You might gain some insight by just measuring the resistance of the rack in the electrolyte (empty rack, no work). You can do this by immersing the rack and applying power, note the voltage and the current. The resistance is then R = V / I. Since it won't anodize, this resistance should remain constant if your electrolyte temp. is reasonably constant. It should not be important what current you make the measurement at.
Servisure should be able to provide you with the SA for the rack components, but it will probably be easier to come up with a rack resistance for each rack configuration that you use.
For a given rack, the rack resistance will appear as a resistance that is in parallel with the work, as though it was a seperate resistor across the power supply. The power it is dissapating in the electrolyte would be:
P = V x I, or P = I squared x R, or P = V squared / R, all work equally well.
This will tell you how much power you have to allow just for the rack.
It will be more complicated to account for the series resistance of the rack and the contact points to the work. Maybe you could dispense with this by calculating the resistance again, this time the rack and some typical amount of work (R = V / I) when you think the work is sufficiently anodized. If you subtract the rack resistance from this total resistance, you will have the anodic resistance, plus the rack series resistance, plus the contact resistance.
If the difference between these two calculated resistances is small; you are going to have issues with knowing what current density you are anodizing at, and keeping it constant throughout the anodizing process.
Sorry M_D; I know you didn't want to hear this, but you might need to get good at "Kentucky Windage" anodizing. Its a PITA, but others do it successfully.
Let me think about this a while longer.
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