Problem cutting arc with lathe.

I'm having a problem cutting a simple arc on a lathe (HF 9X20
converted to CNC). First some info. Running Mach2 version 4 on a
1Ghz computer. I use this same set up on my mill with no problems. I have some switches on the step driver (Xylotex) so I can switch between mill motors, and lathe motors, and also disable the Y axis. I wrote a simple program to cut a ball end on the end of a piece of .500" stock.

G01 X0 Z0 F5
G02 X0.5 Z-0.25 I0. K-0.25 F5

There seems to be a conflict with the fact that the machine is in
dia. mode. When this program is run, the tool makes a Z positive
move from Z0 and then swings around to attempt to cut the arc. If I change the Z-0.25 to Z-0.50 and the K to K-0.50 it cuts a .25"
radius the way I would expect it to with the first program. Is there something I'm missing here?

Quote:

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Is there something I'm missing here?

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Yeah, a Fanuc control system :D

Seriously though, I dont think the problem is being in diameter mode coz radii values are the same in both modes I think.

One possibility that might be worth checking is your choice of disabled axis. Most retrofit cnc lathes will use a mill's X and Y motors, but transposes the names to Z and X respectively. I am not saying this is the case here, but perhaps there is special logic written in your cnc that expects the "Y axis" to be the lathe X axis, and this might be the only axis that can handle the diameter logic correctly? Just a guess.

And to put a ball end on wouldnt you be using a G03 ??

Have you called out the Z-X arc plane, G18 for a lathe arc?

Fred Smith - IMService
http://www.cadcamcadcam.com

Thanks for the inputs. This problem has got me banging my head on my desk. I wish I could afford a Fanuc control, and a better machine to put it on for that matter. As for the Z and Y axis being transposed, I don't think this is the case. I'm using Mach2 turn. When you set up your motors you tell it the step and dir pins from the parallel connection. I have done this and disabled the Y axis. The X and Z axis are behaving well in every respect except in arc movements. Mach2 turn is in G18. This is set in a screen called state where you set the active plane (X Z in this case). Mach2 turn also has an option where you can set arc movements in absolute or incremental. I have tried both of these with the same results. I tried posting this question in the Mach1 Mach2 message group on Yahoo, but got no answers at all. I was curious if anyone else has seen this problem using the Mach2 controller software.

mudwhump I use Mach2 but have never used the lathe. Are you saying you are using the mill program as your lathe program? Don't get mad :D cause sometimes it is the simple things. Just so you know I understand simple!:D Have you done configs for both programs?

Mike

mudwhump?? you from the south?

turmite,

I'm using Mach2 turn which is the lathe program. Each program (mill and lathe) have their own config files. I'm using Mach2 mill to run my mill with no problems whatsoever. It seems to me that the mill program is supported much more, mainly because there doesn't seem to be alot of people out there who have converted their lathes.

I'm from southern Cal now living in northern Cal.

Thanks

I figured you were using turn but I just wanted to encourage you to look for something simple. I had a problem early on with my router that I have Mach2 on and low and behold it was a simple little matter of me changing my z upper limit bracket and had not looked for any kind of interference. I found it.

Souther Cal huh, I knew you had to be form some part of the "south"! :D

Mike

Does Mach2 Turn make the proper response to normal X diameter commands? A movement from X0 to X.5 should be 1/4 inch on the cross slide.

It is possible to "fool" even mill software by fudging the scaling factor on the X axis, for the purpose of obtaining linear diametral movements. However, this trick will not work with arc movements, because the Z amount is never scaled, whereas the X is. Therefore, the arc center will never be correct unless you command all arcs with radial values. In real cnc's, "U" is a radial movement command in the X axis.

So you need to "tell the truth" in your controller setup about how many steps it takes to move a radial inch.

You might play around with your code and see if you can make it work, knowing what I have told you. If you are using a cadcam program to write programs, you can often switch off the option for diameter output. All X moves must be radial amounts for this experiment.

If you determine that this is the problem, then send in a bug report to Mach2. I am sure it is a problem that is easily fixed.