On Thursday, June 16, 2011 11:48:47 AM Dave did opine:
> On 6/16/2011 1:27 AM, gene heskett wrote:
> > On Thursday, June 16, 2011 12:56:34 AM Kent A. Reed did opine:
> >> Gentle persons.
> >>
> >> Recall that, on 6/3/2011 3:41 PM, Viesturs Lācis wrote:
> >>> Hello, gentlemen!
> >>>
> >>> I would like to ask, if anyone can suggest me a way to generate a
> >>> g-code for a single-time situation:
> >>> The part consists of 3 pieces of tubes - 2 of them need to be welded
> >>> to main piece.
> >>> What I need is to get a g-code that describes the intersection lines
> >>> of each 2 tube pieces.
> >>> I have SolidEdge model, IGES, STEP and STL models for the whole
> >>> part.
> >>>
> >>> Does anyone have any idea, how do they usually generate toolpaths
> >>> for such kind of machines?
> >>>
> >>> Viesturs
> >>
> >> I replied that it seemed pretty straightforward to work up and Gene
> >> Heskett then suggested I put my workup on the Wiki.
> >>
> >> I realize this may be moot since Viesturs received g-code to play
> >> with from Stuart Stevenson but I still like the intellectual
> >> challenge.
> >>
> >> I assumed that any two intersecting cylinders (aka tubes or pipes)
> >> have equal diameters and that their centerlines lie in a plane. If
> >> that isn't so, then the following must be replaced by something much
> >> more complicated.
> >>
> >> With my assumptions, working out the analytic geometry for the
> >> intersection lines and for the normals to those lines was
> >> straightforward, but I've discovered that I don't understand the
> >> g-codes available to emc2 as well as I thought I did. (Do you think
> >> the fact that I've never touched any 5-axis machine, let alone a
> >> PUMA-like robotic arm, has anything to do with this?)
> >>
> >> With my assumptions, the intersection lines Viesturs seeks are two
> >> half-ellipses, each lying in its own plane, with the two planes
> >> perpendicular to one another. I had in mind an elegant g-code
> >> solution which would, for each half-ellipse, define the plane
> >> containing the curve to be a working plane, and then send 2D-points
> >> and 2D-vectors (actually, these would be mathematical functions
> >> defined in subroutines) that define the half-ellipse and its normal
> >> in the working plane. In this solution, the welding head would trace
> >> around the curve while rotating about an axis perpendicular to the
> >> plane so as to remain pointing inward along the normal.
> >>
> >> Now that I've read and reread the relevant material in the Users
> >> Guide, I'm not sure I can do that. Am I just misunderstanding or do
> >> I have to send 3D-points and 3D-vectors that define each
> >> half-ellipse and its normal in space?
> >>
> >> Also, is there any purpose served if I post my analytic geometry to
> >> the Wiki as a "first half" score to the problem, so to speak? My
> >> wife is going under the surgeon's knife next week and it may be a
> >> while before I get to the "second half".
> >
> > I don't see why not, maybe someone else will finish it while you are
> > tending to the missus.
> >
> > You folks are concentrating on the welding, but before you can weld
> > it, the ends of the pipes must be prepared. If they butt meet at an
> > angle, and are the same size, then its a simple miter saw problem.
> > If however a space frame where the pieces are triangulated, even with
> > dis-similar sized pipes, then again it seems like a simple jigging
> > setup problem, one where you want to drag the end of the tube being
> > welded to the side of the other, slowly past a ballnose that is
> > tracing a half circle whose diameter matches the other pipe. Once
> > one pipe is properly seated on the other, and all such pieces are
> > assembled, then rather than welding, I would be tempted to 'furnace
> > braze' the whole assembly in one pass through the oven. Obviously
> > not as strong as properly welded, but done in one swell foop, and
> > with less stored stress than welding would leave.
