A lot of questions, so here are the answers:
JasonB,
I looked at that website, but didn't find that particular table. I suspect probably because I was somewhat bamboozled by all the different tables, tolerances, etc and I ended up going round in circles, Thanks anyway – that certainly would seem to suggest that this particular bearing might just be within tolerance.
SOD/Dave,
Interesting reference which I didn't find before. or maybe I did, but ignored it. As above to JasonB, I do have a tendency to go round in circles, especially when I'm trying to discover information about which I have never had any training.
To everyone else.
What has happened is that a cast iron hub has broken right at the point where the inner edge of the bearing housing occurs. Which also happens to coincide with the narrowest diameter of a V on a PolyV drive. The bearing make appears to be XMCXV and the type is 6000RS. As mentioned in my original post, there is definite wear on the inner diameter so the bearing will have to be replaced. I haven't yet checked, but I do wonder if there may be matching wear on the axle on which the bearing sits. When all said and done, for wear to occur on the bearing ID, that suggests that the ID has been moving on it's shaft.
Now, the shaft, or axle, is actually inside, along the centre line, of a hollow hub. Think, if you like, of a bicycle wheel where the shaft/axle is stationary, but the hub of the wheel rotates around, but is clear of, the axle. This diameter is of the order of 22 mm whilst the axle/shaft is obviously 10mm to suit the bearing ID. My thoughts are to make a replacement, or perhaps I should say addon, hub which will carry grooves for the Poly V drive, carry the bearing housing for a new bearing, and which has a longish hollow spigot to fit inside what is left of the original hub, and glued in place possibly using JB Weld, that is once the broken bits have been removed. I'm also thinking of possibly slightly increasing the diameter of the Poly V bearings in order to slightly increase the thickness of material at the break point. Ok, this will result in a slight loss of gearing, but that will not matter in this situation.
However, the first thing I have to do is to draw the existing, hence measuring the bearing and what's left of the broken hub. From that, I can then move on to modifying the drawing to show the result of any proposed increase.
It may, of course, be a total failure, but it is already that, ie I have nothing to lose in attempting a repair, and even if it is a failure, I will have learned something, because as I keep saying, I'm into model engineering for self education by experimentation. I've also been somewhat circumspect in that I haven't said what it is that I am attempting to repair – the reason being that I have thoughts about submitting it as a project to MEW if the repair proves successful.
Regards, and thanks for all the thoughts.
Peter G. Shaw