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07-25-2011, 07:16 AM #1
positive or negative rake lathe tooling?
First off I have very little knowledge on the subject. I am looking at getting an Aloris no16(or equivilent) tool holder for my QCTP. It is the holder that uses triangle insert tooling and has one on each end for turning and facing. The question is , I see you can get these in positive or negative rake. This will be in bxa size and used on a 12" clausing 5914, and used for all around operations.
Are these holders even worth purchasing, or am I better off just getting the plain turning/facing holders and then getting insert tooling for them?
07-25-2011, 09:59 AM #2
No way to answer this question unless you describe the materials you will
If you really really want a short answer:
07-25-2011, 10:31 AM #3
It will be a mix of mild steel, stainless and aluminum.
07-25-2011, 10:51 AM #4
But you might want to look at more tool holders than just that one.
07-25-2011, 11:15 AM #5
Carbide requires a lot of sfpm or you get bad surface finishing, chip welding and low insert life. To turn mild steel on negative rake you should be thinking around 700-800 sfpm. Do the math on what you plan on turning and see if it makes sense
Get a few inserts for the holders you already have and give it a try.
07-25-2011, 11:59 AM #6
You're going to get a lot of diverse answers on this, for sure.
Me, I would probably stay away from the expense of that particular holder and just get a few regular No.1 and/or No.2 holders. Part of the reason is that because of the limited HP and available spindle speeds of your lathe, you'd be further limited by the TPG inserts' limited range of molded-in chipbreakers. Most TPG's are just flat-topped inserts offering 0º rake and depend upon a largely-ineffective mechanical chipbreaker.
That's not to say you can't be successful with the No.16 style holder and TPG inserts. I use them occasionally for finishing with a CTGPR 16-3C holder I have (in a CA-size QCTP) and Ray Behner seems to have similar good results. Not a good toolholder for facing unless I kick it out a few degrees and take very light cuts.
I think you'd do better with regular toolholder blocks for your machine's QCTP and use screw-down positive rake inserts. A holder such as an SCLCR 10-3 is a 5/8" square shank and takes a fairly-common CCMT or CCGT 32.5x insert that has a good strong 80º included angle to allow turning and facing with the same holder. Another alternative is the growing availability of WCMT/WCGT 32.5x inserts and the associated SWLCR holders. You get 3 tips per insert like you would a TPG insert, still get the 80º included angle, at about the same price as a CCMT insert. There's just a lot more CCGT/CCMT inserts out there.
There's not a lot of good negative rake tooling out there in 5/8" shanks, but some. You could always get 3/4" and mill it to 5/8", but if you do I'd suggest the smaller 33x size inserts in either CNMC or WNMG for your machine. Triangular are always an option, but you have to either own two holders (better option) or move the toolpost for turning and facing operations.
As for cutting speeds. yes, coated carbide inserts do like to see more speed than you machine may have. But they can still be very productive. I use carbide insert tooling on a manual-only lathe that tops out at 1800 rpm. Most of it is true negative rake tooling, and since I'm very familiar with the technology I don't have issues with built-up edge (chipwelding) or short insert life. At all.
Coolmoney liked this post
07-25-2011, 12:48 PM #7
If my memory is correct that is a light duty clausing lathe. Negative rake tooling is for higher hp machines that are much more rigid. I have a wacheon and I still like to run positive rake tooling I usually run cobalt or hss and sharpen with a steep rake so it slices through the steel like butter I dont mind resharpening it more often. I run production with this method and it is easy on the machine and on me I hate those hot blue chips from carbide inserts they stick to my arms and burn.
07-25-2011, 02:11 PM #8
Guys what can I say. I replied to that question with NO alcohol in my system at all
and I STILL got it WRONG!!
The short answer should have been, positive rake for certain. For the materials
in question, and for the machine in question.
I can only answer stuff like this correctly, with 1.5 glasses of wine in my system.
So there you are.
I humbly apologize for the confusion!
07-25-2011, 02:12 PM #9
Those hot little chips are supposed to be thick and heavy enough to just drop, plus you're supposed to stand out of the way of them and/or put a guard over the chuck and tool.
