Need help with a Coburn 108 generator

[lthouseme]

I need some help not in setting by base curve, but calibrating it. The cross curve is cutting acurately, but when both base and cross are set at 6.00, the base cuts at 5.40. How do I make the adjustment in calibration? I do not have a maintenance manual, only the owner's manual.

[mshimp]

Have you already used the "C" gage to calibrate the wheel yet? Do this first. How are you checking the curve once cut? We use an uncompensated brass gage 6.00 or 7.00 diopter to press into the lens to verify correct curves. You may have to reposition the scale once calibrated.

[lthouseme]

Yes, I used the C gauge first, and then cut and checked the curves with a tonometer. I have a book for the tonometer that coincides with the readings to transpose the number reading to a curve. I did think that I needed to adjust the scale (I worked with a 113 for quite a few years), I just wanted to make sure before I did it. I will go tomorrow and recheck at different curves to see if they are off by the same amount, and then reposition the scale. I thank you for your help, and will let you know tomorrow if that is indeed the problem.