Repairing a ‘Safe-D-Speeder'
Model Engineers' Workshop|March 2020
R. Finch saves a useful device from the scrap box
R. Finch

About 20 years ago, I was given a Mason Master ‘Safe-D-Speeder’ epicyclic speed reducer, photo 1, which I thought might come in useful one day, so I kept it in one of the drawers of my tool chest. When the D-speeder was made in the 1950s, electric drills were pretty well all single speed of around 2800 rpm and had 1/4 inch capacity chucks. If there were a need to drill into masonry or use a larger drill, then the only speed reduction method was to use the D-speeder with its 3/8 inch chuck. The method of use was to hold the 1/4 inch input shaft in the electric drill chuck and the masonry drill bit in the chuck on the D-Speeder, whilst gripping the outside of the casing with the hand to stop the body rotating. This gave a four to one reduction in speed and consequently a four times increase in torque. If the drill bit jammed in the hole, the outer casing would try to rotate and, unless you had bionic hands, it would slip in your hand and not stall the electric drill.

As I already had a two-speed drill, I never used the de-speeder until I came to use a 100mm hole saw to drill an access hole through a floorboard for installing new cables for my Internet connection. My drill, even on low speed (850 rpm), was still rather too fast for such a large hole saw and it tended to overload the drill. I then remembered the D-speeder that had lain unused for all those years and dug it out, only to find that it had almost seized up. It was very stiff to turn and clearly needed a bit of attention.

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