Basic programming for machinists

[tr4252]

I'm new to CNC, and have resolved to learn to do G code programming from the ground up. So far it's been fairly easy; I've milled a few flats and pockets on my new Microkinetics mill, done some drill patterns and slots. Next I'm attempting to get familiar with the G02 and G03 commands, again, very understandable.

Where I'm having trouble is the (evident) emphasis in the various books and on websites, with showing the programmer how to machine, as opposed to instructing the machinist how to program. CNC Programming Techniques (Smid) and CNC Machining and Programming; An Introduction (Crandell) both seem to start with the assumption that the use of G code is familiar to the reader.

My efforts to program a tool path that'll mill a couple of curved surfaces (Y-Z) with a curved intersection (X-Y) have given me that "Lost at C" feeling.

Can anybody tell me of a reference that deals with the situation I'm in; know what I want to do, through 30 years or so of shop experience, but having difficulty telling the computer what I want it to do, in a vernacular it understands.

Thanks,
Tom

[Geof]

I ran into similar things with a half a dozen different books then, after I had puzzled my way through, I found a book by Mike Mattson "CNC Programming Principles and Applications" which I think is very well written.

Also if you post some sketches with dimensions, they don't have to be fancy cad files I couldn't open them anyway, I might be able to give you some pointers. I had just over thirty years on manual machines before teaching myself G-code starting in 1999. Now I don't have the patience to do any handle twirling on a manual machine.

[lakeside]

just a quick web search found this site with some good info http://jelinux.pico-systems.com/gcode.html

[mrainey]

CNC Concepts http://www.cncci.com has a ton of programming info for guys like you - just browse through the Resources and other pages.


This site has a book that's written to teach community college and technical school students to program - very well written, you can download a free chapter.

http://www.betatechnical.com



Here are a couple other links.


http://www.nfrpartners.com/cncfaq.htm

http://www.nfrpartners.com/nfrg2g3.htm

[tr4252]

Thanks Geof, I'd appreciate a few hints on this particular operation. If you picture a couple of quanset huts, a smaller one stuck end to end with a larger one, with a curved vertical surface where they join, it's a rough idea what I'm doing. I could post a dimensioned drawing if you'd be willing to look at it.

I've found that I can import .dxf files with the Millmaster software my machine uses, and studying the resulting G code is very informative. I've only learned to do this with the X & Y coordinates, though.

Thank you all for the advice and links.

Tom

[DareBee]

Doing this with ZX is the same as with the XY for arc calculation purposes. All that you need to do is change your default working plane (XY) which is G17 to (ZX) G19 then your machine knows to interpolate its G02/ G03 in that orientation.

[Geof]

...If you picture a couple of quanset huts, a smaller one stuck end to end with a larger one, with a curved vertical surface where they join,...Tom

Okay I pictured two quonset huts and the first thing that comes to mind is; 'how big is this guy's machine?'

As Darebee says you can change the plane of your circle using G19 (ZX) or G18 (ZY). But are you really dealing with quonset hut type curves? I thought these were some sort of elliptic curve not a true circle. As soon as you get away from true circles you have to get into doing things with CAD/CAM or macro programming.

[tr4252]

This is what I was trying to describe.

Tom

[Geof]

This is what I was trying to describe.

Tom

Can you make your picture bigger? My pooold eyes cannot make anything out.r

[tr4252]

Sorry, trying again.

Tom

[Geof]

Sorry, trying again. Tom

Much more seeable.

As far as I can see you have one toolpath that is not feasible just selecting one of the three planes, XY, XZ, YZ because it requires a curve simultaneously in XY and YZ. You want to move along a radius of 1.8825 in XY and 1.750 in YZ. The plane selection by G17, G18 or G19 is one at a time only so I don't think there is anyway to follow your required path without using CAD/CAM or writing a macro to calculate this path.

[tr4252]

Thanks again Geof, I think I'll concentrate on the basics for now, and tackle this one when I'm more proficient. If I can connect with a local college or technical school that offers programming courses, I should be able to get where I want to be, eventually. Appreciate the advice.

Tom