Lining up the edge

[Trevor]

Hi, I need help lining up the long edge of 2 boards when you cannot see what is going on.

Some sort of jig maybe.

Say you have 2 pieces of timber 4ft long and 2ft wide, and you want to join them at 90 degrees to each other, what is the best way to line up the edges when applying kreg screws. Any ideas welcome.

Trevor

[Jay Boutwell]

Hi Trevor, the first thing that you need is to be certain that the edge you are wanting to join another piece to at a 90 degree angle actually has a straight edges.  Then the board that you are intending on attaching you must be certain that one edge is straight and that the end that your are wanting to join to the other is a 90 degree to the straight edge.  The rest is to use the method of attaching and use a square to be sure that they are at a 90 degree angle.  If they are not and the joint is tight then one of the straight edges is not  straight.

 On very long items you can use the triangulation formula of 3-4-5 and square it up and or check it for a square corner.  To do this measure off a distance of 3 feet on one leg of the configured material angle starting at the very point of the inside angle.  Make a mark at the 3 foot distance.    Without moving any of the material, do the same on the opposite leg only this time measure off 4 feet and make a mark.  Again without moving the position of either leg measure diagonally from the 3 foot mark to the 4 foot mark on the other leg.  It is is at a 90 degree position the measurement should be exactly 5 feet.  If not the amount over the 5 foot mark is the amount that the angle is open and if under 5 feet the amount is how much the legs are closed.

The thing to remember here is that you must be sure that the edges you are using to square up something must be straight and the end of the leg that is butting the other leg must be 90 degrees to its straight edge.  This will give you a 90 degree angle with a tight joint.  

[Trevor]

Thank you but the problem I am having is say you are making a box out of 1/2 plywood and the box is 4ft long and 2ft wide. When you lay one piece of ply on the bench 4ft by 2ft then you stand the other piece up on its edge with the pocket holes in it, the ply that is standing on its edge can have a bow in it. I do put them against a straight edge when driving the screws but still have some sections not lining up exactly.

How this explains it better.

Trevor. 

[R. E. Woods]

You may want to make a jig that clamps to the pieces and holds them at 90 degrees. Watch the video below at about 5:20 you will see such a jig. It will work with the edges but not the bowing in the middle.

http://www.finewoodworking.com/how-to/video/simple-cabinetry-with-p...

[Trevor]

Thanks for that. It does give me some ideas to try.

Trevor