May be something as simple as work heating. The makita router isnt really meant to be cutting aluminum for an extended period of time. The error per cut is really only half the amount you’re measuring, total error on the part is both sides so its double. .1mm runnout with the makita and no cooling could do it.
Does the same error exist on a cut with no chance to heat or deflect? Maybe cut a basic shallow line square and see if it measures up.
Cut a single line groove in the material of your choice with a bit of your choice. Accurately measure the actual cut width of the groove. That is the effective “real cutting” diameter of your bit.
So, just an update.
I think the main problem I was having was overclamping the stock in my mod-vice causing it to deflect then relax once it was released.
I’ve since machined more aluminium parts for my Pocket NC and I’m within 0.02mm.
A good lesson to learn.
Also. Just wanted to say. The accuracy of this machine is actually quite impressive. I made two of the above parts and both were a perfect fit, even down to the 1/8” dowel pin holes that I bored out with a 2mm single flute. For its price I didn’t expect to achieve these levels of repetition and accuracy. Well done Onefinity!!
