Hoping for a little spoon assistance

I’ve been working on some wooden spoon ideas and Will Adams was a huge help in setting up a file for me using a ball endmill and a series of contour toolpaths for a cleaner cut. I don’t have a 1/8’ ball but I do have a 1/2’ diameter cove box bit which i think in theory should basically function the same way. I’m just having a little trouble wrapping my head around how to alter the tool paths of Will’s file to use a 1/2’ endmill rather then a 1/8’. Just not exactly sure of the math I should be using to change the contours and DOC. Thanks for anyone who can help me out, math isn’t my strong suit :slight_smile:
Spoon.c2d (380 KB)

It’s the same process, but with a larger circle. The beauty of this method is you don’t need to do any math. You draw in the tool, manually position it, and then measure the depth & offset of the tip of the tool from each position.

Here’s the basic concept in a nutshell. Each position/point the tool moves to is the position of the “Tip of tool”. When machining a 3D contour the Tip of Tool is not on the part, it’s floating in space above the part. The “Contact Point” is the point on the tool touching the part.
By drawing in the tool you can position the tool tangent to the Contact Point, then measure the relative position (Over & Down from the original vector) of the Tool Tip.

In the image the Contact Point is on the original vector. You can see that in order to make that first pass tangent to the Contact Point, the Tip of Tool needs to be offset inward, and downward.
What Will did to make measuring easy, was for each Contact Point created a rectangle from the Tip of Tool to the point on the vector. Then just select the rectangle and use the width & length for the offset & depth.

So, the first thing you need to do is establish where you want your Contact Points.
It looks like Will started out using incremental depths. This will work, but it results in varying stepovers.

This will mean varying Scallop Heights. On a shallow contour (Not Steep) it is better to use stepovers rather than depths to determine contact points. For wood, I like to shoot for a 0.001" - 0.002" scallop.
For the purposes of this topic, I’ll shoot for 0.005". I use this stepover / scallop calculator
Milling Step-over Distance Calculator. I enter the tool dia & my desired 0.005" scallop height, which gives me 0.0995" stepover. I’m going to round that off to 0.1

image

This makes my offset easier, as they are all now multiples of 0.1
So I draw a vertical line & position it going through the design vector, then use the array feature to copy it at 0.1" intervals.
Then for each stepover line I move the tool tip down that line until the contact point is tangent to my shape.

Now, draw a rectangle from each tooltip to the edge of your original vector. The size of this rectangle will be your offset for the vector, and the depth of cut for that pass.

NOTE: Don’t draw the tool with the flat sides, just use a circle. The united vector has many nodes, where the circle has 4. Easier to pick the bottom node (Tip of Tool) to position it.
And you don’t have to draw every tool position. You can just draw one and move it to get each rectangles lower right point.

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For folks who missed the original, it was at:

but @Tod1d 's discussion above is spot-on.

I suppose someone who was better at math could work up an elegant solution for this sort of thing in OpenSCAD or METAPOST or some similar tool.

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Thanks so much for laying that all out for me, i really appreciate it! I have a much better understanding of the whole process now :slight_smile:

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