Adjusting mitred shooting board

[Tiger]

I am trying to build a shooting board for mitred joints like in the attached photo. The ramp is exactly 45 degrees to the base however the resulting cuts are continually less than 45 degrees not by much but as you know unless the mitre joints are exactly 45 degrees then they're useless and I'm planning on using these to make boxes. Any suggestions on how to fix this so that I can get the precise cuts I need?

[Groggy]

Are you clamping the workpiece?

[chrisb691]

Is your blade parallel with the plane sole? At the very least you should be able to compensate by adjusting the blade out more on the required side.

[Tiger]

Groggy, not clamping the workpiece, should I be?

Chris, blade is parallel.

It didn't take too long to build but I've spent a few hours trying to rectify and making numerous test cuts, I'm actually thinking of rebuilding but this time with some adjustability but so far haven't found any plans that allow for this.

[Groggy]

Tiger, since you are trying to be very accurate I'd try clamping to eliminate movement of the workpiece as a possible cause of the problem.

[wattycoo]

Tiger can you not just shim the workpiece to compensate? I use strips of paper, Ross

[IanW]

Clamping might help, as Groggy suggests. The problem could be that your blade is ever so slightly out of whack, perhaps, but since you say the angles are consistently less than 45, I'd postulate that you are simply pressing a little harder on the upper edge of the plane - a not un-natural consequence of using it in that position.

In my experience, these sorts of jigs don't of themselves gaurantee accuracy - there is still a little skill demanded from the operator. We were shown way back in school how a little altered pressure on the plane in the right direction can change either the vertical or horizontal angle of the shot end. It may be that with a bit of practice, you can shoot those mitres spot-on. I always sneak up on the last bit, checking with try-square or mitre-square after each couple of passes, to make sure it's all coming along as desired.

Cheers,

[Tiger]

Thanks guys for the replies.

The jig itself didn't take too long to build and I tried numerous test cuts which included using strips of paper, perhaps I put them in the wrong spots.

The bevel gauge against the jig says 45 degrees but the cuts are less than 45 which of course makes it useless for box mitre joints. Ian, good point regarding the accuracy of the hand plane but what I like about this style of jig is that you can move the plane by holding the handle so you get good purchase on it, I tried another type of jig previously where the workpiece is angled and found there was indeed some movement so gave up on that. I don't have a table saw so am using a Triton workcentre to make the initial cut maybe it's time to look at the table saw so I don't have to muck around with a shooting board.

[bridger]

use the lateral adjuster on the plane to fine tune the cut.

[pmcgee]

If you applied a thickness or two of paper to the wooden strip along the top front of your jig, it would tilt the plane up from the 45o angle.

Cheers,
Paul

[thumbsucker]

Not wanting to be a party pooper. However you are seeking to achieve the humanly impossible. To achieve two perfect mitres both of which are 45.0000. This is impossible. Instead of focusing on abstract numerical values. It would be more productive to mate the two faces. Giving scant regard to the numbers. If one mitre is 44.88888 and the other is 44.11112 you will never pick it with your eye, what you will pick is shadow line indicative of a gap.

As bridger said

use the lateral adjuster on the plane to fine tune the cut.

Cut one miter then fit it to its partner by adjusting the plane.

Remember the wood will move, so even if you get a perfect miter today, tomorrow it will have changed. The other problem is that the jig made from virtually any material will also move, even metal so it will never be a true datum. You will always be shimming or adjusting something.

If you get a chance to examine antique mitres you will notice that few are mated perfectly, because over time all mitres will distort.

[Tiger]

I rebuilt the jig and made doubly sure that everything was 45 degrees, the guide rail was cut on the triton bevelled fence and was a slightly wavy cut but I added strips of masking tape to keep everything in the same plane, I now get 45 degree cuts but the mitre length along the cut is not even . I moved the front fence but I'm not getting repeatable accuracy, also tried moving the lateral adjuster but still no cigar.

Thumbsucker agree that as long as the mitres add up to 90 result is fine but how do you do that with this jig? If it cuts 44 3/4 degrees on one cut it will always cut at 44 3/4 degrees.

[IanW]

...... I now get 45 degree cuts but the mitre length along the cut is not even . I moved the front fence but I'm not getting repeatable accuracy, also tried moving the lateral adjuster but still no cigar.

Tiger, from your description, I would consider the following possibilities: either the shot end is not at right angles to the lengh of the board, or that your board is uneven in thickness across its width, or it is cupped.

You haven't said what you are trying to make, but I take it from the jig that you are trying to mitre two wide, solid boards? This is a fraught exercise for even the oldest & boldest woodie - getting everything spot-on is exceedingly difficut, as you have discovered. I think I'd be searching for a different design, myself, though you don't have much alternative if you want a 4-sided box where all corners come together at a single line.

If it's wide mitres you must have, you will eventually get there, if your patience holds out. You've solved one problem, now all you need to do is figure out what's causing the new problem, & correct that. I think what TS is saying is that absolute precision isn't essential, but the degree of precision you will need to achieve to get a sound glue joint (if that's what you need) is still pretty high. The thicker & wider your stock, the more any small deviations will show. And of course, the deviations you are getting are going to be additive, as you say, so you can't just live with them........

Cheers & good luck,

[lightwood]

I rebuilt the jig and made doubly sure that everything was 45 degrees, the guide rail was cut on the triton bevelled fence and was a slightly wavy cut but I added strips of masking tape to keep everything in the same plane, I now get 45 degree cuts but the mitre length along the cut is not even . I moved the front fence but I'm not getting repeatable accuracy, also tried moving the lateral adjuster but still no cigar.

Thumbsucker agree that as long as the mitres add up to 90 result is fine but how do you do that with this jig? If it cuts 44 3/4 degrees on one cut it will always cut at 44 3/4 degrees.

Tiger,
Just a thought, sometimes I get a clue by imagining I am actually inside the jig or machine and looking around at what is happening to me as the tool whistles by...then thinking how a problem can be solved from the inside looking out, and not from the outside looking in.

Also another thought...
Are you getting repeatable inaccuracy?
That might tell you if it is something you are introducing in your technique, and the jig is doing what a jig should do, repeating the inaccurate result.

Further to TS's suggestion....One jig I've had in the back of my mind for making small boxes with mitred edges is similar to the letter
K
with two windows where the stock pokes through, and two angled parts are separated by an accurate 90 deg, or by another angle for other boxes with 5, 6, 8, and 10 sides...and hangs of the edge of the bench, donkey ear style and the 2 pieces of stock are clamped to the boards and shot in the one action....


good luck,
Peter

[pmcgee]

I absolutely understand wanting to build something that works as designed ...
but on another tack, couldn't two edges that are close to correct be 'kerfed-in' with a saw?

Paul