Rounding Corners with Arcs

[rimcanyon]

I'm getting an error in D4 due to adding a G7 between a straight cut and a G3 arc. Not supported? e.g.

N5 Y-100.534
N6 G07 R5.0
N7 G3 F80 X21.763 Y-100.534 I21.763 J100.534
N8 G07 R5.0
N9 Y-67.937

That code raises error 90 on line 7. 90 says "G07/G08 programmed outside compensation on contour, 3D interpolation or interpolation with C axis blocked."

I'm not using G41/42 but I think the error is due to the 3D interpolation clause. Probably I should just do a 45 deg. bevel on the corners (not using G08) starting 5mm before the end of the straight cut.

 

[AlfaGTA]

It was my understanding that rounding (G7) was only applicable when running using the cutter compensation (G41/G42) which is exactly what the error message says if i am not mistaken.
Write your code to use comp and i wager the radius will work provided the arc is greater than .02mm.
Cheers Ross

 

[rimcanyon]

Thanks Ross. I guess I could use a cutter radius of 0 and run my existing program under G42. I didn't bother with G41/42 because I had to calculate the arc intersection points anyway, so it wouldn't have saved any work. I was making T-nuts for a circular t-slot.

 

[AlfaGTA]

Guess I am a bit confused.
Most work starts with a plan and a drawing.
If you have a drawing of what you need/want then you just write the code at the actual geometry and use comp to do the math of the needed spindle path.
This is where a simple drawing program can be a real time saver.
Don’t need to have one that writes code for the machine , although that is nice, just need something to solve all the circle centers , tangent points, and angles. Just need end points for lines.

When I first got my FP4NC ( 93’) I got a demo copy of SurfCam ($10.00) and used it to draw parts. It would solve geometry but not write code. Geometry with cutter comp did everything I needed( 2-D )

Business grew and eventually I bought the full 3D+ version, which could do full 3D profiling and post code. I don’t do much long hand programming anymore, sort of miss it.

Cheers Ross

 

[rimcanyon]

Ross, I see it the other way around I guess. Yes, I have a drawing, the t-nuts are cut from 34mm square stock, 19mm thick. Four arcs needed to be machined: 64, 70, 92 and 98mm radii. Since the cutter is 4.7625 mm radius, that changes the arc radii A to 59.238, 65.238, 96.763 and 102.763. The X coordinates of the sides change to +/- 21.763. Cutter comp done.

The Y coordinates are just simple Pythagorus: SqRt(A^2 - X^2). However, it would have been nice to use G7 to round the edges. I ended up doing a second pass and doing a 45 degree cut 6mm from the end of each arc.

The program to cut the arcs was about 20 lines long. I did try Fusion 360 on my last project. I liked the drawing tools and the ability to have it generate the coordinates for all the intersections. But adding in toolpaths and generating programs took much longer than just writing G-Code.

 

[AlfaGTA]

Well everyone to their own.
My point is that you needed to make an actual part drawing not just for the arcs ( easy) but to set and solve the end intersections. All that needed solving ( again easy) but needed to do that before
doing the additional calculation for the tool radius. Operative word here is “ additional” Not to mention that you could have taken advantage of the “ auto” rounding feature.
Compensation is not difficult to use, it’s a nice feature, saves time, effort and errors.

Cheers Ross

 

[EmGo]

If you write your program from the cutter centerline initially, then these things are never a problem.

If you want to use g40-1-2 for "wear offsets" then you can, but there aren't big missing sections in the actual toolpath, like there are if you do work surface programming and hope the control can figure out those blank spaces.

To each their own, but it's either sad or funny watching people struggle because they insist on doing it "the easy way".

To further rattle some cages, for most 2 axis, simple 3 axis non-surfacing work APT is still faster and easier. But you guys go ahead and beat your heads against the wall, it's like hiring the handicapped, fun to watch

 

[AlfaGTA]

Yea, APT. used to teach a class ( machine tech) at the local JC on APT programming.
Student work was sent and complied by the main frame computer at Lawerence Livermore national. Labs. ( was the only place then that had the program)
That was convient……..
Cheers Ross

 

[EmGo]

That was convenient……..

I have a copy that will run on a dos peecee, if you'd like. Big bubbles, no troubles

 

[AlfaGTA]

Not sure I could figure it out now, too far back.
Got other stuff that works for me.
As to the part programming, can’t say that I have ever had any issues with “ missing sections” when programming with cutter comp on the Dialog4.
Lots of other issues for sure, but not with the control failing to complete and connect the geometry.
I like the comp, but maybe it’s because I am “ handicapped “
Cheers Ross

 

[rimcanyon]

Sometimes cutter comp is good, but G-code has functions to make it largely unnecessary. e.g. G9 G3 will rotate around a fixed point with the radius being implicit, determined by the control on the fly at the start of the arc. So as long as you started your path in the right spot, you can follow any contour that consists of straight lines and arcs.

 

[rimcanyon]

To further rattle some cages, for most 2 axis, simple 3 axis non-surfacing work APT is still faster and easier. But you guys go ahead and beat your heads against the wall, it's like hiring the handicapped, fun to watch

Thanks for mentioning APT. I like it. I would be interested in getting source code for an APT compiler or interpreter. I saw your comment in another thread:

There is also an open source version of the IBM version, but it's a translation of a translation and kind of gnu-ified. That would not be my first choice.

Or is there anything better?

I used to work on the Rational ADA compiler, so masochistic must be built into my genes.

 

[AlfaGTA]

Original question here was about implementing the auto corner rounding.
Answer is simple on the Dialog4 control!
If you want to take advantage of the G7 or G8 function on your machine, you HAVE to use cutter comp.
Lots of other ways to skin the part shape, but only one that allows the auto G7,G8 with this control.

Cheers Ross