Möller Combination Action Refurbished


The following images show a Moller tripper combination action completely disassembled.  The core component consists of a cam.  Depending on the direction of the “finger” on the cam, it moves its corresponding drawknob either on or off.

Moller built an extremely durable action.  A university instrument may be in constant use, almost 24/7 during academic terms.  Despite 60 years of continuous service, it was decided no restoration was needed to this action other than timing of the power pneumatic actions.

During the 2010-11 restoration, the builder decided to raise the wind pressure in the console from the original 6” to 8”.  While the generals were very prompt, no one understood that this increased pressure would sheer off the tip of the spring mechanism in the cams.  For divisional pistons when this higher pressure acted on a single power pneumatic (divisional pistons) rather than spread over 5 power pneumatics (general pistons), this pressure proved to be a catastrophe.  As a result of several month’s use at the higher pressure, most of the divisional pistons showed the tip sheered off between the on and off position of the cam.  Drawknobs would not stay set on or off, becoming unreliable.

Curtis Bobsin examined the issues and was convinced that the bad cams could be replaced and regulated, assuming a supply of good cams could be located.  Mark McCrary furnished a supply of these cams in excellent condition, and Mr. Bobsin replaced the damaged components during two sessions in 2018.  Regulation was initially taxing until it was understood that the set screw determining location of the arm connecting to the drawknob was where the critical regulation had to occur.

Many builders warned over the years that Moller cams would eventually wear and become unreliable, but the experience here contradicts that belief:  If the wind pressure is left at the intended setting, the cams are all but indestructible.

Bravo Curtis Bobsin!!