Originally Posted by
ian maybury
Guess as is often the said 'the devil is in the detail'. Or more to the point - only your specific case is your reality. Rules by definition are standardised one size fits all procedures...
This post is actually just to say that my 80 and 180 grit CBN wheels have arrived from WoodTurnersWonders, and to offer some thought on boring them to suit the grinder shaft size.
The stock 5/8in bore on the WTW wheels requires opening up to the 18mm nominal of the (UK market) grinder shaft in my case. (actually a shade under - measure each shaft end in several places with a micrometer before deciding on the required bore size - roughly 0.001 - 0.0015 in clearance -diameter difference- should deliver a precisely located sliding fit at this shaft size) Some of the other CBN wheel makers bore their wheels oversize, and offer reducing sleeves to suit common US shaft sizes. I'm planning to bore both wheels to the same diameter to suit the smaller end of the grinder shaft (both ends are not quite the same diameter on my grinder), and to adjust the fit by reducing the diameter of the larger end using emery cloth - so that either wheel can go on either shaft end/side.
It's maybe worth putting up a few thoughts on boring wheels like these - feel free to add views/options. On the basis that there's potentially a few pitfalls in getting the job done right. It's important that both wheels end up running true - both in terms of runout, and of side to side wobble. (the WTW wheels grind off their side faces as well as the periphery to do flat bevels as well as the hollow ground variety, and are 6061 aluminium)
The simple way would be to try it under a drill press, but unless everything is very well set up indeed there's for me an unacceptably high risk of the bore ending up misaligned - plus unless a machine reamer is used after an undersized drill there will likely be problems in achieving a correctly sized hole too.
One method is to use a small boring bar on an accurate engineer's lathe - making sure to check for wobble and runout first (that the wheel is accurately centred, and chucked square) using a dial gauge in both directions. Hitting the diameter with the boring bar and setting the chuck requires a very skilled machinist, but has the advantage that it by definition finds the true centre of rotation.
It's easier to bore in the lathe using a Morse taper drill and then a machine reamer off the tailstock (and it's certainly the simplest way to accurately hit a given diameter), but there's a risk of inaccuracy if the tailstock is not accurately set up/aligned. Which isn't always the case on lathes in less precision oriented machine shops, or on older/worn machines.
The other task is to dig up four sets of 18mm + bore self aligning/spherical washers (M16?) to go at each side of both wheels. This reduces the risk that a less than perfectly square cut thread or shoulder on the shaft will tip the wheel out of alignment when the retaining nut is done up....