Centre of Effort - Part II

[derekcohen]

This is part of my effort to understand aspects of hand plane design. So, a little theorising put to the test with the re-handling of a plane.

http://www.inthewoodshop.com/Commentary/CentreOfEffortPart2.html

Your thoughts and ideas very welcome.

If you have not read the first article, Part I is here: http://www.inthewoodshop.com/Commentary/CentreofEffortinaPlane.html

Regards from Perth

Derek

[IanW]

Hmmm, not much comment needed, Derek. I think you covered anything I might say. As I said earlier, I was talking about planes with roughly the same geometry as the garden-variety Baileys. I have no, or virtually no experience with planes like that big mutha you were playing about with. When you start altering the toe-to-blade: blade-to-heel ratio it's like going from rear-wheel drive to front wheel drive on a car - the dynamics are altered, and a whole new driving style is required. With that long toe on your plane, you are bound to get a good deal of understeer, to prolong the metaphor, so the handle position & slope will have to accommodate that. You also wrote in another thread some time back how critical the actual placement of the handle along the body is, in controlling a plane.

So I think it would be very hard to lay down other than some very general principles when it comes to sticking handles on planes. One needs to consider the plane itself, the bench height at which it is commonly used, the size & dynamics of the plane in question (especially its centre of gravity), & all of these must be overlaid with a large dose of individual preference for what fits your hands. The planes I've mucked about with have been metal-bodied jobs with the shortish toe of the Bailey type, and a low centre of gravity, and the handles were tailored specifically to fit my smallish hand & my way of working. They are but a subset of the variations possible.

To tell you the truth, & something I meant to mention earlier, the nicest planes in my kit, are a couple of small smoothers with no handles at all! And the sweeter of the two is the little Ironwood coffin smoother I made a couple of years ago - very tactile, & gives 100% feedback as to what's happening where the rubber meets the road (must have cars on the brain, this morning! :roll:). However, I know I couldn't scale it up as-is, because anything larger wouldn't nestle in my hands the way this tiddler does. I also suspect that the feeling of control would not be as acute in a larger tool, and it so would not be anywhere near as pleasant to use for heavy work. The handle-less grip suits this plane, which is only used for short sessions polishing some small object or small areas of recalcitrant grain on a large surface. For a long, heavy planing session, handles (sited & angled to suit me :U) make life a lot easier, I reckon.

Lots of different courses, & lots of different horses required, I think? :U

Cheers,

Cheers,

[pmcgee]

Also there are other cultural approaches, but I'm no expert.

These I think are Dutch ... http://lumberjocks.com/topics/45111 ... I'm sure I've seen that sort of 'handle' at the rear also.

A couple of 'hotdog' style ones here ... http://www.sindelartoolmuseum.com/Wood_Planes.html


I meant to ask Derek (+ anyone) ... would you say your elbow/forearm is pretty well horizontal when you are planing?

Thanks,
Paul

[derekcohen]

Well Paul, I shall refrain from commenting on those planes! :)

Arm bent? I think there is no fixed position.

I am going to copy here a response a made to Warren at WoodCentral. Warren queried the handle design, compared it with one of his own, and this focussed me to write the thoughts that had been swirling in my head.

Warren wrote ...

I have a beech trying plane that I have used on almost every board for 35 years. It is 22 inches long, the mouth is 7 inches from the front and the angle of the tote is somewhere around 65 degrees. I think it is a good design. I would say that you want a fluid wrist rather than a rigid wrist; the wrist angle changes as the stroke progresses. I think that for the least stress on the joints they all should be fluid, not trying to hold something rigid throughout the stroke.

The new design looks awkward to me. If someone had a large body of work with a traditional design then tried something new for a few years and liked it, it would be worth noting. However using an altered design for a very short period of time does not give much information.

After reading this post I compiled a set of measurements about several planes, which are meaningful to me. Hopefully also to others. While I do not mean to suggest that they should create rules for the design of a plane handle - since I do agree with you that the wrist changes as it pushes a plane ... and that it changes (or needs to change) position and angle as the conditions change - there is a pattern that is recognisable.

I'll start with a comment about the new handle for the Trying Plane. It may look awkward, but it works. The question is "why does it work when the previous handle - so close in angle to the one you like (above) - did not work at all?".

One answer to this is simply that the handle angles work for the respective plane designs. Your plane has a handle of around 65 degrees (which is the same as Stanley), while the Trying Plane handle is similar to a Veritas at about 75 degrees. Your trying plane's toe/mouth is 32% of the length of the plane.

