So, I’ve just used a 1/32" Solid Carbide Downcut Fish Tail Spiral Bit for the second time, after successfully cutting out a shallow pocket yesterday, to cut a series of pockets in 18mm plywood to test cut three pockets and some lettering, with the following settings:
Depth per Pass: 1.270mm
Plunge rate: 203.2mm
Feed rate: 254mm
Max Depth: 3mm
But the bit snapped (my first one!)
Are these settings a bit too much for such a small end mill?
It waited until the second of the three pockets to break and, of course, I don’t have another one!
depth per pass looks a bit too much to me: 1.270mm per pass is 1.6 times the endmill diameter, at about 50% stepover, which is higher than my goto rule of thumb of 50%D max (as a starting point at least)
You could input those values in @gmack’s spreadsheet to figure out how much deflection you had, for a more precise answer.
And then there is the matter of runout which becomes predominant when doing micro-machining (which I consider using a 1/32" endmill to be). If you have e.g. 1/64" runout in your router, it won’t matter much when using a 1/8" endmill, but when using a 1/32" endmill it would be 50% the endmill diameter, which at that scale is a huge deal (breaker).