I have a 6-wire motor which I plan to operate as a 5-wire motor. As such
I've found the two center tap wires and will treat them as a single wire
going to a supply voltage of 40.5 VDC. Measuring the resistance of the
coils gives me 2.2 ohms to each of the remaining wires.

The motor itself is rated for 2 A. Using i = V - (Rated A * motor R) /Rated
R yields a result of 18 ohms for a current limiting resistor.

The closest I can find (would like a power resistor) is 15 ohms which would
give 2.35 A to the motor. (17% over)

Will this overheat the motor?

The motor is on a desktop CNC machine run by a unipolar driver (???) and is
for the Z axis. Best guess is running short periods of time (30 seconds
max, but usually only a couple of seconds).

Or, can someone suggest a source for a 18 ohm resistor? (To replace an
Ohmite TCH35P7R0J resistor).

Thanks in advance,
Thermo