How to: Initial cut with 1/8, deeper cut with 1/4?

Software Carbide Create
1

I would like to cut out a shape in soft wood, starting slowly with 1/8 bit so there’s no tear out…and then switch to 1/4 (or larger bit) to finish off the deeper levels quicker - making sure the edge is the same location throughout.

What’s the best way to accomplish this in the toolpath?

2

So why not just cut with the larger bit for the whole depth? What advantage would there be for starting with a 1/8" and finishing with a 1/4" bit. If it is a pocket in the end you get a hole.

3
  • A shallow contour path with the 1/8" to break the surface. Using a downcut bit will leave a cleaner top edge.
  • A pocket slightly wider than your bit to clear the bulk of the depth, down to the point you want tabs
  • A final contour cut to cut through and leave tabs.
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CutOutTest.c2d (64 KB)

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4

See:

Basically use the smaller tool (ideally a downcut) for the pocket, then the larger tool for the contour.

That said, usually folks do this the other way 'round — use a large downcut, and a small downcut.

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5

In my limited experience so far, the smaller bit was a cleaner first layer cut when working with plywood. The larger bit created more hairs (some quite large).

So, is it an accurate assumption that starting with a smaller bit (to pilot cut the outer edge) would be less likely to cause tear-out in softwood or plywood? …then following with the larger one to cut deeper down the outer edge?

6

I have not necessarily found that to be the case. Using up or down cut definitely makes a difference.

If I’m concerned with clean Final Cut on ply products I will offset roughing cuts, use 1/4”down cut bit (unless smaller size needed for project). Once majority of material is removed I’ll follow up with a compression bit for final pass with no offset.

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7

Start with your downcut 1/8" and cut just enough to get through the first ply or about 75% of the tool dia. Climb cut and make 2 passes.

Cut to depth with your 1/4", staying a very small amount away from the wall (0.005" / 0.1mm).
Now make a finish pass on the wall at full depth, assuming you have enough flute to clean up the entire height of the wall. Otherwise you may need to set depth per cut to your flute length.60
You can offset the curve, or a simpler way is to lie to the software & program it with an oversized tool, say 0.260" and cut with your 0.250" tool.

If you can, a good heavy coat of sealer that soaks into the wood will also help bind the wood fibers & prevent ‘burrs’ and tear out.

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8

Try a compression bit and see if you like the results.

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