If you build things, squares are a must have tool. What if, instead of checking if your works is dead square, clamping it directly to a square for a good result : first time, any time ?
You can't always find Clamp It Squares in your local store. Especially in Europe. And if you finally find some, serious models will cost you about 10 bucks each !
The Clamp It Squares I designed are actually available in three sizes : Large, Midi and Mini. They will be useful in various kind of jobs, from light DIY jobs to serious furniture making.
One last advice : don't over-tight the clamps, as the job is well done, no joinery needs extra pressure.
Edit : Added a new size : the Clamp It Square Mini, for smallest jobs, expecialy designed for spring clamps.
Edit : If you're looking for holders for your clamping squares, I recommend Gromax's holder for midi size: https://www.thingiverse.com/thing:3135812
Edit : added a beefy version of the Clamp It Square mini, by onlytobeking.
Use preferabily strong and stiff material, like ABS, PETG or PC. Don't use flexible filaments like Nylon ones, because you won't be able to maintain a trustable squareness. PLA is possible, but be aware PLA can explode without warnings when overtighted if the part have a low rate infill. My large Clamp It Square are made out PLA, 100% inflill with no issue.
My advice, don't be cheap with infill : think life time tool.
Edit : the Clamp It Square Mini size will probably don't need to stand high pressure. Otherhand, stick to at last 50% infill to be sure it stays in shape.
Prevent work pieces marking !
Depending of your printer's accuracy, you may print artefacts and sharp corners. Look forward any print problem on the sides which can mark your clamped parts, and do a little deburring.
Life time tool wanted !
To me a tool must be trustable, first time, any time. I did a bunch of prototypes to get the right shape. Actualy the Clamp It Squares uses less material possible and allows any clamp shape to be used :
I added a special feature. Someday you may want to apply extra pressure to the corner itself. Instead of needing another tool, I changed the shape to allow to secure a corner between two squares, with a single clamp. That clam won't need a huge amount of pressure, so I limited it to 28m (more than 1"). See below an exemple of clamping process. Believe me, that parts are not going anywhere.
Mini size added !
The Clamp It Square Mini is for smallest jobs
It's expecialy designed for spring clamps.