you know that the inserts you buy today will perform the same as the ones you bought last time. Also you get more choice in coatings and chip breaker geometry of the insert which can make a big difference to the tools ability to cut and control the chip effectively.

 

[JPower6210]

Thanks for the detailed response- I have a PM 1236, so not a mini lathe, but not as heavy/stiff as yours either- I don't get much chatter, but I also have not used a lot of carbide and the bigger DOC- sounds like it is worth experimenting with though-

 

[Mitch Alsup]

Thanks for the detailed response- I have a PM 1236, so not a mini lathe, but not as heavy/stiff as yours either- I don't get much chatter, but I also have not used a lot of carbide and the bigger DOC- sounds like it is worth experimenting with though-

I have a Grizzly G4003G 12-36 and use carbide insert tooling almost exclusively. CNMG, CCGT, and some threading inserts. I can take cuts deep enough and fast enough that the steel turns purple as it unwinds off the nose of the tool.

 

[Karl_T]

One trick to try is inserts made for aluminum. I use CNMG tool holders. even thought this is a negative rake two sided insert, the chip breaker is big enough that it actually cuts with positive rake. You still want to run faster and deeper than HSS. Also carbide will not do a skin cut - just rubs.

 

[Bamban]

I use DCGT and CCGT turning inserts on my JET 1024, and the 16ER AG60 for threading, all carbide, ground sharp intended for aluminum. Threading I plunge straight in with the cross slide since I have the compound set sort of permanently for taper boring.

 

[Mitch Alsup]

Are you the Bambam that knows Art Luppino in Kerrville?

 

[P. Waller]

The size and power of the machine is far less important then the size of the part.
A small machine may produce small parts using insert tooling with excellent results especially if it has sufficient spindle speed.

If producing parts at the middle to maximum size that a machine will hold this is when the problems begin.

 

[mmcmdl]

I've run cemented carbide and inserts on 9" minis - 8' T lathes . The only time carbide or ceramic was not used in the last 30 years was when form tools were used . I'm not sure why I keep reading that carbide is only for bigger machines on the site .

 

[Bamban]

Are you the Bambam that knows Art Luppino in Kerrville?

Yup. We chat quite often.