Very impressive roll off roof design Lorence.
What kind of rail system are you using...steel wheels or some kind of rubber wheeled caster. You sure have plenty of them.
The rails are 3 inch C channel steel mounted vertically. The hard rubber casters ride on the narrow side of the channel.
The roof must weigh 5 to 6 hundred lbs. I can push it with one hand. I'm only guessing but I'd say it takes about a 40-50 lb. push to move the roof.
I did use a lot of casters. Temps. here drop below -40 deg. in winter. There is nothing harder on any sort of machinery than extreme cold. That and the possibility of a extra ton of snow on the roof were my reasons for spreading the load out over a lot of casters. The additional cost was negligible and well worth the peace of mind knowing that even under the most extreme conditions the load on each caster is well within it's design capabilities.
Buy the way these casters are very quiet, not that it's important where I am, but where neighbors are close it may be an important consideration.
As for my reasons for doing what I did, I'm on my own out here. I only know of one other amateur astronomer within a hundred miles. The only things around here resembling an observatory would be referred to a chicken coop or granary. Every decision was based on better to be safe than sorry. There is just too much time and material involved to cheap out and have to deal with problems down the line.
Good luck with your project.
I'm impressed with your appraoch. My designs study shows that compression is minimal and even less when using pressure treated lumber.
I'm planning on using pressure treated top plates....so they will transition well into the pressure treeted 4X6's that the roof will rest on when open.
The casters I got permit pleanty of room for them to be off set every other one. I've amended my design to include an additional caster per side..making it 7 per side. I'm also going with the steel wheel design. It is much more hardy.
I ordered the casters today and the total was $42.
They are rated at 150lb each...that gives me loads of room. Since each caster will be loaded with 35lbs....this reduces compression each will impress on the cap plate.
It also leaves 1.75" for the center guide. More wheels less friction. Solid wheels...less friction.
The center guide will be treated lumber stripped and when fixed..be retreated.
It's all sound and will save me bundles of time and money.
PLus the profile is so short...it provides great security.
Here's a pic of one.