In my limited experience, I think it is commonly done that way because of the different hardness of the materials. I think you can wind up wavy on the wood as you sand over the harder shell. If the wood is already radiused, you can quickly bring the shell down flush with a file and then use a radius block to blend it all together and remove scratches.
I don't build enough guitars to justify over $800 for the SM buffer. I thought about this plus a speed controller of some kind, but I'm afraid a speed controller on a motor that wasn't built for that will burn the motor up after a bit.1750 rpm with buffs that size is anything BUT "low speed". I'd never recommend that on a lacquer finish, and even on a urethane automotive finish I'd use it with great care and never let heat build up.
If you want a serious buffer for guitar work, get the StewMac guitar buffer sold by Stewart Macdonald. It's not cheap but it's the right tool for the job.
I use one very similar. I have the Shop Fox. Very similar to that .
i did infact change to 10 inch wheels, and the main reason i will go to 12 one day....if i can find them...is for more clearance. 8 inch wheels will put a guitar dangerously close to the grinder body in certain positions. it's bad enough with 10,s, but one needs to be very careful when they get to this stage of a build anyway. oops isn't a word one likes to mutter at this stage.I don't even have a buffer setup but I would think as Dave mentioned to use larger diameter buffing wheels. at least 10 and probably better off with 12". The larger the diameter the slower the outer perimeter speed. I'm pretty sure that the buffing wheels can be pretty pricey.
I've got a ShopFox arbor, three pulleys, belt on the largest pulley for the slowest speed. The factory says 8-inch, but it easily accommodates 10 inch. the buffing wheels are thin at 1/2 inch each, so you have to spend a bit and put multiple wheels on each side to build that thickness. I use one side for medium compound, the other side for superfine finish compound. At the end, I'll use a hand-held with carnival wax,. Then another super soft bonnet with nothing .I don't even have a buffer setup but I would think as Dave mentioned to use larger diameter buffing wheels. at least 10 and probably better off with 12". The larger the diameter the slower the outer perimeter speed. I'm pretty sure that the buffing wheels can be pretty pricey.
I've got the shop fox. Superb machine . I love itLike others have said, I think that the rikon buffer will be way too fast for lacquer. A quick calculation says 3665 Surface Feet Per Minute. From what I've read you will want the buffs to turn about 2500 SFPM for lacquer.
I would recommend getting a Shop Fox buffer arbor and motor and build your own.
The diameter of the buffs become part of the equation for finding the correct ratio of pullies from the motor to the shaft. Larger buffs give you more room to get into tight areas like cutaways, I use 14" (I use this arbor and it recommends 10" but I have been running 14" for years with no problem). So about 700 rpm at the shaft with 14" buffs
Jescar is a good source for buffs and they carry Menzerma buffing compounds which I like. Always use different buffs for each grade of compound. Doubling the buffs will make the the point of contact larger so that you don't heat finish as easily and single buff will get into tight areas.