Tight mouths in wooden double iron planes.

[Kees Heiden]

During my trials and tribulations on the planemaking front I happened upon a curious situation. I am making a coffin smoother right now and I had my fair share of troubles with a clogging mouth. I used a narrow piece of beech so I could determine easier where the clogging appeared: Shavings were jammed tight in between capiron and the wear of the plane allready on the very first few cm's cutting.

Let me put things in clear order.

I started with a mouth of 0.4 mm. Capiron angle is 45- 50 degrees. Bedding angle is 47.5 degrees, wear angle 75 degrees: Instant clogging.
I turned all my attention towards the capiron. It is now as smooth and polished and gap free as a capiron can be: Still instant clogging.
I cleaned up the wear, opening up the mouth in the mean time. The wear is now highly polished and smooth:
- With the capiron set a little further from the edge: Perfect performance. Thin and thick shavings.
- With the capiron set very close to the edge: Still instant clogging, especially with thin shavings.
I raised the wear angle to 80 degrees: Perfect performance, thin and thick shavings.

So in the end with a 1 mm wide mouth (almost 3/64"), a wear angle of 80 degrees, the capiron angle 45 - 50 degrees and bedding 47.5 degrees, finally a nice working plane.

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I think this is what happens. Shavings love to start with a tight curl. If there is no wear, the shaving keeps on curling and you get a tight roll instead of a long straight shaving. You can see this very well in the Kato video. The wear actually stops the curl from curling any tighter and moves the curl upwards, thus straightening out the shaving.

Curl.jpg

I think there is critical mouth configuration in a wooden plane. Allthough there seems to be plenty of space with a 1mm mouth, you still get a constriction between the bulge of the capiron and the wear which is leaning towards the iron. When there is enough room for the curl to curl, below this constriction, then a clog is almost inevitable. Setting the capiron closer to the edge increases how strongly the shaving is directed towards the wear, thus increasing the problem. And it seems to be worse with lighter shavings, it also seems to be worse when you move the plane slowly over the board.

I couldn't test if a really very tight mouth (0.2 mm?) would prevent this from occuring (preventing the curl from appearing in the first place). But the constriction tightens quite a bit when you make the mouth smaller.

Of course, this was just one example, and I am still very much a beginning plane maker. But I wonder if other people have similar experiences, or maybe had completely different results.

[Oskar Sedell]

I had the exakt same problem with my first plane. Perfect shavings with the chipbreaker backed up a little, and total clogging with a fine CB setting. My smoother is based on a Hock blade, and its cap iron was not rounded at all when new.

I tried to solve the problem by opening up the wear angle, but wanted to keep the size of the mouth. This only worked halfway, and the mouth got a little bigger as well. Now it works very well and I think the solution was the combination of rounding and polishing the cap iron, and at the same time opening the wear angle a bit.

I also had the experience that thin shavings was more problematic than medium ones.

[Derek Cohen]

Good analysis, Kees.

Regards from Perth

Derek

[Kees Heiden]

It's not like I am very original. In 1980 Akinori Yamashita investigated the same thing and came to the same conclusion. This one had sunk pretty deep in my conscious, but now I remember it again. I got this from Bill Tindal. Two illuminating pictures:

Curl (2).jpg

Japan1.jpg

They had a bed angle of 40 degrees and a capiron angle of 50. As you can see, my experience is more or less the same. With a distance to the edge of 0.2 mm and a wear angle of 70 degrees, there is trouble with 0.5 and 1 mm wide mouths. That is more or less equal to my troubles. Tighter mouths don't really fit when the wear angle is less then 90 degrees. That's why in a Stanley plane this is less of a problem.

[Nicholas Lawrence]

I don't know the answer yet, but I have been thinking about this a lot, and the timing of your post is helpful to me. The try plane I have has a bed at 47, wear at 77. The plans on the Caleb James site have a 55 bed, 70 wear. I watched some of the videos you mentioned on Sunday, and the angles there were still different (between 80 and 90 for the wear I think, with a similar bed to the try plane I have, which gives an almost 20 degree difference in the wear angle from one set of plans to another).

