I'll have a crack at speculating on the answer here (but it is just guesswork). According to tom's techniques the problem with tiny twist drills breaking is having a drill that can run fast enough. And of course any twist drill has a thinner core than it's cutting diameter which essentialy makes it weaker still and more prone to bending and wandering. A spade end is also going to be less challenging to sharpen and easier to hone without losing temper.

I've never tried drilling such tiny holes in steel but I have used tiny bone pins like that for orthopaedic fragment repair and as pilots for wire holes..less prone to wandering on starting the hole and can be used in a hand chuck (into bone). If the hole wasn't of any great depth then I have popped bur-holes that size through orthopaedic steel using a high-speed water-cooled dental drill bit but at 1 to 300,000rpm it's a different ball-game.

pgk

His is of a similar ‘time warp’ to the ETW era plans, where all(?) were centred around hand tools – and a lathe as the only main mechanical aid required/expected. Perhaps an electric drill, of some description, might be added, but most certainly not a milling machine.

No, but they work very well.

Hi,

The method of making very small hole by hand holding the drill bit is a "standard" trick. I use a graver to catch the hole/rotation centre rather than a centre drill (which is generally too large for the job). See the videos below for my take on it:

Gravers:

Catching a centre:

Drilling:

The finished hole:

(The last video includes the workshop cat and the little kid from next door who always came round when he heard the "Grumpy Old Man" doing stuff in the workshop)

The reason the method works is simple physics:

If you have a rotating drill and a fixed work piece, the drill has an axis of rotation and there are cutting forces on both lips of the drill bit – the forces are not equal (the drill bit will not be perfectly symmetrical) and so as the force on one side of the drill bit is greater than on the other, the drill bit gets pushed off axis and the hole "drifts"

If the work rotates, the same physics applies and the drill bit will move until the forces on each side of the drill are equal – this happens no matter how deep the hole is, the drill bit is always forced towards the axis of rotation of the work piece

Holding the drill in a fixed (i.e. tailstock) chuck results in a conflict between the path the drill bit wants to follow and the path being forced on it by the chuck – this can result in a small drill bit snapping. With very small diameter bits, it is best to hold the bit by hand to allow it freedom to "float" – it also allows you to let the drill "slip" in your fingers if/when the drill grabs, or something else goes wrong

I've been using lathes for 50 years and have broken loads of things in that time, but I've never snapped a small drill using the above technique

All the best,

Ian

Ian,

Some good tips and videos there.

Most of the small holes I need to drill seem to be in workpieces that can't be rotated in a lathe chuck though, so I end up having to resort to the drill press…..