Drag knife corner paths / cutting full part?

Hi, apologies in advance if this question has been answered, I looked.

I’m wondering if I can adjust the swivel moves on a drag knife operation so that the whole part / path is actually cut. The default move always leaves a small segment of the part/path uncut.

Apologies for bad screen grabs and MS paint work. The first attachment has an example of typical swivel, second attachment attempts to depict what I’m looking for.

The tool paths are the swivel centre line. On corners the tip of the cutter remains stationary while the swivel centre line rotates around it. I know it is a bit difficult to get your head around but try holding the swivel in your hand and replicating that move manually.

So what about that ‘missing’ space on the corner? Look at the top of the A. What you lose on the first corner you gain back on the next corner. The tool path is the same length as the line but it is offset because the tip of the cutter trails behind the spindle centre line. You don’t see that effect as much on arcs because the offset is spread out over the arc.

Thanks Les. I have a decent handle on the theory, and have made some “fairly” successful parts, but am running into quality and repeat-ability issues.

For example the code in the attached screen grab produces the part in the second attachment.

Looking for pointers on why? Some parts are really clean, others, as you can see, are completely unusable. I’m going to contact Sean at Donek tools as well to see if I might get some insight from his end too.

Thanks again.

Here’s a shot of a fairly clean (at least usable) part produced from the same job last week, as well as screen jobs of the current settings for the job.

In the clean part, you can still detect lines that “should” be straight are absolutely not (inside part on “A”). I can absolutely live with this, as long as the parts are cut cleanly and easy to remove/replace from the stock material, and repeatable weeks, months, or years from now.

I’m assuming some sort of software-side variable has changed since last week, but I cannot track it down… just looking for a general road map to success. I’m sure a return to clean parts is somehow just a click away.

Are you sure your work isn’t moving as you cut it?


Talked with Sean at Donek Tools, he suggested that the blade needed replacing, and/or there is a Z0 issue. I’ll be running some tests in an hour or so. I’ll let you both know how things go tomorrow.