Saturday, September 1, 2012

Shaped planes, part V

My previous expenience with moldings disclosed that my hollower is not satisfactory. The plane chatters. This may be due to saveral reasons. The most likely is that the plane blade s not thick enough. So, sucker for punishment that I am, I decided to make a thicker blade. Double sucker that I am, I decided to use a different style, based on a picture in David Fink's book, Making and Mastering Wooden Planes (q.g.). Glad I did. I have learned a lot.

This style of plane is a lot more like the traditional wooden shaped planes.
Here you can see the overall scheme. We have a block of wood 145mm by 20mm thick by about 50mm wide. The bottom of the plane has been shaped to a 10mm radius curve, by guess and by gosh. In the block a mortise has been cut. Into this mortise will fit a blade. The blade for now is just roughed out. The mortise has two angles. The one on the left is critical. It is the bedding angle for the plane. The traditional angle for bedding is 45 deg and this is what I use, standard pitch. However for hardwoods you might want to use a steeper angle, like 57 deg which as I recall is called York pitch. These are traditional pitches, and assume the blade of the plane will be sharpened at 25 deg. If you do not sharpen the blade at that angle you will have some math to do. It is all about angle of attack. I recommend reading Garret Hack's The Plane Book, q.g.

It took me some time and a few trips to the 'net to figure out what the plane blade looked like. Mr Fink did not tell me. But eventually I figured it out. The roughed-out blade is shown on top of the plane. I cut it out from a piece of worn-out circular saw blade. This is almost 2mm thick. Approximately twice as thick as the old ripsaw-derived blade on my previous incarnation. I like this a lot. The thicker the blade the less the chatter.

The place where the blade goes in a not-so simple mortise. Leftmost is the ramp where the blade will go. I will call this the blade ramp. It is 45 deg, the bedding angle. If you go make one of these things, under no circumstances can you touch this blade ramp! At right is another ramp. It is traditional to cut this at 62 deg but I cut it at 60. Easier, (with a 30-60-90 square), to lay out and the exact angle does not matter; cut your wedge to suit. This ramp has two functions. One, it holds a wedge to keep the blade in place. So I will call it the wedge ramp. Two, you can see I can slide my 30-60-90 square along the plane towards the front (right in the pic) any amount I want. The amount I slide it towars the front will determine the throat opening. Planes are very fussy about throat openings. My rulae of thumb is that the throat opening should be about the width of the shaving you want to take. So my current strategy is as follows. The wedge ramp should be the thickness of the blade ahead of the place where the blade ramp comes out. The goal is for a zero throat width. I can take wood off. I can only put it back with great difficulty. In fact, only with Plastic Wood (tm).

So when we have fiddled with this a bit, we can get a decent fit.
A decent fit to me means that the blade will fit exactly flush with the bottom of the plane with zero overhang. So the throat opening is zero. That is what I want. To get away with this we have to look at the other side of the plane.
There is a blade-ramp shaped cutout on the other side of the plane. It hasto be deep enough to take the plane blade all the way down, until it is flush with the bottom. Took some doing.

My next post, part VI I suppose, on the subject will tell you about my adventures in throat-cutting. Fortunately, human life is safe. The only throat I intend to cut is that on the hollower plane. I must also relate my learnings on ramp-cutting. And there is yet the chip-escape hole to drill. So much to post, so little time.

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