long shaft design
long shaft design
(OP)
I’m trying to design a 20-foot shaft to roll up 100 feet of tarp. The shaft would be simply supported on two pillow block bearings. For a bare bones budget the shaft would be hand cranked (very low use ~ 60-80 rpm’s and used maybe once a day).
For a preliminary design I came up with a (SCH 40) 2.5-inch steel pipe with a 10-inch PVC pipe on the outside. The PVC pipe would be bolted to (QTY-3) 1-inch steel flanges (cut out to reduce weight).
My concern is (based on a fixed-simply supported beam calculation) the pillow block bearings would be taking moment loads of around 730 in-#’s along with a 150 # normal force.
Should I be looking at a different type of support like a loose fit pipe hanger wrapped with Teflon or Delrin? Timken makes a spherical (4 bolted) pillow block bearing which could probably handle these loads but would be too expensive for this application.
Any advice on long shaft design would be appreciated.
For a preliminary design I came up with a (SCH 40) 2.5-inch steel pipe with a 10-inch PVC pipe on the outside. The PVC pipe would be bolted to (QTY-3) 1-inch steel flanges (cut out to reduce weight).
My concern is (based on a fixed-simply supported beam calculation) the pillow block bearings would be taking moment loads of around 730 in-#’s along with a 150 # normal force.
Should I be looking at a different type of support like a loose fit pipe hanger wrapped with Teflon or Delrin? Timken makes a spherical (4 bolted) pillow block bearing which could probably handle these loads but would be too expensive for this application.
Any advice on long shaft design would be appreciated.





RE: long shaft design
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: long shaft design
RE: long shaft design
RE: long shaft design
RE: long shaft design
RE: long shaft design
I would suggest that you simply support the ~300#? load of tarp and 20 ft. x 10" dia. PVC by the ends for a few weeks to assure that you are not going to get some sag and permanent deformation in the PVC. I am always suspicious of using PVC for structure. Otherwise, you may end up really needing the 2HP that Greg calculated.
RE: long shaft design
Barry1961
RE: long shaft design
Thank you all for the advice!
Any ideas on the shaft design?
I figured it has to be roughly 21-feet long (20 feet for the tarp (standard length) + around a foot for bearing supports, etc...).
Most pipe comes in 20-foot lengths max. stiffness/weight should be maximized. The shaft may be hand cranked so the amount of revolutions should be kept to a minimum. An option in the future may be to add a motor or gearing.
Any ideas are appreciated.
RE: long shaft design
My reccomendation, should it be plausible would be to make your spindle at least 4 inches in diameter, and consider your material options more carefully, since your proposed aspect ratio seems to be deflection prone no matter the application. were it me i think i'd be happy with the standard 20ft length with pieces that can be turned, attached at the ends. This would allow you to explore bearing options.