If you are going to put slabs on a full tang with pre-existing holes in the tang, you first use the tang as a "template", or guide to mark and drill the hole through ONE of the two slabs. If you drill more than one hole, then put a pin in the first hole in the tang you drill and the corresponding hole in the slab. That will orient the slab's hole with the hole in the tang, while you drill the next hole.
Once you have the holes drilled into the one slab for all the holes in your tang you are going to use, there are a couple of ways to "match up" the other slab.
One, if you are careful, you can simply repeat the same process used to drill the holes in the first slab. Just turn the knife blade and tang over and clamp it to the slab to drill the holes in the second slab. OR, you can clamp both slabs to the tang, using that set of pins, to center the holes in the first slab, and use the hole in the slab as your drill guide to drill through the hole in the tang an on into the second slab. Again, when you complete one hole, put a temoporary pin through the hole to make sure that the two slabs remain aligned before you take the other pin(s) out of the tang to drill those holes.
When all the holes are drill, remove burrs on the outside of the slabs, and chamfer the hole with a chamfering bit( or countersink), for your rivets.
Don't try to hammer those rivets down in ONE BLOW. That is how you crack the slabs.
Lots of little blows will close the rivets, assuming the length of the rivets are correct.
I put brass pins in my first handle, and carefully peened over the ends to hold walnut slabs. Within the year, the walnut had dried out, and shrunk enough to allow the slabs to rattle, and the hilt to rattle two. That lead to my second rebuild of that knife, with no more success.
Finally, 2 years later, I ground the tang down to half its width, then cut leather pieces to fit down on the tang and cover the entire tang. An end cap was made from a piece of scrap steel, drilled and tapped, and screwed down onto a matching stud I filed into the end of the tang.
I used Elmer's glue between the layers of leather, pounded the layers down tight as each piece of leather was worked down the tang, and then added another piece of leather, so that I was Barely able to begin to catch the thread with my pommel to turn it down. I turned the pommel down using Vise Grip pliers, holding the knife blade in my bench vise. Boy, did the glue squirt out of those pieces of leather. The next day I used rasps, and coarse files, then fine files, and sand paper, to shape the leather handle to something we now call " ergodynamic". This was back in 1964, and the word did not exist, yet.
I still have the knife. I keep it because it reminds me of all my mistakes, so I don't repeat them making other knives. There are still a host of other mistakes for me to make with knives, so I am not too worried about "being perfect". Hah! :rotf: :shocked2: :grin: :thumbsup:
On your next knife, don't drill the holes in the tang before you drill the holes through the handle, whatever it is. Then you can use the holes in the handle as drill guides to at least mark the exact location on the tang for the corresponding holes in that steel.
If your tang is made from laminated steels, or very hardened steel, you can heat up the tang with an ordinary Propane torch to red hot, and drill the holes while the tang is red hot. Just clamp the blade in the BARE jaws of your bench vise. The Vise will become a heat sink, to keep the heat applied to the tang from heating up the hardened, and tempered blade. Drilling through red hot steel is like drilling through balsa wood. :thumbsup: Oh, put a good tap oil on the flutes of your drill bit to keep the bit cool while drilling the red hot steel.
