which is the more important - the leading or the trailing edge/rim??
which one do you want to match for the best result?
Leading edge is the most important when it comes to the highest strength. The hardest part of matching tips in a ceramic magnet either molded or machined is the tips on both sides being the same and also all the pieces being the same after machining.
All molded ceramic magnets are "machined" after sintering or as it is called in industry...."qualifying". The magnets after sintering have rough edges that have to be ground to knock off flash and to fit to finished dimensions. If you seen how this was done...you would laugh at how they do it...nothing precision about it..... the make a "fence" on the grinding table and usually push the magnets past the grinding wheel...... there is deflection and if a magnet has a "high side" on the edge up against the fence.... it takes off less material on the tip than a magnet with a lower side on it.
It's not very accurate nor precision and therefore you get un equal tips and tip dimensions among the batch of magnets.
Machined from block material magnets can have the same problems and seen this a zillion times at RJR when I worked there.
So if you have a magnet with a thicker tip than a magnet with a thinner tip.... you will find two different gauss reading/numbers.
Why you want the leading edge to be the stronger tip......... when the armature comes into the field ( this also has to do with magnet height, timing, air gap, wind just to name a few factors ) the leading edge of the arm laminations start to fire and you want to fire or charge the coil as the tips intersect. If you fire past this point or before this point....... loss of performance. You also do not want the arm firing or charging with the leading tip of the lams at the center point of the magnet either.... that's almost too late.
This is why certain arms with certain timing work with a certain magnet. There is a "sweet" spot for the firing/charging and over the years we have all figured out that a X-12 arm with 38 to 42 degrees is raceable versus a 50 degree X-12 arm. Sure you can use the 50 degree arm for drag racing or qualifying as it won't be ran long and get excessively hot and then fail.
Generally speaking.... the lower or shorter height of a magnet.... one has to reduce or retard the timing..... the taller the magnet more advance can be used.
But again this varies based on turns and wire size as well as air gap and magnet strength and energy.
Perfect example is the RJR Big Diameter 16-D arms.... being the tip width across the crown was reduced and a smaller width.... timing had to be reduced as the arms with 38 degrees and higher were firing way before the leading edge of the tip got to the leading edge of the magnets..... this caused heat and no RPM or torque. We reduced the timing to 32 and 36 degress and had a totally different animal and one that changed 16-D racing in a hurry.
So you always want the leading edge of the magnet tip to be the strongest. The "push pull" guys had it all wrong a few years back.