cvoinescu
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Yes, if the G-code has lead-ins, then the start of the cut becomes moot.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

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

yea, my idea doesn't work for anything but G01. Also, it would offset to the tip, which isn't necessarily pointing in the correct direction. So the lead in would still exist. The problem with lead ins is if the lead in is on the inside or the outside of the geometry, there will be a little slit in the geometry somewhere... Which maybe we don't care, but my interest would be in making stencils and decals. stencil... eh who cares but a decal would peel at that cut.

What about your idea cvoinescu, searching the code for the first move after a drop in the Z height to the build level. Then do some math on that first move's angle, use a second tool offset to shift over to the side of the platform, and make a short move in that direction.
Then offset back to the part and start the next cut... Again, it would need a post processing algorithm, but the code could be generated to just move the blade into position somewhere else.

The other idea I just thought of is make a holder that has on offset adjust built in. Rather than the blade rotating in the holder, the blade would be fixed in the holder. Then the holder would fit into a larger cylinder with the offset of the blade that the holder fits into. This way the offset blade tip stays on center and a lead in could be used to maintain the cut lengths...

cvoinescu
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I thought of using a "scratch pad" area to get the blade turned in the direction I wanted it. It would be best to do that very close to the actual cut (to save traverse time), but that would be difficult without human assistance. If you had lots of closed cuts and the scratch pad was in one corner, it would kill the cutting speed (death of a thousand cuts).

The offset of the blade is intentional and necessary, because it's what turns the blade in the right direction. Without it, it would just plow sideways or backwards or whicheverways through the material.

What you can do, however, is mount the blade, ideally without an offset, on a rotary axis (C axis). The math is simpler, and you actively control the orientation of the blade, so there's no need for lead-ins. It's also more precise and allows thicker materials to be cut, can use larger X-Acto type blades, and there can be a spring-loaded presser foot, a little like the one on a sewing machine, to assist in holding down the material. The downside is the added complexity.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

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I used to use a Roland sign cutter, and I don't recall it being significant which way the cutter was oriented --- it did seem to overcut the corners slightly, except for the last one (handled in software?), but that was easily addressed w/ an X-Acto when weeding --- it did seem to have the point of the knife perfectly centered where it rotated and was spring-loaded w/ vertical adjustment.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

cvoinescu
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Will, I have a knock-off Roland holder and blade, and the blade tip has a tiny, barely noticeable offset. The spec says the offset should be 0.25mm for Roland, which seems about right.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Posts: 8616
Joined: Mon Apr 09, 2012 6:11 pm
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Hmm, I don't remember such an offset, but it's been almost 2 decades since I had the plotter.

Perhaps this will help?

part of grecode ( http://code.google.com/p/grecode/ ):

-knive <delay mm>
This should compensate partially for foil cutters, where the cutting point is lagging. The lagging distance should be specified in mm. Arc movements could be problematic currently. The implementation is not very good.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

T3PRanch
Posts: 10
Joined: Sun Jul 01, 2012 2:34 am

Just found this that might be of interest. High Price but very adaptable.

http://donektools.com/

Thurmond

ijsga
Posts: 2
Joined: Sat May 18, 2013 3:13 pm
Location: Amsterdam, The Netherlands

Hey all,

First post here, I’m currently awaiting the delivery of my super-sized eShapeOko. The Donektools Drag Knife seems like a very good alternative to a tangential cutting module to cut thicker material (those units cost about € 1300,– here in Europe). That is; if you get the software part right. There’s some good examples on how to do that in some of the videos on the Donektools website. They show how to do this using Sheetcam and Vectric software. Think I’m going to order this Donketools Drag Knife when I have my eShapeOko built! Should be somewhere this summer

Best regards,
Thijs

bjbsquared
Posts: 102
Joined: Mon Nov 26, 2012 10:48 am

It seems to me that this would not be too hard to make. Even 3d printed and use common razor blades. All you really need to know is the offset and the software.
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