Back by popular demand, here is an SX2 build thread. It was decided that I'd split this up into two parts. This part will be the actual "how to" portion of the thread, though I prefer to call it "what I did". My techniques may not be perfect but they seem to work!
Let's get started!
One of the first questions I had when first working with EPP a few years back was how to remove the little strands of solidified foam that gathered after a hot wire cut. It's really quite simple. I lay the pieces down flat and run over them with a sanding block, pulling away from my hand. This ensures no tears in the foam and will quickly rid you of all but the worst strings.
In terms of construction, I recommend starting on the wing first. I didn't but will on my next build. The reason will become apparent. I started by finding the centerline of the sheet, which equates to the leading edge of the wing once it all gets folded around. I then drew on all of the rib positions. For the sake of my SX2, I like a blunt wingtip, so I put one rib out near the very end of the sheet. I kept it inboard about 1/4" to ensure that the sheet would cover, and I'd trim it down later.
Using the pinned down wing sheet as reference, I then positioned and glued all of the rear wing rib halves in place on the main spar. As the goop takes a bit of time to set, I used 1" T-pins to hold the ribs in position.
Removing the spar from the table allows you to glue on the leading edges bits. Again, I used T-pins to hold them in place while letting the glue set.
To locate where the main spar should be situated on the skin, I used the leading edge portion of the rib. To do this, I started with the rib aligned as shown on the centerline of the skin.
Rolling the rib down into position gives you the location of the spar. I'd add another 1/16" onto this to account for error. I then drew a straight line across the wing at this location. As it turns out, the spar for my build ended up being 1 7/8" behind the leading edge centerline.
Prior to doing any gluing, I pinned my ruler in place to use as a guide and to keep the sheet straight.
I started to glue down the spar/rib assembly at one wingtip. In retrospect, starting at the wing root would probably be as good if not better. I gooped the underside of two ribs and the spar and laid them down, securing in place with T-pins.
To continue, I made use of the bendiness of the EPP, prying each section of spar and each rib up to smear glue underneath with a stick.
Once complete, I let the whole deal sit, pinned to the board, to dry.
Once set, I removed it from the board and did a quick fit check to ensure alignment once I fold the wing skin over. Once happy, I gooped all contacting surfaces (don't forget the leading edges) and then folded the whole deal over.
Smoooooosh! Have no fear - the EPP won't break.
When I was satisfied with alignment and positioning (basically, that the skin was pulled tight), I weighted the whole deal down with books. In this case, I'd recommend leaving it overnight for a good, strong cure.
While the wing is drying, feel free to mark the centerline and wing/stab position ticks on the inside of each fuselage half.
While the carbon on the top was setting, I took the opportunity so seal the trailing edge of the wing. The picture is pretty self explanatory, but I just pried the foam up and laid some goop in before squishing it down.
Again, I used some weight here. The straighter your trailing edge, the better. Once this was mostly dry, I turned the wing over to repeat the carbon performance on the other side. Wow! This wing goes from flimsy to solid with the carbon on there!
While the wing is setting, construction on the fuselage can begin. I started by pinning down both halves, one over the other. Ensure an accurate alignment.
Per the measurements Mark has provided, I drew lines on the top fuselage side. You can then use the wing to draw an accurate outline of the cutout needed on the fuselage.
As stated in the other thread, if this is done before wing construction, the cut out area can act as another rib.
Also per Mark's measurements, I made the cutouts for the stab. This cutout can be made the same thickness as the stab itself in the long plastic bag of parts.
I then took the sides off of the bench. I opted for two strings of strapping tape on the inside of the fuselage. The top one is the main strengthener while the bottom will aid in preventing tear either ahead or behind the wing. Note that these are on the insides of the fuselage and not on the outside. I sprayed the sides lightly with 3M 77 prior to sticking the tape down.
I then glued the main fuselage keel in place, pinning it down as I went. The front is located at the trailing edge of the wing. At this point I'm making no allowances for straightening the fuselage. Note that this is glued on on the same side as the tape but does not cross the tape.
I opted to route the keel underneath the stab rather than slice it up for the stab.
Once set, I flipped the fuselage over and glued the keel to the other side, making sure the position was identical but again not worrying about how straight the fuselage is as it's pinned down.
