Part off tools

[Zumba]

I'm getting a new QCTP (a large Aloris CA probably) and am deciding between a standard HSS cut off blade and one of those fancy carbide insert (throw-away) blades. They use different holders.

Any real benefit to using the carbide inserts? I've never had any problems regrinding my cut off blades... only takes a couple seconds. Just wondering if I'm missing out on anything. Thx.

[HuFlungDung]

Yes, you are missing the better cutting capability of carbide. There is a critical speed to cutting steel that influences whether the chip tears out of the surface or comes off smooth.

Look at chips produced by a regular HSS twist drill. Both sides of the chip are fairly rough. A carbide tool running at a suitable surface speed produces a chip with a smooth side.

Carbide cutoff inserts can have a chip former groove on top with a 'drop center' which rolls the sides of the chip inwards, making the chip narrower than the groove which is being cut. This greatly assists in getting the chip to come easily out of the groove with minimal jamming.

Often with good cutting parameters (correct feed and speed) the smooth sided chip will easily roll up into a clock spring, rather than producing a tangled mess of chips which are prone to wrap around everything nearby.

The action of parting off with carbide requires a quite positive feed. This can be learned on manual machines, although it may seem unnatural and reckless to feed the tool in like a man , that is the way they work best.

Coolant is highly recommended to cool the chip, lubricate it for easy removal and reduce the temperature at the cutting zone.

Once you see a carbide insert properly applied, you may be tempted to toss your HSS blades and holders in the garbage. But don't HSS with a simple flat top (neutral rake) does a fine job in brass, bronze and cast iron.

[Zumba]

Thanks Hu, I will go for the carbide.

[BobWarfield]

Originally Posted by HuFlungDung This can be learned on manual machines, although it may seem unnatural and reckless to feed the tool in like a man , that is the way they work best.

Right on Hu, feed carbide like a man!

It's funny, but I have an Aloris indexable insert cutoff rig for my teeny little 9x30 lathe, not to mention a bunch of CCMT tooling as well. Whenever the carbide is misbehaving I have learned to try in this order:

- Feed faster!

- Crank up the spindle speed! BTW, it wants to go faster as you progress into the cut to smaller diameters, sometimes noticeably. CNC will do this automatically.

- Crank down the spindle speed?

- Feed slower??

- Check my setup: DOH!

9 times out of 10 the carbide gets happier when I work it harder, even on this dinky lathe. Chatter goes away, chips behave, finish improves, and life is generally grander.

I must also say I have conditioned my reflexes to crank the spindle up any time I get strings instead of 6's and 9's, not to mention ducking when the chips are flying out blue!

In addition to the Aloris, there is a guy on eBay selling really nifty pre-ground cuttoff blades that fit as a regular tool in various shank sizes. For example, see eBay item 300075779855, seller "samsws". I have found his product to be very convenient, and it works well when I need something a little more delicate than the Aloris No. 71 provides.

Lastly, let me circle back to the "Check my setup" item above. Parting off seems more sensitive to getting the tool at the right height than any other operation. It is nearly as sensitive to have the tool be square to the cut. When I get all this right, I swear the finish on my parted off piece is as good or better than what I see from a facing cut.

Best,

BW

[JooJoo]

Originally Posted by HuFlungDung Yes, you are missing the better cutting capability of carbide. There is a critical speed to cutting steel that influences whether the chip tears out of the surface or comes off smooth. Look at chips produced by a regular HSS twist drill. Both sides of the chip are fairly rough. A carbide tool running at a suitable surface speed produces a chip with a smooth side. Carbide cutoff inserts can have a chip former groove on top with a 'drop center' which rolls the sides of the chip inwards, making the chip narrower than the groove which is being cut. This greatly assists in getting the chip to come easily out of the groove with minimal jamming. Often with good cutting parameters (correct feed and speed) the smooth sided chip will easily roll up into a clock spring, rather than producing a tangled mess of chips which are prone to wrap around everything nearby. The action of parting off with carbide requires a quite positive feed. This can be learned on manual machines, although it may seem unnatural and reckless to feed the tool in like a man , that is the way they work best. Coolant is highly recommended to cool the chip, lubricate it for easy removal and reduce the temperature at the cutting zone. Once you see a carbide insert properly applied, you may be tempted to toss your HSS blades and holders in the garbage. But don't HSS with a simple flat top (neutral rake) does a fine job in brass, bronze and cast iron.

I agree mostly, tool clearances, rake, chip breaker,nose rad., speed, feed, for the size of the material,blah, blah, whats important once thats sorted is having your part off square to the job and on centre and your slide can handle it cause if your gibs are loose you'll struggle buddy.
ps. Hang on to your HSS it's good for nylon as for non ferrous stuff carbide sharpen correctly for the application is chalk and umm anyhow HuFlungDungs on the money