Drag Knife Offset

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thewolf
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Drag Knife Offset

Post by thewolf »

Hi,

I am trying to use the vectric software to cut vinyl decals using a drag knife. I really like the lead in and overcut features, they help a lot for what I am doing. The only problem I have is that I can’t set a “knife offset” which would compensate for corner and sharp cuts. Right now my process involves using a program to create text with “knife offsets”, export that to a different program that’s vector based, then import into vectric software. Finally use the node edit to hand fix and close most the vectors, oh and setup leads and tool paths. I would say this takes me about 10-15 mins for about 5-8 letter word.

Is there any way I can accomplish similar results using just the vectric software? As in adding a offset to corners like in the picture

Would this ever be a added feature?

Thanks!
Capture.PNG

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Adrian
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Re: Drag Knife Offset

Post by Adrian »

Try the fillet tool on the corners and see if it does what you want. The shapes it creates are similar to what you've posted so hopefully it will do the job.
fillet tool.PNG
fillet dialog.PNG
result.PNG

thewolf
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Re: Drag Knife Offset

Post by thewolf »

Thanks for the replay. I gave the tool a look and it is very similar to what I am looking for. I was going to give it a test cut but it seems like it doesn’t work on inside edges.

With the drag knife the actual knife point is offset from center to allow for swiveling. Ideally to make a perfect 90 degree cut I would need to overcut by the knife’s offset and rotate a radius equal to the offset .

With the fillet tool it looks like I could adjust the radius but I believe it would still round the corners, although I have not actually tried it yet because it couldn’t get the inside corners.

Here is another picture. You can see how some of the offsets get messed up and are inconsistent because of the process of using different programs. But I can get away with it most times
Attachments
p.jpg

Dclifton2
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Re: Drag Knife Offset

Post by Dclifton2 »

you shouldn't need to do offsets for the corners with a drag knife just for the end of the cut because the blade is trailing. The blade should follow a sharp corner without any problems.
Don Clifton

thewolf
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Re: Drag Knife Offset

Post by thewolf »

Without having a offset correction the corners will be rounded over. For a real vinyl cutter either the machine or the plotting software corrects for this. It will overcut the starting point and correct corners.

Here is a video that can explain it better than I can. Examples start at 3:00 mins in.
http://www.youtube.com/watch?v=Ne71aXXp4BY

I know if I want to cut vinyl I should get a vinyl cutter but I am just trying to do more with what I have.

Pete M
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Re: Drag Knife Offset

Post by Pete M »

I am somewhat confused about the drag knife. Does it follow the path, being dragged along, as it were, and at sharp corners has to be turned to align with the new direction with those strange moves you added in? In a real vinyl cutter, is the blade pivoted ( another axis) to align with the path?

I have a small cnc router, and wanted to do some of this, but wondered if was practical.

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metalworkz
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Re: Drag Knife Offset

Post by metalworkz »

Hello,
I know nothing about the use of the drag knife but was wondering if it might be possible to do the work with separate vectors and start and stop at each corner with the blade cutting direction changed? Just thought perhaps that would allow cutting up to the corner and then starting the next vector after the knife was turned from that new start point? I guess it would involve a lot of extra work but if possible it might yield sharper corners? Sorry if I am off in my line of thought.
Best regards,
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esteeme1
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Re: Drag Knife Offset

Post by esteeme1 »

Hi Wes,

Here is a crude representation of what I know. The knife actually cuts on the trailing edge of the movement and swivels freely with every change in direction. If the knife is picked up and moved and the motion of the X Y axis changes the cutting edge could be facing the wrong way as well as offset from the next start point. So if you lift the knife and move it to the next vector and the direction doesn’t match the knife edge there will be a nick taken out of the edge. I'm not sure how the plotter compensates for this but I'm sure it does. I think that will be the next problem to work out. The start vector will most likely have to be offset the distance of the cutter’s offset.

