This is probably the most complicated step in the entire build up, and is the one part that is not fool proof. You actually need to pay attention here, be careful, and not screw it up. With that said, lets jump into the steps to making the stepped styrene pieces fit inside the pass body.
These are the pieces that you will be using for this step in the tutorial. Here we have the body of the pass, in its current state. Two pieces of stepped or ribbed styrene, and the template that comes with the kit. Yup, THAT is what that little piece of styrene is for!!!
The method I will describe uses two sided tape. Any kind will do. You could also just hold the pieces really steady, and not use the tape. Or you could come up with some other method. The method I demonstrate here is the one I developed that works for me.
Start by putting a piece of uncut stepped styrene onto one side of the two sided tape.
Peel off the backing, then attach the template to the other side of the tape. Save yourself some time and line up one edge and the top of the template to the piece of styrene. I used a jig to cut the stepped styrene that goes into the kit, so the edges along the side should be very perpendicular to the ribs. The point is, you don't need to place the template into the dead center of the stepped styrene and then cut out along each side.
Using an x-acto knife with a fresh blade, cut along the edges of the template directly onto the stepped styrene. Just like before, you're better off doing 10 or 12 shallow cuts, rather than trying for one deep cut. You get much more control with the smaller cuts, and better results. Once you cut the side, then do the arch along the bottom. Whatever your method is, just make sure the end result is that the piece of stepped styrene is the same shape as the template. Don't worry too much about precision on the arch. That part is hidden below the surface of the pass anyway, and cannot be seen. It's the flat edges that are important.
Once you finish your cuts, pull the two pieces apart. In case your two sided tape is really strong, be extra careful not to bend the styrene when you are pulling them apart. Go slowly.
Repeat the process for the other piece of styrene, though be sure to use the OPPOSITE side of the template for the second piece. The picture here shows what the two finished pieces should look like.
Glue the two halves together.
I recommend using a flat surface to line up the two halves along one side. This ensures that they are registered properly. Wait at least 15 minutes for the glue to set before continuing.
Grab your 220 grit sandpaper, and flatten the edges. As you go, be sure to test fit the finished piece in the body. Ideally, with just a little bit of work, you should be able to get a snug fit along the sides. Don't worry about the top and bottom arch while you are doing this sanding. We'll get to those parts next. What's important here is making sure the piece of stepped styrene fits inside the body nice and tight.
This picture shows how I'm test fitting the styrene into the body. Just keep working it until you get it right. Once it is fitting in snugly, flip it over.
Using your x-acto knife, the trick here is to mark lines where the top of the pass and the arch of the button mount are. The end goal is to remove some of the ribs on the styrene so that it sits flush with the body. No gap. By using the tip of the blade to score the styrene, you are making a mark that shows where you need to remove the ribs. Here I am marking the top of the stepped strip.
And here I'm marking the arch. I'm not cutting deep. Just scribing a line into the styrene that I can use as reference. You could also do it with a pencil or whatever. I just happen to find the blade to be very precise.
Once marked, I remove the stepped styrene and start cutting off the ribs outside of the lines I scribed. Use whatever technique works for you. I used my x-acto to whittle the ribs down, then went in with sand paper to smooth things out. I used a couple of different blades, just so I could get into the tight corners and cut out the material as needed.
And here's the end result. The stepped styrene strip fits snugly into the body, and the top and bottom are flush with the underside of the top plate. If this seems at all confusing, the way to understand what I'm trying to explain is simple: Just stack up the bottom, center and top plate with the ribbed styrene in place. Without the ribs removed as I've described, the plates won't sit flush.
We now need to repeat the process for the stepped styrene on the other side. We'll need the top plate for this part.
Hold the top plate in place, and using the same technique as described before, score marks in the stuff using the x-acto blade. Then whittle down the ribs.
This picture very clearly illustrates what you are going for. This is the final result. See the non-ribbed parts at the top and bottom of the stepped styrene? That's what you've been working on.
Now that the stepped styrene piece is all prepared, it's time to glue it into place. Do NOT glue it in prior to finishing both sides of the rib removal. That will make it really hard to get it right. Put a little glue directly into the cavities in the body where the styrene will sit, then press it into place.
Let the glue dry for a few minutes. This is what it should look like now.
Now it's time to attach the top plate. Just like when you attached the bottom plate, get the thing good and wet with your glue. One thing I have tried that seems to work is to wet down the side of the body, but not the arms. Stick the halves together, then once the glue has set, go back in and do the arms next. This gives you a little more time to position it properly, and do it right.
Once the top plate is glued into place, it's starting to really look like a Multipass!!! Great work so far!