I have a crossfit gym in my garage. I had no way of doing back squats though, other than cleaning the weight and then jerking it over my head until it rested on my shoulders. I decided to build a squat rack 'hook' that fit over my pull up bar. The concept is placing a U-channel to fit over the pull up bar, welding some vertical risers to it, and then welding some angle iron at the appropriate height to rest the bar. It worked like a champ, as you can see from the finished picture.
Step 1: Step 1: Making the U-Channel
I didn't have any U-Channel iron laying around, but I did have two lengths of angle iron. I welded (brazed, really. I've only got an oxy-gas rig...) two pieces of angle together to make the U-Channel. Make sure that you make the channel wide enough to fit over the pullup bar. For my pullup bar, I used 1.5"(37mm) angle. I made it 44" long, my pull up bar is 48" wide.
Step 2: Step 2: Adding the Vertical Risers
Once the U-Channel is made, weld a vertical riser to each side. The riser has to be long enough to make up the height difference between 1)the pullup bar and 2)where the bar sits on your shoulders, plus 3 inches.
Step 3: Step 3: Adding the Bar 'hooks'
Take a small piece of angle, and weld it to the vertical risers at the right height. Ensure that 1)both legs of the angle are touching the vertical riser(the 'V' should be opening to the riser) and 2)the angle is on the 'inside' of the riser, directly beneath the opening of the U-channel
With the small pieces of angle in place, I then welded some 2" angle on top of it, so that the "V of this angle is facing up. One face of the small angle and one face of the bar hook are in full contact with each other. These are the channels that the bar is going to rest in. I made these pieces of angle 6" long.
Step 4: Finished!
At this point, the squat hook is done. Place it over the pull up bar, put your bar on the device, and squat your butt off!
A few notes....
-I used an oxy gas rig. Any welding method is suitable here.
-I'm not so worried about the pull up bar supporting the weight. I weigh 185lb(83kg). When I do pullups, I put more weight than that onto the pullup bar when I hit the bottom of my pullup. The pullup bar is rated to 600lb(272kg). I don't anticipate putting more than 315lb onto the squat rack.
-I didn't really give any dimensions to the vertical riser. This is a pretty custom squat rack, put the hooks where you need them. Just make sure that you put them on the risers low enough so that you don't have to stretch to get the bar back onto the rack!