Please recommend turning inserts for my lathe

[pontiac428]

Merely convenience, both can do a good job here.

GsT

I don't disagree at all. I think my tack is bent toward cost, necessity, and practicality. Carbide comes at a significant cost and is (for the most part) disposable. The benefit and the reason inserts are dominant is speed and time. On the lathe, the versatility and low cost of HSS is nice. In general, HSS grinds are capable of finer DOC and finer feeds, which are nice when a computer program isn't stepping up to your dimension for you. When they burn or get chipped, a pass on the hone puts you back in business. Chip an insert and break out another $10 bill, and if you're lucky, you don't have to re-make your part.

I feel differently about milling cutters for some reason. I don't use them for general purpose, but will quickly jump to a suitable insert tool when needed. I also like brazed carbide on the lathe, because they can be ground and re-ground a number of times and customized on a whim, making them versatile and recoverable when damaged.

 

[mksj]

Have had no issues using inserts, most that I buy are NOS so $30-40 for 10, which I may use one box every few years. I have used the same laydown Carmex threading insert for years, I am on the 3rd cutting edge and have yet to wear out the cutting edge. Pretty cheap when you consider the cost of machine, tooling and materials. I have had no issues with the inserts lasting and if one breaks, I just replace it and keep on going, not so if you are using HSS and you need to spend the time reworking it and realigning to your work. I also run deeper more aggressive material removal with inserts and have not had any problems with tuning the scale off of hot rolled stock or difficult to turn material. I use the same inserts in most of my boring bars, so they serve multiple purposes, and one has between 2 and 6 cutting edges per insert. Agreed that on smaller machines HSS is preferable, but then you have a newbie who will spend a lot of time figuring out how to grind his tooling, and yet one more variable that they cannot determine why they are getting poor results. They all work well, it is all a learning curve as to what one prefers.

 

[G-ManBart]

Even the old saw that carbide shouldn't be used for interrupted cuts is questionable anymore (though it should at least be given consideration).

I use HSS for probably 80% of my lathe turning, but I'd probably choose an insert for peeling mill scale - I have inserts that will cut that with no discernible deleterious effect whereas it would probably at least warrant a re-honing of any HSS cutter that I used. Merely convenience, both can do a good job here.

GsT

True. I was really concerned when I first tried carbide insert tools on interrupted cuts and found it really wasn't anything to fear...worked just fine.

I've had similar good luck using carbide on heavy mill scale. It's messy, and I don't like doing it, but it seems to work just fine. I do try to make sure I'm cutting at least deep enough to get past the mill scale entirely. I have no proof, but my perception is that it seems to make it work better.

Bonus points for you using "deleterious"

 

[G-ManBart]

Carbide comes at a significant cost and is (for the most part) disposable. The benefit and the reason inserts are dominant is speed and time.

Chip an insert and break out another $10 bill, and if you're lucky, you don't have to re-make your part.

No argument about the speed and time, but inserts don't have to be terribly expensive and certainly not $10 each if you're careful.

While I try to avoid buying a lot of stuff from China, there are times I think it can be justified. Heck, after Uncle Sam lost all my personal information to China I'm confident they already know where I live, so I might as well have them send me stuff I can use, right?

I recently bought 100 CCMT inserts for $63 shipped off one of the eBay sellers that ships direct from China. If I chip an insert I've only lost $.32 since there are two cutting edges...seems pretty insignificant to me. Granted, I don't expect them to be the highest quality inserts, but for most work they're more than good enough and I don't feel bad peeling through nasty mill scale with them.

For more critical work I tend to buy brand name inserts from a couple of sources on eBay that buy from shops going out of business. Often they are partial packs and they are literally a fraction of what new cost...many in the $3-6 an insert range and there's more than one cutting edge, so still not too bad if I trash one. The downside there is you can't always find exactly what you want, when you want it, but more often than not it's worked out well for me.

I'm probably biased towards inserts because I often have a limited amount of shop time and I'd rather spend it working on parts over grinding cutters (although I still do that sometimes).

 

[GT-6 Racer]

I totally agree with John. Grinding and using hss lathe tools your self is a cost effective, highly useful, and satisfying alternative to carbide inserts. I’ve found that good U.S.A. hss holds up very well on everything below about RC 30. I’ve ground a set of hss bits on the T&C grinder and just keep honing them. Keep speed down and tools sharp and they last a long time before needing reground.


I use lots of NOS carbide too, but on my Monarch lathes with lots of rigidly and power. The SB is primarily running hss. Recently, I’ve gotten a couple tools for the high positive inserts I used for customer jobs on the 10EE. Great results, low forces, beautiful finish. I get them at reasonable cost from Haas or even Shars. These may be a much better choice for smaller lathes Than the old negative inserts.

if I need to take passes under a few thou then it’s razor sharp mo-max. I try and use the 3 equal cut method to final dimension with at least 10-20 thou depth of cut each pass if I have enough stock To avoid the thin cuts.

in any case mild steel is tough to get a nice finish, keep experimenting. Make sure tool height is right. Follow the feeds and speeds as a starting point.

 

[7milesup]

Like many others (I'm sure I want to get the best possible finish on my parts, but here's what I'm struggling with right now. My lathe is PM-1130 and I primarily work with mild steel and 4140 steel, up to about 2" in diameter, just making small parts, nothing fancy. With my lathe I got a box of holders and inserts sold by Precision Matthew, and they are CMMT coated and uncoated. I spin my lathe at about 400 RPM, give or take a few, and my feed is .001 - .002, and normally I'm taking .025-ish roughing cuts and .005 finishing cuts. That being said, the surface finish these CMMT inserts leave is pretty bad and I spend a lot of time with emery cloth trying to get rid of these deep grooves. So I'm wondering if there are inserts better suited for my needs. What would you machining gurus recommend?
Many thanks in advance!

@javaduke One of our members here (@davidpbest) wrote a book regarding lathe insert tooling. Ironically it is called Introduction to Indexable Tooling for the Metal Lathe. I found it to be very informative and have referred back to it many times when working in the shop. I would suggest adding it to your library.

 

[rodm1]

I'll give it a try. Forgot to mention, the chips are not breaking well, I'm getting very long spirals, this probably adds to the poor finish. So clearly something wrong with my approach.
I tried increasing the feed, up to .005 but it makes it progressively worse, so far the slowest feeds produce better finish (but still not good).

Like said you need to push it harder for carbide. You are running in the machine in high speed tooling range.