In the conventional manner I used to properly balance and apply East Biasing to my AP1200, following that I ran PemPro to PEC characterize the RA Worm. Yet I continued experiencing poor RA guiding when in the Eastern Hemisphere.
PemPro requires the mount be centered on a star near the Equator and close to the Meridian on the West side. Thinking about the gear contacts I realized PemPro characterized one side of the Worm to Main gear surfaces, when in the Eastern Hemisphere the opposite gear surfaces are in contact. This was causing my problem of good guiding in the West and poor guiding in the East.
To solve this dilemma I came up with what I call my “Compound” East Biasing technique. I have been using this method of imparting an East Bias on ‘both’ sides of the Merdian for over a year now with good results. Guiding on either side of the Meridian is very accurate and nearly identical with minimal effort.
East Biasing is a method of adding weight to the counterweight shaft in the East side to keep the Worm to Main Gear surfaces in contact, the Worm is “lifting” the Main Gear. Without this additional pressure corrections to the Worm can cause the Main Gear to loose contact with the driving Worm, this is known as Bounce. Bouncing can require additional corrections possibly leading correction oscillations.
In the conventional East Biasing method when on the West side the counterweights pull the Main Gear downwards. This causes the Worm to Main Gear surfaces to change sides and the Main gear “follows” the Worm gear instead of being driven by the Worm. This condition can also introduce Bouncing leading to oscillations.
My Compound method does not require moving counterweights up and down on the counterweight shaft in the dark, it does require the use of hanging Biasing weights as the end of the counterweight shaft in the Eastern Hemisphere to maintain proper Worm to Main Gear contact and pressure. When changing to the West side simply removing the hanging Biasing weights automatically compensates keeping the ‘same’ pressure and the ‘same’ gear surfaces in contact as in the East side. It’s all in the manner in which you plan and apply your Biasing.
First figure out how much weight you require to normally East Bias with the counterweight shaft in the East. I use Lead 8oz Egg Sinkers which have built-in holes and are readily available in most fishing departments. Simply run a string through the holes and loop one end over the counterweight stop on the end of your counterweight shaft. You will need "double" the amount of lead sinkers you needed to impart your normal East Bias. Half will be used in Step-2, half in Step-9 below.
Here’s the tricky part. You are going to East Bias on “both” sides of the mount. Your mount should already be balanced before performing this procedure.
This technique effectively makes your mount drive from the same side of the 'Worm and Main Gear' surfaces with the same pressure regardless which side of the Meridian you are in. All you have to do is add the weights when imaging in the East and remove them when moving to the West.
There's an additional benefit when using the “Compound” East Biasing technique. Regardless how you used to PEC characterize your Worm now do so in the West near the Equator. Afterwards you should not need to retrain your PEC when you move to the Eastern Hemisphere. “Compound” Biasing maintains the same gear surface contacts and gear pressures so retraining upon a Meridian Flip is not necessary.
It took me awhile experimenting to develop this concept. If you wish to ask questions please feel free to eMail me at firstname.lastname@example.org I’ll be glad to help.