Re: [rp-ml] Drag knife and STL question

From: steve <>
Date: Wed May 24 2006 - 00:04:15 EEST

Liam MacGinley wrote:
> Hi there
> i hope that someone on the list can help me out with these two questions.
> 1) I have noticed that the Graphtec XD700, the 3D System's Invision LD
> and the Kira Katana 3D printers all seem to use a "drag" knife. How can
> these machines cut sharp corners if they have no theta motor to
> orientate the knife? will it not simply round off the corners?

I once worked on software to drive a drag-blade vinyl cutter (basically
just a drum plotter with a swivel blade holder in place of the pen) it
sounds like a similar problem.

It didn't have a theta motor - but sharp corners could still be managed
reasonably well by carefully moving the center point of the swivel in an
arc that would leave the knife blade tip stationary.

The harder part is when you have to cut out an interior hole since
picking up the pen holder and moving it tends to make the knife blade
swivel unpredictably so you don't know where it is when you put it
back down again. This can be somewhat ameliorated by starting the
pen off inside the 'scrap' area and moving in an arc until you are
running along the cut line.

The trick here is to adjust the bearings in the blade swivel such
that it's stiff enough not to swivel as you move it away from the
surface you're cutting - yet flexible enough to trail behind the
plotter head accurately while cutting.

You can do it if you have to.
Received on Tue May 23 23:21:14 2006

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