It looked like they were big enough to handle the added load. :-)
> It also INCREASES the bending load in the shaft between the bearings.
Bear with me... hold your long printout so the dec shaft is horizontal and the scope is on the left. Ignoring the counterweight for a moment... the scope will push down on the bottom-left surface of the left bearing, which will cause the right end of the shaft to want to come up. The top surface of the right bearing stops it from doing this. The longer the distance between the bearings, the more bending force is exerted on the center of the shaft between them. The counterweights add to this force from the opposite end, causing the center of the shaft to bend "up" even more.
Now look at mine. The short shaft transfers it's load to the top of the right bearing (and the c.w.'s load to the top of the left bearing) before it can bend. Yes, we've increased the SHEAR load on the shaft and the load on the bearings by a tad (the left bearing is still carrying most of the scope's load and the counterweight's is on the right bearing), but reduced the shaft's bending load (a function of the shaft's length, which we shortened).
Also, in your design, the load from the bearings was being transferred to the 3/8" aluminum plate supporting them. In my design the bearings are mounted much closer to the thicker main housing instead of hanging out in the breeze. All the weight is being transferred to the ground and your 1-5/8" shaft, oversized bearings, and the main mount housing can deal with the weight better than the long thin aluminum plate you had supporting the bearings.
The only positive thing about a long shaft I can think of in this instance is to give the mount better leverage on the slop in the bearings. Maybe Opticraft's design lets them get by with cheaper bearings. ;-) Don't use sloppy bearings and you don't have to worry about it.
> > 3. Countersunk all your bolts/nuts...
> Good idea for the graphic, but I don't think the 3/8 Inch plate will allow it.
> The 1.5 Inch (Now 1.0 Inch) collars will countersink just fine.
So will the 3/8" plate. But, the only place where I show countersinking into that is on top of the scope plate. There you would use bolts with countersink heads (look like a "V"). I have a bunch of losmandy stuff made with that plate, and it's all countersunk.
> > b. How do you intend to control the tension on the DEC shaft?
>
> I don't know what this means.
Well, right now that scope would go whirling around the dec axis at the slightest push. You need some way to loosen it so you can move the scope in declination and then tighten it back down so it doesn't move.
> I was planning on a tangent-arm drive with a small bidirectional motor.
Sounds good. Allows finer motion, but for a limited distance. No computer slewing for this scope then? :-)
take care... and thanks for humoring me!
Andy Steere dmislas@clark.umsystem.edu