Hi David - Glad to see the torch being carried for the Speeds. I would offer a couple of observations which may or may not be part of your thinking already. Hopefully they will be of some value.
First is that even a 3x4 has a huge distance across the film plane. So even if the slit appears to be crawling across the plane, each area may only be seeing a tiny bit of exposure. For instance, if you have a 1/8 inch slit that takes a relatively eternal 1/8 sec to cross the film plane, then each film grain is only seeing a bit under 1/200 seconds of exposure.
Second, I have found that a good lube is hugely valuable. In my experience, folks have come to assume that Speeds have a naturally graunchy shutter song. Having actually built up a shutter from scratch, I discovered that a well-lubed, factory new Graphic shutter sounds quite sweet and positive. Not much tension is required to move a fresh Speed shutter. So before tensioning up, I would definitely take the time to lube all points. This may buy you quite a bit of shutter speed.
If the shutter is a completely crispy pretzel, it is definitely within he reach of an average amateur to perform a complete rebuild. This is a lot of fun and the results will amaze!
I would not worry about breaking the shutter spring or any other component. The main worry I have seen is the screws taking too much wood with them upon removal.
Just my two cents. Hope it helps!
Jon
I just took delivery today of another Pacemaker Speed Graphic, a 3x4" model in very good condition. According to a rough test with a Mk I eyeball, the shutter is working well and running at a steady speed, but I would estimate it is 1 1/2 stops slow (i.e. marked 1/1000 is actual 1/300, etc.). My question is this: Among APUGers who use the focal plane shutter of a Speed Graphic with barrel lenses, is there anyone who has had the shutter tuned up to the original speeds, or do people just use the shutter as found and make mental allowance for the slowness of the speeds? Do the (over 50-year-old) springs start breaking if a repairman tries to set the shutter to accurate speeds?
Regards,
David