> >
> > For the weld by emc, it strikes me that this same profile of motion
> > could be done, with the 'wrist' holding the migs wire feeder being
> > auto turned so that it always splits the angles. I can visualize it,
> > but I have no clue how the math that controls the 'wrist' angle can
> > be done in real time as it moves around the joint. Don't forget too,
> > that generally speaking, one must move the fire in a 'j' stroke,
> > always pushing the heat ahead of the puddle. Maybe it can be done,
> > but I've had relatively poor luck just trying to push the puddle in a
> > straight line, so I usually revert to a j stroke of about 3/16" out&
> > back, with the dwell at the 'bottom' of the j on the heavier gauge
> > metal if there is a difference.
> >
> > OTOH, I've never tested for a cert for arc welding of any kind, so
> > take that with a suitable measure of salt. My work with a smith
> > wrench has stood the test of time quite a few times though. One has
> > so much more control over the composition of the weld puddle with gas
> > that you can do almost anything with it. Even magnesium, but you'd
> > need to be better than me. A lot better. ;-)
> >
> >> Regards,
> >> Kent
> >>
> >>
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> > Cheers, gene
>
> One of the problems with tubing and pipe is that there is oftentimes a
> lot of stress in the pipe or tube when you get it.
>
> I have slit lengthwise some 3x8" 3/16 wall tubing only to have it pop
> open or clamp shut on the saw blade depending on the tube. Also welding
> rectangular tubing can be a trick (at least steel) as the heat of the
> welds expanding and contracting can cause further problems that can
> interact with the stresses already in the tube.
>
> I would not be surprised if a length of steel tubing placed into a
> normalizing furnace hot enough to braze would result in a tube "noodle"
> rather than a straight tube. Thicker tubing, 3/8" wall and heavier
> seems to have fewer issues.
>
> Dave
That may explain why the very high failure rate occurred in the space frame
go-kart frame that the RutMans sold to the kart racers back in the 60's.
That thing was a work of art, made out of 4130 steel tubes no more than
5/8" in diameter with many of the cross braces out of 3/8" tube. The whole
thing, with axles & wheels mounted, could support nearly 4k pounds in the
seat. Sans wheels and axles, IIRC less than 20 pounds. Selling for an
elevated price that put it only within reach of the really serious racers,
it's lifetime on the dirt circuit was often less than one summer season.
One fellow that showed up with 3 West Bend 580's timed to fire every 120
degrees lined up on the back axle, ran like a jato bottle but broke chains
quickly. Next week he showed up with a pair of West Bend 700's that
weren't quite as fast at the far end of the straight. Broke it that night
right behind the seat, showed up with those 700's on a fox frame the next
week & ran that the rest of the season.
One could build a plumb serious class B (two engines, 6.1 CID) that could
put you through Otto Crockers clocks on the back straightaway at Riverside
at nearly 135 mph burning booze and 120+ for the gas burners, and the
finished weight was under 100 lbs. Adding driver & enough fuel they even
had a 200 mile race there one summer. But no Rutman framed kart finished,
the frames broke. At random places it appeared.
I never broke my old Gopher frame, but between the frame, water pump &
radiator plus 2 gallon saddle tanks, one for water, one for fuel and the
engine it weighted 185 lbs, so while I had fun, I never won the race. A 14
CID, all hard bearings, rotary intake Pacific Marine bilge pump 2 cylinder
engine first made in 1937, it weighted about 70 lbs all by itself even
after I put it on a diet. That was truly racing on the cheap. Ball bearing
mains and loose needle rod bearings, the rods were machined to size but
because the crank was 1 piece, the rods were drilled and tapped for bolts,
then broken at about where the usual mating of cap & rod was, and re-
assembled so the fracture fit back together and was invisible. I pinned
the bottom two ring grooves shut & ran only a top ring, which was probably
good for 2 or 3 horses gain. Serious torque from 3000-6500, all done by
7000 as it was a deflector piston engine. I had to use 35-2 chain &
sprockets to get a full nights use out of a chain.
Cheers, gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Disclaimer: "These opinions are my own, though for a small fee they be
yours too."
-- Dave Haynie
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