Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: nik on July 10, 2008, 01:30:01 PM
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hello
I'm just looking for vinyl cutter blades, and they all have an offset about 0.25-0.5mm, they work in blade holder with bearings, so 4-th axis is not necessary , this offset helps blade to find the proper direction, the only problem is how to set mach3 to work with this offset. the problem appear in changing directions - on 90 degree corner the blade cut small raduis, and mach3 should compensate this
any ideas?
thanks
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Nic,
What does a vinyl cutting machine do? does it lift the knife and reposition in the corner before going in the next direction on a 90 degree cut? For that matter a small radius may not be all so bad unless your working with real small cutouts as it would prevent the edges from lifting.
Kristin
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Commercial vinyl cutters have the blade offset set so they compensate on corners.
I'm sure there is a way to compensate, maybe cutter compensation, no that'll offset the blade to one side. This may take some thinking about.
Steve
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if the software make these corrections , the tool is not necessary to lift up even in 179 degree turn, the only question is how to tell mach3 that actually the cutting edge of the tool is always behind, should be somethink like backlash, but modified when direction is changed, even in circle movement
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HUM the blade would have to over run the corner by the amount of offset so when it turned it would square the corner then retract the offset before the axis moved beyond the offset amount. I don't think MACH has that capability directly it would have to be done through gcode.
Hope that helps
(;-) TP
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Could the blade be set up as a tangential axis?
Brett
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yes, but this is one more motor, more cables, and etc, vynil ploters use that offset on their blade, so the blade is always in the correct direction, and this offset is set in their software
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Having trouble visualising if this would work but I am thinking if you just add 0.25mm to your straight line dimension before the arc would that not work?
Hood
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I'm not sure how it's done but the offset is set in the machine, you can do a test cut and alter the offset to get sqr corners.
Too much offset and you get pointy corners, to little and you get rounded corners.
I must point out that I'm a sign maker and have a few of these cutters.
Summa graphics machines tend to use 0.45mm offset and Roland use 0.25mm offset. I also think even the cutters with tangential heads use an offset.
Why do you want to make one of these cutters, they're not expensive and I would have thought by the time you've made the machine and bought the steppers, screws etc your up to the price of a good quality cutter.
Or are you making a flatbed cutter for thick materials, in which case you need the tangential head anyway.
Steve
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the machine is ready and working, this is just one more attachment, i think for new vinyl cutter but i dont have more space, my workshop is not verry big, i have allready trubles with the space
i dont use often vinyl, so one attachment will be enough
i just finish with the blade holder, soon im going to test it without the offset, but im sure will be problem
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first test: 90 degree - 1 problem round corners
angle >90 degrees - 2 problems - round corners and while the blade is trying to turn, also trying to lift the vinyl :(
in any movement the offset must be calculated, and machine should make smal circle with same radius as the offset, this will turn the blade in to the new direction, and then can continue with a next cut
how i can do that?
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Nik,
Not that I ever actually learned how to use the likes of autocad, it would seem that you need to explode your drawing, extend the lines by the offset and reconnect the path with a radius equal to your offset. So if I am following what your saying if I were to look at a cut vinyl sheet I should see tiny circles at the outside of each direction change? I have some vinyl logos coming in a day or two, sure hope he didn't harvest out the scrap as I would like to see this. I am pretty sure when I worked at a laser and waterjet place about 10 years ago the software took care of this automatically as it converted the vector graphics to g-code or whatever they were using, I do know that a broken path would ruin a thousand dollar brass sheet in a second.
Just thought of this option, using a software like signcut to generate the HPGL file then convert the HPGL to DXF, process through lazycam .... Well I didn't say it was the shortest distance between two points but neither is the cutting path.
Kristin
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is it the offset included in HPGL file?
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Again I am not a user of this but I am pretty sure the offset is generated in the software, including the loops you mentioned, bigest hurdle is trying to convert hpgl to dxf although I think I found a source at Guthry software for a trial converter you could give a try with and it's only $30 USD for a single license if it works. Let me know how things turn out, I might just mount a swivel knife in the mill and have a wack at it or build a small table just for cutting vinyl.
Kristin
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yes, you are right, the offset is included, i just generate one hpgl file with signgo, then i open it with corel draw, on all corners there is an arcs, so.... may be this is the way
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Nik,
Great, I think if you can open it with Corel you can save it as DXF so problem solved I hope. Let me know how you make out.
Kristin
PS- just downloaded signgo and can't find how to export as HPGL, it was the full ver not the lite.
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job done :)
it is tricky but if you are patient you can cut some letters :)
when you install signgo, go to your windows control panel and add printer HP > HP-GL plotter
then properties on that plotter and set output to file
then in signgo when you press cut, you have to set output device your hp-gl protter, the rest you know how to do it
the only problem is that i didnt find how to set the path for output file, now is going in windows/system32, but it is not so bad
now with this offset, the blade is turning much easyer on the corners, i think that this could be a nice plugin for mach3, so any drawing cuold be cut straight with mach, the attachment is a test with offset 1mm, so you can clearly see how should be, the file is opened with import in corel draw
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Nik,
Interesting might be my system but I am seeing 2 quarter round segments on each turn and they look like it would swing a weird path, it's getting late so I am not going to let it keep me awake. Can you post the g-code for that one, I'd like to load it up and run it on the desk just to see what it looks like. Perhaps some of the others that do sign cutting will pop back with a comment also, I can see this as useful for the occasional one-off things I want to do and not pay the big bucks to the local printer for their setup charges.
Kristin
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there is nothing wrong with your system :)
here is the g-code for same thing, but this is with 1mm offset, it is too much for regular blades