Thread: Climp vs conventional cutting: speed, feed, finish, life

I was talking with Exkenna tonight and thought I would post up to get some more thoughts out there on the comparison in different materials. We are always looking for ways to increase tool life, improve finish, or just go faster.

Originally Posted by viper

I was talking with Exkenna tonight and thought I would post up to get some more thoughts out there on the comparison in different materials. We are always looking for ways to increase tool life, improve finish, or just go faster.

I figure I can go about 5x as fast climbing in alumium and get a better finish doing so. Carbide cutters all seem to work better climbing in steel.
HSS end mill seem to work better CONVENTIONAL milling in mild steel.

for some strange reason, I've though about this a lot, not so much recently, but I did for a while. I've come up with many theories/hypothesis, I've disproven quite a few, but I think I'm getting better.

You need to get right down into what is happening at the cutter/metal interface. With a conventional cut you are going thin chip to thick. The cutter begins touching the metal parallel with it, so first its rubbing, then the cutter deflects because the cutting edge of the flute has not been able to dig into the material yet, which causes even more rubbing. Then finally, it will dig in and then pull into the cut. So you are really beating the crap out of the outside of your endmill, causing a lot of additional heat, and it seems to leave a whole heck of a lot of burrs. Its basically the same thing as running far too small of chipload on a climb cut, you are rubbing and burning up the outside of your cutter, slowing turning the geometry into that of a drill.

With a climb cut, you are slamming the cutting edge straight down into the material. You aren't going to rub, you aren't going to create extra heat. Sure you are slamming into the material, but how else are you going to cut it? You can either rub it off or cut it off, I'll cut it off.

I'm sure I'm not the only one that has ever played with an axe, When I was 12,13,14 me and my buddy built a 12'X12' log cabin, 7 foot tall, never got a roof on it, but it kept us out of trouble and it was fun. Smack the axe straight down into the wood at a 90 degree angle, and it goes right in. Come at it at a shallow angle, to take off the bark or whatever and the axe would skip right off. Pretty much the same thing just on a different scale, different materials and a different cutting tool.

I hope that made sense?

The sharpest guy I ever worked for insisted that we climb mill when roughing and conventional mill the finish pass. He thought that the conventional finishing gave less pushoff and straighter walls. We made a lot of nice parts that way, in all kinds of materials.

So, I guess there's plenty of room for debate.




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Originally Posted by mrainey

The sharpest guy I ever worked for insisted that we climb mill when roughing and conventional mill the finish pass. He thought that the conventional finishing gave less pushoff and straighter walls. We made a lot of nice parts that way, in all kinds of materials.

So, I guess there's plenty of room for debate.

You're right, when climb cutting the bit has the opportunity to spring away from the cut, when conventional cutting the bit is drawn straighter into the cut. But that's what spring passes are for, mill once for roughing, second for finish cut, third time for a spring pass, all climb. It's very prominent with something like a 3/8" with a long DOC.

Climb across, conventional back. The conventional back is the spring and finish cut.

You can use a faster rpm and associated feed rate climb milling; because the heat from the cut is directed into and absorbed by the material mass, clear to the end of the cut.

When conventional milling the heat is directed to the outside of the piece. When approaching the end of the cut the thin fin type section at the end has little material mass for the generated heat, so the temperature goes high and can dull the cutter.

This is noticable in steel cutting.

Regards,

Stan-

Funnily enough, I noticed the difference big time today on our protrak.
It's got an R8 spindle, and is a quill / turret mill, so no where near as rigid as our vmc's.

Material was delrin/acetal
Tool was a carbide 12mm 2 flute high helix e/m
Depth of cut was 6mm
RPM was 3000
Feed was 250mm/min
Toolpath was what the CAM system spat out, so it was climbing and conventional pocketing with a 70% stepover.

It climb milled full dia lovely, fed back conventional and squeeled like a pig!
Stepped over climb milling sweet, stepped back conventional and squeeled again!

I'm with Bobw on this.
Beat it off climbing, opposed to rubby rubby conventional!

But that's what spring passes are for, mill once for roughing, second for finish cut, third time for a spring pass, all climb.

3 passes to rough and finish a wall?If you conventional mill a finish pass, the deflection pass can be eliminated.

Originally Posted by Dave K

3 passes to rough and finish a wall?If you conventional mill a finish pass, the deflection pass can be eliminated.

That is if you don't leave too much for the finish. Climb rough, conventional finish seems to be what they say...

has anyone marked a distinct surface finish difference between the two passes? What about tool life?