radioman
Super Member
Thats good to hear that the issues I thought might be there, you got it covered. Keep on building. :thumbsup:
BX25 Full Cage Rollbar
- Thread starter Artisan
- Start date
- Views: 67370
-
- Tags
- kubota bx25
Artisan, it looks like they are held together with tabs and slots. I caution you that when working with metal this a failure point. You should never design a structural member this way. I think you'll be ok this time but don't do it in the future. It's like nicking a candy bar wrapper to make it easier to open.
It is tempting to do though
It is tempting to do though
Like I said, that pic is "pre" welding as in nothing is welded yet.
Once it is welded it will all be one piece. No tab or slot is bearing.
tabs and slots are simply for assembly alignment purposes alone..
There won't even be need to weld the tabs and slots although I will
have it done to keep water out. Everything will be uniwelded, inside
and out. This will support not just the required 8.5 times pressure
over static weight but I would venture to say 12 times. No problemo's
If the tractor weighs 3600 x 8.5 = 30,600lbs. Thats like 1.5 times the weight
of my work truck. This will support that I am sure when welded up tight.
I "think" i am close to ISO standards for FOPS. Will I be sending my cage
out for certification? Nope...it's a sunshade!
Once it is welded it will all be one piece. No tab or slot is bearing.
tabs and slots are simply for assembly alignment purposes alone..
There won't even be need to weld the tabs and slots although I will
have it done to keep water out. Everything will be uniwelded, inside
and out. This will support not just the required 8.5 times pressure
over static weight but I would venture to say 12 times. No problemo's
If the tractor weighs 3600 x 8.5 = 30,600lbs. Thats like 1.5 times the weight
of my work truck. This will support that I am sure when welded up tight.
I "think" i am close to ISO standards for FOPS. Will I be sending my cage
out for certification? Nope...it's a sunshade!
Assuming an ideal pinned column buckling case for 1.75" OD tubing with 1.51" ID, the buckling load of a 60" member made from mild steel is 16,860 psi. This translates to a total static load on the end of the tubing pointing straight down of 10,352 pounds force.
This is a rough estimate, as any holes, cracks, or side loading will rapidly decrease the load it can support.
For these calculations, i'd use a factor of safety of two, and assume the rear rops will be able to support the recommended 8.5x static load without deflecting much, so your cage might be able to support a total of 10,352 pounds on the front edge if the supports are completely vertical.
In reality, I wouldn't worry about it. This is a rough number. If you put a cross member between the two tubes that goes over the front hood, like most FOPS do, you've just about doubled their buckling strength.
Here's a good demonstration of what's happening: http://en.wikipedia.org/wiki/File:Buckledmodel.JPG
http://en.wikipedia.org/wiki/Buckling
As you can see, a fixed joint will have over twice the strength of a pinned one. I know you are using fixed joints, so you could almost say that your failure load is around 20000 lbs
This is a rough estimate, as any holes, cracks, or side loading will rapidly decrease the load it can support.
For these calculations, i'd use a factor of safety of two, and assume the rear rops will be able to support the recommended 8.5x static load without deflecting much, so your cage might be able to support a total of 10,352 pounds on the front edge if the supports are completely vertical.
In reality, I wouldn't worry about it. This is a rough number. If you put a cross member between the two tubes that goes over the front hood, like most FOPS do, you've just about doubled their buckling strength.
Here's a good demonstration of what's happening: http://en.wikipedia.org/wiki/File:Buckledmodel.JPG
http://en.wikipedia.org/wiki/Buckling
As you can see, a fixed joint will have over twice the strength of a pinned one. I know you are using fixed joints, so you could almost say that your failure load is around 20000 lbs
Last edited:
Well....I don't quite understand it but OK!
yes there will be a horizontal bar or few here and there
and maybe a "X" member as well. I have a set of dimple dies
as well so I will make some functional gussets on the bar at
it's bends too. I think i will be A-OK when done and I'll
say it again, I am betting my life on it.
yes there will be a horizontal bar or few here and there
and maybe a "X" member as well. I have a set of dimple dies
as well so I will make some functional gussets on the bar at
it's bends too. I think i will be A-OK when done and I'll
say it again, I am betting my life on it.
The tabs don't stick through the slots far enough to twist or fold over to hold it together! That's how all my metal toys were held together back in the good old days.
Bruce
The reason you want to avoid tabs and cut out text is because even on a welded object stress concentrations will still be there. The concentration factors for simple shapes are easily found in charts such as these:
http://www.mae.ncsu.edu/courses/mae316/eischen/docs/Appendix_C.pdf
Unfortunately its much harder to estimate with a complex part but I can assure you that you have reduced the number of load cycles to failure even though your parts are welded. Being located near the center of the part and being loaded in compression helps tremendously but I just want you to know it is a bad practice. This part should be fine but you may have problems in the future with other parts that employ this technique. If you must do this place circles centered over the corners so that you don't have any sharp corners. Nature designs skeletons without sharp corners for a reason. I'm not trying to nag, just inform.
http://www.mae.ncsu.edu/courses/mae316/eischen/docs/Appendix_C.pdf
Unfortunately its much harder to estimate with a complex part but I can assure you that you have reduced the number of load cycles to failure even though your parts are welded. Being located near the center of the part and being loaded in compression helps tremendously but I just want you to know it is a bad practice. This part should be fine but you may have problems in the future with other parts that employ this technique. If you must do this place circles centered over the corners so that you don't have any sharp corners. Nature designs skeletons without sharp corners for a reason. I'm not trying to nag, just inform.
Here are some similar links:
