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A project log for MultiBot CNC v2

A low cost 3D printed CNC that can be built with minimal tools yet is capable of great things.

David TuckerDavid Tucker 06/17/2021 at 03:440 Comments

I got a chance to test out my new drag knife holder and it works great!  I was worried it would still wiggle around a bit so I lowered it onto the bed with the blade retracted and ran it around for a while and it looked great.  I still think you want to be careful not to lower it too much to reduce friction.

I ran two tests, one a 20 mm square and then a 70 mm tall Tin-Tin and Snowy.  I ran each twice, once with the raw gcode from Fusion 360 (marked NC above) and again with the correction using the DragKnife plugin for Fusion360.  I had previously experimented with different values and settled on a blade offset of 0.6mm and a swivel height of 0.2mm and the default tolerance of 20 degrees.  These seem to work ok, although I think the blade offset is set too high, I may try 0.5mm next time.

You can see from the pictures above that without correction the corners are soft and sharp turns tend to be lost.  The correction seems to have helped a lot.  I'm not sure that this blade needs any lift at all to work, it is so small and the cardstock paper is so thin (0.3mm) that it did not seem to do much at all.  I need to experiment with setting the lift height to 0 to see if we can save time on the corners by avoiding the lift motion.

I just taped the corners of the paper to my waste board and I ended up having trouble with the paper moving a bit.  I had to hold the paper down during the cut to keep it all stable.  I really need to look into how to apply a sticky substance to my cutting mat that will hold the paper still without holding it too well. You can buy special matts with sticky applied that are made for cricut style cutters from Amazon as well.

The details are amazing, it looks as good as with the laser cutter, or at least close enough. That brings us to the question of what is better, a laser or a drag knife.  The answer is (as always) it depends.

Drag knife pro's:

Laser pro's:

I'm not sorry to have both, I'm sure I will use each.  For now I'm more attracted to the laser but the drag knife really is the better place to start.  I have the parts to try and make a larger drag knife based on a utility blade.  This would allow me to cut thicker material like cardboard and cork.  I'm working on a 3D printed holder that is strong enough for the job but that only uses a few bolts and some skateboard bearings. 

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