Vinyl Cutting Blade

misan2
Posts: 22
Joined: Tue Jun 19, 2012 8:32 am

Re: Vinyl Cutting Blade

Post by misan2 » Sat Dec 29, 2012 3:46 pm

Did you make any progress on this? I've just bought a blade holder and some blades, but it will be a while till I get them.

Thanks,

misan2

jluther
Posts: 40
Joined: Tue Sep 25, 2012 6:15 pm

Re: Vinyl Cutting Blade

Post by jluther » Fri Jan 11, 2013 3:59 am

Sort of, I was able to get a spring and hack it, and get a PVC piece to fit over it. However, the rigidity is not sufficient, I'm thinking along the lines of a c-channel now, drilling a hole in a piece of plywood, then feeding the blade holder into it, then with some creative bracketing putting a bolt over the holder with a nut on it. The spring holds the blade holder down, and is adjustable in pressure by turning the nut back and forth...

Doesn't help that I've spent the last month in the process of moving from wisconsin to florida. However, I have my shapeoko reconstructed and I'm getting back into my projects on it :)

ThatOtherGuy435
Posts: 108
Joined: Sat Feb 16, 2013 2:08 pm

Re: Vinyl Cutting Blade

Post by ThatOtherGuy435 » Sat Feb 23, 2013 3:14 am

Should you have any updates on this I would be quite interested myself!
ShapeOko1 #??? - 1000mm Dual-drive Y, Double X, S2 gantry motor plates, ACME Z-Axis.

misan2
Posts: 22
Joined: Tue Jun 19, 2012 8:32 am

Re: Vinyl Cutting Blade

Post by misan2 » Tue Mar 19, 2013 11:11 pm

Ok guys, some good news:

I've bought the suggested blade holder and I have created a small holder for ShapeOko. You can download it from here: http://www.thingiverse.com/thing:63747

The bad news, at least for me, is that though it was designed for pushing the blade holder in an out easily, I cannot do this. My spindle is too close so it blocks the way. So I need to screw the holder on when I want to use it.

I have noticed the blade depth adjust is critical for success. Too much blade out and you cut through vinyl and substate (not good). But after a while (screwing and unscrewing the adapter) I set it right. I am cutting at 1400 feedrate (mm) and I guess it could be done much faster.

ThatOtherGuy435
Posts: 108
Joined: Sat Feb 16, 2013 2:08 pm

Re: Vinyl Cutting Blade

Post by ThatOtherGuy435 » Tue Apr 23, 2013 12:22 pm

Has anyone found a way to get the blade offset into CAM? I would think mounting the thing would be the least of our problems, given that by the time we're trying to mount additional attachments, we already have a functioning mill!
ShapeOko1 #??? - 1000mm Dual-drive Y, Double X, S2 gantry motor plates, ACME Z-Axis.

jluther
Posts: 40
Joined: Tue Sep 25, 2012 6:15 pm

Re: Vinyl Cutting Blade

Post by jluther » Sun Apr 28, 2013 11:42 pm

G54 Z0.XXXX should do it right? LinuxCNC has made me soft in those offset codes...

roughly... if you're on a fanuc type controller. Most controllers will have the ability to just offset it. Or you can enter a tool offset into T1, T2... etc. depending on how many tools and how good you are at putting them in the exact same spot again.

Remember that when you cut too deep and want to adjust up G54 Z0.001 does not increase to Z plane 0.001" it moves it to Z 0.001" off the home position.

cvoinescu
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Location: Camberley, UK
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Re: Vinyl Cutting Blade

Post by cvoinescu » Mon Apr 29, 2013 2:34 pm

That's a different type of offset. The cutting blade is mounted in such a way that it can rotate, and the blade is offset so that the drag turns it cutting edge first. At any moment, the offset is the same magnitude (typically 0.25mm), but oriented differently in X and Y. The machine needs to take this into account when moving, which is not terribly difficult to do, but a different algorithm than cutter offset compensation.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

jluther
Posts: 40
Joined: Tue Sep 25, 2012 6:15 pm

Re: Vinyl Cutting Blade

Post by jluther » Wed May 01, 2013 12:11 am

oooohhhh... That offset... :/ I could see doing it in a postprocessing script maybe.
EDIT: The concept here is that the code is known, and therefore the offsets are known. The code can be modified before execution to include the offsets when the drag knife is re engaged. The Nx, and Nx-1 would need to be stored from when Z increases. Added this to the code and storage values to hold the last x and y move while blade engaged...

