In all probability, both of the bearing will be deep groove. The drive end one will probably be the locating bearing, i.e. it will be held on to the shaft with a nut or a circlip, and the outer race will be held into the end plate by a circlip. The non drive end bearing will probably also be held on to the rotor by a nut or circlip, and the outer will be able to "float" in a clear bore to allow for differential thermal expansion.
OK, a mid-range 5/8 bore deep groove bearing has a static load capacity of about 725 pounds. This means that your thrust load won't put bad "dents" in the races if you apply it when not rotating. The dynamic load capacity might be about 1400 lb. This means that at a load of about 470 lb the L10 fatigue life will be about 81 million revs. I'm neglecting all the usual fudge (service) factors here, including the one because thrust loads are a bit worse than radial ones. In other words, at 1000 rpm, you would have a 10% chance of bearing failure after 1350 hours. For 50% failure rate, you probably run for nearly 7000 hours.
Assuming you know how long it takes to drill a hole, that gives you a ball park estimate of the number of holes you could drill between bearing failures.
I'm assuming here that the lubrication is OK. All bets are off if it runs really hot, or is sprayed with sand and seawater. If there's a lot of vibration from the drilling, reduce the predicted life by a factor of
- And we tribologists don't normally claim to be able to work anything out to better than a factor of 10, so if you were paying me for my advice (and might sue me!) I'd add another factor of 10 to be on the safe side. In truth, most bearings from reputable suppliers survive ten times longer than the simple catalogue calcs suggest.
But superficially, with a simple catalogue calc of around 1000 hours of drilling between bearing failures, this motor sounds as though it might be OK in many workshop environments, although you probably wouldn't want it on a 24/4 car production line.
As others have said, adding a proper thrust bearing or even just changing to angular contact or taper roller bearings makes a lot of difference (but at a cost).
These numbers are self verified (but they are not hard to check against a bearing catalogue). Hope this is helpful.