There is some real good advice above. One thing I can’t stress enough is to make sure the gluing surfaces are shaped, mated, and fit properly:
Here some of the methods I use for overlays:
For wood bows
1. I flatten both surfaces with my oscillating belt sander (any disc or belt sander works) and make sure there are no gaps, ANYWHERE. Files can be used for the flattening but I (and most everybody that I seen attempt it) round the edge and enlarge the glue lines.
2. Like the others I taper one end and leave the top of the overlay flat to allow my clamps a good clamping surface (sometimes I this isn’t possible with materials like antlers and horn).
3. I put the overlays on before rounding the belly of the limb tip so the clamps have a good clamping surface.
4. Do a test runs using your clamps, before using glue, to make sure your clamps will not slip.
5. I use spring and small C clamps, depending on which one has the best hold I prefer the spring clamps).
6. Leave you tips and overlays wide then reduce the width using either a file or belt/disc sander.
7. Round over and rough shape the tops using a file and/or the belt/disc sander.
8. To get a uniform roundness take some fine emery or cloth sand paper and “shoe shine” the tips to remove and ridges and dips.
9. After the tips are shaped, put the string groves and round them over the top. If you had groves in the limb tip before installing the overlay follow those groves, if they are properly aligned.
10. There are many different styles of nocks sot the techniques used might be different, but all of them should be rounded and smoothed out. No abrupt edges, which is what kills strings.
11. The belly side of the string groves needs to be wider than the rest of the grove, if not then the string will rub the edge of the grove and either be cut (left square) or come partly out of the grove when the bow is drawn. I can feel a tip like this lift out and pop back in to the grove when the bow is drawn and let back down; you can hear it when an arrow is released.
Glass Bow
1. I use the same method except when shaping the gluing surfaces.
2. I rough up the glass with 100 grit paper.
3. I shape the bottom, the surface that will be glued, of the overlay to fit the back of each limb tip. For longbows I flatten it on the planner and then rough it upon the disc or belt sander. For a recurve I shape it to fit with the belt sander.
4. Once again, it is extremely difficult to keep from rounding the edges with files.
Anyway, this is the method I developed through trial and error over the years. There are other methods that work but this is the most efficient one for me.
For glue I have used Recorcinol (sp), Urac 185, Smooth On, Tite Bond 2&3. Zap-a Gap (a thick Super Glue), and Wal-Mart super glue, they all work if the guling surfaces is properly prepared and cleaned. My preference is super glue because it is easy to use (no mixing) and allows me to start shaping the tips in ten minutes.