Edit: and the end point will need to pass the end vector as well
Attachments
cutter.jpg
Jim Darlas
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metalworkz
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Re: Drag Knife Offset

Post by metalworkz »

OK, I was way off and I can see the problem better thanks to your explanation.
Best regards,
Wes
wes.spence@comcast.net
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Lathe, Horiz. Mill, Shaper, Leaf Brake

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Mark
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Re: Drag Knife Offset

Post by Mark »

Hello,

I am afraid that the software is designed to run mainly with cnc routers that cut with rotating tools,
it is not targeted at vinyl cutters, which is why will you will not find any features that
are specific to the operation of these machines, (such as travel overlap to compensate for drag knives).

If you wish to do this, you would need to manually add the overlap yourself to the vectors.
To do this, enter node editing mode, type “p” to insert a start node where you wish the cut to end on the
shape, then type “c” to cut the vector at the same node, click on the green node and drag it further along the vector
to the point where you would like the cut to start, to create the overlap.
Do not try to re-join the vector leave it open.
Profile On the vector as an open vector.
(or you can profile to the left or right of the open vector).
Don’t forget to check the “Use vector start points (don’t optimize)” option on the 2D Profile Toolpath form,
to ensure that the cut starts from the start point that you have created.

I hope that this helps,

Cheers,

Mark.

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esteeme1
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Re: Drag Knife Offset

Post by esteeme1 »

Mark,
Hope you don't think I was suggesting make changes. I was just pointing out possible issues. The software does what it is intended to do and I love it. Maybe you can start a new version vinyl cutting, you can call it vynrics. :lol: Okay it's funny to me.
Jim Darlas
"Can Do!"
http://www.esteemedwoodcrafts.com/
http://www.esteemedplaques.com/

Pete M
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Re: Drag Knife Offset

Post by Pete M »

I found the answer. The link below is to the shopbot forum, where you can download an excel spreadsheet that adds the required corner moves. It works on shopbot files, but the enterprising person should be able to cope with that.



http://www.talkshopbot.com/forum/showthread.php?t=15959

Greolt
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Re: Drag Knife Offset

Post by Greolt »

I cut vinyl regularly with my router. I use a Roland knife holder and blade.

We all know that vinyl cutters are not expensive and if wanting to cut it professionally then just go and buy the right machine.

However for what I do, using my CNC router suites me just fine.

A couple of observations;

Overcut can be done quite simply using the "Lead In" facility. No need to manually draw overcuts.

Select "Add Leads" then set the lead length to zero. This allows you to then set a overcut distance. I use 2mm.

Secondly regarding trailing knife;

The video mentioned above is to do with cutting venner, which is much thicker than vinyl and requires a much heavier knife.

The vinyl cutting blade I use trails by 0.25mm. That is about ten thou.

I cut quite detailed shapes and small lettering and, to my mind at least, the results are very good.

So in my opinion worrying about compensating for trailing knife is overkill. Your opinion may be different. :)

Greg

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Re: Drag Knife Offset

Post by GraClay »

I'm bumping this topic. We also use our CNC for knife cutting just as we do on our various vinyl cutters, digital printer etc.
Sometimes it just has to be on the CNC because of the size of the cutting area or the type of cutting required.

My first CNC had this feature back in 1989.

e.g. we sometimes apply vinyl to an acrylic sheet then knife cut the graphics, then profile cut the background panel so that everything aligns etc.
Sometimes we cut the maskant on acrylic sheet or other premasked substrates then peel and paint etc. etc. etc.

A drag knife tool with compensation would be a welcome addition to Aspire and that would include compensation for start and end of shape plus compensation for every corner.

Apologies if this already in version 4. I have 3.5

4DThinker
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Re: Drag Knife Offset

Post by 4DThinker »

Has anyone tried the Plasma/Drag Knife' Fillet option? My VCarve 7 has that as an option.

"These external fillets are
used for machining past a
corner when using plasma
tools or drag knives"

Seems to me that would solve the OP's problem.

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