Once that was semi-set, I removed it from the board and went to work joining the bottom of the fuselage. I laid in a generous amount of goop and clamped the whole deal together using some 3/4" sq hardwood I had to keep it straight. At this point I only glued as far as the wing trailing edge and no further forward.
Here's a shot from the back. I've come to realize how important it is to use something that's very stiff to keep the fuselage straight in this step.
Here's another angle of the same clamp job.
Once the bottom is set firmly, do the same to the top of the fuselage. At this point, don't worry about sealing the trailing edge of the fin. Again, I only glued as far as the wing trailing edge and no further forward.
Once the top is set, go to work on the fin. Note that I didn't do the fin last, but instead first. I'd recommend doing it last to ensure it's straight and aligned properly with the rest of the fuselage.
Now that the back half is together, let's work on the nose. The motor block in my build got cut out for a 3/8" sq motor stick for my EPS gearbox equipped Razor 400. I used a straight edge to get the line and a saw to cut the grooves. Once the grooves were cut, simple needlenose pliers will let you pull chunks of EPP out with ease.
The motor mount block is to go back against the leading edge of the wing and be centered such that the motor shaft is on the same line as the wing. As it turns out with an EPS gearbox, that means centering the block itself on the thrustline.
Gluing in the motor mount block need not be done on the bench. In fact, I preferred to do it in my hands to ensure a perfect alignment as shown below.
Oops! I forgot to add this to the wing construction. I cut the small amount (1/8" or so) excess foam off of the wingtips and used a sanding block to make it pretty. The sanding block takes some work but leaves you with a nice finish on the EPP.
Once the motor block is in place, I glued the bottom of the fuselage but not under the wing. This is where I'll be installing the aileron servo later on.
I also glued in the triangular piece on the top of the fuselage, though admittedly I shouldn't have glued it in quite so far yet. This could even wait for after the landing gear is in but that's up to personal preference.
While that stuff is setting, let's get to work on the tail feathers. I opted for two strands of strapping tape per control surface, leading from the control horn location outwards to the opposite tip. Again, I used 3M 77 before laying the tape down. Also, I was pulling the tape slightly to stretch it as I was putting it on.
Yes, the stretched strapping tape will flex the EPP slightly as it wants to pull back into shape.
Put a piece on the other side in the same direction and that bend will go away. How much tension should you put on the tape? Well, I find that I tend to pull the tape pretty close to the same tension each time without any effort. I'd think that's natural. It's not much tension, anyway.
To stiffen the newer, softer stab, I used a length of 0.04 carbon.
I simply cut a slot into the stab and glued the carbon in with a bit of weight on it to keep it from warping. It worked like a charm.
Once all the surfaces are taped similarly (diagonal from control horn location to opposite corner), I made a little tool for cutting the bevel into the foam. This came at a recommendation from Mark.
Here's an end-on shot. Ignore the top shallower bevel as I initially screwed up on the angle.
Here's the tool in use. It can take some getting used to, and a straight edge pinned in place can help, but once onto it, it makes quick work of hingeline bevels.
Join the elevator halves per your favorite method and you're set.
In between the last picture and this one, I added some color to the airframe. Finished painting waited until I was completely done construction.
Here's a closeup of the bend pattern at the top of the gear leg. This is the U that will straddle the motor stick.
I like to hold the soldering iron on the end of the wire until my fingers, about 1 to 2" back, can barely hold onto the wire. With my 35w iron, that takes about 30 seconds.
Here are the two gear legs in position. You'll want to position them so that their U crossovers don't interfere, of course. These can be glued into position before bending the axle portions of the legs.
Here are the finished gear legs. I made them long enough such that 13" prop touches the ground with the tail up level but with no wheels on.
Here's my tailskid pattern. It's totally "That Looks about right" with enough clearance to keep the rear of the rudder off the ground while sitting normally on the wheels.
I glued the tailwheel in position with a generous amount of goop and clamped it as shown
Here's a recent development I should interject with at this point. After a little bit of indoor beating up on the SX2, I noticed the tail at the skid was a little floppy as shown below.
My solution to this was to inlay some 0.07 carbon (arbitrary choice), a step which would be better to do before fuselage assembly, of course.
