Indexable lathe tools

Hi there,
lately someone told me that is not possible to take very fine cuts (dust)
with those highly promoted indexable turning tools.
Anyone out there with experience?
Novice
Reply to
Novice
Loading thread data ...
Yea, mostly true. If you want accurate work with indexable tooling you need to plan on your cuts to be several thou. On my 10EE with CNMG insert, I make my last ruff cut 0.050 over. Then take a 25 thou finish pass and measure. Then cut to size (another 25 more or less). I have no trouble doing +/- .0005 this way.
With finely sharpened and honed HSS on the same machine, I try to keep my cuts to .002 minimum.
YMMV, different lathes/operators get good results with different techniques.
Karl
Reply to
Karl Townsend
True. Carbide inserts have a radius on the cutting edge. It's on the microscopic scale, but it's there. If the cut is near that radius, it's like pushing a ball into the surface, burnishing, not cutting, and the tool forces will change, altering the final part diameter.
If you lap carbide with 1200 grit diamond it's possible to take fine cuts, so I've been told.
Carbide should NEVER be allowed to rub on a surface. One hand manual feeding on a lathe or mill is a bad practice. Learn how to set your machine to at least .002" per rev or per tooth when using carbide.
Just my view. Dave
Reply to
Mechanical Magic
It depends on the tools.
Most carbide inserts have slightly rounded edges, in part from the TiN (or other) coating process. And they are usually sintered to shape.
However, I do have some which have no coating, and which have been ground to final shape which are quite sharp. These are rather small tools, and came for my Emco-Maier Compact-5/CNC (only a 5" swing), but I keep one of the insert holders in a BXA size holder for my 12x24" Clausing -- and I use it for nice finish turning when it is not possible (for whatever reason) to figure out a heavy cut which will come to the proper final dimensions.
Without those, I would be using more HSS or equivalent for finish cuts.
Enjoy, DoN.
Reply to
DoN. Nichols
Uncoated inserts. Mmm. Do the normal suspects carry them (before I get too excited)?
KBC, Enco, ...
D> However, I do have some which have no coating, and which have
Reply to
Louis Ohland
depends on the nose size. Some are used to large nose sizes on the triangles or squares, but there are small - and real small radius inserts.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.
formatting link

