Quote:
Originally Posted by BLUNT
0.1mm is 4 thou - that is a massive interference!
..... "You cannot be serious"
|
No, not exactly (John ?) .. the figures were only there to illustrate the method really and I plumped for the simplest ballpark ones that came to mind.
But yes, "maybe, something like" 4 thou probably is a bit toppy.
In old money, off the top of my head, without spending hours deciphering the tables, I probably would have recommended "a thou or two" .. but in metric that goes to three decimal places, which seemed excessive in the context.
I may also have allowed a thou or two to cover an inexperienced machinist (pardon) and some measuring error (which would likely be undersize).
And its funny how a bore in ally can grow a few tenths once you knock the crests off the machining marks, so maybe I erred on the side of caution.
Whatever the tables (eventually) say (in tenths of thous .. beyond the accuracy levels of most turners for a one-off part), I would aim for the top (ie tight) limit of that as a minimum machining tolerance, and err tighter if anything.
It may be sacrilege to say so but you can always lick a few tenths out with emery if its a bit tight (even if it's been previously removed from the chuck) .. but you can't stick any back.