Tools (2):
mini-drill

Original page created on 24/08/2015.

Mini-drill

A mini-drill is an essential tool, it’s often the first one bought. The simplest are actually made up of a motor, a switch and a chuck with collets. In my opinion, the main selection criteria are:

• maximum rotation speed, which should be around 20.000 rpm;
• obviously, variable speed;
• quality of chuck and collets;
• concentricity.

This last point is not essential for hand working, but very important if the drill is mounted on a stand.

That point made me eliminate a Dremel drill: the collets (aluminium, therefore too soft) did not rotate smoothly! I preferred a Proxxon model, which for years, although not free from defects, has given me satisfaction.

Proxxon Micromot 50/E

Drill equipped with collets, the chuck is in front of it.

Characteristics

Power supply	18 V CC max
Maximum speed	20.000 rpm
Maximum power	40 W
Collar diameter	20 mm
Equipment	Steel collets ⌀ 1 - 1.5 - 2 - 2.4 - 3 - 3.2. Optional: chuck ⌀ 0.3 to 3.5

Operation

The control is made by a turning knob, potentiometer type, with integrated switch. This button is graduated in rotation speed, but if you connect the drill to a direct current source, you will find that it is impossible to vary the speed by turning the knob!

To actually vary the speed, there are three solutions:

• Use a variable voltage source, such as an electronic lab power supply, or even an old transformer rectifier for model train. In this case, the speed variation is done on the source and not on the drill. The advantage of the lab power supply is that it is possible to limit the current, and therefore the torque, in case of delicate work. By adjusting a low speed and a moderate torque, it is possible to work as with a hand drill holder: the drill is started, the chuck is locked with a finger, the drill is placed in the desired position, and then the chuck is progressively released.
• Use a conventional transformer with a rectifier bridge, but without a smoothing capacitor. Indeed, the drill internal speed controller works with rectified full-wave current.
• Use a dedicated Proxxon transformer: the Micromot NG/2 model, not very powerful (24 W) and not allowing to reach the maximum speed, or the 60 W NG 5/E with a variable speed drive. In this case, there is no need to have a mini-drill with speed controller, and therefore prefer the model 50 without speed controller.

Connector

The centre pin is only used for coding and is not to be connected: a cut in the insulation of the terminal block gives it a place. I have generalized this solution to all sources of direct current or even DCC, obviously taking precautions of polarity and coding.

The good choice?

After all this, one wonders whether it’s not better to choose a drill that connects directly to mains, like the FBS 240/E! Apart from perhaps the price, but if we take into account the power supply, we end up with about the same price to pay. I still see a disadvantage: the minimum speed of this drill is 5000 rpm. It’s still too much for delicate freehand drilling (see above).

Disadvantages

The revelation!

With a lathe, it may be feasible in a few minutes. I don’t have one, but since the piece is made of aluminium, there is no difficulty in cutting it with a hacksaw, then rectifying it with a light milling.

But how didn’t I think of it earlier? But why, at Proxxon’s, have they made two different models for so a little difference? Conclusion: it is better to buy the model 50/EF with chuck plus a set of collets, rather than the model 50/E with collets plus a ref. 28941 chuck, although it costs a few euros more!