Sometimes Things Bug Me...

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Blog entry by RobH posted 05-10-2007 10:26 PM 843 reads 0 times favorited 2 comments Add to Favorites Watch

Ok, I yesterday that I was off and rocking after having completed much of a cabinet over my long weekend. However, this has been a very frustrating experience for me. As always I broke down the large plywood sheets using a clamp-on crosscut guide and a circular saw. The only problem was that this time, I could not seem to get the pieces square.

Ok, so now I have analyzed it back to the break-down of the plywood. Now I just need to know how to aviod this the next time. My largest acurate square is 6”. I need something larger and I am thinking of either a drafting T-Square (which might get in the way of the clamping mechanism, or a drywall square. Man, now I only need a little while to think.

If any of you have any secret techniques or tools to use in getting things a little more square, let me know.

-- -- Rob Hix, King George, VA

2 comments so far

View coloradoclimber's profile


548 posts in 4217 days

#1 posted 05-10-2007 11:36 PM

If you have one straight edge and you want to get 90 degrees from it you can use the right triangle rule. The two short sides of a right triangle squared equals the angle side squared. Measure a distance A along the known straight edge, measure up a distance B from one end of the measurement A and measure at an angle C from the other end of the measurement A. Where B and C cross is 90 degrees from the end of A.

Basically you are drawing a right triangle on the plywood. A simple set of numbers to use is 3 4 5. 3 squared + 4 squared = 5 squared. 3×3 = 9, 4×4 = 16, 5×5 = 25. 9+16=25. So a 345 triangle is a right triangle. Measure 3 feet along one edge, measure up 4 feet from the end of the 3 foot measurement, measure 5 feet from the other end of the 3 foot measurement and where the 4 foot and 5 foot measurements cross you now have 90 degrees from the 3 foot edge.

You can do this to any size. We use this technique to lay out floors, foundations, panels, basically anything you don’t have a square big enough to fit. If you have an odd size material and a calculator you can calculate the exact sides for any size.

To layout a big foundation we layout one side, then grab two big tapes, hook one tape at one corner, hook the other tape 30 feet over along the first edge, drag out the tapes crossing over each other until one tape reads 40 feet and one tape reads 50 feet and where they cross is 90 degrees from the first side.

View Don's profile


2603 posts in 4326 days

#2 posted 05-11-2007 01:44 AM

How about this (similar to above)?

  1. Mark a point on the bottom edge of the sheet where you need to cut.
  2. Now place your straightedge (clamp-on circular saw guide) on the cut mark.
  3. Measure the distance along the bottom edge of the sheet to the farthest corner.
  4. Next, measure a point in the opposite direction the same distance from the cut mark as the distance measured to the corner. This point will be along the same plane as the bottom of the sheet and will likely be off the sheet. (It may be necessary to lay the sheet on a large table or the floor to establish this point.)
  5. Now take two measuring tapes and pivot the top the the straightedge until the distances from the top edge of the sheet where the straightedge intersects the edge to the two points on the bottom of the sheet are equal. Clamp the straightedge and you have a ninety degree angle.

-- CanuckDon "I just love small wooden boxes!"

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