[Interhouse] - Stairs 2018

October 22, 2018

Overview:

The bow stairs prior to painting. Photo credit: Ethan Jaszewski

Blacker's 2018 interhouse featured 5 staircases, all cut and assembled fresh for this year's platform. We made 48” staircases running from the lower platform to the upper platform, and one 53.75” staircase running from the ground to the lower platform. All five staircase units were structurally self-contained units, bolted onto the main platform. The 53.75" module was constructed relatively early on to aid with general platform construction and allow viewing platform access during PFW. The four 48" units, although nominally freestanding, were assembled in place so they could be adjusted to the real gap between the upper and lower platforms.

Our overall assembly time ran about 16 student-hours per unit, with efficiency peaking at three people for fabrication and four per staircase for assembly. Discounting costs associated with elevated construction, each unit had a real-world cost of 100$, with an expected amortized cost of 40$ and would have cost 150$ using all-new wood. More details about construction time and budgeting can be found below.

After helping rescue last year's debacle, my big focus this year was on establishing efficient fabrication practices, and using good documentation to parallelize construction. Although there's still a lot to work on next year, I was successful in cutting our assembly time by about 60% per staircase, while reducing the total unit cost by 30%. Having full mechanical drawings let students with a passing interest take over fabrication of a single component, and made it easier for more engaged students to get up to speed on the overall design.

My role:

I ran the project, managed the budget, procured the materials, created the cad, wrote the documentation, and oversaw the assembly. However, this is a strange project for me in that I did relatively little of the physical cutting and assembling of wood. Having a complete drawing packet meant that I could outsource most of the parts fabrication and focus on cutting stringers and teaching people how to use our tools.

General Fabrication:

With 5 staircases to produce, we focused on trying to produce as many of the parts as possible in batches. This was largely successful for the stringers, support posts, treads, and kick-plates. However, we found that irregularities in the platforms themselves necessitated custom fitting for the railings.

Stringers:

Stringers are always the most difficult part of a staircase to source and fabricate. Since we had fairly non-standard stair heights on this year’s interhouse I decided to fabricate the stringers from 2x12s instead of purchasing them ready-made. The appropriate mechanical drawing can be found at the end of each design packet (below). The generating cad is parametric in nature (along with the entire stairs assembly) and so easily accommodated our two different stair heights. That file can also be found below.

We experimented with two different types of stringer fabrication:

To begin with, 5 high quality stringers were fabricated as follows: a reference edge was cut onto each of several 2x12s. Then the critical points for that stringer were marked according to the drawings, and then connected to form the stair outline. The outline was then cut-out with a circular saw, placed against measured and clamped straight edges.
Once 5 high quality stringers had been fabricated, we picked the best 3 and used them as drawing templates for the remaining stringers. This removed the longest step (measuring and marking), and allowed us to quickly produce the bulk of our stringers. These stringers were cut either with clamped guides, or free-hand depending on the confidence and skill of the saw operator.

In both cases, we found it necessary to finish each cut with a hand saw, so as to ensure clean corners. This added about 5 minutes per stringer, but provided a 10% increase in strength relative to over-cutting with the circular saw. Likewise, we found that teams of 2 people were most efficient for both types of fabrication.

Reflection: Stringers cut free-hand using drawn templates were substantially less consistent than those produced directly from measurements. However, they were structurally equivalent and proved largely sufficient in practice. The 70% reduction in speed was more than worth having to throw out 2 wasted blanks.

Assembly:

Assembly went very well this year overall. I was able to train both our work-frosh to manage assembly groups. This fread me up to do the safety checks and help out where needed. We were generally able to keep two groups working at a time, and were largely limited by our clamp supply more than people or materials. The general process we used ran as follows:

Place, clamp, and bolt vertical alignment posts. Where possible these were bolted directly to the main platform supports with 1/2" bolts, but in some cases we used an additional 4x4 to act as an intermediary so the stair supports and platform supports could be placed corner to corner.
Clamp both outer stringers and drill the stringer to post bolt holes. Note: In the future I would recommend creating a drilling jig for this process. It was difficult for some participants to remember that consistent drilling is important for re-use.
Place the central stringer, and connect it with treads at the top and bottom of the stairs.
Continue up the stairs from bottom to top, placing treads. We used three 2x4 treads per stair, with all three pressed towards the outside of each stair. This left no gaps between treads, but a significant gap between the kickplate and treads. It was determined that this was better for students wearing heals.
Once the treads were all placed, they were then screwed down. We found this to be most efficient with two people (one per side).
This process was then repeated for the kickplates, placing them with the gap towards the top of the kickplate.
Finally, railings and railing supports were added. We cut these parts beforehand according to the CADs, but ended up needing to make some slight adjustments to account for the placement of the dance platforms.

