TABLE TOP Approx 27" x 32" ? I decided I didn't trust MDF not to sag; and I didn't think I could laminate layers of MDF with contact adhesive and ensure they were flat at the same time. So I:
built a shallow (~3") torsion box out of 1/2" birch ply. I knew that despite my best efforts it wouldn't come out completely flat, but it would be (and was) easy to tune with my #8.
used a piece of 3/4" MDF for the working surface, with Formica contact glued both sides. Bolting it to the top of the torsion box ensured flatness (I inset 6mm T nuts before adding the Formica).
The whole was bolted to the base from below via 8mm T nuts in the top of the torsion box.
Insert plate - I used a phenolic Kreg one.
Insert plate height adjustment - I embedded 6mm T nuts in the underlying ply and threaded long grubscrews into them, such that the plate corners sit on the grubscrews.
Finished size approx 27" x 32" ?
FENCE 3/4" birch ply sub-fence, approx 7.5" x 8" (x 32" long); 3/4" Formica-laminated MDF fences with 6mm T-nuts embedded for holding it to the sub-fence.
The fence is in 3 parts: 2 pieces approx 4" high which can be moved apart/together according to the size of the router cutter; above that a full width piece with a piece of 3/4" T track in it for mounting feather boards.
The sub-fence fixes to the table top with a clamp at each end: adjustable, and avoided the bother of insetting T track just to clamo the fence down.
BASE 1/2" birch ply box, with 3 compartments open to the front. The router sits in the middle compartment.
I routed dust extraction through the base - my vacuum extraction (~2" diameter tube) plugs in on one side, and is routed to the router and the fence separately via a Y connector (ABS waste pipe) and pieces of vacuum hose.
I made 2 butterfly valves in the Y connector (4mm s/steel rod + aluminium sheet) so I can route dust extraction according to where it's best placed. Rather elegantly, imho, those valves are controlled by a pair of levers sticking out the side, which connect to the butterfly spindles via a pair of 2:1 ratio plastic gear wheels (to reduce the angle through which the levers turn to 45 degrees). OK, a touch OTT, but fun to make, and it does work well :)
I was planning to extract dust from below the insert plate by extracting from the compartment as a whole, but all that happened was a massive build up of dust in that chamber (it works a bit like a bag-less vacuum cleaner). So I routed a piece of vacuum cleaner hose to the router dust-hood thing itself.
Oh, and an NVR switch.
WHAT'S GOOD It works! It's solid and doesn't move; It's flat enough (variations in the glue thickness between MDF and Formica are apparent - probably my poor application technique; I used liquid glue, and I suspect I could have applied a spray more consistently). The router is quieter - the ply base seems to absorb the nasty high-pitch whine of the motor. The fence is excellent. Dust extraction is good enough - there's always a bit of dust on the table that seems to escape but most is caught. It may be that my vacuum unit (Trend T30A) might not be quite powerful enough.
WHAT I'D DO DIFFERENTLY I sized the whole thing so that it would fit under my neander workbench for when I'm enjoying proper tools, but it's too heavy and cumbersome to move. Not sure what I'm going to do about this as I don't have room to leave it out all the time. And I need my sawhorse/workmate back.
Not use the Kreg insert plate, or at least measure more, cut less - I spent *ages* attaching the router such that the spindle comes out "exactly" in the centre of the 30mm guide bush hole. Then I found that that guide bush hole wasn't actually in the centre of the reducing ring, off by ~0.5mm. Hmmm.
Use a different router - I used a Freud FT3000VCE because it was reasonably priced and had above table height adjustment and cutter changing. However it also had these problems specific to use in a table: - the base wasn't flat, or square to the spindle; - the above table height adjustment involves an access hole in the insert plate positioned right underneath the fence - not useful. So I don't actually have above-table height adjustment, grrr; - the template provided on the Freud website for insert plate fitting has the holes marked in the wrong places! - the dust extraction attachment relies on the router's plastic sub-base being used. As well as not being remotely flat, it also prevents the collet nut from protruding above the table sufficiently to enable above-table bit changing. So I made a dust take off hood out of ABS plastic sheet (with much use of a heat gun and glue (the type plumbers use for ABS pipework). Yawn. - the plunge depth stop turret is sprung - I mean the thing with the pillars on it for setting different plunge depths - it's located using a spring and ball bearing, which works well, BUT the spring is right underneath the point where the adjustable rod thingy presses on it. So the plunge depth varies a mm or so according to how forcefull the router is pushed down. OK, not an issue in the table, but it's so useless I had to mention it! - one of the plunge pillars has a bit of play in it. Had I known the total set of issues I would have returned it, but by then I'd already flattened the base (coarse silicon carbide paper on thick glass), and drilled the insert plate. It'll do.
WHAT I'VE YET TO DO (SOMETIME, OR NEVER) Height adjustment. I'm toying with the idea of using a stepper motor attached to the router to drive the "above table" threaded rod mechanism. With a nice digipot control of course :)
Fine tune fence - I'll probably fit the fence with a pivot around the clamp on one end, and at the other with a piece of threaded bar.
Buy another router - I intended to use the router interchangeably in/out of table, but it's a faff to change it around (unscrew dust hood, remove sub-base, attach my dust hood, screw to insert plate, insert into table, attach dust hose) so if I find myself having to swap it around a lot I might end up leaving it there, and spending more money :( On a router where the plunge depth stop turret isn't sprung!
SOURCE OF T-TRACK Finally, T-slot is easy to get in the UK - best value I found was Tilgear. But the T-bar that goes in it seems unavailable in the UK except in overpriced little kits. So along with a mate I imported some 48" lengths from peachtree USA. Even with the postage and import duty it was still cost effective. Now I can make mitre guides etc as I choose.
Phew! That was longer than I as expecting.
regards all, g.