How can I cut circles without creating projectiles?

[CanisLupus]

I'm working on a design based on a 12-inch circle with a series of 1-inch holes spaced every 2 inches around the perimeter. Using a 1/4-inch bit, how do I toolpath the 1-inch holes so the bit starts near the center of the hole and works its way outwards to avoid leaving a piece of scrap inside the hole.

My concern about starting on the outside perimeter is being left with a 1/2-inch diameter scrap piece in the center and having that scrap thrown when the bit finally cuts through the bottom of the material and frees the scrap. I don't think tabs are really an option in this case so I plan to machine the hole centers away.

It looks like I can use a 2D Profile toolpath with the spiral ramp option but I still need to obliterate the scrap in the core of the hole. Is there any way I can use this approach and start in the center of the circle and spiral outward?

Thoughts?

[dealguy11]

My first take would be to use the profile with ramping strategy with a 1/2" bit instead of a 1/4" bit.

If you really must use the 1/4" bit, then do the hole in 2 toolpaths. Make a smaller hole 1/2" in diameter, centered in the larger hole, using a profile/ramp approach, then cut the larger hole.

[CanisLupus]

Thanks, Steve. I thought about using a 1/2-inch bit and my only reason for not using one is everything else can be done with a 1/4-inch. Sounds lazy but I was avoiding a bit change. Thanks for the suggestion!

[tomgardiner]

I have had good luck with a last pass allowance and the final pass depth of .050" or less. I would try a last pass allowance of .025" or a little more. Ramp in. The allowance will keep the bit away from the center loose piece and the light final depth imparts minimal load on it.

[FixitMike]

Use the Pocket toolpath rather than a Profile toolpath if you want the bit to remove all of the material from the hole, Check the Offset path box. Ramping the plunge moves is always a good idea.

[ozymax]

Could you use the Spiral gadget to create a profile path that removes all the material in one pass and
apply a ramped plunge also?
https://gadgets.vectric.com/spiral.html