I do not know any thing about electro magnets
What measurements do I need to work out the maxman magnetic force to obtain from a microwave transformer
1) Measure the space you have available in your core. Find the area of your core that will be the narrowest section for wraps of wire. Measure that cross section (you will be determining how many turns of wire will fit in that narrowest passage.
2) find a list of wire sizes and cross sectional area.
3) find the formula to determine Magnet strength, it will have length of coil, number of turns, amperage, diameter of wire.
4) start the hard trial-and-error work of calculating various wire diameter, the max amps of the wire diameter, the number of turns that fit in your core, etc. then try with thicker/thinner wires. Once you figure it all out, make sure to calculate how long your wire will be, the diameter and finally, the resistance. From that, you can determine what voltage you'll need to power the th8ng to achieve the amperage determined in your optimal design.
Good luck.