What can Donald Rumsfeld teach us about prototype development?

I occasionally work with a student-led group working on an innovative building project.  The project involves building a small home on top of a custom steel trailer frame.  Recently the trailer frame manufacturer delivered the first of several trailer frames, and word came around that the frame was out of square by about 9/16".

While not a total disaster, it is not a fixable problem; the frame is too stout and too large to attempt straightening it.  The problem with an out-of-square frame is that the rest of the house must be built on top of the frame, and it's important that the house itself be square.  Building a square house on a non-square frame is definitely doable, but it would've been significantly easier had the trailer frame been squarer.

I made some inquiries as to how the error occurred.  Apparently, in drawing up the specification for the trailer frame, the team had simply not thought to specify a squareness.  It would've taken seconds to add that specification.  Doing so might have avoided many hours of re-design or re-work.  Whoever wrote up the specification seems to have done a fine job otherwise.  They simply didn't think of specifying a squareness.  It was an unknown unknown.

Call it the Donald Rumsfeld problem.  As Rummy famously said in discussing WMDs in Iraq,
[T]here are known knowns; there are things we know we know.
We also know there are known unknowns; that is to say we know there are some things we do not know.
But there are also unknown unknowns – the ones we don't know we don't know.

In WMDs and in developing prototypes, even just one unknown unknown can be a doozy.

The trick with prototype development is to maximize the known knowns and minimize the unknown unknowns.  Easier said than done.  Every time I go through the process, I get a little better at spotting the unknowns.

In my current capacity as Resident Metalworking Geek, I'm sometimes approached by colleagues and students about building things.  The first conversation is often an interesting one.  Often the "client" is thinking of all the exciting possibilities, while I'm simultaneously trying to anticipate everything that might go wrong.  I'm not trying to crush dreams (although it probably feels that way); I'm trying to keep the dream alive long-term by anticipating the unknowns.

Summary of Fluxes and Fillers for Brass and Silver Brazing

I compiled the following for my welding teacher here in Boone, NC, Steve Ward.  Steve's taught me a lot about all kinds of welding & fabrication.  He teaches a little brazing with flux-coated low-fuming bronze rods.  He's the kind of guy who's always looking for the best tools and supplies, so I compiled this summary of the brazing supplies I've used and heard of, so he can order some of the really nice stuff in the future.

These are but the humble opinions of one brazing nerd.  Please comment freely.

Brass brazing flux:
- The blue flux I have is Gasflux brand Type B.  Excellent stuff.  I have bought small quantities (1-2 lbs) in the past year+ directly from Gasflux, but was told during my last order that that would no longer be possible and that I should order from an Airgas dealer in the future.  Details here: http://www.gasflux.com/paste.html
- If that's not an option, there is some even more obscure stuff called Brazage LFB Light flux, produced and sold by a bike framebuilding old-timer, Freddy Parr.  Freddy's stuff is well-regarded by some of the big names in the bike building world.  I've not used it, but I expect it is superb, based on his silver flux:  http://www.cycledesignusa.com/lfblight.htm

Brass brazing fillers:
I like 3/32" diameter best but 1/16" is fine for many things, and gives you more rods per lb.
- The stuff I like best if Gasflux C-04 nickel bronze.  This stuff flows much better than anything I've ever used, especially on stainless.  $9/lb for my last order, which was over a year ago.  Again, I've bought 1 or 2 lb quantities from Gasflux directly, but was directed to Airgas last time.  http://www.gasflux.com/brazing.html
- All-State 11 nickel silver.  I've used several pounds of this, unfortunately in 18" lengths.  They were samples that sat in the back room of a welding store in Richmond for years until I called up asking about brazing rod and someone offered me them for free.  They were flux-coated but the flux was stale so I soaked most of it off.  Very strong stuff, 85 kpsi, but a little less fluid than low-fuming bronze, and harder to file/machine post-braze. Makes small fillets.  http://www.esabna.com/euweb/as_handbook/596as5_2.htm Here it is for sale from Airgas: http://airgas.com/browse/productDetail.aspx?Category=10&product=ESA69063020
- Again, Freddy Parr offers a rod that is presumably excellent: http://www.cycledesignusa.com/brazage_lfb.htm
- Bare low-fuming bronze (LFB).  Any welding store should be able to order some.  Harris or whatever brand they have should be fine.  LFB may not be as consistent quality-wise or as quick to wet out as some of the higher-end stuff, but it gets the job done nicely in the right hands.  I've seen some beautiful fillets laid down with plain LFB.

Silver brazing flux:
- Hands-down the best I've ever used is Stainless Light from Freddy Parr.  Protects beautifully and washes off quickly.  This is the grey flux that inspired my friends & I to start mixing fluxes: http://www.cycledesignusa.com/stainlesslight.htm
- Harris Stay-Silv white flux and black flux.  These are the workhorses of silver brazing fluxes.  It's easier to see what's happening with the white flux, but the black flux remains effective at temperatures 200 F hotter, so is more tolerant of overheating. http://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Fluxes/Stay-Silv-White-Flux.aspx and http://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Fluxes/Stay-Silv-Black-Flux.aspx
- Gasflux Type U white flux and Type H black flux.  This is good stuff, but I haven't used it in a while.  From what I remember, the Gasflux washes off faster than the equivalent Harris, but it's also harder to buy.  http://www.gasflux.com/paste.html
- Mixing white and black flux is pretty straightforward.  Once you've added water to both your white and black fluxes to make them into pastes, spoon some of each into a baby food jar.  We've had good luck with something like 3 parts white to 1 part black, but it's not super critical.  Adding more black flux will make it more opaque but more resistant to higher temps.

Silver brazing fillers:
- 56% silver is the "runniest" and most expensive of the silver fillers mentioned here.  Requires tight fitups, but goes liquid at low temps.  It'll join steel to stainless if everything is squeaky clean and the heat is just right.  50N is a better choice for stainless if those conditions can't be met consistently.
- 50N has higher nickel content, which enables it to wet out onto stainless really well.  From what I remember it has about the same "runniness" as 45%.
- 45% works best with relatively loose fitups.  Brazing temps are slightly higher than 56%, and it's noticeably less runny.  Never tried it on stainless.
- I've only used Harris brand silver fillers, and always been satisfied.