Shooting board problem

[Toni Ciuraneta]

Hi guys.
This is driving me nuts. I've just made a shooting board, and I've taken all the care in making it, and squaring everything right double checking everything; and evrything seems to be correct.
What happens is the followoing:
I square one edge vs the one which is in contact with the front. No problem so far; a few passes with the plane and they are at 90º.
Then I square the following edge with the previous one, rotating the board 90º counterclockwise; and again I get a 90º angle.
So far I have three consecutive edges that are at 90º to each other.
Then I rotate the board again in order to get the fourth edge at 90º and no matter what I do it never gets at 90º, or if it does, the the others are messed up.
I believe that it is a very small deviation that keeps adding up and that it only shows on the fourth pass, but honestly I do not know what to think, maybe my shooting technique is wrong and I do not hold the piece properly and it moves??
Maybe I should apply the five cut (passes) technique to adjust it?

Any suggestion will be appreciated, thanks in advance.

 

[Steve Southwood]

Yep, your getting a compound error there at the end. To be honest, I have never tried what you are doing.

I have the Lee Valley shoot board, with the adjustable angle head, I bet it wouldn't do that either.

 

[glenn bradley]

It does sound like a very slight error is adding up to where it finally shows on the 3rd cut. How much error is it? Just enough to show with a square applied to the corner? We would, of course, like to have it perfect but, we often have to settle for very close.

Here's something to try. I don't know that it will reveal how to correct your result but, it may give you more info for your quest. Take a piece of wood about the size that you have been using. Be sure you have a flat face (face jointed), a parallel opposite face (thicknessed) and one jointed edge. Now we feel we have three true reference surfaces; parallel faces and the one jointed edge. Place one face down and the jointed edge against the fence. Shoot one perpendicular edge. With the same jointed edge against the fence and the opposite face down, shoot the opposite edge.

We now have two edge results using the same original jointed edge against the fence as our reference surface. Do both edges that you shot appear to check true to the original jointed edge using whatever you are using to check for square?

 

[Toni Ciuraneta]

Hi Glenn thanks for the advice. I'll do as you suggest. To explain it more clearly have a look at the pics included.
Edges 1 and 2 are planed square after a couple of passes.


Then I plane edge 3 using edge 1 as reference. And both are at 90º


Then I plane edge 4 and it is not parallel to edge 1 and obviously not square to edge 3, but square to edge 2.

Checking the angle with a digital protactor it is half a degree off.


So I guess that the only way to go is doing what you suggest. It well maybe that one of the edges although square it is twisted due to bad technique or bad cutting causing that deviation, although I shooted it straight with the shooting board prior to plane the rest of the sides.
I'll do it tomorrow with another scrap and I'll let you know.