Carbide inserts not lasting long?

[MrCrankyface]

Morning!

I'm trying to figure something out with my carbide inserts.
I mostly use CCMT09 and DCMT07 inserts and am finding that they have very short lifetime.
I dial in the speeds so the chip comes off gray/brown-ish but turns blue rather quick and try to feed as much as possible without getting a wavy finish(due to small nose radius).

As an example I was lathing some steel yesterday, nothing overly hard.
Diameter was around 70mm
RPM 440
DOC between 0.5mm and 1mm radially.
Feed ~0.15-0.2mm per revolution

Higher rpm will create sparks, lower makes a very dull/grainy finish.
Lower feed seems to rub more than cut and higher feed makes thick swarf that refuses to break.

With a fresh insert it'll cut really well but the insert quickly(like 10 minutes of cutting) becomes dull and from there it quickly goes downhill.

From what I've read these feeds and speeds are pretty low for carbide, which is why I'm so confused as to why it seems to react so negatively to increased settings?
Any help, suggestion and ideas would be much appreciated!

 

[Barncat]

Name brand or Chinese carbide?

 

[Ken226]

So diameter about 3"
depth of cut .02" -.04"
feed .006" - .008" per revolution

Sorry, I had to convert the numbers for them to make sense to me.

What size lathe are you using? Those inserts are typically good with aggressive feed/speed, but don't respond well to lighter, less rigid machines.

 

[MrCrankyface]

Barncat: Typical ebay inserts, the expensive brand inserts have scared me a bit but then again, if they last longer it might be a better investment.
Ken226: The lathe is called BL250G, haven't seen many of them around but a lot of similar versions are on the market.
About 250mm swing and 700mm length, ~150kg.

Same as on the picture except mine is benchmounted so it doesn't have the cabinets.

 

[Ken226]

That's about a 10" x 28" lathe. About 330 lbs, and I'm guessing 1 to 1.5hp. About 1000 watts.

I think you probably will need to use hss tooling. The feeds and speeds needed to get good results with carbide insert tooling are going to require more rigidity than a lathe that size can deliver.

When I need to use insert tooling on a machine that small, I use the razor sharp inserts designed for non-ferous metals.

But, your lathe will give best results with ground HSS.

For inserts, try something like these. They will let you reduce the feeds and speeds to a level your lathe can handle without chatter destroying the inserts.

RISHET TOOLS CCGX / CCGT 32.51 High Polish Carbide Inserts for Aluminum (10 PCS) | eBay

Find many great new & used options and get the best deals for RISHET TOOLS CCGX / CCGT 32.51 High Polish Carbide Inserts for Aluminum (10 PCS) at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Or these:

RISHET TOOLS DCGX / DCGT 32.51 High Polish turning Inserts for Aluminum (10 PCS) | eBay

DCGX / DCGT 32.51 High Polish turning Inserts for Aluminum (Box of 10). Style DCGX.

www.ebay.com

 

[MrCrankyface]

You're most likely right about the rigidity part.
Do these inserts still work OK in steel, despite being designed for non-ferous?
I have HSS blanks but I really dislike having to resharpen them, it ruins my workflow.

 

[Ken226]

Yea, it's certainly more convenient to pop in a new insert than to fire up the grinder and start burning fingertips.

Yes, those inserts are still tungsten carbide, and will cut steel fine.

They don't break chips very well, but they leave a nice surface finish and they last alot longer than 10 minutes. They aren't ideal for your lathe, but probably better than what your using.

Arthur Warner Co. In the USA makes and sells HSS inserts. Some guys love them for small lathes, but I hear they are expensive.
Link:

Turning

 

[ttabbal]

I can't say for sure what you have, but you didn't specify the grade of steel. I have some mystery metal here that the group here suggested might be 4140PH. It eats import inserts. I tried some Iscar inserts and they hold up really well and give a much better finish. The cut parameters were the same for both inserts. I was quite surprised. My PM1127 is similar to your lathe, so it might help to try some better quality inserts.

I use HSS most of the time and rarely need to resharpen them. Once in a while I pop them out and hone them, about 5 minutes on a diamond card, but I don't have to grind them much. For harder materials that I need a couple of passes on, I sometimes switch to carbide to rough quicker as it can handler higher SFM.

 

[JimDawson]

The DCMT inserts are for soft materials. DMNG are the same size but are for steel. For general manual turning I have found the Accusize inserts from Amazon seem to work OK. I get about 10x the life out of the Mitsubishi DiaEdge inserts turning stainless in CNC production, but they are about $18 each.

 

[C-Bag]

Quite a while ago somebody posted pics of brand new economy inserts under a microscope scope and they were chipped right out of the box. Couldn’t see it with the naked eye, nor jeweler goggles but sure could see it with a microscope. Got me paying attention to local CL and was able to pick up a stereo microscope for $40. Best bang for the buck I ever spent. Really upped my sharpening skills as what looked passable under goggles was a mess under the microscope. Cured my chatter and finish problems.

For my 9x20 I use mostly HSS but have several Kennemetal and other name brand brazed carbide bits I picked up used. I leave my baldor knockoff tool grinder set for the relief angles so it’s super easy to hone a nice sharp edge on my bits in seconds. Probably less time than it takes to change an insert.