I have a Donek drag knife. My goal was to cut out foam board airplanes ala FliteTest. A drag knife ought to give better edges than a pin cutter, at least that was my theory. Quieter too.
However, we’re not getting good corners at all. We’re trying to use the corner actions excel spreadsheet from Donek.
Is anyone doing drag knife work that can help me figure out what to do differently?
I have a Donek drag knife as well… but not being a Windows/Excel-kinda guy and reasonably happy with the cuts I get with my needle cutters – I’ve never seen reason to pursue it. I suspect that, even if you can get those corner actions dialed in, the “crown” (and similar detail) might always present problems 
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The fuzziness is, of course, the bottom-side paper on DTFB… note the foam is cut very cleanly. Un-papered foams cut beautifully.
Yeah, the knife is quieter… maybe not the operator
– David
Which needle cutter do you recommend? Those cuts look better than what I’ve seen elsewhere.
Jim,
There is no “standard” needle cutter but one of the most popular is jhitesma’s Improved Needle Cutter (https://www.thingiverse.com/thing:2450613).
My current needle cutters utilize a new slip-on flywheel I developed in conjunction with my version of Mark “moebeast” Moebes’ LowRider-inspired Foam Ripper (https://www.thingiverse.com/thing:2520214). I documented the build (with mods). of both the machine and the needle cutter in my FliteTest needle-cutter thread, starting here
Here it is in action (turn down the sound)… the cutter is an Emax CF2822 running at approximately 8000 rpm (no load) and the feed rate is 610 mm/min
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– David