Recommendation: Purchase an additional six 18" fast acting clamps before next year's interhouse season begins.

Documentation:

Mechanical Drawings (Short Stairs)
Mechanical Drawings (Tall Stairs)
CADs

[Interhouse] Stairs - 2017

August 28, 2017

Story:

I have always wanted to work on the interhouse stairs, and when stairs team ran into personnel issues (through no fault of their own) I got a wonderful chance to put together our front staircase on the night of the final safety inspection. The experience itself was rather surreal - the only other person avaliable to help had never worked on stairs either, but ultimatly succesful.

Documentation:

To hopefully make he build process a bit faster next year, included below, is my solidworks model of the staircase we actually ended up building. As of now, the only significant design change I would make, would be to use three stringers in place of the two stringers and the 4x4 supports. Although the latter option is stronger, and marginally cheaper using pre-made stringers, it is also much slower to build and significantly less elegant than the three-stringer build.

Model Files

Purchasing Note:

The home depot in Pasadena has expressed a willingness to loan us stringers for tracing as long as we also purchase the wood we use in the final project from them. Since we buy all of our wood from them regardless, that seems worth pursuing.

3d printed model:

One of the great things about having a CAD of interhouse is that it becomes easy to print 3D models of parts of the build. This is especially useful for projects like stairs that are a bit harder for new folks to visualize. With that in mind, I decided to print out the individual parts and glue them together to make a 1/20th scale model of last years staircase.

Build photos can be found below. Each stage was glued using CA glue with no kicker (to keep it clear), and then allowed to dry for 12 - 18 hours before the next glue stage. All parts are 1/20th scale.

[Interhouse] River - 2017

May 12, 2017

My guess is that if you are reading this then Blacker has decided to do a river for interhouse and you were foolish enough to volunteer (It's actually an easy project aside from the paperwork). This page outlines how we did the river for Blacker's 2017 "Japan Through Time" interhouse, but the design is modular, so you should be able to use it for whatever setup you want. For the pump system and waterfall I have included notes from our postmortom design review with things to watch out for or possible improvments that could be made to the system.

River Sections:

The river itself is composed out of 8ft sections (see right). Which can be built before hand and then raised to height and connected when needed. These units are intended to be single-interhouse and so emphasize cost over durability. That said, they should be good for a few short uses.

The assembly procedure we used for each 8ft section runs as follows:

Cut the two 6" lengths, two 4' lengths, two 22.5" lengths and the 18" by 8' plywood section.
Lay out two 2.x3s 18" apart (from outer edge to outer edge) and check that they are parallel (if bowed, place so the center bulges).
Put a continuous line of glue down each board (this acts as a last ditch sealant).
Place the plywood on the two boards and fix it in place with a screw at each corner. As far as we can tell it is safe not to drill pilot holes if the house is out of bits.
Add a screw and washer every 6-10 inches down both of the two 2x3s.
Measure 33 inches from opposite corners of the structure and secure the two 6" sections with two screws. It is important to drill pilot holes.
Connect one 4' sections to the main structure 36" inches in from the ends using a single screw. It is important to drill pilot holes.

At this point the structures can be moved into place, lifted, and then the legs can be fixed in place using an additional screw at their pivote points and two screws where they cross eachother. I find it also helps to add two braces connecting the sides. Once the structures are in place, make sure to use hot glue (or simiilar) to seal any remaining cracks. This is best done last since moving them will open up new leaks.

Note: During our post-party design review we determined that the seal between plywood and the 2x3s would be improved by the presence of a 1x3 underneath providing additional support. This board should be pre-bent so that it can be used to compress the plywood against the 2x3s. This should help prevent the small leaks that sprung up on 3 of the 4 sections we deployed. This design can be found in the V2 version of the uploaded documentation.

Unit Cost: 15$

Unit Time: 30 min

Materials:

[4.5] 2x3 soft wood.
[40] 1.5" Deck-Mate screws (go torques).
[5] 1cm diameter sticks of hot glue
[1/12] of a medium sized bottle of Elmers wood glue.
[1] 18in by 8ft section of thin plywood or press-board.

Documentation:

Water Reciculation

Water for the river is pulled from the catch basin, down a length of 3" pipe, and into the pump. It is then pushed up to the waterfall, where it runs out a series of holes drilled in the bottom of the pipe. It then falls down the waterfall, entering the river. The remaining water is then piped back to the collection basin to be re-circulated. Of particular note, the pump sits at the bottom of the waterfall structure and below the level of the water in/out takes. This allows the pump to be primed by poring water down the intake until it begins to overflow back into the basin.

