Tuesday, September 7, 2010

Planing hook

a'la Roubo...using both sides of my bench enables me to use a planing hook as illustrated in the original documents.  One thing I've noticed: most of the modern interpretations of the planing hook do not try to make it look like the original.  To me this is heresy - the original shape of the hook is quite plainly shown in the original engraving.  It has a long bearing surface for maximum bolting/pegging area, for rock solid stability, and short, steep shallow angle hook area because that's all you need.  It seems people want to get uppity and go changing things.

Let the word go out from this time and place: You generally cannot improve this stuff, you can only modernize it.  To wit:

This is by far the most common form of planing hook I see when I look at modern Roubo interpretations.  Notice that the parameters have flip flopped: you have now a short area for the mating surface (hook to bench) and a long, shallow hook.  This is exactly the opposite of the original.  And why is that wrong?  Because what you've done is very effectively reduce the hook's ability to stay attached to the bench while at the same time dramatically increasing the power that the planed board has to rip it off.  By making the hook shallow you allow the board to "get under" the hook and lift it out - perpetually out - with every stroke of the plane - against whatever tiny little bolts will be crammed into that small mating area.

Part of what's going on here is that this hook form is often coupled with a face vice - they're depending on the vise to do the bulk of the holding and the hook is just there to help out.  To each his own, but I think there are better ways to skin this particular cat.

This is as the original was drawn:

A long mating surface for glue/pegs/bolts/whatever to hold this thing onto the bench for, oh let's say maybe 200 years, and a short steep hook angle so that the planed board doesn't get under the hook so much as slam into it head-on...a direction of force which is much easier to counteract.

The old stuff isn't the way it is for no reason.  These people weren't bored hobbyists.  This stuff fed their families and kept them out of debtor's prison.  It had to be right.  It had to make sense.  It had to work.  (If it seems like I get worked up about this stuff it's probably just because I get worked up about this stuff.)

So anyway, I free-handed a little swoop onto a piece of oak scrap (it even had a nice S curve in the grain that nearly followed the profile, so much the better.)  I cut it out and dressed it up a little.

I decided that I would hold it on with three lag bolts (I had acres of room to bolt it to the bench - my options were limitless...see how this stuff works?) and would orient two of them at an angle away from the direction of planing, so that the force of planing would push the hook on the long axis of the bolts rather than at right angles.  The middle bolt would just be perpendicular.

Countersunk heads, lag bolts with washers.  Notice the front and rear holes are at angles to the middle one.  There would be no way to accomplish this much holding power if I used the modern permutation of the planing hook.

And "soured down" as we say, it was the veritable Rock of Gibraltar.  I slapped on some BLO so it matched the rest of the real estate.


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