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Lathe advice ... Y axis or C axis interpolation?

S

steel hand

Cast Iron
Joined
Dec 12, 2006
Location
Campbell CA
We are in the market for a CNC lathe. Our goal is to combine some milling operations with turning on a live tool equipped lathe. Most of our parts are aluminum, but there is some SS and Ti too. Our parts involve milling slots and pockets across the face of the part. Some of the parts have tolerances to +- .0005. I have been talking to some salespeople who say they can make our parts using just the live tools and the C axis interpolation. Others tell me having a Y axis is the only way to go for this kind of work. Other options we want are a sub spindle to finish the back side of the part. Our goal is to run some parts at night, unattended. Anyone have experience with these kind of machines?
 
Once you use a Y axis lathe, you'll never go back. With a C axis machine, the walls of a pocket are not perp but tapered.
We are looking at a 2000SY Daewoo. Lot of machine for the money.
 
Any work on the face of the part can be done with C-axis interpolation.
I am 95% sure of that.
I use c-axis interpolation with a z-live milling unit to engrave any text on the face.
Machine off-center bores, I.D or O.D.
Machine hex, a star, any funny shape. on center or off center.

Now if you need a tapped hole on the side of the part off-center then y-axis is a must. But if you just have fancy face work you can save a ton of money without y-axis. Don't get me wrong I love machines with y-axis and wish all of my lathes had it. Just don't get fooled by a pushy salesman.

Yes a subspindle is a very valuable tool. That for sure is a must in my shop.
 
Mr. Mari is right, you can do almost any geometry that you want on the face of a part as long as it is within the x axis work envelope. I would certainly test your parts on a candidate machine before purchasing it however. Your tolerances are fairly tight for c axis interpolation, not impossible but tight. You also must consider the effect of thermal growth as the machine warms up. You can set everything up just fine but as temperatures climb, the turret moves in relationship to the spindle centerline and you will have to pay attention to positional tolerances. I find with my machine that during the first hour things move a bit (x moves -.001") then we are OK. Just for fun I would test your part on both a c axis machine and a y axis machine. The extra cost may justify itself.

Glenn @ Metro North.
 
I like my Y, but C can doo quite a bit.

Unless your werking offcenter on the side of the part - C can doo most everything. However - while my Y axis machie does in fact have C, I have never used the C on that machine. Y is MUCH easier to program!

I have held .0005 in Y axis before, but I wouldn't want to count on it unattended as you are mentioning.

---------

Think Snow Eh!
Ox
 
If you have it in your budget, go for a Y axis. C axis polar milling is a PITA to program.

Scott
MMT
 
One very nice little feature is that you dont have to shim tools on a Y axis machine, its allot easier to tweek in.
 
vmcman said:
If you have it in your budget, go for a Y axis. C axis polar milling is a PITA to program.

Scott
MMT
Click to expand...

Not hard at all once you understand it. Also, different controls have different ways of programming the polar interp. Face slotting is very easy on the C-axis. I haven't had the opportinity to program a Y-axis machine. Ox said that the Y machines also have the C, so maybe that would be the way to go, so you may not have to kick yourself down the road. +/-.0005 is kinda iffy for lights out, IMO.
 
Mari, would you mind posting an example of a square or hex or something using polar and live z axis tooling. I have yet to do it on a production run. I typically like starting with a working model vs. book code.

Thanks,
Rosie
 
C on a Y machine could mostly be there for indexing purposes. It'd suck to have a $200K+ machine and not be able to pop a hole @ 22.5*. :eek:

Many Y axis machine are not as sturdy as their C axis counterparts. Something to keep in mind if looking for heavy cuts or even really good finishes.

------

I've got a babys brain and an old mans heart
I don't always know what I'm talkin' about
Ox
 
Ok lets say you want to mill a 1 inch square on center.
Stock is 1.5 inches in diameter.
Please keep in mind you can program 100 different ways.
This works for me.

T505 S3000 M44 ( live tooling start rotating)
G98 (inches per minute)
G40( cancel cutter comp)
G13.1( cancel c-axis interpolation)
M13 ( c-axis mode)
G28 H0.0 ( home c-axis)
G0 C0.0
G0 X2.0 Z0.0
G12.1 ( start c-axis interpolation)
G01 G41 X1.5 C1.0 F200.0 ( rapid to the cut while starting cutter comp)
G01 X1.0 C.5 F20.0 ( notice the x is double. x-is always in diameter mode )
G01 X.5 C-.5 ( lower right corner of square if you are looking at it)
G01 X-.5 C-.5
G01 X-.5 C.5
G01 X.8 C.5 ( travel a little past the square)
G01 G40 X1.5 C.9 F200.0 ( cancel cutter comp and move away)
G0 G99 X3.0 Z3.0 ( go back to inches per rev)
G13.1 ( cancel c-axis interpolation)
T808 S3000 M3 ( turning tool or whatever)

I think this is right. My son is hitting my head with his toy car. I am a little distracted.
 
