Carbide inserts or HSS for small machines???

[Anglepoise]

First off I should say that I have never owned or operated a small table top lathe. So this post is more a question to those owners.

Lately there has been much talk about using inserts on these small lathes and one photo I saw showed a quite severe negative rake combined with a large tip radius.

How does all this work with a table top lathe??

Are we misleading ourselves that this combination can actually work on anything but a 'tiny' cut?

My first reaction is that we should never recommend carbide inserts to users that have less than 2 horsepower motors. And if we do , the inserts must always be at least 7° or 11° positive ( example TPMR,TPG insert ), preferably in a neutral tool holder, with minimum nose radius, and ground sharp or positive chip breaker.

What happened to HSS? Do the purveyors of small lathes even off HSS as an option ?


Is my thinking too 'old school', or have we missed something and are going in the wrong direction.

 

[wquiles]

I use "only" use tools with carbide inserts. Use them in the 7x12 that I sold to Milkey, and use them now again on the HF 8x14 - I really like them, and use these carbide insert tools for all operations. I only use HSS when I need something unique where my carbide insert tools would not work. They worked well with the small motor on the 7x12 and they work just as good with the 2HP variable-speed motor I now have in the HF 8x14. Big cuts, small cuts - anything that I throw at these tools works great.

Pretty much every single project I have shown here in the forums in the last 2-3 years have been done with carbide insert tools - they work awesome, and I love it that when worn I just put a new corner (or a new bit if all corners have been used) and I am done. The cutting action/angles is always the same - repeatability is great as well. I actually have yet to find anything wrong with these cutting tools for the projects that I do, except that not all carbide inserts are very sharp (some are pressed instead of cut/shaped) - but they still work well

Would HSS tools do the job? Of course - but in some way knowing how to properly sharpen and get the correct angles in HSS (and keep them sharp as they don't stay sharp as long as carbide inserts in my experience) is more of an advanced skill. I actually found that carbide insert tools are easier to use as a beginner - nothing to guess, nothing to adjust. Cutting angles and chip-breaker geometry is all there, always the same from insert to insert.

It is now that I have more experience that I am starting to understand and appreciate HSS tools for some smaller/difficult jobs, and I hope to keep learning more and more how to use and keep them working properly. Still, I see me using carbide insert tools for the majority of my lathe work.

I know I am still a newbie but I can certainly recommend carbide insert tools for "any" small/bench lathe like the 7x12 and my current 8x14.

 

[Anglepoise]

Well that's great news. All the written instructions and suggestions that carbide needs 'power' to work well maybe should be retired.

Do you get any chatter problems or other vibrations that effect finish??

 

[wquiles]

I would not discount well conceived suggestions/instructions just on one persons' count - I must just been lucky since carbide insert tools work well for me on a small/bench lathe. Daniel (gadget_lover) recommended them when I got started, and to this day I still thank him for his recommendations :thumbsup:

I have experienced chatter and vibrations, and I do notice that sometimes these affect finish. That being said both of the lathes that I have used have a particular RPM speed that gives the most or lowest vibrations - I guess that comes from relatively cheap lathes such as the ones I had/have. Hopefully one of these days I will have a nicer, more rigid machine such as the one Mac has or the one Mirage_Man will be getting soon.

Typically I do a final very fast, very thin pass to get a great finish, and adjusting the speed of the chuck to minimize these vibrations/chatter - it seems to also depend on the material and operation. Parting is still difficult for me to master - I get chatter with HSS (although I get less with carbide), so I prefer to cut on the metal band saw and then face on the lathe.

Several other folks with small/bench lathes use carbide insert tools as well. It would be great to hear from more folks to see what works well for them.

 

[gadget_lover]

I think it all depends on your definition of 'small cuts'.

I routinely take a .025 cut on 6061-T6 using TCMT2152 inserts in a 3/8 inch tool holder. Sometimes I use the smaller radius TCMT2151, but we are not talking inches here.

The .025 is an easy number to keep track of. If I'm taking off a lot, I'll take a .050 cut. I consider that deep, but I've never gone deeper for fear of breaking something.

The inserts have a built in chip breaker, and work well. It really makes the cutting oil smoke when I do a deep cut.

Like Will, I make a skim cut on the final pass to get a shiny, smooth finish.

Daniel