To start, you'll need to work out the dimensions of your shadow box. We made our four sides 450mm x 290mm. Mark this out on the timber and use the mitre saw to cut both ends at a 45° angle. Repeat this for the three other sides of the shadow box.
Apply PVA wood glue to the mitred edges of the timber. Join the four pieces of timber together to make the box shape. A good tip is to use masking tape to hold the box together and keep the edges flush. Then use a nail gun to secure the pieces of timber together. Make sure you use a damp cloth to wipe away any excess glue.
To make sure the box is square, use a tape measure to measure the distance between the diagonally opposed corners. The box is square if the distances are the same. If not, you can make some minor adjustments to square it up.
Place the piece of 42mm x 19mm timber for the top fixing rail at the back of the shadow box so it's flush with one side. Mark on the other side of the timber where it needs to be cut, then use the drop saw to cut it to length. We cut our timber to 412mm.
Apply wood glue to the top and sides of the top fixing rail and press it into place. Use tape to secure it and make sure it's flush with the edges of the shadow box. Then use the nail gun to secure the rail to the box.
Measure the length of the bottom fixing rail so that it's the width of the shadow box, in our case it was 412mm again. Cut the rail to length. You might want to mitre the ends of the rail to 30° so that it isn't visible.
To attach the bottom rail, apply glue to the top of the fixing rail and put it in place against the shadow box. You'll need to clamp the rail to the box to make sure it's flush with the edges. Use the nail gun to secure the rail to the shadow box and wipe away any excess glue.
Use a putty knife to apply putty to the nail holes and gaps between the timber joints. Let the putty dry and give it a sand so it's smooth. Then give the shadow box a light sand for the best possible finish.
After deciding where you want your shadow box to go, have someone hold the box in place while you use the drill and screws to secure it to the wall. Use a spirit level to make sure the box is square before properly securing it through the top and bottom fixing rails. If you're not attaching the shadow box to studs, use hollow wall anchors to fix it in place.
Now you're ready to style your box with your favourite ornaments.