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Mach Discussion => General Mach Discussion => Topic started by: kb18951452 on March 12, 2009, 11:11:04 PM

Title: Is CV my Friend?
Post by: kb18951452 on March 12, 2009, 11:11:04 PM
 I'm still having trouble with Mach 3 and the CV settings.

I am trying to carve very detailed woodworking, but the CV keeps rounding allot of the details out. If i run a cetain design s 100 IPM it comes out rounded all over the place, but if i get it at 50 IPM it comes out "sharp edged.

I tried putting the unit distance setting from 180 to 50 or less , but didnt see and significant change.

I read a help text on the CV and it says that the unnit distance setting, ...... yea, what are those units?

Anyone with ideas on how to get mach to give me high detail at a higher speed? I know its gonna slow down on the detailed stuff, bt maybe it going faster on the "straitaways????"
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Title: Re: Is CV my Friend?
Post by: jimpinder on March 13, 2009, 06:06:55 AM
The units surely are the units that your machine is set up in - in your case it would seem to be inches - so I don't see the difference betwen 180 and 50 would be noticeable. Whether this changes if you then use millimeters, I wouldn't know, i.e. does Mach 3 take a setting in inches and convert it to millimeters, or does it use the raw numbers.

If you want sharp edges, then you must use exact stop, but as you probably know, this will shake your machine about. You can, of course, introduce GCode to change from one to the other in your program, using CV for the wavvy bits, but using exact stop for the sharp bits.

On CV the next line begins to accelerate up to speed, as the previous line is slowing down, therefore the faster you go, the sooner the "blending" starts. However, if you limit the distance at which this starts, the machine will begin to slow down for the end of the line (depending on your acceleration setting on motor tuning), then it will blend the corner, then it will accelerate back up to speed, but you should get a sharper corner.

I don't think Mach 3 (or any CNC program for that matter) can be all things in all circumstances, and you will have to adjust settings to get the best results for what you are trying to achieve.

Title: Re: Is CV my Friend?
Post by: ger21 on March 13, 2009, 07:16:56 AM
You need faster acceleration to prevent rounding. If you can't increase your accel, then your machine is underpowered for what you want it to do.
Title: Re: Is CV my Friend?
Post by: kb18951452 on March 13, 2009, 09:46:23 AM
When you say higher acceleration what exactly do you mean?


Right now i have Acceleraton a 5 for X and Y, and 8 for Z,

I can bump these to 20 or so (i think my max is 45?)

I'm going to have to try that.

So the 'unit' look ahead, its in inches huh? Can i put a decimal in that place, like, look ahead .1????

Thanks again for all the help.
Title: Re: Is CV my Friend?
Post by: ger21 on March 13, 2009, 11:10:47 AM
Yes, set the accel as high as you can.

Say for example, you're cutting a 90° corner. With CV on, as you get to the corner, one axis has to decelerate, while the other accelerates. This is you're rounding. The faster the acceleration, the smaller the rounding will be. You can also play with the angle settings so that it reverts to exact stop at a certain degree angle. You might want to read the CV docs on the documentation page of the site.
Title: Re: Is CV my Friend?
Post by: kb18951452 on March 13, 2009, 11:16:45 AM
thats fo the reply, will give it a try at the end of this job i am on (on hour 3 of 12 lready)
Title: Re: Is CV my Friend?
Post by: olf20 on March 13, 2009, 09:14:22 PM
When you speak of "unit look ahead" are you referring to the number of lines
that Mach3 looks ahead??? Config - General Config - Center below Shuttle Wheel???
Somewhere back Art wrote a very detailed description of CV, among the information
I believe he said to set the Look Ahead lines as high as possible, 200+.
Someone else may jump in and correct me if I'm wrong.
olf20 / Bob