As promised last week, after rounding-off the American lime Wall Shelf project, I’ll now show some more detail on the jig I used to accurately position the shelves and also, how I made it.
I started off with a sheet of 18mm MDF, about 700mm long (to allow plenty of room for a 600mm capacity). Of course, depending on the scale of the job you’re working on, you could also make it larger or even shorter than this. From memory, I think it was about 150mm wide but, the important point was that it finished slightly wider than my biscuit jointer for adequate support.
After squaring off each end, I then lipped them using a 12mm width of hardwood (ash) which should prove to be more durable where the ingress of moisture and damp could easily ruin the MDF ends (not ideal when you’re trying to get an accurate reference!).
By now, I’m sure you’ll have noticed the groove running down the centre of the board. This was cut with a router (hand-held, using the side fence) and a 5/16in straight cutter for M8 hardware.
Parallel to that, we also have two shallow, ‘square’ grooves running the full length of the board…
…And, in the hardwood stop block (a scrap of oak; 50mm x 16mm), there are a pair of wooden keys which locate in these grooves. This idea is to keep the block square and parallel to the reference ends of the MDF, so that it cannot twist as it slides. I machined both grooves on the router table and, after carefully cutting the block to a length identical to the width of the MDF, I pushed that over the cutter using the base board, in order to ensure that all the grooves were aligned perfectly.
It seems to work very well. I would’ve gone with ‘diamond’-shaped keys (as Steve Maskery does) but, I do not currently have a way of accurately thicknessing squares of timber less than, say, 6mm x 6mm (ie. a drum sander!). With a bit of wax though, these keys are fine. There’s also an M8 hex-bolt with its head sunk below the surface of the block. On the otherwise, a wing nut and large washer are used to lock the setting.
Speaking of setting up; for most jobs, I can use my combination square to set the distance between the reference end of the jig and the sliding block:
For anything beyond the capacities of this setting tool, I can either use a long steel ruler or a tape measure with reasonable accuracy. One other possibility is that I could add of self-adhesive scale; the same thing I used when making a scale for the fence on my bandsaw, a few months ago.
Hopefully, the above photo now makes more sense, if you’re seeing it for a second time.
One advantage in using 18mm or 19mm (¾in) finished shelves is that, working off the base of the biscuit jointer (as this jig is designed to do) gives you a slot that’s pretty much as central to the thickness of the stock as you are going to get. So, the measurements used to set the jig are only calculated by simply measuring to the underside of each shelf. For thinner or thicker stock though, you may want or have to factor in some other figures as well.
As a jig, it certainly performed well in its trial run on this simple project and, by referencing off the same end (top or bottom) of each of the sides, you do end up with shelves that are spaced within even and equal measure. When making cuts for a bottom shelf, say, where the stop is set within inches of the reference end of the jig, I found its necessary to support the other end of the jig from below with offcuts equal in thickness to your side. Otherwise, this overhang tends to fall away, unbalanced, and can cause some difficulties. Another option might be to clamp it in place but, I really wanted this to be a jig where you could set it up and go… Without having to release and replace a cramp in between each cut. Perhaps lining the underside with a non-slip/abrasive material might improve this?
I hope you’ve found this to be of interest. Thanks for reading.