Building the Mirror Blaze in Pictures IV: How do you Make Posts Withstand a Windstorm?

Last time, we showed our first integration test of the mirrors for Mirror Blaze. Later, we would test out the ‘Blaze’ (flame effect) part.

But in the meantime, we had to figure out the solution to a different vexing problem. There was a list of constraints we were designing for:
– Make a mirror maze
– Large enough for the public to walk through
– Large enough to feel like they’re getting lost
– Small enough (or with enough escape hatches) that they can get out quickly if something goes wrong
– Tall enough that people feel like they are completely inside and cannot escape that way
– Able to withstand alkali playa dust for a week
– Able to withstand 4 hours * 7 days of intermittent flame effect firing
– Inexpensive enough that we could afford it
– Able to withstand a 90km/h windstorm

It was this last constraint that vexed us the most. I had calculated that the wind force could reach something like a ton, but we didn’t want to go with the obvious guywire solution, because they would need to stick out for meters in all directions, and we’d be constantly tripping over them[1].

So, with this in mind, we returned to Home Hardware (New Canadians Lumber, really friendly and helpful people, we recommend them).

We looked at a number of different options for holding the posts in place. The one below was the most expensive option (They were about $15-20 each, IIRC), and I couldn’t imagine how back-breakingly difficult it would be to remove them from the ground when we were done. (Also, how would the mirrors fit around them, at the base? And, how would they stand up to wind? Would they bend up out of the hole?)

We kept coming back to this style of post holder.  What kept stopping us was the idea of trying to remove them from the ground when we were done, how we would attach the posts, and how horrifically expensive they were.

Some other options were not much better:

An even more expensive post holder?
An even more expensive post holder?
This would work fine, if you could simply bolt things to playa.
This would work fine, if you could simply bolt things to playa.

But we kept coming back to this one:

Feels almost like the right idea...
Feels almost like the right idea…
Just not quite deep enough, but if it was...?
Just not quite deep enough, but if it was…?

It felt mostly like the correct shape, if only we could make the rebar longer, and better connect it to the post… (We had been told that for proper securing against a 90 km/h windstorm, you want your rebar to be 1-2′ into playa. We also knew that would torque the posts around a small connector like that something fierce.)

Then it hit us[2]! Just drill the rebar into the center of the post! Brilliant! All we needed was a 12-18″ drill bit[3]. It was time to go and test!

But first, we needed to go purchase some 1/2″ rebar:

I enjoyed this sign every time I saw it.
I enjoyed this sign every time I saw it.

Welding, or un-welding, the sparks are always impressive:

Rebar purchase is exciting!
Rebar purchase is exciting!

Then it was time for drilling[4]:

Mel and Geoff help S drill a post.
Mel and Geoff help S drill a post.

We managed to wear out more than one of the 18″[5] spade bits. Sawdust jam was frequent, even with the corded drill. (I can’t imagine doing this particular job with a cordless.):

We wore out a number of drill bits during this project.  Note the sawdust, and that this was an 18" bit.  (And that we used a 5/8" bit to drill out a hole for 1/2" rebar.)
We wore out a number of drill bits during this project. Note the sawdust, and that this was an 18″ bit. (And that we used a 5/8″ bit to drill out a hole for 1/2″ rebar.)

And success! Here is the finished post:

Note my classy protective gloves.
Note my classy protective gloves.

And here it is, freestanding, showing that we could put them up using only rebar, and no guywires[6]!

"So, how'd you end up as a post?"  "Ssh!  I'm trying to hold my balance for rebar monthly!"
“So, how’d you end up as a post?” “Ssh! I’m trying to hold my balance for rebar monthly!”

Tune in next time, for when we go into production, and a wide and varied cast of characters literally come out of the woodwork to help. Stay tuned!

[1]And they look terrible.

[2]I honestly don’t remember where this idea came from. We had been asking people this question for months. It might have been one of the kind gentlemen at New Canadian. (I really cannot recommend them enough.)

[3]Spade bit, but we’ll cover that later.

[4]This is actually a picture from much later, in our production process, but I couldn’t find any from the prototyping stage.

[5]18″ or 24″, I can’t recall.

[6]Well, we would also need top wind-bracing, but that’s a story for another time.

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