Which is better Polygon or Arcs?

[Normsthename]

I have had my Homebuilt Plasma up and running now for a few weeks and I am using Mach3
I would like to know what is the best method to draw DXF files for the smoothest movement of the machine.
I know that the CV Settings can affect the smoothness.
At present I have a part that has about 6 Arcs joined end to end in a tightening radius.
When I Plasma this, I can see the machine visibly pause for a split second when it encounters the next Arc start.
So which are best Arcs, Circles or Polygons?

Thanks

Andy

[under-dog]

I assume you mean polylines.

At my last job I designed parts to be laser cut.

In order to get continuouse smooth tool path we had to polyline(I assume thats what you mean) the tool path.

The geometry was made up of arcs, lines etc but when polylined it is viewed as on continuous entity.

If we failed to polyline it would do as you said or worse. It looked at each entity as small subpaths so ti might cut an arc in one place and then shoot 3 feet away and cut a different segment and basically keep skipping around. The whole part would cut but extremely inefficiently and with poor quality as it woule leave a mark on th pierce and exit of eac cut. Consider endpoint bieng coincident and these marks amplify.


Another good thing to to is create your own lead ins and outs in your geometry and not leave it up to the software. For instance if I were to make a 4" x 4" square I would make one corner my desigmnated lead in lead out and extend the edges there so that my pierce and lead out was off the desired finished geometry. (see pic)


I have never used a plasma but I assume some of the things I mentioned are
common to all tool path generation

[ger21]

I don't think it really matters. In Mach3, if you have CV turned off, it will pause at each line of g-code. With CV turned on, it shouldn't pause at all. One important thing is that all the CV settings should be turned off, both in the general config page and the settings screen. If any of the CV settings are turned on, you'll get mixed results.

How your CAM program interprets your drawing and creates the code is the only thing that the way you draw the part will affect. Imo, there only one way to draw a part in a 2D CAM program. A circle is a circle, an arc is an arc, a line is a line. You can't substitute one for another and end up with the same drawing. You either draw your part correctly, or you don't.

Bottom line is what's in your g-code, not what's in the drawing.

[Normsthename]

The geometry was made up of arcs, lines etc but when polylined it is viewed as on continuous entity.

When I used to do drawings for a Trumpf Laser, we had to draw everything with Lines, arcs and circles.
The software would just ignore polylines! we had to convert everything to arcs, lines or circles etc

In order to get continuouse smooth tool path we had to polyline(I assume thats what you mean) the tool path.

What software did you use to convert Arcs etc to polylines? or did you just redraw them?

Another good thing to to is create your own lead ins and outs in your geometry and not leave it up to the software.

I do this already, because Sheetcam cannot set a start point in the centre on a line

How your CAM program interprets your drawing and creates the code is the only thing that the way you draw the part will affect.

That is the problem, because I am joining several arcs end to end, the machine pauses for a spilt second between the arcs.
Doe'snt Mach3 when using CV have a 'look ahead' feature, I don't know what works best with tis feature?
I think if it was drawn as a Polyline hopefully it will cut in one smooth continuous movement.
I need to do some tests to see what works best.....

Thanks

Andy

[ger21]

Originally Posted by Normsthename That is the problem, because I am joining several arcs end to end, the machine pauses for a spilt second between the arcs. Doe'snt Mach3 when using CV have a 'look ahead' feature, I don't know what works best with tis feature? I think if it was drawn as a Polyline hopefully it will cut in one smooth continuous movement.

Read my last post about using CV mode. if you have multiple arcs with a different radius, it won't make any difference how you draw it. It all has to do with CV mode.

[Normsthename]

Hi Gerry
Thanks for the input
I will have a look into the CV settings, I see a lot of people struggle with CV (myself included!)
I was told to turn off CV Feedrate, and I did this for a while.
But I was getting a very wavy line coming out of a sharp corner.
On testing my machine I could visibly see the axis 'juddering' as it was accelerating out of a sharp corner.
So I turned CV Feedrate back on, and the juddering disappeared!
But I am still not 100% happy with the cut quality, on some parts it is superb, and on other parts it is not so good....
I will try your suggestions, you say that I should have CV mode turned on but all the settings turned off.
In the Config screen under CV Control I should have the 4 items unchecked?
Also in the Program Run screen I should have CV Feedrate turned off?

Thanks

Andy

[ger21]

Originally Posted by Normsthename I will try your suggestions, you say that I should have CV mode turned on but all the settings turned off. In the Config screen under CV Control I should have the 4 items unchecked? Also in the Program Run screen I should have CV Feedrate turned off? Thanks Andy

Yes, unless you know what each one does, and not many people do.

[Greolt]

Originally Posted by Normsthename In the Config screen under CV Control I should have the 4 items unchecked? Also in the Program Run screen I should have CV Feedrate turned off?

"CV Feedrate" is turned on/off on the Settings Page, not Program Run Page.

These terms seem to get confused fairly often. "CV Mode" on and "CV Feedrate" off

There is a check box for "Plasma Mode" I don't know what it does. Gerry is right, info on these settings is hard to find.

Greg

[Normsthename]

"CV Feedrate" is turned on/off on the Settings Page, not Program Run Page.

Hi Greg
The Plasma Screenset that I use has a button for CV Feedrate on both screens, and they both do the same thing
Like I said earlier at the moment I have CV Mode on, and CV Feedrate off and then another couple of items are still checked under CV Config.
The machine definitely ran smoother with the CV Feedrate turned off.

I will try the suggestion of having CV mode on, and everything else turned off.
Not tried that configuration yet!.......fingers crossed

Thanks

Andy

[Greolt]

Originally Posted by Normsthename Hi Greg The Plasma Screenset that I use has a button for CV Feedrate on both screens, and they both do the same thing

Ah my mistake. Sorry. I'm not familiar with the plasma screen.

Greg