new to G18 & G19 for Z-plane arc cutting

[kendo]

I need to cut arcs in the XZ or YZ plane, but not perpendicular to the X or Y axes.

Basically, I need to rotate the G17 XY plane 45 degrees, then cut some arcs in the Z direction, but when I play with this kind of stuff in NCplot, it does some weird things I didn't expect.

I can get it to cut arcs fine if they're perpendicular to the X or Y axis. But specifying G18 or G19 after G17 rotation is in effect is a no-no I learned.

Im trying to write a macro for cutting a slightly curved surface with a bunch of stepovers and a ball endmill - but the curved surface needs to be oriented to any angle I specify. It would be pretty simple if I could just use G68 rotation. If not, it looks like I'll have to trig out the rotation and steer the macro based on the quadrant so G18 or G19 will be used correctly.

If anybody's tackled this before I'd appreciate some insight,
thanks,
Kenny

[Geof]

You get some weird shapes when you try cutting an arc in Z across the XY plane. What you are talking about was discussed a bit in this thread:

http://www.cnczone.com/forums/g-code...on_please.html

Down near the bottom I have some pictures.

I think Torsten's solution in Post #14 is probably the easiest.

[kendo]

thanks Geof,

those cuts you made in the photos are about the same thing NCplot is showing me will happen

Referring to post #14, I would hate to have to use a cam system to accomplish this cut.
I'm surprised these machines can't handle this kind of thing better.

[Delw]

Kendo cad system side code it just fine to an extent, but you need to tweak the code generator for what you need, and sometimes thats pretty hard to do. if teh code generators are tweakable you should be able to make them work.
Mastercam so Far It looks like a definate NO. Smartcam and a few others were you have 100% control it looks possible as you can use mathmaticle functions ad other functions to change your code output.

just a simple 45º in the x and y and the z you want a radius slot a cam system will automatically put it at a polyline ie line segment. like start points of x0 y0 z0 to x2.0 y2.0 z0 and you want at x1 y1 z-1.0 you get a poly line automatically not a rad.

I have found that unless you are running g18 or g19's at 0 90 180 270 360º its always line segmens that get outputted.

another exmple is take a rolling pin and put external grooves on it and make a mold of it(grooves will be rad slots in the mold). in the degrees listed above theres no problems with g18 and g19s however turn that 45 degress or any angle other than the above and it will be line segments and not rads.
I can do it by hand and the machine works just fine older machine and new machine. but my cadcam it wont.

[kendo]

OK, thanks guys

You've given me an idea, I think I can make my macro output line segments. If I can get that to work cutting parallel to the X axis, then rotation of the G17 XY axis will give me what I want.