Something like

Current line = Nx //gcode line
X value = CX
Y value = CY
Z value = CZ
x storage 1= x1
x storage 2= x2
y storage 1= y1
y storage 2= y2
offset X = Offx
offset Y = Offy
offset = Rx //radius of cutter

Nx=2

if(CZ(Nx)-CZ(Nx-1)>0)
x1=CX(Nx)
x2=CX(Nx-1)
y1=CY(Nx)
y2=CY(Nx-1)
end if

if(CZ(Nx)-CZ(Nx-1)<0)
While(Nx is not null)
Offx=(x1-x2/(x1-x2+y1-y2)*Rx
Offy=(y1-y2)/(x1-x2+y1-y2)*Rx

Cx(Nx)=Cx(Nx)+Offx
Cy(Nx)=Cy(Nx)+Offy
Nx = Nx +1
End while
End If

The radius offset will be constant. So if we look at the change in x/Magnitude overall and y/Magnitude overall... before the blade disengaged (hence the storage value), together they should add up to 1 and point in the direction the blade last moved in while engaged.

So if

N01 is G01 X0 Y1
N02 is G01 X1 Y2

then it should be pointed 45 degrees over. So CX(Nx)=1, CX(Nx-1)=0, CY(Nx)=2, CY(Nx-1)=1. we'll say Rx =0.25 then
Offx=1/2*0.25 =0.125
Offy=1/2*0.25 =0.125

The fun part is constructing the code as you go. It wouldn't be crazy to post process using a visual basic, Java, or C program process the data to do this. Just would need to have a good method of making sure that you had the entire X, Y, and Z values and were able to easily change them, might be better in Java using arrays... That way the post processor wouldn't be anything anyone wants rights to...

cvoinescu
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Re: Vinyl Cutting Blade

Post by cvoinescu » Wed May 01, 2013 9:54 am

All the straight moves need to be offset 0.25mm in the direction of the move. To get the knife re-positioned correctly between two moves, there should be a 0.25mm radius arc between them (which would cut nothing, just pivot the blade). The arc would be perpendicular to both lines, centered at their intersection (the desired corner of the cut). This is all very simple math (except maybe the bit where you decide whether the arc is clockwise or counter-clockwise -- but there's a simple "trick" for that too).

If the cutting path includes arcs, it gets a little more complicated. The resulting cut is still an arc, same center and spanning the same angle, but slightly larger and shifted in a weird way. If the arc meets other cuts at an angle, there will be the additional arc to pivot the blade; if the arc is tangent to the cut next to it, there won't be an additional arc.

The only part I don't know how to do is the beginning of a cut: I have no way to know what direction the blade is facing. The only way I can think of is to punt on this problem and assume that it does't matter for the first cut (which could be a small cut outside the useful area, just to get the blade in a known orientation) and that the blade keeps its direction when lifted, moved and lowered again.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

ThatOtherGuy435
Posts: 108
Joined: Sat Feb 16, 2013 2:08 pm

Re: Vinyl Cutting Blade

Post by ThatOtherGuy435 » Wed May 01, 2013 10:58 am

I would assume the start of cut would use some sort of >0.25mm lead in movement - that part is pretty easy to do even in CAM programs not designed for it.
ShapeOko1 #??? - 1000mm Dual-drive Y, Double X, S2 gantry motor plates, ACME Z-Axis.

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