As far as I understand, you use a 3/4" radius roundover bit to round the edges of the baffle. The radius is quite important. To be sure, does this mean that the diameter of the bit is around 2"?
Given a 1/2" ball bearing, this 2" diameter seems about right.
"I am afraid of burning the wood or not being able to maintain firmly the router with such a big bit. "
Your router speed is a bit fast, but with a sharp bit you should be fine. I find sharp bits are more important than router speed when trying to avoid the burn. Also, if you burn, just manually sand the discoloration.
Do you have an idea about how I can do to perform the round over with a fixed 27,000 RPM router ? Can I use a bit with a smaller radius/diameter, or should I consider another router?
Yep, I suggest you accomplish the roundover in 3 steps. Each step will gradually cut deeper into the lumber. The final cut with the router will be mild/thin so you can move fast without burning. I don't think you need a new/different router.
I suggest practicing this a few times first.
Concerning the trim bit. What diameter is the best to trim 1/32" or 2/32" of MDF. I have the choice between 3/8" and 3/4".
I normally use a 1/2" diameter but, but only because my bigger 3/4" bit vibrates. If all things are equal, I think the 3/4" bit should work better. It will have a larger bearing&cutting surface and be less likely to grab the lumber. However, either bit will work just fine.
Please let me know if I addressed all of your questions, and if you have any more of them.
