Ok, at -6 degrees celsius which was what the bearing temp measured using a digital temp probe on my mm when it came out I got 27.98mm
it started at 19c
so correct me if I’m wrong with the following maths
Temp difference is 25c
Diameter change is 0.02mm
0.02 divided by 25 is 0.0008
Essentially for each degree dropped in the freezer is 0.0008mm diameter smaller.
For this bearing to fit in the pocket, it needs to be less than the pocket dia which is 27.96mm so let’s just say 27.95. which is measured at room temp at
so I then heated the mag case, this only took 120c (remember me saying about older saws and much sweeter fit)
so
To get a clearance of 0.05mm I needed a change of 103c
103 divided by 0.05 is 0.00049 (0.0005 rounded) so every degree c extra is 0.0005mm extra in dia clearance.
So in summary
if I rely on freezing alone I’ll need a temp of -75c theoritically
if I rely on heat alone I need 103c
if I freeze the bearing as cold as I can get it I’ll need a clearance of 0.03 still which means I’ll then need a temp of 60c
I’m sure the maths isn’t perfect here for sure, I’m not sure expansion is this linear.
Anyway, now I’m going to re freeze the bearing and see tomorrow if it will drop in a 60c case
will report back. If it does work and I really can reduce the temp that much I’ll eat my words and apologise admitting I’m wrong. Watch this space.