Graphite

[Andy]

I machined a piece of graphite 2.5 x 5 x 11.

I removed about 50% of the volume of the block.

3/4 Carbide 2Fl ticn Ball EM

4000 Rpm, 20 ipm.

Aproximately .300 Deep for roughing and

.030 for finishing.

Small stepover for finish.

Ran about 3 hours.

End mill is now dull. Is this normal?

Graphite was AR-8 for a glass mold.

We would have had a faster ipm but the shop vac couldn't keep up with the dust.

We rarely do graphite.

Any ideas on the end mill?

[Rekd™]

Andy, wear is normal. Graphite is very abrasive.

 

It cuts very nicely though. You can more than tripple your current speeds/feeds if your machine can handle moving that fast. Horsepower is not an issue here, fast movement and RPM is.

 

Watch for breaking out of walls, you may get some chipping, (better grades of graphite are better about this).

 

Consider diamond coated EM's, as they last like 10 times longer than regular carbide.

 

Always use seperate finisher, because of wear.

 

Hope you got a nice vacuum system for the dust

 

'Rekd teh crank that sucka up and letter rip!

 

:edit:

 

After re-reading your post, you can dis-reguard half of what I said , but do consider diamond EMs.

 

:/edit:

 

[ 07-01-2003, 05:51 PM: Message edited by: Rekd ]

[Mark Lovelace]

After re-reading your post, you can dis-reguard half of what I said

 

Which half?

[Dan_AKA_ROY]

Mastercam calculates very slow speeds and feeds for graphite. My milldemo v.9 at home is showing me a feed of 1.464 ipm and a speed of 305 rpm- using a Carbide 3/4" 2fl ball endmill.

 

Perhaps the endmills wear would have been half had the cut taken six hours instead of three. Slower feeds should help alleviate tool wear, correct? I've never cut graphite so what do I know. It just appears to me- from common sense; not experience, a big difference I realize- that the amount of wear incurred on the bit in the amount of time cutting seems excessive. Or graphite is a tough S.O.B.!

[Andy]

Actually, I was thinking, (Smell the smoke), that a faster feed rate would reduce cutter wear because the cutter does not linger as much. However I cannot feed faster and keep up with the dust. I should just turn down the graphite jobs.

Bad for machine if not careful.

 

Rekd, thanks for the 1/2 suggestion. Diamond coated huh. What is that, like a diamond dust coating. I have never heard of diamond coated.

I might consider that one if their not platimum.

 

Thanks,

Andy

[Hardmill]

quote:

---

Actually, I was thinking, (Smell the smoke), that a faster feed rate would reduce cutter wear because the cutter does not linger as much. However I cannot feed faster and keep up with the dust.

---

If you can't feed faster then slow down your rpm.

Feeding slower will just kill your endmills.

And a definite yes on the diamond coated mills

Rekd'

[kyle]

Diamond coated endmills work very well in graphite, we currently use 2 types, there are typed that have whats called an amorphous thin

film diamond coating with is fairly thin and edges of endmill stay very sharp and are a little easier on the pocket book, then there cvd diamond coated endmills which in the last year have come down alot in price and they are much more available in a wider range of sizes. They tend to have a thicker coating although companies like osp now offer a thin film type, just for reference say a 1/4 dia. ball will run around $100 but they last very well. There are numerous suppliers now some include osg,tesco, and sp3inc. Sp3inc.com has a pretty good website explaining the coating. Here in Wisconsin we have a supplier that grinds there own endmill and sends them out to get coated and have a pretty extensive range of sizes and lengths, if you would like any extra info let me know. Hope that helps a bit.

[Andy]

This is great!

Thanks for all the great info.

Andy

[kkominiarek]

Like rekd said...graphite is very abrasive on tooling.....cuts easy but hard on tooling.

 

Diamond tooling will last longer...but you'll need more rpms for it to be effective.

 

I would think you need to double your feedrate for roughing and up your rpms and feedrate for finishing.

 

hth

[Jammer™]

Crytallume....A good diamond coated end mill company. We buy all our cutters from them. We cut alot of graphite. On a cheaper level, Duramill cutters work very well.

[Lucky]

Diamond coated is the only way to go on graphite.

 

Roughing: 1/2 Dia end mill, 25,000 RPM, 400 ipm, 0.05 to 0.15 DOC.

 

Finishing: 30k to 42k RPM depending on cutter size, 150 to 350 ipm (depending on cutter dia. and length), stepover to suit desired finish.

[I.C.O.N.]

quote:

---

Roughing: 1/2 Dia end mill, 25,000 RPM, 400 ipm, 0.05 to 0.15 DOC.

 

Finishing: 30k to 42k RPM depending on cutter size, 150 to 350 ipm (depending on cutter dia. and length), stepover to suit desired finish

---

That's what I call kickin up dust. YEE HAAA, let'r fly

[Mark Lovelace]

Having worked with Andy on this and other graphite jobs, another thing we have tried is using woodworking-style router bits, which are carbide tipped and have no rake. They seem to cut the carbide just fine (since it creates dust rather than chips), and last about as well as a standard carbide cutter, but the advantage is that they are cheap enough so as to be expendable. At around $17 for a 1/2" ball, it's no big deal to just toss it when we're done.

 

Has any one else tried this 'bargain basement' approach? Do the diamond coated cutters last long enough to make the cost worth it for a shop that doesn't do a lot of graphite?

[Rekd™]

quote:

---

Has any one else tried this 'bargain basement' approach? Do the diamond coated cutters last long enough to make the cost worth it for a shop that doesn't do a lot of graphite?

---

Yes. It's worth the money to get diamond.

 

They'll last at least 10 times longer than carbide. Even if you get those router bits for $17.00 each, it will take 10 at a cost of $170.00 to do the job that a $100.00 diamond coated will do, and you don't have to change tools 10 times.. a real savings in itself if you have to worry about blending an new tool on the same part.

 

'Rekd

[kathy]

We have used diamond cutters on our graphite panels. Now we find that a fiberglass cutter works much better. Only the facesheets are a graphite laminated weave, and we don't need to bottom cut with the tools. However, I have cut facesheets up to 3/8 thick. Those facesheets were pretty resin rich which helped. Our worst problem is resin starved thin facesheets - we can't have any fiber delamination at the edge of the cut.

 

Kathy

[Jammer™]

I agree with rekd. We cut a ton of graphite, all grades. We have tested and tested and tried everything. Results>>>>Diamond coated is worth every penny!

[mold100]

Graphite, whats that?

 

 

Corey teh' Diamond only way to go, We gottem stocked.1/2 to .010 Dia. flats balls and various bulls.