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I haven't found the lift angle for the Benrus BA movement. I did find 51 degrees being the lift angle for several other Benrus movements, so I have tried that. Not much of a difference in amplitude reading from 52 degrees, of course. I'll attempt to center up the hairspring collet and tweak the position of the regulating pin and retest. Trying the old mainspring is certainly an option, but it is quite coned. Plating was worn off of the barrel lid, so this wasn't from me removing the mainspring. -
By nickelsilver · Posted
The barrel may have been roughed out, then later machined for the lid (for example). That would open the possibility of the lid mating surface not being perfectly concentric with the barrel hole. A lid would be fabricated, fit to the barrel, then the barrel centered up in the lathe, lid fit, and hole bored. They had techniques to center up stuff really well, but it's time consuming so they might cut corners on lower end stuff, or if there was a way to make a certain eccentricity a non-issue. Some books show boring the mounted cap and barrel in the same operation. -
The setting lever is a complete unit with the 3 pointed star gear so isn't available as a separate item. The 5 pointed star is part of the calendar plate so again not available as a separate item. -
By nevenbekriev · Posted
What is seen on the first video (by the hairspring breathing) is that the amplitude is really high. The other thing seen is that when expands, the hairspring probably touches the stud. So, what You can do is center the hairspring better as it will stay a little away from the stud. Then, check You amplitude. One way to do it is to put a dot with marker on the balance rim and observe it's movement. The other way is to check if the lift angle for the movement is different from the magical number 52 and insert the correct number in the timegrapher. And if really rebanking happens, then You can return the old spring and check what will happen then. Yes, You can close a little the regulator pin. But it will not solve the problem. -
I have to double check the lid. I do remember seeing an index mark on some part of it last night that I didn't expect to see one. I don't remember if it was the lid or not. Why would they have created them where orientation is necessary? Or was it a limitation of the fabrication technology available at the time? Will do. Thank you. Though I should mention that the barrel did not have the mainspring in it when I took the picture.
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