Corner turning with a drag knife can be done by raising the knife until the
point is just into the material. Then sweep an arc with a radius equal to the
knife point offset. For inside corners that's the way to do it. On outside
corners that method works or you can have it go past the end then loop around
to come back in-line with the cut on the other side of the point. Software that
does drag knife cutting should support both methods, the operator has to enter
the point offset distance and the material thickness.
Assuming the knife pivot has enough sticktion to not spin freely during rapids
with the blade out of contact, making an initial drag to align the knife to one
axis should allow the software to calculate what the angle should be any time
it needs to lift out for a rapid move, then drop Z to touch and spin to change
angle with minimum movement. Or it could go to a safe area and do an alignment
drag to ensure the blade angle is correct.
Software takes the place of having power blade turning.
On Saturday, July 25, 2020, 1:15:02 AM MDT, Marcus Bowman
<[email protected]> wrote:
I bought a cheap drag knife some time ago, from a far off land, but I have not
yet used it, because:
(a) it does need routines for turning corners, and
(b) upon inspection, I decided that a critical factor is likely to be the
ability of the knife to swivel very freely; and this cheap one didn't. Rather
than embark on yet another 'small' project, I put it in the 'later, maybe'
drawer.
I machine a fair amount of plastic, but not thin film.
For a small quantity, I might try clamping it between thicker sheets and using
a very sharp single-flute carbide router cutter (like an AccuPro from MSC
Direct). These are just the job for plastics like Acetal/Delrin, although they
are relatively expensive. They work marvellously well in aluminium too.
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