I've just completed further modules and thought I'd share how I did stuff - if only to remind me! Comments welcome on what I've done but also on this post - is it at all useful and could it be better (written, laid out, pictures, whatever)?
Starting with design - I have a 1.3 m x 1 m surface using 6 mm plywood, with a similar piece for the bottom of the module "box". The box is 100 mm deep, plus the 6 mm top and bottom. The sides are 12 mm thick plywood on the short end, where it connects to the other module and 9 mm thick on the long sides. I make the 9 mm thick bits 2 mm longer and then take make a groove 1mm deep and 9 mm wide in each of the 12 mm bits so I have a groove to aid connection. I then have inner stiffeners 4 mm thick every 300-400 mm and chisel out a 1 m slot in the 9 and 12 mm bits so they slot in there. I get everything cut to exact size at the wood shop - they have the kit that does it at speed! This is effectively a monocoque design, so it isn't rigid (or rigid enough) until everything (so including the underneath) is connected.
So dimensions for the pieces end up looking like this:
And the wood looks like this!
Some of the ply was a little warped - in practice it's not possible to see that when you're in the shop and it's all these huge sheets which of course are flexing like billy-o with their weight and being moved around. It barely matters as it's all going to be held straight in the structure but I did try dampening them with warm water and pressing them overnight - it improved things quite a bit.
With the wood as straight as I can make it, the first thing I do is make sure the end pieces for the different modules are going to be aligned. I use two sets of the pattern makers dowels from Station Road Baseboards - not cheap but very accurate - and follow the instructions. I take what is going to be the end of one module (so the 12 mm thick pieces) and the corresponding connecting end from the other module and clamp them together so they are perfectly aligned at what is going to be the top edge. I then drill two 3 mm holes where the pattern makers dowels are going to go, use a 25 mm spade bit to cut an inset for the dowels and then bore out the centre to 9 mm. I make the holes and insets a little bigger than needed so the dowels can move about a bit.
This is where I maybe deviate from usual practice - if I was to just fit the dowels at this stage I'd be a fraction of a millimetre out. What I do instead is to coat the mating surface of dowels with Vaseline such that they stick together (and keep out epoxy glue). I then put epoxy glue in the insets in both pieces of wood, put the dowels in one inset and then put the other wood onto it and clamp them in place making sure the top edges are perfectly aligned again. Leave glue to dry and then un-clamp and finally use the (supplied) screws to fit the dowels. If all goes to plan, then each dowel is now connected to its respective bit of wood and they mate in a completely aligned and repeatable fashion. That's alignment sorted - I then re-clamp in position and drill three 6 mm holes that I will use for bolts to give strength.
Next step is to work out where the stiffeners are going to go and that's determined by the points and their motors. I print out the AnyRail full size, put it on the floor and put points and motors in place.
Stiffeners are going to have to go at the 300 mm mark in this case. Armed with this information, I can now chisel out the grooves in the inside of the 9 and 12 mm outside sides of the module box and cut slots half-way though all the stiffeners such that they slot into each other. Do NOT try and be clever and make these slots a tight interference-type fit in the belief it will bring strength - you will just break the wood! Finally cut big holes in the stiffeners for wiring connections.
I now have all the bits I need to make my box so it's out with the nails and the glue - note that I do NOT connect the underneath at this stage.
This bit I do quickly as wood glue doesn't hang around - so no intermediate photos! I use a mixture of nails and glue as the former holds it in place while the latter dries, but the glue will give more strength as it is over the whole surface. I put nails in the top (1 m x 1.3 m) surface every couple of inches ready for the sides so either 6 mm or 4.5 mm from the edge depending on which side they will be holding. I hammer the nails just enough so they stay - not to go through. Then offer up each side and hammer the nails fully home, making sure the ply edge is flush with the surface edge. Also put nails to connect edge piece to edge piece, though the grooves should also help that. Then glue the stiffeners in place - no nails as the wood is too thin. It might be necessary to make some final adjustments to the grooves so keep chisel handy. I then put the box top surface face down and put weights (paint pots in my case) on each stiffener cross and leave overnight.
So that's the main body done but we need to think about the underside. This is going to be removable and I use bolts and wing nuts for this, with the bolts installed permanently in the topside of the structure. So first step is to fit some corner pieces - these are 45 degree bits cut off a 44 x 18 mm length and I glue them to each main corner and to four of the inner corners. I also fit one on each long side, so ten in total for the module shown. Let them dry and then measure up where the holes need to be made in each one of these corner pieces to take the bolts. Mark that out on the underneath piece and place the underneath on the rest of the module and drill pilot holes (say 3 mm) through the underneath and the 45 degree corners.
Lift the underneath and check the holes actually went in the right place. If not then I correct them, if OK then I put the underneath back on and open them out to 6 mm - as I'm using M6 bolts. Then tidy up the holes with the Dremel. (OK - picture out of sequence as this is obviously after painting.) I make some countersinks on the inside of the underneath 9 mm holes.
Last thing is to glue on the supports for the legs - these are just 50 mm lengths of the 44 x 18 wood that will get holes through them later.
Then it's painting time - I use two coats of acrylic primer - I water it down about two parts primer to one part water. Two thin coats seem better than one thick one. It makes things look a little tidier but main reason is protection of the wood - I really don't know how long I will want the module or how long it would last without painting compared to with painting but I do it anyway.
I also prepare the bolts and their washers - whenever I use bolts on wood I try and use washers to spread the load and for joints that are going to be made and unmade a lot, I epoxy glue the washers onto the bolts.
With the painting done, I glue each bolt underneath each corner piece, with a wing nut to hold it in place while it dries.
And then with all those done, put the underneath in place and glue washers round each hole on the outside of the underneath.
And we're done! (Again, forgive the continuity error as this is the module with an additional stiffener driven by point motor placement.) Remember that the box is not stiff enough until the underneath is fitted - that's monocoque for you.
Like I say, comments welcome on what I've done but also on this post - is it at all useful and could it be better (written, laid out, pictures, whatever)?