Indexable lathe turning inserts - just a few quick questions

I recently upgraded my Logan 922 lathe with a quick change tool post setup and went with some 1/2" indexable turning holders

I am looking to stock up on some inserts
the ones that came with my holders have the following specs

C6 Carbide with chip breaker
TCMT 32.52

I have to be 100% honest in that I have no idea what brand or what type of inserts I should be buying or using for each material before this I was hand cutting HSS bits on a grinding stone to suit my needs

I mainly cut chromoly steel, 304 stainless steel, and aluminum on the lathe

what inserts should I use for the following ?

1. 304 Stainless Steel

2. 4130 Chromoly

3. Aluminum

4. General Cold Roll Mild Steel

I run a small motorcycle shop that specializes in vintage Harley Davidson Choppers
so everything I do is mainly small stuff where I need to face off a piece or turn down a piece and every now and then some boring and some threading work
I mainly turn lower lower fork legs to make them smooth
make up some mounting bungs
make up some wheel axles
small stuff like that

I am not a big industrial type of shop
I do spend a few hours a week on the lathe and its basically a learn as I go type deal as I never took any formal machinists school or classes (although I wish I would have)

so any recommendations on what type of inserts I should be buying would be greatly appreciated and what type I should be using for each material and any specific brands of inserts etc would be greatly appreciated

Also I dont have an unlimited budget I would like to find something that is reasonably priced as I am not doing any type of precision work etc.
This forum has been a huge help in me learning the things I have so far to operate my lathe and make up the pieces that I need

A logan is a bit light for getting much perfomance out of a carbide insert. A hss tool would work better and wouldnt tax your lathe. Plus they are way cheaper. I run HSS on all of my lathes and it works fine for mild steel I have carbide tooling but find it is not worth it on most jobs. I am running a Lodge and Shiply model x with gobs of HP and rigidity. I hate chipping an insert on some bonehead job for a friend and thinking there goes 10 bucks. I can just regrind the tip of my hss and be back in business. I used to run cnmg inserts on everything but have since just gone back to hss and life is good.

Carbide tip tools on a manual lathe are never working like they are engineered to work, as a result the grade you use is not that important. Most tool suppliers will have a general purpose grade, usually one used for softer steels, they will be fine.

The only tip I can offer is use a strong feed rate and a faster speed than that of HSS and try not to let the tips idle in one spot as some materials can work harden, that is when you will loose the tip edge. On aluminium components smear a tiny amout of oil along the cut surface (I use my finger) this will prevent build-up on the tool, but only a tiny amount of oil as the fumes can effect non-machined surfaces by disscolouration.

thanks guys
for cutting stainless and hardened materials I should be looking at a carbide tip though right ?

For a light Logan I would run the "M" style chipbreaker for al and steel, for the stainless and hardened bump that chipbreaker up to an M5 or so. On the hardened you should go for a harder grade (C2) and the rest run a tougher one (C5-C6).
Regards

Yes that is right, remember the tip radius is important, a cut should be of greater depth than the tip radius or you can get 'push off', but a small radius and tip the wear can be high. a starndard over here would be 0.4mm for finishing and 0.8mm for roughing or general purpose stuff.

Stainless is a soft material but the second you allow a tool to idle the tip will go, especially on HSS tools. So in answer to your last question yes, the tip tools are better, but harder to get a nice accurate finish.

IMHO you must be doing something wrong to be getting a bad finish on stainless with a suitable TCMT tipped tool (getting a finish on soft gummy mild steel is were i struggle, just run out of RPM to get to a good cutting speed). Good tips oftern have basic steel and stainless cutting data on the back. Read it and apply it. Speed, can be the hardest thing to get, but generaly the more the merrier on smaller diameter work on a manual lathe.

Alu specific tips absolutely rock in plastics and of course aluminium. Due to how they cut there a not speed sensitive. A alu specific insert will leave a lovely finish on even a 1/4" rod going around at 10 rpm. Its just slow!

The Super Alloy style inserts have alu like geometry but coatings and better angles. There designed to cut at the kinda speeds you can hit with smaller diamiter work on a manual lathe. The finish will be brilliant, tips last damn near forever. But you must not tap them with anything hard or bump them into anything when there not cutting or they chip. I use them a lot of free cutting steels were i just can't get the RPM to make other inserts or even Hss tools realy work well without running coolant - oil.

