I decided to try to make a drag knife for my CNC. In architecture school, we were constantly making models out of museum board and chip board. I wish I had one of these back then!
I know that there are examples of utility drag knives on the 'Zone going back before 2003, but I didn't pay too much attention as the real trick is the G-code. The knife needs to be reoriented at each corner as well as a slight compensation on curves. Imagine taking a turn while pulling a trailer since the blade is trailing the center of the tool... There are also commercial drag knives available, but for almost $250 I decided to DIY one instead.
Fortunately, ten years later there is also now plenty of software out there that can do the compensation. I do not have this software yet, so I asked some of the other Platform owners to help me out with the g-code. David Hill came through with not only the gcode, but also the geometry for the tests!
Here is an image of the first prototype knife...
What it looked like assembled...
From this, I realized that the front part of the blade should be vertical to aide in the rudder effect... This meant that I should look at how to orient the blade for better results.
This concept came to me while I was milling another test out of acrylic....
Looks great, but I never tried it before I cut the most recent one out of aluminum.
Here is the assembly...
Fully assembled, ready to test!
So, does it work?
Guess you'll have to watch the video!
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Happy Holiday Tinkering!
-Brian