Motion when .dxf is made up of small lines

[Down&Dirty]

A lot of my files are dxf format and consist of small lines instead of curves. My machine seems to do just fine with curves, but when it is driven with a bunch of really short lines to make up a curve the speed drops dramatically. For instance, in arcs I could be cutting up to 120+ inches per minute, but with the lines I am only getting 4-50 inches per minute.

Do I have to fix this by finding software to convert the lines to arcs, or am I just an idiot and missing something in my machine setup?

[lumberjack_jeff]

what do you use for cam software?

[Down&Dirty]

Sorry, for CAM I am using sheetcam. It outputs a lot of small linear moves that match the drawing.

[lumberjack_jeff]

In my experience, Sheetcam does a good job of turning line segments into arcs.

Attached is a screenshot of my settings.

Could you post a small dxf which demonstrates the problem?

[samco]

if you are using g64 or g64px.xxxx - most likely the issue is that your acceleration is too low. Speed on short line segments is all about acceleration. With G64Px.xxxx - emc tries to combine the short line segments that fall within the P tolerance. This helps also - but you still need the acceleration.

I seem to be rambling - hope that made sense.

sam

[Down&Dirty]

Originally Posted by lumberjack_jeff Could you post a small dxf which demonstrates the problem?

My settings were a little different, but even with changing to yours I still get a bunch of small lines to make a curve. I understand the sample is a complex one, but it really shows what I am talking about.

Originally Posted by samco if you are using g64 or g64px.xxxx sam

I will have to check my version when I get home tomorrow. If it helps I just built the machine 6-8 months ago.

[lumberjack_jeff]

The shape of that part suggests significant allowable tolerance from the precise shape drawn. Attached are settings which consolidated line segments in the imported drawing quite a bit.

But be aware that this undoubtedly allowed Sheetcam to deviate from the drawn profile by a few thousandths.

I'd be looking at acceleration and your expectations of the trajectory planner. I settled on G64 p0.003 which seems to work pretty smoothly for me.

[Down&Dirty]

Thank you. The only time this is an issue is on artistic parts. On actual machine parts and other things that actually have tollerance I don't end up with the segments. Unfortunatly when you work with stuff like converting jpg and other files and then manipulating them to a cut file you end up with some weird results.

I just upgraded the motors on my table so I will recalibrate and increase the accelerations to match to also help when the line segments are part of the cut file.

[jmelson]

Originally Posted by Down&Dirty A lot of my files are dxf format and consist of small lines instead of curves. My machine seems to do just fine with curves, but when it is driven with a bunch of really short lines to make up a curve the speed drops dramatically. For instance, in arcs I could be cutting up to 120+ inches per minute, but with the lines I am only getting 4-50 inches per minute. Do I have to fix this by finding software to convert the lines to arcs, or am I just an idiot and missing something in my machine setup?

There may be an EMC problem just discovered in the trajectory planner handling transitions between linear and arc segments. We've just gotten word of this in the last couple days, so
we don't have an analysis of exactly what the problem is, or whether it affects all systems or
only certain configurations. I'll update as soon as I hear more.

Jon

[Down&Dirty]

Jon,

That would be great to hear about. Unfortunatly I haven't had a chance to get home and test anything out. I was traveling last week trying to find a new job and then spent my weekend up in the mountains doing a little camping with friends.

[jmelson]

Originally Posted by Down&Dirty Jon, That would be great to hear about. Unfortunatly I haven't had a chance to get home and test anything out. I was traveling last week trying to find a new job and then spent my weekend up in the mountains doing a little camping with friends.

Well, I did a little testing here, and saw significant speed dips where they might not be expected when using G64. I then changed to G64 P0.1 (with everything set for mm) and the speed dips went away. But, I'm not absolutely sure the P0.1 was taken as a mm tolerance. The program the guy gave me was G21 (mm) and with 1800 mm/min feedrate.

Jon