How to get started with CAD/CAM for machining and engraving?

Sorry but I have to disagree with this statement in the terms of what this post is about.

What Russell says is absolutely true but sub routines are not for the beginner. Take a simple G Code of a ring of 6 bolts on a PCD. ignoring the Z moves and startup moves the code is 6 lines long, each line being the co-ordinates of each circle - very simple.

If you were to stop the program at any point you could see where you were and where you wanted to go next.

With a subroutine you get a short piece of code what is usually a mathematical equation and looking at it doesn't really tell you much, when you come to run the program all you see on screen is this subroute which for a beginner might as well be written in Serbo Croat.

If for some reason you need to pause then you have lost all information on the program as only a few very very expensive top end machines can restart inside a sub routine.

By all means learn to walk with G Code but leave sub routines until you can run.

Subroutines were originally written to make code very compact as Russell says but mainly because early machines often had a 999 program length limit.

Today with machines running direct off hard drives with massive capacity this really no longer applies.

This reminds me of the early arguments about the benefits of writing code in assembler rather than C (or whatever) - I used to love assembler but those times are gone.

John,
Did your investigations into a "cost effective viable alternative" get anywhere?

No sorry, got side tracked, had to rush down the pub for a pie and a pint.

Bastard job but someone has to do it !!

Will get onto it.

Point taken, John. I guess we come from different backgrounds. I've been writing programs since the mid '60s so subroutines are second nature to me. I have however found them to be useful being an impoverished retiree and using the evaluation version of Mach3 with it's code length limit.

Russell.

I am curious.

Do any of these packages cope with engraving on a curved cylindrical surface ?

Regards,

Richard

Quite a few do as all they do is break arc up into samll lines and substitute the Y axis moves for A [ rotary ]

but there are programs out there that will tak any G Code and convert it to rotary no matter what program has done the code in the first place.

Wrapper is one that comes to mind.

**LINK**

Thanks John, Looks good.

Regards,

Richard

For CNCWrapper to work, you need to ensure that the G-code you feed it doesn't contain any arcs (G02 & G03), but only straight line moves such as G00 & G01.

The upshot is that you might need to alter a setting in your CAM program to make it output only lines, or alternatively, use a 'lines only' post-processor.

Martin.

I think I should be able to write a little program to convert any arcs to straight lines and substitute into the relevant lines.

One of my 'hobby' programs was to convert HPGL to DXF, so a little G Code routine wouldn't be too much of a problem.

Regards,

Richard

I have an old A3 pen plotter made for use with a BBCcomputer (using VDU commands), but it also takes HPGL and Sweet Pea commands.

I might try fitting a small engraver head to it and try some CNC engraving.

Neil

Neil,

Because a pen plotter is usually limited bythe fact it has a simple up / down for a Z axis you might be better going the diamond drag engraving route which is idea for a plotter as you only need up / down and the spring loading does the rest. no spindle motor.

This is an example of diamond drag engraving done on stainless, as a guide the OD is about 2"

That text in the centre is TTF and has an inner and outer and is 0.5mm high

Edited By John Stevenson on 01/06/2013 10:52:31

So a diamond drag cutter is just a metal bar with a diamond point on the end, and you just pull it around uder its own weight. Interesting - I wonder if my printer can pull hard enough? I'd imagined using my little electric engraver with a counterweight so the pen drive can lift it.

Neil

Neil,

The diamond I use is a 1/8" diameter rod with a diamond in the end that has been sharpened to a point 90 degrees and 120 are the usual angles. It's spring loaded into a holder and you zero it onto the top of the work and I usually use 2mm as depth of cut.

It obviously doesn't cut 2mm deep but that depth puts the pressure on via the spring load.

Bit of experimentation is needed as regards materials depth of cut and spring pressure.

Doesn't't take a lot to pull it in X and Y but Z needs a bit of force to overcome spring pressure.

I currently use an old Roland PNC2200 engraver which is a gutless wonder and moves the carriage via fine bowden cable and capstans so I wouldn't worry too much about X & Y movements.

**LINK**

Hi John,

That looks more robust than THIS which is what I have got, less the pens. It also uses bowden cable, but the pen is at the end of that long, unsupported arm. I once used it to print a double sided circuit board using a dalo etch pen! It's great for technical drawings, if slow, but a nightmare for text.

I might stick with photo-etching for the time being

Neil

Reminds me of the A0 pen plotter in use when I first joined the company I work for. That plotter used a rolling bed for the paper and drew the lines in completly random order, doing one corner then randomly flitting to another corner to draw part of the text before whizzing elsewhere. It was as fascinating to watch as a shaper. And just as slow.

Regards,

Richard.

Hi Richard,

You be interested that modern rollerball pens work far better than the various original pens. Nice consistent line and clean lift-off.

Neil

It is hard to believe, but even with things as old & established as pens, there have been amazing advances in the last 10 years.

I got my first Chinese made fountain pen in 2008, and it was .. let's just say 'poor'. Five years on, one of my regular carry pens is a £14 Chinese re-interpretation of a £435 Parker pen, and it is every bit as good as the Parker.

Regards,

Richard

I do so little hand writing these days sometimes all I have written all week is my signature on an electronic receipt pad. Yet I have a nearly full bottle of ink on a pile of papers just behind my desk which has been there for a year or two. Not sure where my Parkers are now as I haven't used them for about 35 years.

edit : well I'm blowed . Found them right in the drawer they were supposed to be in. helps to keep thinhgs in place if you don't open the drawer every decade.

Edited By Bazyle on 04/06/2013 15:36:53