Engraving with a lollipop bit in Fusion

Hi everyone,

for a small decoration project I am trying to engrave a dotted pattern in fusion. attached are my fusion file, image of first attempt with my Shapeoko 3xxl and example of desired result (similar).

the starting point is a 2d pattern that I model in rhino + grasshopper, which is imported in fusion via dxf.
My first idea was to simply use the engrave tool path in fusion but with a lollipop bit, but fusion does not allow me to do so.

then I thought to use the engrave tool path anyway (generating the TP in fusion with a “virtual” 90° v-bit with same diameter as the lollipop) but actually mounting a lollipop bit on the cnc… but this obviously didn’t work either because for a given depth of cut the virtual 90° v bit has a different width of cut with respect to the lollipop. The image I attached shows this, that the machined circles are too large (besides other attempts with simple engraving of the edges…they look terrible on mdf but the final piece will be birch ply…)

Before understanding the nature of the problem I have also tried to tweak the bottom height, but this did not have any positive effect on the outer edge of the circles, with are still machined too large, so much that they intersect with each other (visible in the upper part of the sample).

How would you solve this (hopefully without having to model every circular slot)?

Thank you

Marco

test+engrave+lollipop.f3d.zip (756.9 KB)


It’s difficult to tell from the 2 images what you are trying to achieve. Your part looks like ovals, whereas the dented wood with the round head nail looks like spherical dots.

I don’t use fusion, so the file is no good to me.

Substituting a V-bit won’t work because the angle of the tangent on the ball changes with depth.
You might be able to get close with much higher angle v-bit, like a 150°. YOu could calculate the angle based on the maximum depth and the ball diameter.

Ideally you want a toolpath that does the same thing as a v-carve, but with a ball mill.

If it’s round / spherical dots, then I think a drill toolpath would be the most efficient. You again would have to calculate the depth based on the tool dia & desired depth.

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Hi @Tod1d

Thanks for your reply. As an exploratory project I am not sure either about where I want to get and what I want to achieve. However in my mind there is probably something more like this

Where the engraved shapes are not necessarily regular circles or ellypses, but you got the point, ideally I am looking for something like a v carve toolpath but with ball mill. I am not too worried about the inside of the shapes (no big deal if the “cups” are not smoothly cut) but I would like the outer edges to be respected…

The 150° virtual v bit solution is a good one, I will give it a shot later in the day but it will somehow imply an iterative process that I might not be able to replicate for each project to get the right depth.

Thank you very much

Marco

The opensource program F-Engrave has an option for doing a V carving like toolpath with a ball-nose endmill — so long as you don’t expect undercuts it might work:

https://www.scorchworks.com/Fengrave/fengrave.html

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Hi @WillAdams, yes that looks exactly what I am after…they call it B-carve! However I am not quite sure how to run it on a Mac…

See: