I'm about to embark on a project made from boards recycled from an old kitchen. This will involve cutting the individual planks from the doors of the units into specific lengths. An afternoon of chewing the end of a pencil resulted in a cutting list which will give me pieces I need from the material which I have, but which involves making almost a hundred cuts. These cuts are mainly into just two lengths.
In order to get an accurate and repeatable cut I built a jig which would allow the same length of piece to be cut precisely time and again.
In hono(u)r of the fact that I will be cutting recycled timber, I managed to make the entire jig out of scrap plywood and 4x2 (100x50mm) which I had acquired from a dumpster at a building site.
In the interests of enhancing the knowledge of different cultures, please note that the practice of "dumpster diving" is referred to as "scaffie raking" or "midden raking" in Scotland.
Step 1: Cutting to Width
The offcut of ply which I was using was the full length of a sheet of very low-grade treated 1/4" ply. Since it only needed to be wide enough to hold 4" wide boards, the width was adequate but inconsistent.
I clamped a square steel tube to the plywood as a straight-edge and ran a circular saw down it to give a consistent width, and a useful strip of ply about 4" by 4'.
The ends of the plywood were warped and curved upwards (I did say that it was very low-grade) so I used a handsaw to remove about a foot from one end and six inches from the other. This left about six and a half feet length for the jig, which is plenty.
Step 2: End Stop
The workpieces are going to be inserted into the jig for each cut, so the end stop had to be pretty solid to take repeated knocks. I used a piece of 4x2 which had previously had a chamfer cut from one edge.
The wood was cut to be as long as the plywood board is wide, then mounted with the vertical face towards the insertion end to give a consistent stop.
For strength, this was glued and screwed into place, with the screws also serving the purpose of avoiding the need to clamp while the glue dried.
Step 3: Side Board and First Cutting Bridge
The shortest cut which this jig is needed for is 16" (400mm), so I marked that on the plywood once the end stop was secure.
A good find from the dumpster had been a couple of feet of chamfer which looked as if it had been cut from the edge of a piece of 4x2. This was aligned up the length of the jig to one side and then glued and screwed into place. This needed the screws as there wasn't any flat surface at the top to which a clamp could be reliably applied.
A little table for the circular saw to run across was built from a couple of chunks cut from some scrap 4x2, oriented so that both pieces were a standard 2" high. They were aligned with the side board and again were glued and screwed into place. Since the saw is going to cut right through the piece of 4x2, take care to put the screws where they will not foul the saw blade.
The foot-long piece of scrap ply from the previous step was screwed over the top of the pieces to form a cutting bridge.
Finally, a thin strip (about 1/2" thick) cut from the side of apiece of 4x2 was screwed in place to give an edge against which the saw could be run. Both the guiding edge and the surface of the cutting bridge are significantly longer than the bridge itself, in order to allow the saw to be positioned smoothly before it starts contacting the workpiece.
Once the guiding edge was secured, the circular saw was adjusted to the correct depth and a cut made through the bridge. Just for paranoia's sake, check that the edge of the cut is where you want it to be. Better to find out now rather than after you've cut fifty pieces too short.
Step 4: Long Piece and Second Cutting Bridge
The longest pieces to cut with the jig are 1100mm (43") so that was marked and then another piece of chamfer was used to continue the line of the side board. To make sure that the line was perfect, I aligned against a straight steel ruler rather than risking anything which might get out of line.
The second cutting bridge was basically a repeat of the first. Again, I was careful to use the machined 2" thickness of wood as the height, so that both cutting bridges were an identical height. Since I had used the longer piece of waste plywood for the first bridge, I built the surface of the second one out of strips from the thin piece of scrap I had removed earlier. Looks ugly, but works.
You may notice a difference between the second bridge here and in later photographs. After screwing the guiding edge down on the second bridge, I realised that it was too high and would foul on the saw's motor. Since it was only screwed down it was easy enough to replace with a piece of plywood which was thick enough to reliably guide the saw.
Step 5: And Test
Holding the jig onto a worksurface with clamps means that it shouldn't move during work.
I (deliberately) only put a side board on one side of the jig, so that different width of planks could be cut. Using a caul underneath the clamps holding the jig in place means that you can set up for different widths.
I think that I'm most happy about the fact that this entire thing (apart from glue and screws) was made from a skip. The fact that it works really well, doesn't take up much space, and will massively accelerate the cutting of the pieces is just "gravy."