07-25-2012, 08:23 PM
William
Your weak link wil be the floor joists. Especially if you bring your rails in 26 in from the walls. The bridge can be a single member if you have your wheels spread to disperse the weight on multiple joists. The wheels should be spread as much as possible to stop the bridge from skewing as you travel.
Are you going to make similar to barn door track from the 3x4 tubing?
Here is one of two I have in my shop to cover the 24 foot width. Think its 3 in I beam I used for the rails with lag bolts going through the top flange into the joists. Was a while ago I designed it but think it was 7 or 8 hundred pounds safe load with a factor of safety of 2 based on the holding power of the lag bolts. The bridge is way over rated to that, the thought being I could block the ends off the rail if I needed to lift something heavier. Could take some more photo's and measurements if you'd like.
![[Image: IMGP0824.jpg]](https://lh6.googleusercontent.com/-ZmvhJs0T5Mk/T1ojkuSFBsI/AAAAAAAAATU/pwalr-QHRtI/s912/IMGP0824.jpg)
Your weak link wil be the floor joists. Especially if you bring your rails in 26 in from the walls. The bridge can be a single member if you have your wheels spread to disperse the weight on multiple joists. The wheels should be spread as much as possible to stop the bridge from skewing as you travel.
Are you going to make similar to barn door track from the 3x4 tubing?
Here is one of two I have in my shop to cover the 24 foot width. Think its 3 in I beam I used for the rails with lag bolts going through the top flange into the joists. Was a while ago I designed it but think it was 7 or 8 hundred pounds safe load with a factor of safety of 2 based on the holding power of the lag bolts. The bridge is way over rated to that, the thought being I could block the ends off the rail if I needed to lift something heavier. Could take some more photo's and measurements if you'd like.
Free advice is worth exactly what you payed for it.
Greg
Greg