Re: librecad

[Gene Heskett <gheskett@shentel.net>]

On Friday 07 December 2018 20:54:44 Erik Christiansen wrote:

> On 07.12.18 09:17, John Hasler wrote:
> > Gene writes:
> > > Thats a huge part of the problem, but theres another fence to
> > > jump. most of these so-called cad programs cannot generate even
> > > the most basic gcode.
> >
> > I can see not wanting to learn even a small part of a CAD program if
> > all you want to do is draw a simple floor plan and then never use it
> > again, but doing CNC without CAD is baffling.
> >
> > Freecad can produce gcode which you can inspect and modify.  The
> > post-processor can be customized for your particular machine.
> > Solvespace can also output gcode.  I have no idea how good the gcode
> > produced by either of these programs is because I have no way to use
> > it.
>
> Gene would have no trouble tweaking that if it was in the ballpark,
> after his years of writing the stuff from scratch. (Although
> auto-generated gcode will be a bit primitive, with a lot of data
> points, rather than a few optimised functions.)
>
> While I'm the one who did the 8 house plan drawings in Postscript, I
> wouldn't advocate that path for CAD for CNC. OK, Postscript can
> "print" text to stdout in addition to its drawing operations, so it
> could spit out gcode equivalent to what is drawn for inspection, _but_
> you'd have to hand knit the gcode to be generated by each of your hand
> knitted drawing functions. After a couple of months of development
> you'd have a nifty library available for re-use, but it's quite a hike
> to get there.
>
> > The major feature of these CAD programs is the constraint solver,
> > which understands geometry and does a huge amount of work for you. 
> > You can draw a part with dozens of equally spaced holes, change the
> > length of the part, and the holes will move appropriately.  Draw an
> > angle bracket with a brace, change the angle, and either the bracket
> > length or position will adjust appropriately depending on how you
> > constrained it. Draw a gear specifying pitch and tooth count and the
> > diameter will be computed. Change the pitch or tooth count and the
> > diameter will change. The diameter will only change by a
> > commensurate amount: no need for you to calculate allowable
> > dimensions (unless you want
> > fractional-tooth gears).
>
> If moved to try that in Postscript, you'd have to program the
> computations, and therefore decide in advance what would be
> auto-adjusted, e.g. input gear pitch and tooth count, then diameter
> will result. (While tolerances may appear on a drawing, gcode
> specifies a precise toolpath, and it's up to the machine to do its
> best to follow that. LinuxCNC will issue a "following error" and stop
> if it can't meet run-time tolerance specs.)
>
> > You can also do assemblies and specify constraints between
> > assemblies so that a change in one part will cause appropriate
> > changes to others. Interferences that would result in two objects
> > occupying the same space won't happen.  You can animate assemblies
> > and watch the machine run.  No more making cardboard models of
> > linkages and then having to stick to the tested ratios.
>
> Hmmm ... D for design, not just drawing. Powerfully tempting, if I
> ever have to do more than shuffle bits of house plans around on a
> sheet. (There the human utility, convenience, and comfort
> considerations, and even building regulations aren't amenable to
> automation, so drawing suffices, I found.)
>
> Sounds like Gene's bitten the bullet and done the job with what he
> has, by the sound of it. That's never a wrong move when it works.
>
> Erik

Thanks for the flowers Erik. What would probably amaze all the"papered" 
folks on some of these lists is that I am a C.E.T., and carry a long 
expired 1st Phone (because the commission thru us all under the bus 20 
years ago by downgrading the license and makeing the new one lifetime) I 
have a GED too, but I quit school in the high school freshman year to go 
to work fixing the then new fangled things called tv's, then switched to 
broadcasting in late 62, and have accumulated 23+ years as the Chief 
Engineer of a tv station, all on an 8th grade education. I was a "nerd" 
before the word was invented I think. I had the great good fortune to 
have a mother who was somewhat technical, the only girl in the 1929 
class on aviation technology at the Des Moines IA technical high school. 
If a little boy asked a question she did not know the answer to, she did 
know where the library was, so along with the McGuffy's readers, I was 
also reading high school physics textbooks by the age of 7.

But now I'm an old fart of 84, playing nursemaid/housekeeper to my 3rd 
wife of 29 years last week, she is late stage COPD. And harassing these 
email lists. Keeps me connected to the world, and outta the bars 
don'tcha know. :)

> (Who's gone owner-builder (swore I wouldn't do that again), and is
> currently too flat out to look at Freecad.)

Take care Erik, you are at times one of my teachers. :)

-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>