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.

03 February 2014

Kato and Kawai video

Like many others I have seen the Kato and Kawai video.  The video looks at a usable back iron set between 0.2 and 0.1 mm for shavings of  0.05 and 0.1 mm And if I go directly for the end conclusions:
1. for shavings of 0.05 mm and less there is no tear out even without back iron. 
2. the back-iron must be set proportional to the shaving thickness
3. a steeper back iron angle gives less tearout.

I looked in an earlier post at the Howal Universal Plane, the back iron has a minimal set compared to the Howal values between 1 and 0.3 mm for the back iron setup.  I have also seen descriptions of jack planes favoring a back iron set at 2 mm.  Here the Howal description, that I dated back to the seventies:
1. Schrupphobel  (scrubbing plane):  Use the rounded blade and open the mouth
2. Schlichthobel (jack): Mouth to 2mm
3. Doppelhobel (double iron jack): back iron at 1mm, mouth at 1.5mm
4. Putzhobel (smoother): back iron at 0.5mm, mouth 1mm
5. Reformputzhobel (high angle smoother): back iron at 0.3mm, mouth at 0.5mm and raise the bedding to 49°

What I missed in the Kato and Kawai video was one more test,  they tested on shavings of 0.05 mm and 0.1 mm,  I wanted a test on 0.2 mm shavings.  Just to see how in their setup the ideal distance for a back iron relates to the thickness of a shaving.  But they do mention it in their end conclusion 2. talking of a distance proportional to the thickness.  At first sight Howal also proposes a linear increase with the thickness.  I have read people favoring a nearly static setup as opposed to this linear setup: "1/64 ( 0.4 mm) is at the outer edge of what will actually reduce tearout" I see this as a static setup as Kato and Kawai conclusion 1. sets 1/128 at the inner edge. So setting the back iron close to 1/128 (0.2 mm) would be the only useful position. That idea probably works, but is rather strange as the back iron would protrude under the sole for thicker shavings making it a giant scraper.

I talk about their setup as it misses a mouth. This gives a tightly rolled shaving.  That's different from normal planes where the shaving would come in contact with the mouth that redirects the shaving backwards,  as if confronted with alternating irons. So conclusion 3. is not necessarily the whole story as there are alternatives to a high angle on the back iron to increase the downward pressure on the shaving.  A mouthed plane a well set back iron can give a tell-tale straight shaving.  But any irregularity in this shaving chimney will ask for a lessened back iron position.

My conclusion,  very watchable (... maybe not with the family) video.  And by lack of bevel up planes, more or less setting up a back iron is part of the fun.