Installing "Railroad Spikes", by Peter Roehling, firstname.lastname@example.org
When all is said and done old-fashioned capo-spikes are probably the best way to change the pitch of your 5th. string when capoing. When properly installed, capo spikes are quick to use, out of the way, not unsightly, and don't put the 5th. string badly out of tune when employed. The following will take you through the installation procedures one step at a time.
Step #1 is to procure the spikes. Unfortunately, the spikes best used are H.O. gauge model railroad spikes, and they normally come in lots of 500. Check with your local hobby shop and see if they'll sell you just the few that you need. If not, you might check to see if there are any local model railroaders who use these spikes and will part with a few. You might also inquire onlist at BANJO-L to see if anyone has leftovers they want to part with.
With spikes in hand, we are ready for Step #2., figuring out what size drill bit you will need: Unfortunately, there is no standard for the spikes, so you will need to measure the shaft size of YOUR spikes with a micrometer or a dial caliper. First measure the shaft across the flats and then across the points. (Mine measure .034 across the flats and .042 across the points.) Now divide the difference in half (.038 in my case), and you have the proper drill size. In case you can't find the exact size of drill, going upwards a couple of thousandths in diameter won't hurt. Going downwards in diameter is risky, as you might split your fingerboard driving in the spikes.
The 3rd. thing that you need to do is ask yourself just how many spikes you will need: For instance, if you only play in the keys of G and A out of a G tuning, you will only need 1 spike, 2 frets up. I personally try to have as many bases covered as I can, never knowing what tunes I will meet at a jam, or what keys someone may want to sing them in. Therefore, I install 5 spikes under my own 5th. string, giving me the keys of G, Ab, A, Bb, B, and C out of open G tuning, and the keys of C, C#, D, Eb, E, and F out of C tunings. For those of you who weren't counting, that leaves out only the key of F#, which is not a commonly used key in bluegrass or old-time circles.
Step #4, we locate the spots to drill our holes: With the 5th. string still on the banjo and tuned to pitch, measure back exactly 3/8" from the edge of the fret you have selected, and mark the spot with a sharp pencil. Now rest the drill bit gently against the 5th. string on the fingerboard edge side, and drill straight down into the fingerboard at the 3/8" distance we previously measured. The hole will need to be just a bit deeper than the shaft of the spike is long, so flag the drill bit with a scrap of masking tape to make sure that you're going deep enough, but not so deep as to drill right out through the back of the neck! Now turn the banjo upside down and smartly tap the back of the neck to knock the remaining sawdust out of the hole.
For Step #5 you will need a pair of needle-nose pliers, a small hammer, white glue, and paper towels. But before installing the spike we need to determine which way the head of the spike should face. On most banjos we want the spike to lie directly beneath the string, and on those banjos the open side of the spike should face the string. (The reasons we place the spike beneath the string are twofold: One, under the string the spike is out of the way, and will not snag passing fingers. Two, putting the spike off to one side means that you have to put the string way out of tune to capo it.) Alas, on some banjos with extremely low frets there's no room for the spike under the string as the spike would be higher than the fret-tops, and would act as an extra, and unwanted, fret. To determine if this is the case, add together the thickness of the spike's head, the thickness of the string that will go beneath it, and add a couple of thousandths for clearance. (My spikes' heads are .020 thick, the 5th. string is an .010, and adding the extra .002 gives us a total of .032.) If your fret's height is not at least a couple of thousandths higher than the top of your installed spike, you will need to face the open side of the spike AWAY from the string.
So: Taking the head of a spike in the pliers, put a small drop of glue on the tip of the spike and start the spike into the hole. When The spike starts to get hard to push in with the pliers, stop pushing and take a moment to wipe the excess glue off with a paper towel. Now tap the spike gently into the hole until the 5th. string just barely fits beneath it. (DO NOT hit the fret-tops with the hammer.) Make sure that the head of the spike is set at 90 degrees to the edge of the fingerboard before the glue dries. Note: Properly installed, the string will be hard to get under the spikehead at first, but will smooth out with use.
Step #6 consists of cleaning any excess glue off of the fingerboard with water and a paper towel. If your spike has sharp edges on top, and some do, you can mask off the fingerboard and frets and carefully round of the sharp edges with a small file or fine sandpaper.
By the way, we used white glue on the spikes both to add a little insurance to the friction fit and to make it easy to remove the spikes if you need to. If the head of the spike were to be broken off, you can simply touch the remaining shaft with a hot soldering iron and the glue will melt, making it easy to pull out the remaining part of the spike with the same small pair of pliers you used to put it in.
Repeat the above process as many times as is needed to get the number of hooks that you personally need.