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Making Long Boring Drills

There many methods for long boring, some are tried and tested over centuries and some are modern requiring quite an expensive array of drills and a compressor, the following information is a complete guide for making a very reliable but inexpensive way of doing the long drilling.

I still use today the system as shown to me by my mentor, it consists of any given length of precision ground silver steel rod, this method is much slower than using modern gun drills, but you can make any size of drill in about fifteen minutes each, sharpen them at your leisure in house for nothing.

To make a drill select the diameter of the drill rod you need, then drill a pilot hole in the centre of the steel 3/5ths the diameter of the rod being used, to a depth of around 5/8", no shorter because you loose a little length when you file across the tip later.

Then cut slightly above and along the centre line of the rod to the same distance along the rod as you drilled the pilot hole, then cut across the rod until the wedge or waste piece falls out, then clean up the flat surface left behind, but file the flat area so it is left with a slight ramp which is slightly higher towards the very end of the rod, and the back of the ramp is no lower than half the diameter of the rod,

this is important on thinner drills because the tip is much thinner and narrower than larger diameter rods, and can break off if forced heavily into the bore, the slight ramp effect helps the swarfe or plug which has been compacted into the end of the drill to stay in place when the drill is being withdrawn from the bore/hole each time.

Now you need to file two 10 degree angles into the end, for this I use a triangular file, one angle must go across the tip and the other, underneath the tip, so your left with a very sharp corner, see photo's, I will add however that this angle needs to be filed in the correct direction, the one pictured is filed for drilling in the forward rotation/direction, for a lathe in reverse the front angle needs to be filed in the opposite direction.

The small central half pocket in the centre of the tip creates a spigot on the inside end of the bore hole, once an accurate pilot hole has been drilled to a depth of about 25.00mm and cutting has begun, it self centres itself perfectly each time the drill is inserted.

Then its plain sailing to drill at a very slow speed, (let the drill cut at its own pace, do not force the drill when cutting) once the drill has stopped moving forward, the tip will be full, hold it for a second in order of letting the swarfe compact, then remove it, try not to get the drill hotter than can be touched, cool it down, once you are well practiced, you should be able to drill an 1/8" hole right the way through the length of a Bb chanter ,and its very satisfying when she comes out in the middle at the other end, the worst case scenario should be no more than a half hole out of true, and the cost of each drill, about a Dollar US, or one pound Sterling, the home made drills that I use are definitely slower but they still get the job done.

Silver steel is fairly soft in its raw state, so you will also need to heat temper your drills once made, to do this simply heat the end 2 inches of the drill until cherry red, and quench in some old dirty black diesel engine oil, this partly impregnates the metal with carbon deposits, when cool clean up the drill rod so its nice and shiny for the next stage.

Now re-heat the rod from about 2 inches behind the tip or end, apply the heat steadily and wait for the colours to start showing, once they are visible, you will notice that you have several different colours like a rainbow appearing on both sides of the flame or hot spot, watch the flame closely as you advance forwards towards the tip, and as soon as you see the colour yellow or straw colour appear right at the tip, quickly quench the drill into cold water, this will freeze the tempering process, leaving the metal slightly softer at the cutting tip where the yellow colour lies.

All you need to do now is hone your drill before use, job done, see tempering pictures below.

Additional Notes

1. Each time you sharpen the drill, it will loose a little length, if you make each finished tip about 9/16" long, it will keep cutting efficiently down to about 3/8" long, after then you will need to re-make the tip again, you should be able to get a least 30 goes before doing this.

2. When sharpening the drill tip, file or stone it across the tip and leave on any burrs that appear, as this helps to clear the side better, the drill should slide into the hole without squeaking or binding, if it does, either re-sharpen the tip or use some lubrication, especially on dry timbers, on oily timber like African Blackwood, Lignum things are much easier and the drill stays sharper longer, because the resins/oils in the timber self lubricate as you go.

3. Gun drills are very quick in boring, but will not come out centre the other end unless the starting pilot is true to start with, as a gun drill gets blunt, it will not drill straight, one of my home made D bits will, because it produces a central guide right in the middle end of the bore which the drill follows.