Here are measurements of other planes I have:

http://i13.photobucket.com/albums/a262/Derek50/Planes/Planestats3_zps2ec180fe.jpg

The first statistic of relevance is that, with the exception of the Trying Plane and Jointer, all planes have a mouth/toe percentage around the 35% mark, which is similar to yours.

The exceptions here are the HNTG Trying Plane and the Jointer, are similar in having a significantly higher percentage (the mouth is relatively further back), with the Trying Plane even further back than the Jointer.

Inference: the longer the toe/mouth percentage, the more the plane will benefit from a horizontal vector, and the shorter the toe/mouth percentage, the more the plane will benefit for down force when planing.

The second statistic is the height where the handle is held relative to the length of the body. The lower planes (Jack, Jointer, Trying Plane) all have a low centre of gravity. They appear to work more efficiently with a low centre of effort (forward vector). The relatively higher planes require more down force. Note that the Krenov smoother (made by JK) has a 45 degree bed, while the lower coffin (shopmade) has a 55 degree bed. It requires significantly more downforce to push than the Krenov. A higher body (3" is common) would be expected to require even more downforce.

My thought at this stage is that Stanley make a handle that has the best of both worlds. It can be held at the upper end, where it imparts downforce. It may also be pushed by the heel of the hand when the vector is horizontal. Some planes, however, may benefit from one extreme or the other (in some cases substitute the hand for a handle). That is for discussion.

Regards from Perth

Derek

[IanW]

This could become an exceedingly complex discussion! I think we have agreed that there are some very general rules for placement of totes on planes, but the operative word is general! I don't take exception to anything in the above post, except the 'fluid wrist' bit. For sure, your wrist needs to move, & it's designed to do that, but I like mine to be in a position where the carpal bones (the two rows of little marbles that form the actual wrist) are all taking the pressure evenly during the powered part of the stroke, i.e., in the straight, or what I call 'neutral' position. That isn't something I work out with a slide-rule from some deep knowledge of mammalian anatomy, it's something that feedback through the handle tells me.

I think you are getting to the nub when you talk about the force vectors required, & how they vary for different plane geometries, but before we can discuss vectors in any meaningful way, even for a single plane type, we would need to establish a fixed height for the stroke relative to your anatomy. This is going to vary a bit during a long stroke as we lean back & forth, and a lot due to different body sizes & relative lengths of arm bones, not to mention personal preference for how much you like to bend your back as you put your main effort into the job. There is also another variable not discussed so far: what is the left hand up to during all this? I like to use planes with my left hand palm-down on the knob or bun, I don't wrap my fingers around the knob as seems to be more common. I started doing this about 20-somthing years back, when I found I got a sore hand caused by rubbing against the body of the plane during a long session with a #4, & just wanted to change my grip for a while. The plane in question had a low, flat-topped knob which made that easy & natural. I quickly decided this had two distinct advantages. One, you tend to apply maximum downward force on the toe of the plane at the start of the stroke, which is where you need it, and as you progress through the stroke, both horizontal & downward forces gradually transfer to the rear hand, which is where you want it as the plane goes over the edge. The advantages are especially noticeable if planing short boards, which always ended up convex, earlier in my career. At the end of the stroke, my right hand pulls the plane back, lifting it slightly so the blade isn't travelling back over the wood. The latter is something that was beaten into us during primary school woodworking classes, & though I have my doubts it's anywhere near as vital as our manual training teacher insisted, I still flinchinwardly if I don't at least ease the back of the plane up a bit on the return. This planing style probably works best with short-toed planes (i.e. your typical Bailey metal plane), where the front knob/bun is virtually at the cutting edge. Anyway, the upshot is that my left hand does much of the control of the downward forces & my right hand mostly only at the end of the stroke.

It's all too complex for this tiny brain! :C The key factor is our subjective assessment of what feels 'right', which isn't always reliable in the first instance, at least not mine. It's so very true that one needs to use a tool for a while before declaring it absolutely fit for purpose. I have had several experiences of making or altering something, trying it for a minute or two & declaring it perfect, wonderful, done! Then down the track, after some serious usage, deciding that I didn't like it at all & needed to think it through again!

But keep at it Derek, it's dogged persistence that gets there, and you may yet come up with a set of rules for handle placement on planes, or at least some sound guidelines for us all. However, despite my love of analysis & the why of things, I think I'll wimp out on this one, & fall back on intuition and experience as my guides for where I stick a plane handle & what angle it is at. Not very helpful for others, & it means I'll make more mistakes, I suppose, but I'm only planning to make a few more planes in this life, & at least one will be a full infill & won't have handles to worry about :shrug: :U

Cheers,