Re: Vinyl Cutting Algorithms

Hi Ballendo,

You've hit the nail on the head with your descriptions of the problem
and its solutions .
The squiggle I was referring to is just a movement to help rotate the
blade into the cutting direction.

Finding the C-axis angle is pretty straight forwards for this (the
software is setup for finding 5-axis toolangles already) and I could
in theory attatch a fixed blade cutter to the center of rotation of
my C-axis although that would slow down the cutting as the C-axis
rotates relatively slowly for this and would have to be programed to
unwind it's cabling if cutting much more than 360 degree curvatures.

If doing full tangential cutting, would the knife always cut exactly
on the tangent, or would it be an idea to 'look ahead' slightly into
the up-coming curve ?

thanks,

Rab
http://www.rainnea.com/cnc.htm


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@y...>
wrote:

> Hello,
>
> Steering angle, as you say it, is easily found using the arctangent
> (ATAN). A few lines of code to handle crossing zero and quadrant
> boundaries, and you have the makings of a c axis "tangential"

cutter

> for vinyl...
>
> As to the drag knife problem, Rab may want to add a small circle

for

> the trailing blade to follow during a "turn-around". At least a
> triangular motion, which could be accomplished with a single

straight

> line "sideways" added movement (is that the squiggle of which you
> speak, Rab?)
>
> Hope this helps,
>
> Ballendo
>
> P.S. You are correct in assuming the problem is from the depth of
> cut. As you increase the cutting pressure (and therefore the depth)
> two things happen, both bad: first, the effective trailing distance
> is shortened (this is the drag in drag-knife), which makes a

shorter

> lever arm to turn the knife. And second, the already harder to turn
> knife is more deeply embedded in the material, which also makes it
> hard to turn. So set the knife pressure for as shallow a cut as
> possible, until you can change to a stepper driven tangential

cutter

> c axis...