My first thoughts were that the wooden planes may be a very forgiving design, and I may end up with lots of useful wooden planes and not as much firewood. But I have also been turning over in my mind whether there is a "necessary" relationship between those angles and if so why, and I think you may be on to a possible reason for the variation.

It would be interesting if someone has a set of planes from the same maker to compare and see if the angles vary from smoother to jack to try or jointer. You could potentially open up a whole new line of argument for the next "did the ancients know about chipbreaker) thread.

ETA: I don't understand the autocorrect feature on this site (or maybe it is my iPad). It turned "chipbreaker" into "chip breaker smoking" and "a possible" into "apostle." And I swear, it changes things after I proof them.

[Kees Heiden]

I have calculated the mouth size from the descriptions in the Seaton Chest book. If the given numbers are correct (the size of the empty mouths and the thickness of the irons), then all those planes have a mouth around 1 mm. The jack is about 1.2, the smoother 0.9. Wear angles are closer to 90 degrees, if I remember correctly, the jack and smoother are 89, the try and jointer are 83 degrees. Bedding is 47.5 degrees for all of them.

[Stewie Simpson]

Kees; those figures on the wear angles are quite interesting; I am near ready to start work on a 7 inch, double iron smoothing plane, East Indian Rosewood body. The bed angle will be at 50*; 47 - 48* taking into account the taper of the iron ; a wear angle of 85*, at a wall height of 10mm ; and a mouth clearance of 1mm.

Stewie;

[Kees Heiden]

I'm sure that'll be a much better looking plane then mine

Your values look like they will work perfectly well. 10mm wear height is a bit short in the traditional sence. They usually were about 1" high.

I have a boxwood smoother, that doesn't seem to have lost a lot in height. The mouth is more like 4 to 5 mm!

[Stewie Simpson]

Kees. When you consider you wont come across too many wooden bench planes that have lost more than a 1/4 inch of original wall height over their lifetime, is their any valid reason to start the wall height at 1 inch.

Stewie;

[Kees Heiden]

No. It's just how it looks from above. Traditional look is with a higher wear. I think that's all, no technical reason.

[Steve Voigt]

It's very possible to make the mouth pretty small, about 1/64", and still have a very close-set CB. Two things help. First, make the wear angle between 80°-90°. Second, make sure the shape of the cap iron is right. The curve of the cap starts about 1/2" from the edge and reaches a max of around 45°-50°. But the acceleration of this angle matters a lot. If it accelerates quickly and stays near 45° for most of the curve, clogging will be more likely. If the curve stays shallower at the beginning and then rapidly increases when it gets close to the edge,clogging is less likely.

Just a note on the history of wear angles. early double irons, like in the seaton chest, had steeper wear angles. In later planes, the angle is often much shallower, but the mouths are larger and always were. I think this was done to make it easier to make the planes with machines. I cant prove that, but it's a reasonable hypothesis.

[Kees Heiden]

Just curious Steve, do you make them with a 1/64 mouth (0.4 mm)?

I have measured several of my old planes, all Dutch from late19th century. The wear is indeed more like 75 degrees.

[Phil Mueller]

Thanks Kees for this timely post. I've laminated a new sole onto a double iron smoother and am experiencing jammed up shavings. Trying to decide if I need to open the mouth some more, move the chipbreaker back or what. This gave me some good info to consider.

[Steve Voigt]

No. It's just how it looks from above. Traditional look is with a higher wear. I think that's all, no technical reason.

The abutments need to end above the high point of the cap iron, say 5/8" above the sole. The wedge fingers should have a sharp taper that starts 1/4"-3/8" from their ends, so the abutments will have a matching taper. Add those numbers together to get 7/8" - 1". If the hard line the begins that sharp taper of the abutments is colinear with the top of the wear, it looks much cleaner. Her's an example of what I mean:
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[Kees Heiden]

Man, that's such a clean look! Sharp lines, spotless surfaces. I'm still a long way off to reach something like that. Hats off.