This is one way and may not be the best, you may find a better way, but I hope this guide will help you. These notes are for building a left hand switch.
Tools:
Files,
Drill and twist drills. (drill press desirable.)
Small hacksaw
Track width gauge. ( Available from Miha Modell
Drill guide.( Make your own or you may be able to purchase one from Miha Model )
Soldering iron (useful)
Build Process.
Fit the 3 pieces of the supplied drawing ( left or right handed ) together and lay out on a suitable board or surface.
Sort all the ties and align them in the same orientation. ( for ease of identification I labeled them “A” and “B” ends.
Set up your drill to drill a 3mm hole 21mm from the “A” end of the ties for mounting the chairs..
NOTE....
The check rail ties are NOT drilled at 21mm ! Check rail chairs are on on a different centre,
Reset your drill press to drill the check rail chairs 23.5mm from the “A” end of the 3 check rail ties.

Set the drilled ties out on the drawing. This will enable you to work out where you need to cut them to the required lengths.
NOTE . There are webs in the under side of the ties and with carefuf cutting the appearance of solid ties can be maintained. Leave the second and third ties from the blade end full length for mounting the switch operation lever.
It aids assembly to join all the chairs possible together prior to installing them on the ties.
Fit together 3 normal chairs, Add a little plastic solvent glue to keep them secure.
Then 6 slider chairs, the left most slider chair should be trimmed as shown in the picture
The check rail chairs have no joining tags. Add normal chairs to the slider chairs according to the number of ties being used.

Add the joined chairs to the already cut to length ties. You should now have something like the following picture.
File the sharpe edges and burrs from the rail profile ends and insert one long straight into the assembled chairs & ties.
Using your drilling guide (47.5mm centres) Drill 3mm holes for the chairs that will take the fixed straight rails. ( To help describe which ties to drill I have numbered them 1 – 20 from the left hand, entry, side)
Drill ties # 1, & #2, #8 - #13, #19 &#20.
Put together more chairs as show below.

Fit the assembled chairs to these ties; # 1, & #2, #8 - #13, #19 & #20.
Cut casting sprue from frog and file burs from rail ends to enable rail joiners to be fitted smoothly.
Take the shorter straight sections of rail and install them into chairs #8 - #13, #19 &#20 with the Frog fitted between them with the supplied rail joiners.
NOTE.
In the above picture I have added the wing rail blades so that the fixed rail can be trimmed to the required length.
Using the drawing as a guide curve another piece of rail as below.
Take two more rail joiners and the cast blade rail and install onto the frog, use a small clamp to hold the movable blade firmly against the already fixed straight rail.

With the small curved rail firmly in place we can use the drilling guide to drill the holes for the chairs to take the large outside curved rail.
With the holes drilled the chairs can be added.
NOTE . Slider chair #6 should be cut down to alow for the rail joiner.,
Use the drawing as a guide to curve the long curved rail to shape.

Insert the curved rail into the already fitted chairs. It is easier to work from Tie #1 end.
Use the drilling guide again to drill chair locations for the short curved rail.
Fit chairs and rail. You should now have this;

Use the same technique with the drilling guide to drill and install the chairs for the final short piece of rail.
With all the rails in place it remains for the final check rail to be installed. The centre
for the check rail chairs is between the rail and checkrail so with the main rail in place the centre for the chair mounting hole can be marked.
Once this is done pull the rail back towards the #1 chair end to enable drilling of the ties.
Install the check rail into the check rail chairs prior to fitting the chairs to the ties. Then re fit the main rail.
(If the chairs do not line up perfectly and the rail will not easily thread through the chair,
Remove the chairs and enlarge the hole slightly. To give a little free movement. )

With the rails all in place now is the time to use the soldering iron to “weld” over the chair “spigots”. Turn the whole switch up side down on a firm flat surface. Wlile pressing each Tie firmly down onto the chairs and rail use the soldering iron to melt down the plastic spigot.
Once all the chair spigot's have been welded the now firmly constructed switch can be turn over again for the blade tie bar to be added.
To fiix the wing rail blades drill the tie bar with 1.4mm holes with 28mm between centres.
The length of the bar is dependent on your requirements and the type of operating lever chosen.
Drill the marked holes in the lugs of the wing rails, the supplied brass pins can be inserted through these holes and down through the tiie bar and then soldered in place.
Alternatively M1.4 bolt or screws can be used instead of the brass pins.

Or make a brass tie bar, drill and tap M1.4 to acept the M1.4 screws .
The switch is now complete and ready to install into railway layout.