Dry Fit The Purfling/Binding Combination at the Heel:
Prepare about 12-24 strips of 1″ masking tape 2-3″ long for each 1/2 of the guitar. Take the purfling and fit it against the stair-step routed groove you made for the purfling/binding combination. Press it tight into the waist and hold it while you grab a binding strip and sister that into the purfling. Carefully line up the waist registration marks.
Center a strip of tape with your finger and pull it down the guitar side, now pull it tight, up and over the binding and onto the guitar plate. If the joints are not tight, place another strip on either side of the one strip and pull as tight as you can without breaking the tape.
Now work around the guitar waist to the upper bout and fit the strips into the channel you made at the heel cap. Carefully pull the binding/purfling tight into the channel with additional strips of tape until you see no gaps.
Now take a sharp Woodworkers Marking Knife and mark the centerline of the back plate center strip.
It should be noted at this point that for Classical Guitars the center strip purfling joints with the guitar body purfling strip and comes together at a 45 degree angle with a very tight hairline joint. The back strip purfling should already be cut to the angle to receive the side purfling. (This is the detail with some Acoustic Guitar too).
Now mark the side purfling if needed and keep the tape in place.
Dry Fit The Purfling/Binding Combination at the Graft:
Now secure the binding/purfling combination the same with the lower bout as you did with the upper bout.
When moving the binding/purfling into position at the graft, carefully mark the center of the back strip so you know what length to trip the binding and purfling. Also mark the binding purfling where it joints the graft purfling. Again these purflings will joint at a 45 degree angle and require a hairline joint to look good. Anything other than a hairline joint will look like a mistake.
Remove the purfling and binding and trim them as close to your marks as possible – right to the center-line of the mark, if you marked it correctly. It is always a good idea to once again do a dry fit to make sure you have no surprises during installation.
Dry Fit The Opposite Side of the Guitar:
When dry fitting a trimming the purfling/binding combination at the opposite side of the guitar, follow the exact same procedure as outlined above for the first half.
Dry Fit The Purfling/Binding Combination at the Top Plate:
You can follow the exact same procedure as you did for the back plate with one exception. You do not have to be nearly as concerned with the binding/purfling length where it travels beneath the fretboard. This gives you so extra lea-way when fitting the joint at the graft end as well. You can compensate for a slight trimming mistake if need be.
GLS Tip #1:
If you need to, make that one last dry fit to make sure everything comes together as it should. Look to see that there are no gaps and that none of the strips are tipped or out of position as this could mean lots of trouble when gluing. If you need to make minor adjustments where the binding meets, you can loosen a few strips of tape and carefully sand with a sanding stick, or a Dremel Rotary Tools with a sanding disc attachment.
GLS Tip #2
Double check all the stepped binding channels and make sure no debris or scraps of wood are in the way. Sight down the channels to make sure they are square. Run your fingers around all the channels to feel for any irregularities. Touch them up now as it is far easier than dealing with this later.