Inside,on the line or outside?

Hi all. Did a test today wanting to confirm the best way to get accurate holes. I was always of the assumption you would cut ‘inside’ to get the required measurement but now I’m just more confused.

Test was creating 3 identical 10mm holes in Easel.
One cut inside the line
One on the line
And lastly outside
Cutting with a 1/8 bit

Here are the results I got…

Inside 4.4mm
On the line 7.5
Outside 10.7

Now I assume my machine needs calibration, just wanted to confirm the correct method to cut a 10mm hole @ 10mm.

Edit: awesome info. Thank you all

Inside means the entire mill stays inside the circle. In your example, the 10mm hole with a 3.175mm bit, would produce a circle with the dimensions 10 - (3.175 * 2) = 3.65mm.

On the line means half the end mill stays inside the circle. In your example, it’d be 10 - ((3.175 / 2) * 2) = 6.825 mm.

Outside means no cutter would be inside. In your example, it’d be 10mm.

As to which to choose, it depends on what you’re going for.

If you’re going for the circle to be positive space (i.e. wood), then you want to go outside the line.
If you’re going for the circle to be negative space (i.e. a hole), then you want to go inside the line or, as Robert mentioned, fill and pocket it. If you’re cutting all the way through the material, an outline cut set inside the line will work and you’ll have a small cylinder come out of the hole. If you only want it a certain depth, you need to fill it.

On the line has its benefits, for instance I was doing a sign where I want to use a ball end mill to create a cove style edge. I set the profile cut to be on the line so that I get half of the round of the ball end cutting into my sign and then, when I did my cutout, I did outside the line to get my exact dimension.

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that would depend on what size bit you entered vs. what size the bit was actually cutting.

P.S. every machine needs calibrating even when you just did it the other day. wear and tear keeps them out a little with every use.

But a circle is a hole in a negative space design :smirk:

I obviously didn’t reads too good this morning.

I found that my holes were off and after a little math, I had to set my 1/4 straight bit diameter to .2323

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If the hole is a through hole, an Inside path cut would be what you’d want. A fill wastes time and creates dust in that case.