I think the Y axis is much more versatile than just a C. For instance if you have to mill a flat or a hex part way down a shaft. Your Z-axis live tool will probably not reach. But a Y-axis will probably add about $30k to the price of the machine.


fmari --MariTool- said:
Ok lets say you want to mill a 1 inch square on center.
G01 X.5 C-.5 ( lower right corner of square if you are looking at it)
G01 X-.5 C-.5
G01 X-.5 C.5
G01 X.8 C.5 ( travel a little past the square)
Click to expand...

Aren't the x values supposed to be 1, -1,-1,1.6?
 
fmari --MariTool- said:
Ok lets say you want to mill a 1 inch square on center.
Stock is 1.5 inches in diameter.
Please keep in mind you can program 100 different ways.
This works for me.

T505 S3000 M44 ( live tooling start rotating)
G98 (inches per minute)
G40( cancel cutter comp)
G13.1( cancel c-axis interpolation)
M13 ( c-axis mode)
G28 H0.0 ( home c-axis)
G0 C0.0
G0 X2.0 Z0.0
G12.1 ( start c-axis interpolation)
G01 G41 X1.5 C1.0 F200.0 ( rapid to the cut while starting cutter comp)
G01 X1.0 C.5 F20.0 ( notice the x is double. x-is always in diameter mode )
G01 X.5 C-.5 ( lower right corner of square if you are looking at it)
G01 X-.5 C-.5
G01 X-.5 C.5
G01 X.8 C.5 ( travel a little past the square)
G01 G40 X1.5 C.9 F200.0 ( cancel cutter comp and move away)
G0 G99 X3.0 Z3.0 ( go back to inches per rev)
G13.1 ( cancel c-axis interpolation)
T808 S3000 M3 ( turning tool or whatever)

I think this is right. My son is hitting my head with his toy car. I am a little distracted.
Click to expand...

Little different from what I'm used to. X is double and C is programmed radial. For a 1" sq, X would be X1., not X.5. Also, for climb milling, use G42. Here's what a 21i-T would look for, if I remember right.

N1 T0101 G97 S3000 M13 (tool 1, direct rpm for LH e-mill- would be M14 with dual geared live holders)
M52 (activate C spindle)
G28 C0. (orient spindle)
G0 G99 X1.5 Z.05 (rapid to start with enough travel to activate cutter comp and ipr mode)
G12.1 (activate polar coordinate interprolation)
G1 G42 X1.05 C.5 F.1 (get to a cleared start for X and height for C with comp)
Z-XXX (get to Z depth)
X-1. C.5 F.008
X-1. C-.5
X1. C-.5
X1. C.5
G40 X1.05 F.1 (cancel comp-no rapids in G12.1)
G13.1
G0 Z.1 M15 (live tool off)
X (safe index) Z (safe index)
M53 (cancel C axis mode-main spindle active)
M1
N(next tool operation)

Timm, I used to draw out the polar X & Y graph (C becomes Y essentially) when I first started doing the thing. It helps. Just remember that there are different rules to polar interp, but X is dimetrical and C is radial. Have fun! :D

Dean.
 
Not knowing but guessing, don't you effectively get a Y axis if you can co-ordinate the C and X axis together? Do they set up the controller so you can do this?

Stephen
 
Blue Steel said:
Not knowing but guessing, don't you effectively get a Y axis if you can co-ordinate the C and X axis together? Do they set up the controller so you can do this?

Stephen
Click to expand...
Yes, but you can only go as deep as the length of your Z-axis tool. Another advantage of a Y-axis is you can do circular interpolation, Helical Milling, and thread milling. It might be possible to do those in the face of a part with the C-X interpolation, but it would be impossible to do in the side without the Y-axis.
 
Metlhead and Mari,
Thanks for the input. My current customers haven't sent me anything that is cool or even warrents the extra capabilities. I want to play with this soon!
Again
Thanks,
Rosie
 
Are both of you werking with 21's? I have 18's and I have NEVER seen a ".1" G code in my life - other than over on the HAAS board.

???

Boy - your codes are a LOT dif than mine.

It's so much easier sticking with one make machine that consistantly uses the same codes. But even at that I messed up a sub collet the other day by thinking I was sincing the sub - but instead I started it up bassakwards. M34 vs M32. It would'a been right on the other machine. :o :mad:


----------

Cooper in '08!
Ox
 
Ox said:
Are both of you werking with 21's? I have 18's and I have NEVER seen a ".1" G code in my life - other than over on the HAAS board.

???

Boy - your codes are a LOT dif than mine.

It's so much easier sticking with one make machine that consistantly uses the same codes. But even at that I messed up a sub collet the other day by thinking I was sincing the sub - but instead I started it up bassakwards. M34 vs M32. It would'a been right on the other machine. :o :mad:
Click to expand...

Ox, I believe I saw some C-axis codes for the 18T before. Isn't G112 Polar on and G113 Polar off? On the 21i-T, there are GXX.1 for Polar, Polygonal and Cam (used for engraving, too). Now, the Okuma OSP-E100-L C-axis codes are waaayyy different and uses IPM instead of IPR for most everything. Talk about some close calls when I first got into that. :eek:
 
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