Here's the way I like to see them fall:
‪victor1640_316ss.MOV‬‏ - YouTube
07-25-2011, 02:39 PM #10
07-25-2011, 03:02 PM #11
07-25-2011, 04:22 PM #12
07-25-2011, 05:18 PM #13
PixMan has given good advice. What I'd add is that there is one way you can sort of get the best of both positive rakes (less horsepower and deflection in the cut) and negative rakes (more edges per insert). This is with negative rake holders using inserts with grooved geometries that create an effective positive rake.
You might keep an eye out on Ebay for inserts appropriate to your lathe and material. If you find a couple dozen cheap (say, $40 for $250 worth of inserts), then you might start looking for a holder to fit.
07-25-2011, 08:15 PM #14
You're right Pix! I've got a small 5hp Sheldon that'll spin 3000rpm and a 20'' 20hp American with 1400 rpm. WNMG or TNMG's are my mainstay for roughing, but I get a better finish cut with a TPG. As an example: facing off a big round of AL. in the Sheldon. I get up to .005 of finish size, reverse the crossfeed and drag a TPG back out to the OD. I don't care if you're not supposed to do such an operation, because the finish is unreal! Yes, of course I spin the hell out of it. I have an Aloris BXA16 and a CA16 for TPG inserts. I like them for the adjustable chip breaker. I understand that a pos. insert won't last like a neg. will, but don't care when it comes to needing a good finish. Now that Pix steered me on to the cermet stuff, it's even better.
4GSR liked this post
07-25-2011, 10:16 PM #15
..................... NIGHTRAIN .......................
To the original poster...... forgitabout carbide for now... YOU KNOW NOTHING about cutting tool geometry....
Start with HSS... you grind it yourself on a bench grinder and after you learn WHY it's shaped like it is, then you will know what tool and what rake angle is used for different materials...
Buy a book on the basics.... LEARN
Limy Sami liked this post
07-26-2011, 12:40 AM #16
Pix has it right with his neutral rake reccomendation of CCMT, WCMT, etc. I did a little calculating the other day and figured I'd turned 115# of 1144 into chips in a boring operation using one edge of a CCMT 32.52 insert, and the corner is still good. The part has a wall of about 1/8" and the bore is held to +/-.0005. Prior to using the neutral rake inserts, I roughed with a CNMG and finished with a TPG. Now I rough and finish with the same tool. Had to watch the TPG like a hawk to avoid size drift due to edge deterioration, and the CNMG put too much force on the thin wall to hold final size reliably.
Another advantage is that neutral rake aluminum specific inserts are available at reasonable prices that'll outperform positives or negatives for size and finish on aluminum.
07-26-2011, 12:55 AM #17
While the CCMT, WCMT, DCMT (etc) screw-down inserts are neutral rake on the top, nearly all are actually positive top rake due to the molded-in top form geometry (a.k.a. chipbreaker.)
The top form, together with the 7º side clearance angle, mimics a hand-ground HSS tool that Gary E insists the OP learn how to make. I agree that if the OP has no tool grinding experience now is the time to learn, but it's not an absolute requirement as long as one learns about tool geometry one way or another.
Who am I to tell someone not to buy or use something? Don't we get 17 yr old squids riding 140HP motorcycles, or 47 yr old blondies driving a 414HP BMW M3? Neither knows how to get the most out of it just as a home shop machinist doesn't know tool geometry, but at least the carbide user isn't likely to kill anyone or anything except maybe their wallet.
Ray Behner liked this post
07-26-2011, 04:06 AM #18
07-26-2011, 04:29 AM #19
I use the CCMT inserts and tooling that Pixman recommended on my 5914 and they work really well both on aluminum and steel, both mild and harder alloys.
They were a big step up over the TPG tooling I was using prior to that because I didn't know any better at time, the guys on this forum straightened me out, thanks fellas.
For aluminum and light finishing cuts on steel you can get some really sharp polished CCMT inserts that give you a really nice finish, better than I could do with an HSS ground tool (ok, I'm not so hot a tool grinder). You can get these inserts at www dot latheinserts dot com.
07-26-2011, 05:20 AM #20
I use a zero rake insert like a TPU most of the time.
If roughing I use a negative rake tool and really horse it hard like .250" doc and .012+ feed rate. the downside is the work gets so hot you may as well pull it from the lathe with .025" or whatever left to go and let it cool off, then Finnish with a zero rake tool.
negative rake works well for bad tough jobs like turning castings, flame cuts and welds.
As far as positive rake I use that on HSS but thats all.