Hi, I have converted an old vinyl cutter to use generic GRBL and am using Lightburn to control it.
The cutter is activated with a solenoid (connected to the spindle output) which has a level of delay between activating and the blade touching the surface. I have played with the ‘delay before start’ and ‘burn through’ but neither of these settings seems to achieve the result appropriately.
The burn through setting would work but between the initial command and the move, it turns off the spindle and then re-enables it, thus making it pointless.
The delay before start just delays before the spindle is started and begins the move as soon as the spindle is activated.
I have overcome this slightly by using the overcut feature but it’s a bit of a band-aid solution. How can this be tweaked? Is the only way to do it with a post-processor?
I don’t have the answer for you today. I know there is something on its way that will help lots. I don’t have a release date for it as of yet.
In the mean time, another user @bLouChip is running a plasma cutter and it may require similar lead-in and lead-out behavior. He has some very detailed posts around start and end macros that might get you going.
I tried a few test cases just now, as in saving and reviewing LB gcode under a few variations of cutting two simple square shapes, and I see what @elnino is stating about the spindle state bouncing OFF/ON right after the dwell time, and thus making the dwell time pointless in his drag knife use case. My test was designed with LB device type GRBL-M3, which I believe is necessary in order to get the M3/M5 combos for each cut. The problem for OP’s drag knife, and for any plasma cutting use cases that are depending on LB gcode for dwell time after M3 (aka ‘cut through’), is that the subsequent M5 that LB places after the dwell (in this case) is bouncing the spindle signal which controls the cutter solenoid(s). This brings back reminders of painful headaches For these and other reasons, I’ve been using SheetCAM for about a year now for plasma process toolpath, while LB is my exclusive 2D design sw for any CNC process, and LB CAM for laser.
I doubt this helps much, I’d rather have Oz @LightBurn weigh in here, he’s the expert of course on the LB logic surrounding all these variables, some I haven’t even mentioned, and then there is the different behaviors of the grbl interpreter, various versions, and its $32 laser mode setting.
That is clever. sorry I missed it on my first read. Are there any problems to that solution ?
It works for fine forlonger cuts but if there is a short cut, going back over the previous cut can pierce the backing which can cause issues. It’s a reasonable workaround and ‘enough’ I guess. It’s just a shame the existing theoretical function doesn’t actually work for this purpose.
For these and other reasons, I’ve been using SheetCAM for about a year now for plasma process toolpath, while LB is my exclusive 2D design sw for any CNC process, and LB CAM for laser.