Here is a quick and dirty way to roughly calibrate your AFM. I tried it on two "unmolested" AFM's ('76 and '80) and obtained very similar results. The method uses two quantities of water as weights to pull the AFM flap to the 1/2 way point and to fully open. I recommend doing this if you swap AFM's or accidentally mess up your AFM.
Note: This instruction is for stock sized NA AFM's. The method is similar for larger Turbo AFM's but the forces and openings will differ.
- Aluminum soda pop can. In Canada, the standard is a 355ml size. This translates to 12 US fl oz.
- Lightweight string or wire. I used a fine wire-wrap electrical wire but monofilament fishing line or strong thread would be fine
- Tape to hold the string to the AFM flap
- Table to hang weight from
- Graduated measuring device
- Coool clearrrrrrrrrrrr waterrrrrrrrrrr
Connect the wire or string to the AFM flap (note this is an early AFM '76 unit with blow back valve)
Connect the wire or string to the AFM flap (note this is a later '80 so I needed to use tape) Eeek my toes!!!!
Here is the general idea. The pop can-water-weight hangs over the table and pulls the flap. Note the sting is unobstructed.
Just fill the can with the correct quantity of water and adjust the spring tension until the flap moves to it's desired location.
The two points I used are the 1/2way point and fully deflected point. (Hockey & Maple leaf eh!)
Here is a detail of the pop can. I cut a hole below the opening to allow for all fluid to drain out (no-"backwash"). A paper clip makes a great hook.
A loop in the sting is where the hook attaches.
Here is the '80 AFM weighted to the 1/2way point.
Here is another shot of the '76 AFM with wiper at 1/2way point. (Note: I used the circuit board from this AFM in the size upgrade of a larger Cressida AFM thus it is missing)
This is the orientation required for measuring full flap motion. (no the can is not on the floor)
OK now the numbers:
For the 1/2way point, I measured 148ml
For the 1/2way point, I measured 4.9 fl oz
For full flap deflection, I measured 290ml (close to double!) (I guess Hookes law stands :)
For full flap deflection, I measured 9.8 fl oz (close to double!)
For those using weights on string:
1/2 way = 148g or 0.326lbs
all the way = 290g or 0.639 lbs
The weight of the pop can must be added to the above weights.
Oh yeah, beer cans work great too! :)