Hello all,

I decided to mill some simple shapes from a 10mm thick alu-plate. Before I always cut max 5mm alu-plates without problems.
So I cut the designed holes and then I used some screw to firmly fix the stock at the MDF fixture. Finally, I milled the countour.

Here the problem: only the bottom side came out with a shiny finish. All other sides have a matt surface in the upper part, and a shiny surface only on the bottom zone:



Why?
I immediately told to myself: "the spindle is not perfectly vertical".
But this explaination doesn't work, the spindle cannot be angled in three different directions at the same time.

Here below the strategy I used (4 mm dia, 1 flute end-mill, DLC):



I'm not an expert, but it seem quite ok to me. The first and the second cut was made by using an helix-ramp with a "DOC" of just 0.8 mm.
All of the three cuts was made as climbing cuts. No chattering at all.


The manufacturer of the machine declare a precision/repeatability of 0.05 mm (i.e. around 2 thou), and I can only confirm that after one year of continuos use.

I'm scraping my head... What is the cause here? Lack of precision? Spindle run-out? Or what?

I'm pretty sure that if I leave more stock material before the final spring-cut all, then all of the surfaces will came out shiny and nice. Nevertheless, I would understand what's the matter here.

Any idea?