Hole Drilling Part II

As a follow up to my last post, I did a bunch of measuring to compare the hole drilling to the original drawing I did. This tests not only the CNC, but my drawing to code conversion.

My goal for this project was fairly ambitious, I wanted an accuracy of less than plus/minus 0.01 “. This is what I was shooting for, but I was realistic enough to be happy with less than that. So my measurements show that compared to my original drawing, I am out by 0.0014″ (1.4 thousandths on an inch), so naturally I am ecstatic! I then measured the repeatability, in other words, the holes are out 0.0014″, but are they consistently that much out. After measuring about twelve different ways, I found the variation between similar holes to be less than 0.001 (less than one thousandth of an inch). I am frankly in shock. Now here come the disclaimers.

1. I could be dreaming
2. I could be inept at measuring, though I have repeated the measuring many times in different ways and I though I was out more until I realized I wasn’t calculating for the right hole size.
3. Hole drilling puts little or no side pressure on the machine. When cutting, there will be much greater loads. This could greatly decrease the accuracy. This, though, can be somewhat controlled by how fast you cut and such and the machine is built fairly heavily with the weak link being any stretch in the drive belts.
4. I believe the smallest step the CNC can take is 0.0025″, so you are dependent of your dimensions being in multiples of a step.
5. I could be dreaming

The thing is that, even if the loading decreases my accuracy, I can still make deer shaped silhouettes like nobody’s business!

Anyhow, wish me luck, I really hope I am not dreaming.