10 February 2014

Hand cranked drill press

Touched by envy after seeing Chris (from Chop With Chris) making a dog sled without power tools, I refocused my envy from his telekinetic abilities to the tools.  So yes, a post drill,  what about that.  Looking on a second hand web site I found one, or rather something close: a hand cranked drill press with closed gear box, unknown to me but the price is probably lower and it's faster (up to 600 rpm).

The first impression is that it has much in common with a standard two-gear closed-gear-box hand drill.  Too much in common, my first reaction was to search how it works, as no separate depth setting is visible. After opening the drill and some trials this is more clear. Surprisingly apart from the extra high speed crank axis, gear by gear the drill is similar to a post drill.  It just lacks two extras: the lateral flywheel and a freely rotating depth setting threading.

So the main difference is that for depth setting the axis is directly threaded and and not through a threaded cap on top of the axis.  The situation is then similar to a bolt and nut where the axis is the bolt and the depth setting wheel a nut.  The moment the drill is cranked, it lowers fast.  When the material is reached and the drill engages, there is a pressure build up on the nut until it starts slipping like nuts do when a bolt is tightened.  When through drilling the pressure lessens, the axis is pushed deeper until the nut fully slips again. To make slipping more easy the nut is set on a ball bearing. And as the nut turns mostly together with the axis it is also build as a flywheel for added comfort.
Some extra fun is that when drilling is done and the crank is stopped, the flywheel will continue turning, pulling the axis back up.  If this is not enough raising the drill can be done by cranking backwards.

There are two bolts at the top of the gear box.  The left one presses through a spring (and a missing part, probably a bearing ball) on the flywheel to increase friction and by this the downward pressure.  The right one needs probably to be filled with grease (it was dry and rusted) to keep everything slippery and wear free. Slightly tightening the screw injects some fresh grease.  I hope that greasing will lessen the friction over time as it is rather high when using second gear,  but that's probably the way it is.
Is it usefull?  With it's automatic pressure control it's maybe too brutal for small diameters on wood.  But as the seller told me it was his favorite tool in his grandfathers workshop fifty years ago.

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