I've found upgrading to a spindle motor from a DeWalt D618 to be well worth the price: quieter, more accurate, more torque. The ones I got were these, though at the time they were a combo package:
http://www.automationtechnologiesinc.co ... ng-spindle
http://www.automationtechnologiesinc.co ... 2kw-1000hz
That one has an ER-20 collet, so will go up to 1/2" bits, but it only comes with one 1/4" collet insert. I switched to a MuscleChuck (type 6A IIRC) and all their collets, including a custom one for 3/16" bits.
http://www.musclechuck.com No more button to push, no more two-wrench juggling. Now it's just a 4mm t-handled hex key, quick and simple.
Those spindles will require a non-standard mount bracket in the Shark too. Well, the spindles are a pretty standard 80mm, but NWA prefers routers if their catalog is any indication. I made my spindle mount clamp out of aluminum, but there are other solutions available. Sorry, I don't have links, 'cause I didn't need 'em. There's probably some post here on the forums with it. Probably search for "aluminum router clamp" or some such.
I'll let you in on a secret. If you notice that 1000Hz at the end of the VFD link/description? The rotating speed of the spindle is:
RPM = 60 * VFDFrequency
Which, if you do some quick math on that 1000Hz, oddly enough gets you 60K RPM. Say WHAT? Yup, that's right, the rated 24K RPM is NOT the fastest they will go, even though the default setup does limit it to that. And, it's EASY to do. It's just the "max frequency" parameter in the VFD. Default is 400 = 24000 RPM. I set mine to 600, and now I can run the spindle up to 36000 RPM, and so far it seems perfect, as long as the coolant is flowing. I don't run it long, but spinning a 1/16 or 1/32" solid carbide end mill in aluminum wants something well into the 30K range to get the proper SFM (Surface feet per minute) for a bit that small.
And, there's a MINIMUM frequency setting, and a torque boost setting for those low-RPM situations. I set mine to let me go all the way down to 500 RPM with about 0.5x of the spindle's 3hp available.
You'll have none of those things if you just go with another router. Whether those things important to you or not, well, that's your call
.
Anyway, that's the one I use. The liquid cooling was a chore to setup, but that's my fault for doing it the way I did. I love the thing, despite some issues.
Regards,
Thom