Trimming out a curved steel framed stair

[Keith Mathewson]

This will be old news to some and certainly not in Jim's league but I have been tasked with trimming out a stair which for reasons known only to the architect was spec'ed to have hidden steel stringers. It was further compounded by sheetrock applied to the outside of both stringers. While the balcony was pretty straight forward the stringers required that the skirt be pre-formed because the structure is steel and I don't know how the sheetrock was adhered and I didn't want to rely on a bond to the sheetrock. I chose to use vacuum bags to form nearly all the parts.

Since a convex surface is easier to form to than a concave surface, on the balcony I made form supports which were offset by the thickness of the balcony skirt, this allowed for the forming to be applied to a convex surface. Yellow glue was used and some springback was expected, this made it easier to attach the finished skirt to the balcony.

Here are some pics of the progress.

[dave_k]

That's a fairly common scenario for our carpenters although typically we have steel pan treads filled with concrete. The reason being a stair is usually a means of egress so the BC's don't allow wood structured stairs in most commercial occupancies. I loath doing them myself, there is always a lot of fitting and dealing with inconsistancies in the concrete and welds .... . They are difficult jobs to put a number to and always take longer than estimated.

That does look like an interesting and difficult project. I hope you continue posting on this as the job progresses

[markhoni]

I did a straight steel framed stairwell, with welded in steel pan open treads. Al the treads and stringers had to be wrapped in hard maple. The inside stringer covers were the worst problem. They had to be cut, the treads cut out, then ripped in half and rejoined in place, after refitting the covers to final fit. It was a big pain in the you know what, and all I heard the whole time I was working on it from the guys I subbed it from was, "We thought ths would go a lot faster." I said, "BS. You guys couldn't figure out how to do it, so you had to call someone in that was smarter than you."

[Gary Katz]

Excellent use of vacuum bags, Keith! Thank you for posting that! I haven't used mine yet, but I'm looking forward to having that tool available when I need it.


And ditto Dave K. Please keep posting your progress.

[Gotstairs]

Hey Keith , Can you give us some more info on the bags and your pump, I would like to look into it. That looks like a pretty hot set up you have going there. I would be excited to try it here back East.

Steve

[Keith Mathewson]

Steve,

Here is a pic of my vacuum pump setup. It is cobbled together but it works well for me. The concept and most of the components came from "Joe Woodworkers" website, with a few changes. It is in essence an air compressor in reverse. Once it draws the desired amount of vacuum it shuts off and comes back on when vacuum drops below a given point.

What I did differently than what is described on the website is to get a better vacuum regulator and I added a second pump to the system. With a second pump a second bag can be pulled down while the first bag is hooked to the system and then the pump hooked back in tandem with the main pump.

The other thing is to buy a 30 mil bag from Quality Vak that is sealed and not glued together with HH-66. The difference is tremendous and worth every dime Ed charges for the service. I now have one bag that works very well and one that at has least one small hole I can't find.

When doing the glue-ups I have a few 2' wide cheap stands and on it is placed 2' wide pieces of 3/4" plywood. It is easy to setup and you can extend to 24' quickly. To contain the glue, by that I mean not getting a drop anywhere, I use a painters taping machine which puts tape on the edge of plastic and folds out to 4' and a hand-held glue spreader. I tape the plastic directly to the plywood and then layout the plys. For skirts/stringers glue is applied to one layer stacked, glue applied, stacked, etc. and then wrapped with the plastic. For caps/balcony starter the plys are shingled out and glue applied all at once. Remember to leave on out or you will have glue on the outside ply. Again everything is bundled in the plastic and then wrapped with stretch wrap.

I get the breather mesh from Lamination Tech and use spray glue applied to the plastic to keep it in place while sliding into the bag.

I've found this approach to be very clean and efficient way to do bent laminations.

[tjbnwi]

To find the hole in your bag, dump some baby powder in it close it up and squeeze. There will be a puff of powder from the hole. That is how we checked saftey suits when we had to enter a live 14.4 electrical vault. A hole in one of those could make for a bad day.

Tom