Well, as promised last week, here's the start of a thread on a two speed belt drive conversion. I did manage to take a look at the existing spindle drive gear and it is a candidate for the pulley hub. The teeth need to be removed and then will yield a 3" dia. hub with what I believe is a 35mm bearing surface. The gear needs to be flipped over on the spindle, putting the internal splines on top. The existing bearing surface is long enough for duplex angular contact bearings placed face to face and a preload nut. I anticipate the seal being placed on the 3" dia hub right now, but there is some room to play with between the bottom of the hub and the top of the bearings. I intend to add a spacer there and that could become the seal surface real easy.
I've modeled a new top plate made of 2" thick aluminum with 1" removed from the bottom surface except for a boss for the bearings. Under that is a bearing plate to trap the bearings in the pocket. Really a simple machining job with a precision bore for the bearings and seal. Bearings are Nachi 35x72x17 angular contact priced just above $20.00 each. Not sourced a seal yet as I'm not sure of the specs on it. The only thing that goes in the old gearbox is the bearings, bearing plate and preload nut. Everything else is on top.
On top of the hub, I am heading towards bolting two timing pulleys to it with three or four cap screws. A 48 tooth on the bottom and a 72 tooth on top of that for now. I already had those models, but the tooth count can be changed. I'm liking a 1.6 ratio right now and a 44 tooth/70 tooth comes pretty close. There has been a little thought to that ratio, but I'm no expert on that so it could change. 1.8 actually takes me to over 6000 rpm without over speeding the motor. That takes a 40 tooth and a 72 tooth. I need to learn more about VFD's before I can commit to anything. Not sure how slow the motor can be spun without loosing torque. Should be easy to do 500 to 6000 rpm though, just want to get into the 200 rpm range if possible.
I haven't gotten to the motor plate yet, but it's an easy deal too. Need to measure the motor bolt spacing before it's finished and added to the model. The old motor to spindle spacing is right at 6", so that's what I'm working to. There may need to be a recess in the top plate for the motor shaft/pulley clearance. No biggy there.
The pulleys have some issues out of the box from the ones I've seen, so more shopping around is in order. The 35mm part of the old gear isn't long enough to mount the pulleys to directly, but an adapter could be made. Like I said, more research to do there. For my needs, I need the spindle sticking above the top pulley some for an auto drawbar.
So, enough typing, here's some pics to discuss. First the existing gear. Never did get it out of the bearings to measure the bearing surface. If need be, I'll by another one.
Then the 3D models. The pulleys are from another project, so they have some issues, but I'll fix it when I know what can be bought.
Bob