"A logan is a bit light for getting much perfomance out of a carbide insert. A hss tool would work better and wouldnt tax your lathe. Plus they are way cheaper."

i hear this opinion again and again, but i even run carbide on a 500 pound 3 in 1 machine and it takes off 2 mm with no sweat. also, how much is the time one spends grinding a hss bit? your supposed to hone them as well, right?

Okay so I was looking at these for maybe a threading bit
Insert, TNMC-32-NV High Speed Steel Threading - LittleMachineShop.com

and these for an HSS bit
Insert, TCMW-321 High Speed Steel - LittleMachineShop.com

and these for a carbide bit
Insert, TCMT-21.52 Carbide - LittleMachineShop.com

this is the place where I found these
if anyone has a better place to buy from please post it up
or a better bit they can recommend from somewhere I will gladly buy it from there

I know MSC is a good source but man I have no clue what I would be looking for in their catalog online for indexable cutters they have over 30,000 to choose from

TCMT is a good start. You want positive rake. Choose the largest nose radius as the insert is tougher. Forget about all the grades, just get the cheaper versions. IMHO you won't be able to tell the difference on a small manual lathe. The people telling you to stick with HSS are trying to save you $. I have broken many an insert on its first edge on a lightweight lathe, to the point where I wanted to stop flushing money. HSS will last and last since you just touch it up with a grinding wheel and a stone. It will survive any interrupted cut and can be ground to form whatever feature you want to make...

Hi
I get good results with Tungaloy Cermet CCMT inserts with a Denford Viceroy (like Southbend, Boxford). I can use them like HSS (fine feed, shallow DoC). I run the lathe at full speed and get a great finish.

With all of my inserts I find they need high speeds and high feeds to get the best out of them. They don't like interupted cuts.

Dazz

matt_isserstedt said:

You want positive rake.

Click to expand...

That is one of the keys on light lathes like South Bends or Logans. The problem is that most of the carbide toolholders are setup for negative rake, and that stuff doesn't work very well on small lathes that don't have much power. There are some positive rake toolholders for carbide inserts, they are just not in abundance when I was looking. Because of that I use HSS on my SB9.

Cheers,
Alan

HSS inserts work pretty well too.

Arthur Warner Co. | Specialists in High Speed Steel

Most negative rake toolholders will take inserts that effectively create positive rake, by means of the shape of the chip breaker built into the insert. Flat top inserts, well, those are true negative, and performance is lousy in continuous chip materials.

I use the same TNMG or CNMG in my 28" swing, 25hp heavy lathe or my 15" Clausing with whatever hp it has. I see no difference in the capability of the insert cutting 4140, and the smaller machine doesn't complain. Maybe that's not a small enough machine

The important distinction: HSS cannot stand a high enough cutting speed to give a shiny surface finish, whereas carbide can. BTDT. I also hand sharpen my carbide finishers.....it is essential to success with carbide. I use a 1/16 radius diamond wheel to grind a hook style upturned nose on all finishing tools. I make my finishing tools out of old TNMG inserts that are spent as roughers. If only lightly damaged, and most of the front radius of the insert is still present, I just gash a groove straight down onto the top of the insert, creating the hook point. This takes about 5 seconds, holding the insert with visegrips and leaning on it a little. I've used the same diamond wheel for 30 years, sharpened thousands of tips with it.

If I had to go mobile and work for somebody else, I'd have my own grinder and its own wheel as described: without it, I'd couldn't produce much of anything on a manual lathe. And so I never need to buy positive rake carbides (they don't have enough rake anyways, IMO) to behave as good as what I can make.

dian said:

"A logan is a bit light for getting much perfomance out of a carbide insert. A hss tool would work better and wouldnt tax your lathe. Plus they are way cheaper."

i hear this opinion again and again, but i even run carbide on a 500 pound 3 in 1 machine and it takes off 2 mm with no sweat. also, how much is the time one spends grinding a hss bit? your supposed to hone them as well, right?

Click to expand...

You do not have to hone them, and if you grind both ends, then touch up both ends once you have used them, less time taken than going to deposit liquid waste in the restroom ;-). I am never let down when I load up a traditional HSS tool and take a cut with it, it has limitations noted, but some positives in it's favor that help balance that out. Esp if the work piece is of a type that wants to generate chatter.

Bill