By far the hardest part of this project was getting the pump system to play nice without giving party-goers an impromptu shower. The pump is significantly more powerful than we had anticipated, and left to it's own devices, was more than happy to project the waterfall a good 3-4ft beyond the catch basin that feeds the river. To lower the pressure, we ended up having to add another stretch of pipe returning unused water to the collection basin. This is clearly not the ideal solution, it would have been nice to pump that water into the river itself instead, but it did work and kept safety happy.

One thing to keep in mind is that the pressure on fittings after the pump seems to be much greater than on fittings before it. It is well worth clamping or gluing any right-angle fittings or the like on the water return run. On a similar note, it is worth watching the system for a bit after starting it up, because temperature effects from the cold water will change the fit of any press-fit fittings during the first 5 or so minutes of operation.

If you end up using one of the houses's large sump pumps it is worth thinking about how you are planning to prime the pump before building the system. In our case we found that placing the pump below the water intake level, and then not gluing one of the fittings so the intake can be trivially turned up and used to fill the lowest foot of the system was sufficient. However, what works will depend on how your system is constructed. The important thing is that you have a way to flush bubbles out of the path from the intake to the pump.

Notes:

3" pipe is much more expensive than 2". Make sure to do flow tests to determine which you need before purchasing your piping (3" is probably overkill).
Placing "spoilers" or some other mechanism to slow water passing over the holes should help increase flow.
Make sure the pump is below both the intake and the outtake to the system. That will make it much easier to prime.
Any fitting which changes the direction of water such that the flow pushes against it should be glued or clamped in pace.
Having at least one flexible fitting in each straight run to reduce the risk of cracking is well worth the extra cost.

Water Fall

After a bit of back and forth, we decided to start the river off at a waterfall and end with a catch basin (vs flat with recirculating water). That helped us hide the pump mechanism, and gave us an impressive backdrop to the left for folks entering the North Gate. Ultimately, we ended up building a platform, and then using a single contiguous piece of thin plywood to form the upper basin for the river. That worked reasonably well, but I'm not totally happy with the solution we came up with, so rather than post a detailed build log, I have included a few lessons/ideas that we picked up along the way below. In a similar vein, you will also find - below - notes from our post-project design review detailing how we think the the waterfall could be done best, and with as little pain as possible in the future.

The general design that we settled, more as the result of time than anything else, was an 8' by 8' by 4' frame made out of 4x4s and braced with 2x4s. We then used 2x4s of varying heights to bend a single sheet of 1/4" plywood so that it would direct water over the intended edge. The water itself was provided by a 3" pipe with holes drilled in the bottom. The waterfall overflowed into a 2' by 8' by 1' catch basin and from there into the river proper.

Notes: (Design Review)

Check the waterfall distance/behavior before building a catch basin for it, could be it needs to be larger than you expect.
Screw a line of 2x4s 3 '- 4' below the top of the platform where they can be used as scaffolding (a built in ladder is really nice as well).
Using an upper basin with the water spilling over a lip will help create a nice even sheet of water.
Creating the upper basin and structure desperately may make it easier to maintain the basin and keep it rigid.
Make sure the Calk you use is rated for water (oops) and that you finish early enough to let it dry for 2 days before the party.
Building a ladder and some scaffolding 2x4s to allow easy access to the entire structure (would recommend a single line running 4' below the top) would make maintenance and assembly much easier.

Notes: (During Construction)

Calk not hot glue!
The top of a tall structure like the water fall will flex enough to break wood to wood calk bonds when picked up and moved.
Black plastic can be pained, although it stops being waterproof if you use staples.
Plywood bends way way better when wet (soak for 2-4 hours in warm water).
Surface tension means that getting a uniform sheet of water from a flat surface is hard. If you need even distribution it can help to build a small lip and then cut channels through it.
Clear plastic drop cloth from home depot turns actually clear under water (whenever possible better than black plastic).
You can soak thin plywood sheets and then bend them to get continuous water tight surfaces as needed.
Water will stick to drop-cloth and adhere it to nearby surfaces, so if you have leaks you need to direct towards more productive destinations than the bricks, that can be a good way.
Most leaks don't really show up until the wood and plastic have had a chance to saturate. That takes around 20 minutes, but once that's take place they don't seem to get much worse until the wood starts to warp (by which time interhouse is hopefully over).

Pictures:

Because pictures are never a bad thing.