Adjusting mitred shooting board

[Tiger]

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?

Hi Ian, just trying to make a simple box with mitred edges, I definitely underestimated how difficult this was going to be. Your analysis is pretty close to the mark as some test bits seem to be fine, others aren't. I assumed that the timber was straight and true as I ran it through the jointer and the thicknesser but on measuring it again there are variations in the thickness. In regard to the shot end being at right angles, I'm using a clamp at one end so that I can fine tune the angle but no one setting works for all the test pieces so far.

[Tiger]

Hi Peter, have already experimented with different designs to the jig but not yet tried the one you attached, I think if the current one I have doesn't work I'll give up.

[pmcgee]

Photos of the results would prob give these guys a better idea ...

[Groggy]

Another thought, you mention the blade is square to the mouth, but is the blade itself slightly concave or convex? Any error would be doubled.

[Tiger]

Another thought, you mention the blade is square to the mouth, but is the blade itself slightly concave or convex? Any error would be doubled.

Am at work now so can't check it but don't think so as I remember flattening the blade.

[derekcohen]

On a mitre jig like that (This is a design by Bob Wearing and copied by Michael Connor), it is possible to use the plane on the same axis - just flip it over.

I would plane one edge from one direction, then plane the mating edge from the opposite direction. Any variations would cancel themselves out and you would end up with a perfect 90 degrees for each corner.

Mark the pieces well. Clamp them securely so that there is no movement.

Regards from Perth

Derek

[Tiger]

Thanks Derek, great idea but why must you clamp the workpiece, isn't the idea of a shooting board not to clamp so that you can move the workpiece gradually into the path of the plane or is there something inherent about the jig that requires it to be clamped?

[derekcohen]

Hi Tiger

A mitred joint will show up the slightest imperfection. It is extremely difficult to avoid slight movement of the work piece without a clamp. In that particular jib, I would glue 400 grit sandpaper to the floor and use a clamp.

Regards from Perth

Derek

[sinjin]

I've just posted a question asking something very similar to this disscussion.
I'm also in the process as of today designing a shooting board using a linear bearing system and machined plates....Only because i have the linear bearing and access to a 5 axis milling machine so the cost is zip. If anyone is interested in the design i would gladly share it.
I just thought if your trying to get accurate results the board would need to be clamped rigidly so there is no movement. The idea of using something like a 51 that had the ability to be able to tilt as well as the board rotate on a platun seemed to go. Anyway as i said i will start to fiddle on the CAD this weekend...see how it goes.
Basically mount tilting carriage to the linear bearing which holds the Lie Neilson 51 which is attached to a machined platun. The fence on the platun will be able to rotate and clamp the work piece. The idea to be able to tilt the carriage holding the 51 then in turn would give you compund angles if you ever needed it. Its the plan anyway....

[Tiger]

Hi Tiger

A mitred joint will show up the slightest imperfection. It is extremely difficult to avoid slight movement of the work piece without a clamp. In that particular jib, I would glue 400 grit sandpaper to the floor and use a clamp.

Regards from Perth

Derek

Thanks for clearing that up Derek.