Anyone seen this?

[Miguel Gonzalez]

I have been creating art pieces and have noticed a problem on several occasions.

The CAD drawing is composed primarily of inter-connected arc elements. At some of those arc endings, specifically where there is a sharp intersection, the post processor will produce a line of G3 code that ends up drawing a tiny circle at the end of the arc.

When the part is finally cut, it looks as if a hole was punched in at some of the end points and sharp angles of the art piece.

Upon inspection of the G3 code at the controller, I noticed that the coordinates displayed on the controller and those displayed in my print-out of the NC code produced by the CAD program were sometimes off by .001. Could this difference of .001 be the source of the error, and be the reason why there is that line of G3? Is it reading that .001 difference as an end point of one arc and then having to start on a seperate point, thus producing a connecting G3?

I dont know if I'm being clear or not... but I was wondering at least if anyone has seen something like this happen when you're drawing sharp angles. I even tried turning off the kerf to no avail.

[inflateable]

Here's a guess: It sounds like your postprocessor might be set up to arc off and around when it comes to a sharp external corner. The reason is that your machine can't decellerate fast enough to get around the corner and overshoots, so you'd end up with a little wedge shape at each corner if you ran like that.

Whoever wrote your post tried to get around this by forcing the code output to do a little loop around so you would get a sharp corner. i.e., it the cutter arcs off, and then arcs back on again.

If that's the case, you need to use G61 (exact stop mode) to force the cutter to decelerate before it reaches the corner and stop exactly where you are telling it to.

[ger21]

If you're using G3 with an R try using the IJ method.

[inflateable]

It's almost certainly not THIS simple, but you never know...

Your G3's should be G2's. G3 moves the cutter anticlockwise, G2 moves it clockwise - you're gong the 'long way round' to the next position.

[epineh]

I have seen this when I was cutting out those dinosaur skeleton's, I downloaded the DXF's (from the zone of course ) and imported into DeskCNC (trial) to create toolpaths, then cut using Turbocnc, I would get the little arcs you mention.

I upgraded to the full version of Desk and controller and did the same DXF's again and used Desk to run the machine, and the problem vanished, so I cannot really say what was the prob, I just thought it was badly drawn DXF's and didn't give it much more thought.

Sorry I can't really give you an answer...

Good Luck.

Russell.

[Miguel Gonzalez]

The problem has been resolved. For those who may have the same thing coming up, here's what we did:

1) the range for the min/max angle on the cutting machine's settings was made more narrow.

2) the CAD/CAM program originally had it's settings set for metric while the cutting machine was set for inches. This only became a problem when these very tight parts came into play - it had never shown any problem previously with larger, mechanical pieces.

This morning we tried setting the min/max angle back to it's original setting before this problem started happening, and the small angles and cuts started showing up even for our simple mechanical parts - so this may be a source of this kind of problem.