Suppose your client sends you a picture of a key and you want to use the picture to make an original. With some locks with only 5 or 6 depths, Kwikset for example, you can just sight read the key and be very accurate. But when a lock has 10 depths, such as Schlage, the job becomes more difficult. Here is a method to use to measure the cuts in the picture and a formula to use the translate the image measurement to the cut depth.
The formula is;
Cx = (A/B) * Cm
A=actual height of a blank (Schlage is approx .343)
B=measured height of the picture (uncut part of blade, 1.26 for this example)
R=ratio i.e. R=A/B, (.272)
C1= 1st cut measured on picture
C1*R = .96*.272=.261 which is close to a number 5 (.260)
Repeat for all cuts. The secret is to get an accurate ratio by measuring an original blank and dividing that by the height of the blank in the picture. The bigger you can make the picture, the more accurate your readings. Multiply the cut measurement by the ratio and you have the cut depth.
So, for the math geeks;
Cx = (A/B) * Cm
Where Cx is the cut dimension you need (C1, C2, etc), A is the height of an actual blank, B is the height of the key in the picture, and Cm is the measurement of each cut in the picture.
Jon Payne Sr., CML, CAI