Hole Outline and Accuracy


I have a design where I need a hole to run a 29.5mm pipe. I created a 29.5mm circle and set the outline to “Inside”. I am using a 3.175mm (1/8) end mill bit.

The hole end up being larger then 29.5mm, something like 30.2mm. What I did wrong? Should I use “On Path” and substract half the bit size from 29.5mm instead?

Thanks in advance.

Step 1:
Fine tune your steps/millimeter value (calibrate)
Will a 500mm jog actually travel 500mm?

Step 2:
Use the 1/8" EM and cut a single line in the material you want to machine
Measure the actual cut width and use that as you tool diameter.

If there is slack/give in your system a hole is typically undersized, yours is not hence my suggestion above :slight_smile:
Another thing to have in mind - if you have a digital caliper: When they run low on battery the readings may be off.

HaldorLonningdal, thank you for the suggestion, I will give it a try tonight :slight_smile:

Quite honestly, I cut a bunch of pieces lately and haven’t check accuracy. Since it was mostly jigs to help with glue up assembly, only the angle (90 degree) was important and it was bang on of course.

I will do the test you suggested and see if it’s calibrated correctly.