I thought I might branch out a bit from the techno-babble and do a little home repair info on this post...
I live in a house that like many others has a wooden folding attic stair case. This is great as it gives me access to store junk away in the attic and it folds up almost unseen into the ceiling- but when they start acting funny they can become a real bitch. An attic staircase could also be considered a 'gadget' by some, so here we go...
My attic staircase was gradually making it impossible for to pull the stairs down without use of a step ladder and a pry bar. In a normal folding attic staircase, there are folding metal bars on either side that act as both as a hinge and a support for the assembly (the piano hinge at the end of the staircase does almost nothing for support- as I discovered when working on this project). In my situation, the rivet hinge on the left side of the assembly was wearing out and allowing the arms to distort and bend inwards to 'grab' the stairs before they could properly open:
Initially the weight of the stairs would cause them to fall free from between the arms with a good tug (and a loud noise), but after a few more months it had progressed to the point where I had to manually guide the staircase arms with a pry bar just to open the attic.
I finally gave up last weekend and decided to fix it.
The first thing I had to do was identify and remove the arm that is causing the problem. The left arm was the main culprit and this was obvious as it was pretty badly bent; additionally the hinge rivet on this side had a great deal of play. The right arm has a little play as well, but it doesn't seem to be causing any problems (yet).
I removed the spring tension from the left arm by removing the nut from the side of the staircase, partially closing the stairs and then pulling the arm off of the bolt:
Once the end of the arm was free, I pulled the staircase down, removed the spring at the top (it unhooks easily as there is no tension) and worked on removing the arm from the staircase framing.
NOTE: if you need to climb on the staircase at this point, be sure that you stand will all weight on the right side as there is nothing supporting the left side!
The hinge assembly is attached to the stairs by two rivets through a metal flange anchored into the 1/2" wood of the staircase framing. I removed these by grinding off the flaring with a 3/8" metal drill bit:
The back of this rivets are not secured, so I needed leverage from a pry bar to keep them from spinning while drilling out the exposed side.
When this was done I had the left stair arm in-hand. There were obvious bends in the metal so I used a bench vise to flatten these out.
I took the arm to Lowe's to see if they had a replacement, but no luck (maybe Home Depot carries such items?). Since this was not available, I used the arm as a sizing guide fro the replacement bolts I would need. I decided on 1/4" lag bolts to attach the frame and a 5/16" hex bolt to replace the upper hinge rivet.
Once back home, a 1/2" metal drill bit was sufficient to drill out the back-side of the rivet hinge- while being careful not to damage the metal plate or the arm while grinding off the end of the rivet.
Re-assembly was fairly easy (compared to removal):
Step 1: replace the rivet hinge
A 5/16" x 1-1/4" grade 8 fine thread hex bolt is used to replace the primary rivet hinge. I probably really don't need a grade 8 bolt (they are a bit harder metal than the standard grade 5 bolts) but it was only about $0.40 more than the standard- and I am all for overkill.
The bolt goes into the mounting plate and projects the thread end out for the arm to pivot on. I used a 5/16" lock washer and a few flat washers between the bolt head and the inside of the mounting flange. The washers are for spacing (1-1/4" is a bit too long- by design) and to push the head of the bolt into the wood- preventing it from turning once the lag bolts are installed (next step).
To allow the bolt to act as a hinge, I put additional 5/16" flat washers on either side of the arm and closed the assembly off with a 5/16" locknut. The locknut is very important as a normal nut will eventually loosen from the opening/closing of the stairs.
Step 2: Re-attach the arm to the staircase.
I drilled pilot holes and installed four 1/4" x 3" lag screws with flat washers to replace the rivets that were removed. Initially there were only two rivets holding the arm in place, but- as stated before- I am all for overkill with these kind of projects.
Depending on the material behind your staircase you may need longer bolts; in my house there is a 1-3/4" LVL beam to either side of the staircase and 3" is an ideal length:
Step 3: re-attach the spring
This part will require to people as it is practically impossible to re-attach the arm to the stairs with the stairs down.
Connect the upper spring assembly to the top of the stairs (i.e. re-hook the spring onto the J-bolt on the end of the arm and go into the attic and have someone close the stairs behind you. They may need to use a step-ladder to lift and support the stairs as it will not want to stay closed with only 1/2 the spring tension it normally had.
While in the attic, re-connect the side of the arm to the bolt on the lower section of the stairs, tighten the nut down and you are done! (as long as your helper will oblige by pulling the stairs down so you can get out out of the attic).
I keep a small ratchet set in the attic to check that the bolt isn't coming loose....