I am building a back yard horizontal bar (think one gymnastics bar) for my daughter to break her neck on. I'm wondering about the strength of my design and thought I'd ask for your input.
My design: I will cement two ten foot 4"x6" PT posts in the ground 4 feet deep (I live in Maine and this is a good frost depth). I will then secure an 8 foot section of 1 1/2inch black pipe (think steel pipe) to these posts by attaching a flange to each threaded end of the pipe. The flange has four holes for screws. Instead of using screws, I will drill through the 4"x6" and use carraige bolts to through-bolt the flange/pipe to the posts at either end of the pipe.
My concerns: The flange only seems to thread onto the black pipe about 1/2 way through the flange (approximately 1/4" - 3/8" into the fitting). Is this enough to hold over the long haul? No matter how much tension I put on the fitting to get it to screw on further, it will not budge. Also, the four holes in the flange that I will attach by through-bolting into the 4"x6" posts will only accept a carraige bolt that is 5/16". I've chosen galvanized carraige bolts in this diameter. Will four at either end have sufficient shear strenght to keep the pipe from breaking free?
Thanks much for any insight or additional ideas you can offer -- either about the design or the strength of the attachments.