Yes, the concern with bit size is due to the power (or lack thereof) of the current head.
Not that it’s necessarily underpowered - just the power that it does have has limitations (hope that makes sense)
There are calculators on the web that will give you recommended speeds depending on hardness of the wood and size and type (# of flutes) of the bit. The larger the bit the faster the outside edge of it is traveling. There’s also a lot more torque for the head to spin.
I think the best thing you can do is listen to the motor and the bit. You can tell pretty easily if it’s straining. You can adjust the speed while it’s running. Err on the side of caution as far as stepdown. Start with .5mm and see what that does.
So far I’ve found running spindle at 12000 with a .5mm step down in hardwoods like oak or maple a work speed of 350 works well. For soft woods like pine I can push it to 600.
(If it sounds like it’s straining (one of my pieces of oak was extra hard) I slow it down on the controller.) Doesn’t seem to matter whether I’m using an 1/8" or 1/4" bit. I would’ve thought I’d want to slow down the smaller bit, but it doesn’t seem to be the case. I think the stiffness of the 1/4" and the increased speed of the cutting edge balances it out.
I haven’t tried a surfacing bit yet.
-S
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