When you do NOT have a 36 inch long  sanding bar
How do you square up a 1/16 sheet to join the edges
Fred Q

When you do NOT have a 36 inch long  sanding bar
How do you square up a 1/16 sheet to join the edges
Fred Q

   I don't have that, either. I use a 4' drywall straightedge, slap it down, take your sharp #1 exacto blade, and make one slice end to end, being careful to hold it upright. Under 5 seconds an edge. Over 1/16" it barely matters if it is perfectly square to the surface, so slight errors don't matter.

   To join it, first - **** clean any glue drips or bumps of any kind from your work surface ******  I use a cabinetmakers hand scraper to shave everything off level. This is of course to remove the chance of leaving dents in the wood. If you do get a few, hit them with water and an iron, unless the fibers are cut, it will pop right back out, but best to avoid them.

    Get a lot of cheap blue masking tape, the cheapest crepe-type is  ideal. Put the edges together on the bench and take a 3 inch or so strips of tape, and tape it together with some tension on the tape to push them together. This takes a bit of feel, because you can put too much tension on it, it just needs to be light. Put it across the joint about every 6" on one side. Flip it over, and then press it down with your finger, softly, to make sure the joint is lined up all the way from end to end. Then take a single long strip of tape and put it longways down the joint, centering it up, with no tension. Push it down so it sticks well.

    Flip it back over, remove the short strips, and open it up like a book, using the long continuous tape strip acts like a hinge. Fold it over flat, press it down to make a sharp crease. Bend  it back up until it is a right angle.  push one thin bead of glue on one side (Hot Stuff Super T or other medium CA highly recommended) right down the middle of the 1/16. Use the other side of the joint, the bare side, to guide the tip along the middle of the glued sheet. Work quickly, it takes me about 2-3 seconds to carefully apply a thin bead - not too much because you want little/no squeezout.

   Then close it up using the hinge, and immediately flatten it out with your hand on the work surface, and then apply a long strip down the entire length. Mostly this lets you put some pressure on it to make sure the surfaces slip back into alignment if they somehow moved, without getting too much glue on your fingers.  Then just move on to the next joint, repeat.

   Some people just grab a sanding block and lightly sand it rather than using the second tape strip, but that is dangerous because you might smear glue across the surface and that will be impossible to remove later without extraordinary effort.

    If you decide to use air-drying glue -which I find messier and unnecessary - then when you flatten it out, apply more strips across the joint to hold it flat. Too tight and you curl it one way or the other.

    Once you are done, remove the tape from both sides, and *very carefully scrape across it lengthwise to removed any glue balls that squeezed out*** remove any tape that might be glued to the sheet, and then vacuum everything clean again. If you try sanding it without doing this, any little ball will be rolled across the surface and make a disaster.

   Once you are sure all the glue-balls are gone, then sand it with 150 or so. Everything should be lined up so it shouldn't take much. Note that this is where you will transfer all the bumps on your table to the wood, so *be sure it is smooth* before you start.

    Brett

p.s. I like Hot Stuff "Super-T" for this rather than any of the others, like Zap-A-Gap, because Super-T takes longer to flash off and almost never goes off without being pressed together in a joint. That allows any misalignment in the sheets to slide back into alignment when you press on it instead of sticking hard as soon as you close it up.

  Also - when I am done, I take .055 music wire (for .062 nominal balsa), tape it to the workbench on either side of the sheet, then sand the whole thing with the rigid sanding block straddling the wires on either side. That makes sure I do not go thin on one side or the other and evens it up. Note that you have to use *very little* pressure because your "rigid" block is not all that rigid and you can scoop it out of the middle if you push too hard. I don't necessarily recommend that you try to get it to a constant .055 or whatever, just use it as a stop so you don't go thin anywhere.

I assume you have a flat work surface?

If you do not wish to outlay any money and you have a roll of sticky back sandpaper stick it to one edge of your work surface. Now you have a straight edge as long as you want!
If you only have sheet sandpaper you could cut it into lengths and glue it down, at a pinch, but not recommended!

Craig

The alternative also works - use the edge of the tabletop as a ruler. I use a 2x4 foot bit if plywood or melamine board from Lowe's, it has 4 straight and square edges. Put the sheet at the edge, use a short sanding block, whatever you have as long as it is rigid, hold the sheet down with a bit hanging off, then sand to the edge of the table - as if that was what you were sanding instead of the balsa. 

    That is pretty much how I do any sanding that has to be straight or square. The right end of the sheet wears out first, because I sand it away doing stuff like this. It's also a very nice square corner, line something up on the long edge, sand the end until you hit the plywood, perfect square in both dimensions.
     
    Brett

     Somewhere around my shop is a piece  of sheet metal about 3/32" thick that I had formed with a perfect 90 degree angle on one end I put this on the edge of the table and used it to sand dihedral angles in glider wings and such. This worked pretty much the same way as you are describing, and if you used sand paper that wasn't too coarse, you would never alter it or wear it out. I retire at the need of next month and hope to purge my basement and garage of teh mess that it is and find a lot of the stuff I'll need and can't find! Time will tell!
    MERRY CHRISTMAS and HAPPY NEW YEAR!!
   Dan McEntee