In the absence of a bandsaw in the workshop, it has long been a project in my mind to build a jig saw table, but I needed a way to cut an accurate recess for the sole plate of the jig saw to fit into. I have in the past used scraps of wood taped to the work piece to guide the router and it can be a bit hit or miss, so decided it was time to make a fully adjustable jig that I can use to make any sized recess (and replicate it) I may require in the future. Trend make an item called the 'Vari-jig', but it's quite costly, the router runs on top of it using a guide bush which can lead to tipping, and it can only do square or rectangular recesses/holes. It also requires careful measuring and setting up in the first instance. My version is going to work like a rail saw, with the router on a flat surface so it can't tip, will be able to accommodate out of square pieces and set up is quick and simple. This thread will show how I made it, and out of necessity will be pic heavy, so bear with me.
The jig basically looks like this and consists of four infinitely adjustable sides.
The strips are 6mm MDF with 19mm aluminium T tracks to allow the sides to move.
The MDF strips are cut to size, Initially 150mm x 600mm. These will be adjusted later.
The 19mm T tracks (from ebay) are 500mm long which is plenty for what I need.
Each side needs to be cut down in length to 450mm. This allows the T track to extend 50mm past the end so it sits onto the edge of the next board. (Bear with...all will become clear!) I ruled an accurate square line 40mm from one edge to allow space for a clamp when using the jig.
As I'm using 6mm board, I have to use very tiny screws (Piano hinge screws) to attach the track to it. This involves drilling some new holes in the track as the pre-drilled ones are too big for the tiny screws and they fall through.
To initially position the track and help with keeping it in place, I applied some double sided carpet tape before carefully placing the tracks along the previously drawn lines.
Pilot holes for the screws were then accurately marked using a centering bit.
At this point, the circular base that I made in an earlier project was fitted to the base of the router, pressed up to the T track and the edge of the board cut off. I used a 9.5mm bit so that when cutting the recesses, the corners only have a minimal radius that needs squaring. This is what will make the jig work like a rail saw. One point to remember, whatever size cutter you use to trim the edge off, you must always use the same one when using the jig.
To connect the tracks together, I needed some 120mm x 19mm slotted plates, but couldn't find any anywhere, so had to make my own. I used 19mm wide x 1.5mm aluminium strip, and cut a 6mm slot down the centre of each 120mm length with the router.
The ends were then neatly rounded off with the linisher.
Next, I needed to make the T sliders for the track. This was cut from some 50mm x 3mm aluminium flat stock.
There are four long ones at 50mm and four at 25mm. The long ones have two 5mm holes drilled in them and the short ones, one in the centre. 5mm is the tapping drill size for a 6mm thread. Here tapping the thread.
The short sliders have a 20mm length of 6mm studding screwed into them and fixed with Loctite green.
The longer sliders are assembled into the end of each track and secured tightly with two 12mm long 6mm hex button screws.
All that is required to do now is to fit it all together using the small sliders with a 6mm wing nut.
Here's the reason for that 50mm T track overhang. It sits onto the next board and keeps it aligned correctly.
Here's the jig at it's biggest setting, approx 315mm.
But it can be adjusted to make any shape square or rectangle.
Here's how quick it is to set up. Say we want to cut a recess or hole exactly the same size as this piece of MDF.
There is no measuring required...simply place the piece in the centre of the jig, adjust the sides to enclose it all round and that's it. Because we know the cutter will travel along the edges of the jig, the hole will be completely accurate.
And here's the really cool bit, it can also be used to cut recesses/holes that aren't square.
Here's the first try out. I mentioned at the start that I will need to cut an accurate recess for my jig saw sole plate. Here's the jig saw with the jig adjusted to fit the base.
Routing the recess (I used a bit of scrap melamine faced board so the contrast can be seen)
Just need to square the corners up with a chisel...
And a perfect fit.
Again, if you wanted to inlay a section of wood...
Hopefully that might have given some food for thought. How much did it cost? The T tracks were around £20 from ebay, and all the other bits I already had, but no more than another £10-15 if you have to buy screws, ally, etc. The basic Trend jig is around the £80 mark, so quite a saving if you make it yourself.