plywood shooting board?

[mike-p]

Want to make a shooting board as in the KMG instructions, Ken states mdf 12x30. I don't have a piece that big but i have ply, is there any reason i can't use that?
cheers all.

[ken cierp]

Ply will work fine as long as its perfectly flat -- the bench you fasten it to must also be flat.

[mike-p]

thanks ken, I will see how flat the ply seems to be tomorrow, if it doesn't look great i'll get MDF.

[Kevin in California]

Made mine out of mdf...remains flat. I have small pieces of plywood in my shop that have not remained flat.

Kevin

[mike-p]

yeah, I'm gonna go buy some MDF today, am not convinced by my pieces of ply.

[mike-p]

ok, major beginner Q's as usual. How straight does the edge need to be?

I don't have an engineer's straight edge, do I just assume that the MDF is cut straight? Or the pine piece for the edge? I would guess they are both 2-3mm out over the 30" length, is that close enough?

Also, as far as clamping the edge on I don't have wide enough clamps, shall i just knock a few thin nails through the pine into the MDF to provide pressure for the gluing?

thanks all.

[Robert Hosmer]

ok, major beginner Q's as usual. How straight does the edge need to be?

I don't have an engineer's straight edge, do I just assume that the MDF is cut straight? Or the pine piece for the edge? I would guess they are both 2-3mm out over the 30" length, is that close enough?
If you're talking about the fixture which uses abrasive to do the jointing, then the edge to which the abrasive strip attaches should be as straight as possible. What is considered "close enough" will be determined during the candling procedure.

Also, as far as clamping the edge on I don't have wide enough clamps, shall i just knock a few thin nails through the pine into the MDF to provide pressure for the gluing?
Should be OK.
thanks all.

Determining a straight edge is sometimes tricky. Known straight references are nice to have, but often the money (or rather lack of) rules out having that nice 36"Starrett. Grizzly sells a fairly decent 36" graduated model made by iGaging for around $50, with the 24" for less.
Lots of folks use a rule(r), level, or even something shop-made. The easiest method for you to determine straightness is to place your wooden strip on a piece of paper, posterboard, etc. and use the edge to trace a line on the paper, then flip the edge over to the other side of the line and look for variance.

For the item you are making, I would first make the pine piece; get it as straight as possible using the method previously outlined. Then use that piece to determine the straightness of the other piece (platform) to which it attaches. If the edge of the platform is not straight, you have two options:
1. Judiciously sand the platform edge until it mates properly with the known straight piece.
2. Simply affix the known straight piece to the top of the platform instead of the side.