Mike, I don't know about my motor at this point. So you think there may be a reason to use a jack shaft, even if you can get a straight shot from the motor? It seems that there should be a better way to control motor speed than adding a jack shaft if it is not otherwise needed.
"Bear" is adamant the use of a jackshaft, set up as small pulley on motor, big pulley on motor end of jackshaft, smaller pulley on flat belt end of jackshaft to big drive pulley is the way around his feeling a given HP-rating motor from today does not have the boot of the same HP-rating motor from the past. I've heard arguments to the contrary and I simply don't know anything about it... and/or, it allows use of smaller than spec hp motor... but I wouldn't go there.
I do know a given diameter of driving-flat-belt pulley will have more or less square inches of belt-grabbing surface area as the diameter of of the pulley is more or less.
Your hammer specs. 13" drive pulley and 350 bpm. With a 3HP 900rpm motor (catalog spec), you need a 5" driving-flat-belt pulley (and
that pulley needs to be crowned... reguardless of having side flanges disallowing the belt to come off... in my opinion).
Our motor is 1140rpm (96# Baldor... heavy, like Bruce said). With a 4" driving-flat-belt pulley, going to 12" drive pulley, the bpm is 380 (catalog specs. 375 with 900rpm and 5" driving-flat-belt pulley on 50#). Close enough, except for the loss of 25% of a 4" pulley's ability to pick up the hammer by grabbing the belt compared to the 5" pulley.
Whether "Bear" is right on modern versus old motor hp-output-torque-??? or not. These hammers use a contact-area to "sticktion" ratio to run... and to clutch through bpm at a constantly variable rate. I don't know as a fact, but it seems a person ought to be able to run any of one-beat through max number of beats per minute. In theory, that is... there are a lot of variables that can get introduced... I like the idea of eliminating possible variables from the start as opposed to finding work arounds later.
I'm not sure the precision apparent in the hammer design and construction necessarily is a function requirement of the driving system. The pictures of Roger Smith's overhead jackshaft drive on his "C"... the first two pictures. Rogers method of mounting jackshaft, etc., has to be solid enough, but there is no way it is an immovable object and it relates to the hammer only though belt contact. Yeah, there are alignment realities, but they are satisfied. I don't know Roger Smith except through his many pictures of many projects on Forge Magic and though a few small comments in conversations with Bruce. If I had to say, one way or the other with no fiddling inbetween, I'd say Roger Smith IS NOT going to have any kind of half-assed anything... it's going to work right or it's going to get made to work right.
You got pictures of your motor/jackshaft and mounting, Bruce? Can you clutch through any number of bpm from 1 to max, pretty much at will?
Last thing... overhead has distinct advantages. The belt can be shorter and the treadle actuated idler can have a longer arc of movement. The shorter the belt, the less treadle movement for bpm number from less. The more idler-movement-range available, the less minor variations in clutching components effect hammer function. Primary effect of both is less belt stretch and better ability to accomodate belt stretch.
Mike
Oh... and please, Bruce, DON'T tell your story of Fairbanks hammers and straight leather belts!!! It makes me cry!