I thens lid the wing into position. If it's a tight fit, it can take some jiggling and monkeying but a tighter fit is worth it for the sake of your glue joint.
Now it's time to do some hinging (ignoring the fact that the stab and elevator are hinged in previous pics 
).
To stick the hinge in, rather than trying to hunt for the cut line, I just pry it apart. Note my funky colored hand from spraypainting the plane 
Once the hinge is in place, I used a toothpick to goop in some goop on both sides. An alternative to this is to slap some goop in there before putting the hinge into the slot. Either way, a toothpick works great.
At this point only the ailerons and elevator are hinged onto the airframe. The rudder has the hinges installed but will not get installed until we're done with the stab.
Access to the stab slot is through a cut made in the rear of the fuselage shown here. No, this isn't a gap but merely a single line cut. The tail can be pried up to slide the stab into position.
Measure and align the stab and once happy, goop it into place. I again pried up on the tail to get goop between the fuse and stab.
Once the stab is in position, I cut away the semi-circular slots above and below to allow for elevator movement. A #11 blade is ideal for this.
The step step is a twofer. I glued the slot aft of the stab closed and pinned it, then glued the rudder hinges in place.
While that's drying, let's cut some holes for servos. The hole on the left side of the fuselage is situated about 1/4" above the keel location. I cut this simply with a #11.
The hole on the right side of the fuselage is located just above the other side so the servos don't interfere with one another.
To re-enforce the holes, I simply gooped on a few plywood rails. These will also allow you to use screws to hold the servos in - no gluing in servos permanently here.
The aileron servo sits on the bottom of the wing. This picture shows positioning before rail installation.
Rails get glued in (ignore the small flap of foam in the hole)...
Now it's time to glue the wing in. There's no trick here aside from aligning it right. Take your time and use a ruler to be sure. The only spot to do with care is the bottom around the aileron servo. I purposefully kept it narrow as shown in the picture below for a specific reason, which will become apparent.
My control horns are nothing more than the little plastic variety you can get at various sources, jammed into a cut slit and gooped generously.
Here's the same servo from underneath. The fuselage width is enough for strength and stability but I can pinch it together to get to the screws holding the servo in if need be. This allows me to permanently glue the bottom together for added strength without worries.
Once happy with the aileron servo, I glued the bottom together. Per a suggestion in my previous build thread, I'm using plywood and clamps for this. The rigidity of the ply helps keep the fuselage straight in a position where using the larger hardwood stock wouldn't work.
Here's another view, showing the beautifully straight bottom keel.
Let's finish this, shall we? 
... and here's my rudder servo connection. The control horn is up high enough such that full up elevator won't interfere with either the horn (with right rudder) or control arm.
Here's a nice overall inside shot showing my rx (berg 5), battery (3s 1200 etec) and part of the ESC (CC Phoenix 25). The rx and ESC are just floating in there, not secured, though they could be attached with velcro if so desired.
Here's a better shot of the ESC. The battery is located partially inside the wing, through an X shaped cutout. It is friction fit only and has proven to be a good way of doing this so far.
Here's the battery cutout. It's simply an elongated X with the foam pushed in but not removed.
I think that about covers it. I made a point of balancing the plane about all three axes so as to make it easier to hover and torque roll. My CG for the few flights I've had is at about 3.75" behind the leading edge, or about 36% MAC. I may move it back slightly, which can be done by pushing the battery in from the front of the slot instead of the back and pushing it back a bit. Control throws are all setup 3D, so basically 45 degrees plus on everything.
Through building yet another SX2, there are a few minor changes I made to my techniques.
I also made some aileron control horns per GW's recommendations as shown here. These extend right from the hingeline back to the trailing edge of the aileron. I did find that I still needed to do the diagonal strapping tape technique as shown earlier as the twist possible from root to tip was unaffected. In the future, I'll cut horns like this for all controls. These were cut from 1/32" ply, by the way.
My servo re-enforcements were cut from a single piece of 1/16 ply rather than making rails. It stiffens the area around the servo slightly. I'm not sure it's enough to recommend it but given the means (I recently acquired a scrollsaw), they're easy enough to implement.
As an alternative to the longer plywood control arms, I stiffened the ones installed with some small chunks of carbon. These were epoxied in place for added strength and did the job fantastically. This is the elevator. The rudder was done identically.
