Dovetail Toolpath Creator

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270mag
Posts: 13
Joined: Thu Dec 16, 2021 9:49 pm
Model of CNC Machine: Shark SD 110

Dovetail Toolpath Creator

Post by 270mag »

I found a strange behavior that seems like an error in the math. I uploaded three pictures. Each have only one difference in how the ramps for the dovetail were done. I changed the stepover for the bit.

Stepover is 80%. See how the ramp is slightly under cut compared to the profile.
bit stepover 80.jpg

Stepover is 50%. The ramp lines up with the profile.
bit stepover 50.jpg

Stepover is 5%. See how the ramp is over cut compared to the profile.
bit stepover 5.jpg

With the 80% and the 5% stepover, the parts don't fit together well; I have to use a hand file to make it work. I like the lower stepover values because it gives a smoother ramp, but the parts don't fit. The 50% stepover yields a good fit but the ramp is not as smooth as I'd like.

Again, all I changed each time running the gadget was the stepover for the tool. It seems to me like there is a math error within the gadget. What say you?

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adze_cnc
Vectric Wizard
Posts: 3053
Joined: Sat Jul 27, 2013 10:08 pm
Model of CNC Machine: AXYZ 4008
Location: Vancouver, BC, Canada

Re: Dovetail Toolpath Creator

Post by adze_cnc »

A quick glance at the code shows that when calculating the number of "back and forth" passes it doesn't take into consideration that the last pass line must not be within "StepOver" of the vector. How to fix that is another matter. The calculation is for the variable "stripe_shift".

270mag
Posts: 13
Joined: Thu Dec 16, 2021 9:49 pm
Model of CNC Machine: Shark SD 110

Re: Dovetail Toolpath Creator

Post by 270mag »

I tried a work-around for this problem, but I think I uncovered another math problem.

The material thickness that I've been using is 1/4-inch. So, both the cut depth and the thickness were set to 1/4". The workaround was to set the thickness to .20-.24, forcing the gadget to not overcut the dovetail.
dovetail thickness.jpg

Dovetail thickness = .25"
dovetail thickness .25.jpg

Dovetail thickness = .20". See how this reduces the thickness. But, there is a problem; it also reduces the cut depth. The thickness and the cut depth should be independent of each other, but the gadget uses the thickness setting in its calculation for cut depth.
dovetail thickness .20.jpg

This shows the two cases overlaid. The gap at "A" is the desired effect of reducing the thickness setting in the gadget. The gap at "B" should not be there. I didn't change the cut depth, but the gadget acts as if I did.
dovetail .25 vs. .20.jpg

Any thoughts where the issue might be? Thx.

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