Most capstan tooling has a hole through the shank. This can allow long workpieces to be made. But this can also be used to hold drills, reamers etc. Of course the drill needed will never be the same size as the hole in the tooling. In industry sleeves would have been specially made so whatever size drill was required would fit the hole available.
Notice that the sleeve is milled away so that a grub screw in the capstan tooling can hold the drill bit securely.
Fig – drill fitted with a sleeve fitted in knee
With very small drills the drill might be soldered into the sleeve.
Using a drill chuck to hold a drill
Another way of holding a drill or similar tool is by means of a drill chuck. Since the drill chuck usually has a taper to hold it this is fitted into a sleeve. Sleeves are often longer than is needed to fit the capstan. These can be ground off or turned off using carbide cutters.
The problem with this is the very long overhang. This is not too much of a problem for drilling but, in practice, all of the tooling on the capstan has to stick out by roughly the same in order to make the best use of the limited range of movement of the capstan. Using a standard drill chuck will affect the overhang of all of the other tooling on the capstan.
Using a collet chuck to hold a drill bit
An easier way of doing this is to use a collet chuck with a parallel shank. The tooling is made with a hole to fit this shank.
Fig – Tooling with a collet chuck to hold a drill
Collet chucks like this with parallel shanks are readily and cheaply available for use with the ER type of collets. The way these collets are made does not seem to allow them to be useable for anything shape other than round.
If other shapes are necessary then it would probebly be better to use 5C type collets. These could be held in a collet block which was held in a four jaw chuck.
When drilling a hole a center should be cut first. In general the shortest drill possible should be used. If it is possible to use a stub drill this can have two advantages. Firstly it is shorter and takes up less space. Secondly it is stiffer and often a hole can often be drilled with a stub drill without having to center drill the workpiece first.
Very often when drilling a hole the flutes of the drill bit get congested with swarf. On a pillar drill the user instinctively withdraws the drill to clear the swarf. There is a problem doing this on a capstan – the user has to choose to do this. This does mean that the user can withdraw the drill as often as necessary. But if he withdraws it too far and the capstan starts rotating the user is in trouble. He will have to rotate the capstan the whole way round back to where he was when he started drilling this hole. With the capstan shown it is not possible to turn the capstan backwards but it is possible to release the ratchet mechanism so it rotates freely in the usual direction.
It is also possible to use more that one drill of the same diameter but each is set to drill to a different depth. But this then requires more than one position on the capstan.