How about, making the bung up with a centre drill dimple in it and gluing ( Araldite ETC) a ball in place.

I think that would be accurate enough.

Accuracy
 

Yes I've been thinking about that especially with the links to Ball Bearing Manufacturers / Sales Outlets. The key is its accuracy as a small degree out at the base will quickly be exaggerated the further out you go (Yes I know there will be a phrase / definition name for this but, sorry, don't know it).

If, as replies suggest, this side of the 'Pond' we don't use a Tooling Ball here - how do you achieve the same ie centering above a cylinder (3" dia in my case) thats at 20 degree angle to the X Y axis - or do we just eyeball it?? (I guess eyeballing will likely be more accurate than a minimally misaligned ball bearing.....?)

Kind Regards,

Andrew

Careful marking out to find your centre,then pick up the centre with a centre in drill chuck or collet. Or the venerable "sticky-pin".

Now that I have had a rethink and watched the video right through I think Henry Maudslay's method above would work fine.

But note that you will probably still have to calculate the distance B, D, + the distance to your holes depending on your drawing information.

https://tractiontalkforum.com/pictur...ictureid=60871