Problem of precision

in January, I made 4mm holes on the aluminum to insert the rivets without problem. Yesterday, with the same file, I redid this project, the holes are smaller than 4 mm. I can’t find the problem, is it due to CM software or my NomadPro machine.

Could the endmill be a different diameter?

Could the aluminum alloy be different?

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Sorry for the spate of questions here, but have you been able to measure how much smaller?

Is it that the rivets no longer fit through?

Rivets tend to be notoriously variable in size and roundness so just want to make sure the right issue is being chased is all.


I use #102-Z. Alloy 6061 form Carbide store.

You are right for the rivets. And also, the conversion of length from imperial to metric poses a problem. 1 / 8`` becomes 3.175 mm.
I measured the diameter of the cutter # 102, it measures 3,150 mm.
So, with Vcarve software, I have to define the circle for the hole at 4.12 mm instead of 4 mm. I had replaced the damaged # 102 with the new one. There is a small difference in diameter between the old and the new cutter.

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Did you measure the hole diameter and the rivet diameter? Are the rivets actually round? I have had tubular rivets that measured on size with a caliper, but were lobed, so they would not fit a nominal hole. Round solid types tend to be much better. What type of rivet are you using-- blind rivet (pop rivet)? Tubular? Solid?

I tend to lean to the conjecture of @PhilG that the rivets may be off size or out-of-round.

To measure a 4mm hole, you will need to use a tool suitable for small holes. Common caliper types will measure undersize for a hole this small. See page 20 for the issue. If you do not have a proper small hole tool-- round-face inside caliper or micrometer, small hole split gauge, gauge pin set-- available, drill bits will do a decent job as a gauge, but they may vary by 0.05mm, or more for lower grades, and still be in specification.

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Pretty much need to check every tool when the size is critical. There is a tolerance. Best test is cut a defined size and measure the feature, then derive the tool size.

Glad you figured it out.


Cutter/EndMill size difference has caught me out a few times too.

I have several designs that require a 6mm magnet hole. Running the same .nc file with different cutters, each specified as having the same dimensions, either sees the magnet dropping in the hole with no resistance or requiring a hammer to wedge it in.

I am fairly confident the Nomad is extremely precise and the cutter vendors are not.


Thank you for your comment / remark. This is really the problem.
So I have to measure the diameter and do some tests.
Then write them down on each endmill box before using.

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