Novice wrote:
Reply to
Martin H. Eastburn
Hmm ... no bets on that based on what I know. You can get uncoated, but they still have not been ground sharp, as they are intended for heavy cutting, not fine cutting like these which I have.
I don't even know who actually *made* these. I got the first few from someone on this newsgroup quite a few years ago, offering a few free to anyone who wanted them. Well ... when I got them, they *were* the ones which I needed -- 55 degree angle diamond shaped, with no maker's name or model number visible on them. (They are only 1/4" IC, so there isn't much room.) Since I was the only one who responded, he offered to sell me the rest of what he had, quite a few bags of different versions -- ground only for right-hand turning, ground only for left-hand turning (the most), or ground for both (the fewest and most desirable :-).
Since they do fit the shanks for my Compact-5 I bought what he had, and I figure that I have a lifetime supply. When I first got the lathe, I wondered where I would find more than the few packaged ones (which were not nicely ground like this), since I had difficulty finding anything which was a match in the MSC catalog pages.
So -- your best bet, I think, is to get one of the diamond carbide grinders with settable table angles, and grind your own.
Good Luck, DoN.
Reply to
DoN. Nichols
Welll..there are wiper inserts...but your comments are largely very true.
Gunner
Reply to
Gunner
As a rule, those inserts for Al are *very* sharp. And even if they are sold for use with alumin(i)um, you can use them on steel (and lighter cuts). They do make a difference!
Nick
Reply to
Nick Mueller
The additional positive rake doesn't hurt either.
Wes
Reply to
Wes
And they are often the only cure when using a boring bar with a long stick-out. Disregarding HSS.
Nick
Reply to
Nick Mueller
Ok, if we have an old manual lathe and no diamond grinder, how do we use carbide?
I use TT221 C6 inserts for stainless but they chip so quickly that HSS is less bother overall. Would C2 be better?
Last week I turned down the OD of a chromed Proto socket with a brazed insert. I had to regrind it after every pass.
Jim Wilkins
Reply to
Jim Wilkins
Well said, Karl.
We have a little Weiler toolroom lathe. Using a ccmt insert, size 21, I can take .001 or .002 on mild steel, but I wouldn't recommentd it if finish is important to you. On a lesser grade machine tool, I don't think it would work as well. Someone else here posted a comment about using the high positive aluminum cutting inserts on steel. I would have to believe that would help. We've had great success with them in aluminum.
I'm curious why you think you need to cut "dust."
Reply to
Jon
snip-----
Exactly.
Only a fool tries finish machining with negative rake inserts----that's where you change to positive rake, diamond ground inserts. They're very sharp and will easily take fine cuts------but never lose sight of the fact that some materials refuse to cooperate. Mild steel is one of the worst of all materials when it comes to light cuts.
Harold
Reply to
Harold and Susan Vordos
Ok, if we have an old manual lathe and no diamond grinder, how do we use carbide?
I use TT221 C6 inserts for stainless but they chip so quickly that HSS is less bother overall. Would C2 be better?
Last week I turned down the OD of a chromed Proto socket with a brazed insert. I had to regrind it after every pass.
Jim Wilkins
Yes it would. C2 is the recommended grade for stainless.
Harold
Reply to
Harold and Susan Vordos
If you have an older lathe with marginal rigidity and you still want to use carbide to turn steel, the newer micrograin carbides are more likely to stand up than any of the traditional grades, including C2. Micrograin carbides are tougher but they're not quite as wear resistant. On an old lathe that should make little difference.
Check with any reputable tool supplier and ask what they have in micrograin types. Don't bother with coatings; extending tool life at high temperatures and/or speeds is not what you're after with an older lathe. You just want something that won't chip. And you'll probably have to sharpen the factory edge anyway, unless you buy sharpened inserts.
-- Ed Huntress
Reply to
Ed Huntress
Every rule has exceptions, but I've found this to be true in my couple of decades of experience. I am not a professional machinist so "production" is not an issue for me. I don't have CNC. I rarely make more than one of anything.
I use carbide only when HSS tooling can't hack the job. That isn't very often. I skin dust routinely on brass, ali, mild steel and SS with sharp HSS toolbits. I seldom need tolerance better than .001" but I seldom work to much looser because that seems to be the threshold of ease. I can skin to a tenth or two with sharp HSS but that's more careful work than is usually necessary for my projects.
Reply to
Don Foreman
Would you except 12L10 or similar from this statement, Harold?
Reply to
Don Foreman
On Fri, 25 Jan 2008 01:56:07 -0500, with neither quill nor qualm, "Ed Huntress" quickly quoth:
Can you recommend any sites or articles for learning more about the micrograin carbides, Ed? What are the different types used for? I see C2, C3, and C4 used on saw blades but don't know the differences.
Yes, hardly anything comes sharp from the factory any more.
-- You cannot depend on your eyes when your imagination is out of focus. -- Mark Twain
Reply to
Larry Jaques
Here are some *old* white papers from SME on micrograin carbides. Keep in mind that a vast amount of progress has been made since 1971 and the real commercial stuff really swept in only in the mid-'90s. But these explain the principles:
formatting link
I wrote several articles on the subject during the late '90s but my archives are not with me. They related to moldmaking, anyway, so you'll probably do better just to search the Web.
The ideal would be a submicrograin carbide with 10% or more cobalt, either as inserts or as tips for brazing. They're available, but I don't know from whom. It would be worthwhile to gather some info if anyone finds a source and post it to the dropbox. This is really the way to go when you need to use carbide in an old lathe, particularly when you're cutting steel.
Let me know if you don't find what you're looking for. I'll do some further checking.
-- Ed Huntress
Reply to
Ed Huntress

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.