Herky Jerky G-code

[basskitcase]

Hello all,

When i cut with my machine, when it does curves, it is very jerky around them because i have each curve broken into linear segments (you can imagine how long this makes the G-code with .001 tolerance). It seems as though each time it gets to the next line, the motors pause for a split second before initiating the next line, so i get vibration in my machine. is there any setting in Mach 3 to make these trasitions more smooth, or is the only way to not do curves in linear segments?

I treid doing curves as circular inperpolations instead of linear segments, but i got a bunch of crazy looking circles in my gcode when i loaded it into Mach 3. What settings would i edit to make Mach3 properly interpret my G-code?

[Slaps]

Sounds like you might have alot af backlash in your leadscrews....do you have backlash comp on your machine?

[stevespo]

Enable "constant velocity" mode with a G64 instruction in your gcode. That should help. There are Mach settings that provide some control over the behavior, and there is a document that helps to explain them.

Mach3 CV settings, V2

The only settings I have enabled are under General Settings, "Motion Mode: Constant Velocity = on" and "Stop CV on angles > 90 Degrees". That seems to work well for me.

Steve

[stevespo]

I didn't see the second part of your question.

Those "crazy circles" can be the result of a number of things. Potentially there is a mismatch between the type of code your CAM program is generating, and what Mach is expecting. Arcs can be generated as either IJ mode absolute or incremental. There is another arc format that takes the radius as a variable as well. Your CAM program and Mach have to be in synch.

The most likely problem is that your CAM program is generating lots of tiny little arcs (smaller than .001") that (due to some accuracy setting) are being rounded down to "0" and are causing Mach to render full circles instead. It might also be chain gaps or some other issue with the artwork. We started calling these crop circles a few years back, and it seems to occur with almost every software package given the wrong circumstances.

Possible solutions to this problem:

• Stick with the straight line segments and see if the G64 helps out. It should.
• Regenerate your arcs in a manner to avoid the tiny arcs
• Modify your post processor to catch them and substitute straight lines instead

What is your CAD/CAM package and where is the artwork coming from?

Steve

[BobWarfield]

Originally Posted by basskitcase I treid doing curves as circular inperpolations instead of linear segments, but i got a bunch of crazy looking circles in my gcode when i loaded it into Mach 3. What settings would i edit to make Mach3 properly interpret my G-code?

Set your CAM to use the right Absolute vs Incremental mode on arcs as Mach3. It's settable on both, so the easiest thing is just to flip it on the post for the CAM to the opposite of whatever it was.

Cheers,

BW

[metalworkz]

It is also as easy to just change the IJ mode in Mach3. If it is set to ABS(Absolute) and you are seeing the crop circles on the file in Mach3 then change the IJ mode to INC(Incremental) and load the file(or vice versa). I believe you will see the difference right away.

Regards,

[basskitcase]

Thanks all for your responses. I will definitely try the different things you mentioned. The "constant velocity" setting is what i had in mind, as i figured there was some way to smooth it out, but i didn't know what it was called. I will also try the absolute vs incremental. Oh, and it's not backlash in the leadscrews, they are anit-backlash.

As a subsequent question to the absolute vs incremental settings, if i change the mach settings to be incremental, do i also need to go back and post process my g-code into incremental. I always thought incremental was different in that if you say x4y4, that instead of going to that position, it will go 4 additional inches in the x direction and 4 in the y, but not necisairly to position (4,4).



Thanks

[metalworkz]

Hello,
If the file you load into Mach3 is showing large circles where arcs should be then changing the IJ Mode to incremental will simply adjust Mach3 to read the file that is already made and display arcs instead of circles. I suggested this because it is an easy change to make and the results are visible when you load your file. If it does not correct the display of your file then it is easy to put the setting back to Absolute. You should not have to change the post processor and this way if you use different programs that vary between absolute an incremental output then you will easily be able to correct it with a couple of clicks.

Regards,

[ger21]

As a subsequent question to the absolute vs incremental settings

They're talking about the IJ mode setting, which is the arc or circle center position, and not the same as G90 or G91.

[basskitcase]

Originally Posted by ger21 They're talking about the IJ mode setting, which is the arc or circle center position, and not the same as G90 or G91.

Oh ok, thanks, that's what was confusing me. I still have a lot to learn about CAM settings.

[stevespo]

Had any luck with the new settings? Smooth motion? Have the crop circles gone away?

Steve

[basskitcase]

Yeah, the motion has smoothed up alot, i haven't run any code done with arcs yet, so i dont know about the crop circles, but i found the setting referred to, and im sure it will fix the problem.