Thanks for clarifying and the detail.My spindle is a pretty standard 80mm 4-bearing cartridge with R8 taper. . The difference with mine vs. a Tormach or similar is that it was designed from the get-go with an internal (to the head) HTD5M belt and not a step pulley V-belt. Uses 20mm wide HTD belt, single speed. Motor output pulley and spindle pulley are inside the head.
I'm using the TTS system for tool holders, with a homemade bellville-stack drawbar. You can scroll up for the external view.
Just guessing here, but I think the reason hobby folks aren't using dedicated 7kRPM spindle servos and drives is that they're staggeringly expensive compared to the cost of a nice hobby-grade mill. So:
1. Cost. Checking ebay for a 2.2/3.7kW spindle servo and matching drive that isn't covered in industrial goo and has no broken connectors - looking at north of $4k unless you find a screaming deal. My research indicates that dedicated spindle servos have built-in fans and either resolvers or encoders with lower-than normal pulse count so as not to overload the drive inputs when spinning at max RPM. Could be wrong, but I think the spindle motors don't need the super-precise positioning capability of the typical axis servo, but they do need to run all day long.
2. Availability. There's very little available in the 2hp+ high-speed servo world that can be powered by 230v-1p power. And if you've got 100A 3p power, why are you messing around with a hobby mill? Pour a new pad and buy a VMC.
3. Complication. Resolvers vs. encoders, trying to match motor/drives from different manufacturers, digging up mostly obsolete data sheets and then deciphering them is challenging. This forum and others are littered with questions about trying to figure out servo drives and motors - I've read hundreds of them over the past year.
4. Mechanical complexity. Some industrial mills use a 2-speed automatic belt drive and a narrower speed range motor. I can't imagine trying to design or retrofit an automatic speed changer to a mill, then programming the controller to do the speed change based on nothing more than an S-word input and M3/M4 command. Well, I can imagine it, but I can also imagine what a winning lottery ticket or world peace looks like, too.
The only thing I've found that's close to a (sort-of) affordable turn-key solution is from a couple of the Chinese motor companies who will sell a1.5 or 2.2kW 220-1p 6/8/10kRPM dedicated spindle servo with matching drive for about $1200 delivered. Specs look promising, but neither of the companies I've contacted will send me the drive manuals before purchase. That's a show-stopper, especially since the typical service & return policies are a little... suboptimal.
So I'm looking for a servo drive that works with 230-1p, has a speed mode with 0-10v input, and is new enough that I can still find a replacement in a couple of years when/if it blows up. Then I find the biggest high-speed servo with an encoder the drive can handle that still fits the physical constraints of my mill.
I could pull the trigger tonight and have a Parker GV-U12 drive and an N0924-HK servo delivered for about $700-800 from ebay. Cables maybe another $100-200. Add an external cooling fan and try not to let the smoke out.
Just not quite ready to drop that dime this minute.
-Ralph
I now see why the hobbyist isn't taking on this project due to the cost impact.
Adam,