Using steel wires to stiffen cube style printer

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Requirements:
  - 2mm steel wire - depends on the size of the printer, take hypotenuse between corners, 
    multiply by 4 and then by number of faces typically 4, should be more than enough - 
    1mm proooobably would suffice but I opted for stronger one. Don't go beyond 2mm there's little to no point

    Everything else is for 2mm wire so if you go with another size, god help you.
    
  - M5 turnbuckle - two per face - roughly matches the working force of 2mm steel wire
  
  - 2mm thimble - one or two per run so two or 4 per face, I went with 1 per run
  
  - mounting - this may wary, but you need some way to attach the steel wire and turnbuckle so don't pick something too wide. 
    I've went with square corner brackets/blocks whatever it's called. Thimble has to be able to attach to it 
    as well so keep that in mind, also keep in mind that it cannot be weaker than aluminium to which it attaches, 
    so no, it can't be 3d printed.
    
  - Crimp tool
  
  - 2mm barrel sleeve - they often come as a kit, crimp tool, barrel sleeve and thimbles, 
    sometimes 1-4 turnbuckles (we need more)
  
Theory:

So this is mostly for wireframe cube style printer, where you have aluminium extrusions going on edges of a cube. 
That is very weak construction and there's a reason why nobody does it that way. If you push on the top part, 
it will bend the vertical columns and top part will move compared to bottom part, aka it will wobble. 
That's the reason why your cupboards have board on the back, so that 3 out of 4 vertical faces have solid wall 
preventing lateral movement. Now you could do that with printer, add panels on 4 faces, it works and is fine for printer. 
But we're going step further.

With panels there's still small amount of wobble left, where when you push on top part, 
it can move right up until the forces put the panel in tension, 
when the panel will start resisting movement with enough force. We can eliminate that by pre-tensioning the structure. 
That way there will be no amount ov movement allowed because it's already at that point where 
there's enough tension to prevent movement. That's the goal of tensioning wires. 
Now you can either pull corners together or push them apart, both put it in tension, but pulling is easier to do.

How to:

Now I'll assume you have prepared the way to mount the turnbuckle and steel wire, 
by either mounting blocks in 4 corners on every face as I did (almost) or manufacturing corner brackets or 
whatever your mind will come up with, you do you, there are million ways to solve this and it's so simple 
I won't cover it and you have exmaple anyway.

Now with crip tool in one hand and steel wire in another, first we need to cut template amount of steel wire required. 
Attach turnbuckle at one corner and extend it to the max. Now roughly cut 1.5x the distance from the turnbuckle 
to the other corner, shuold be enough, don't be afraid to mess it up you can always cut more, I messed my first run. 
Now that you have this template, cut same distance again (so that you still have template) and then 
we shall proceed to making first run.

First put 2 barrel sleeves on the wire, loop it through the corner mounting, then put it into single barrel sleeve 
that's already on the wire and closer to the loop. Then make the loop smaller, minimze extra wire and when it looks nice, 
proceed to crip it. Now also add the timble and put the loop on the thimble (thimble protects wire against rubbing). 
Now loop the wire through closed part of thimble and through the barrel sleeve and make it smaller, 
make sure there's no slack (it doesn't have to be ultra tight and tensioned as we'll tension it later 
just make sure it's not super loose) and crip it. You can cut the excess off.

Voila! Now repeat that 15 times and have fun.

Now that you're back (well done!) we need to tension it. Beware that using these, 
you can make the printer more (or less) square if tension is uneven. It might seem like you made the printer uneven 
when you're in the process, don't worry, first finish tensioning everything, after which it should be back to being okay. 
Now I've tensioned everything to be figner tight, basically grab the part of turnbuckle that has wire attached to it 
and turn the middle part right until you can't anymore (don't force it, if it's difficult to rotate it should be enuogh). 
In this way it doesn't put much force but it's nice and in tension. You can tension it more using tools but 
you have to keep in mind weakness of aluminium and everything else in the chain so just watch out. 
For me just doing it finger tight provided massive results.

Watch out for wires rubbing against the steel wires, they're quite rough and with time could easliy rub through insulation.

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