biomechanics of planes

[bill howes]

I came across the thread on centre of effort and I have come to think that there might be a lot less confusion about a tote's design if one looked at it from the other end-the guy holding on.
As to the plane mechanics- for each plane it would be easy to discover the force vector that is required to plane the wood, a combination of downward pressure to enter the blade into the wood and to assure proper registration of the sole on the wood and forward effort to cut and bend the shaving and overcome friction and inertia. The force could then be applied in a straight line much as in the pole handle of the Stanley #74 floor plane. Intuitively I would suspect this line to be close to the line of the blade. I also suspect the centre or point that this force meets the plane moves forward when one starts the cut and back as one tries to keep the sole behind the blade running true-particularly one is jointing.
However the best angle and shape of the tote have more to do with the mechanics of the user
For example-the size (circumference) of the tote governs the angle of the wrist joint. Test this by making a tight fist and watch your wrist cock back(dorsiflex).
- the wrist is most comfortable in a neutral position(I was taught that this is the position ones wrist assumes when holding a glass of beer) Perhaps those who get pain in the web space get it because their wrist is held too far back.
- the triceps muscle on the back of the upper arm is much more efficient when the elbow is at 90 degrees or more. when the elbow is acutely flexed it can exert only a small % of its strength.
- some planning is done with the arms and shoulders such as planning across a board to flatten it , or with the back and legs as when one joints or moulds a longer board thus the height of the work becomes important as to which muscles are required. If one is using arm muscles the forearm should be horizontal for greater triceps strength and the tote should allow this. If one is using back and legs the angle may be different.
- the texture of the tote is important, If its shiny and slippery and one has to grip harder this changes forearm tension and hence wrist angle
- and of course the height of the board certainly plays into many of the above factors

I'm sure there are lots of other biomechanical factors, but something to think about eh

[Jim Matthews]

You have identified what I think is the most important part of using a plane.

If you're forced to contort in order to stand over the plane,
you're not in the most efficient position.

I think that like the floor plane you mention, there's a proper stance for a given plane.
The smaller the plane, the closer I get to it (less force required to move it across the work).

[Jim Koepke]

Perhaps those who get pain in the web space get it because their wrist is held too far back.

Some pictures were taken today to show my grip on my #4-1/2 type 6. The early handles have more wood toward the bottom and it is kind of crowded to get the pinky finger in there at times. Even the later totes are a touch crowded. With a later tote I do not feel as bad about modifying them to fit my hand.

Two Finger Grip.jpg

Often my grip is like this on planes:

Open Hand Grip.jpg

It is much more comfortable, but the plane doesn't feel as secure if I am walking around carrying it.

In the second image it came to me to push the front of the plane into my hand to see how it presses against my hand.

Now it occurs to me this should have also been done in the first image.

It is most uncomfortable for me to use a bench plane with the tote missing its horn.

For final smoothing I am not pressing down much on my planes. They do not need it if the blade is sharp.

You have identified what I think is the most important part of using a plane.

IMO, a tool that is uncomfortable in use has a design flaw.

jtk

[Kees Heiden]

Nice start of the thread Bill. I think you are onto something.

First about the direction of the force vector needed to plane. I think it is lower then the angle of the iron. Pushing the edge forwards through the wood and overcoming the resitance of the sole is certainly more then holding down the plane. The weight of th eplane helps a bit in that regard too. The exact direction of the force vector depends on many parameters. Cutting angles, dulling of the edge, hardness of the wood, grain direction, capiron position etc etc. So it is good that we as users have such flexible limbs!

I find that I use my legs a lot in planing. Of course I am not a big strong guy, so I have to use as much of my leg power as possible. That was illustrated very well when I was using slippers. I just slipped out of my slippers as soon as I started to plane in earnest! Now I have clogs with closed heels. Still easy to get in and out, but they give much more support for planing. Planing in flip flops must be horrible.

This makes bench height important. Too high a bench and I can't get my hips behind the plane. Too low and I have to bend over too much. I am pretty happy with my bench right now for planing allthough it is less then 38".

[george wilson]

So,Jim,you seem to be using the web of the thumb to push the plane,but don't have the side of the plane to rest your fingers on.

By the way: EGAD!!!!! Not another of these threads!!!!!!!!

[Derek Cohen]

I came across the thread on centre of effort and I have come to think that there might be a lot less confusion about a tote's design if one looked at it from the other end-the guy holding on.

Hi Bill, "the other end of the guy holding on" introduces many, many variables, and this is a separate issue to the centre of effort. Among these other variables are the height of the bench, the height of the Planer's arm, The length of the Planer's arm, their strength, the density of the timber, the sharpness of the blade, the width of the blade - all these are factors that influence the way the Planer uses their weight, height and strength to push the plane.

As to the plane mechanics- for each plane it would be easy to discover the force vector that is required to plane the wood, a combination of downward pressure to enter the blade into the wood and to assure proper registration of the sole on the wood and forward effort to cut and bend the shaving and overcome friction and inertia. The force could then be applied in a straight line much as in the pole handle of the Stanley #74 floor plane. Intuitively I would suspect this line to be close to the line of the blade. I also suspect the centre or point that this force meets the plane moves forward when one starts the cut and back as one tries to keep the sole behind the blade running true-particularly one is jointing.

While this appears intuitive, it is not that simple. It is not just the "line of the blade"; it is also the cutting angle - whether BU or BD the cutting angle may be the same, but the vector of force acting on it alters where the resistance will go - higher up seems to increase resistance, lower down seems to reduce it. So you can have a BD with a low vector or a BD with a high vector. The BD angles may be the same but they will be different to push. The changing of the HNT Gordon handle was an example of this.

However the best angle and shape of the tote have more to do with the mechanics of the user

Mechanics will come into it, however the shape of the handle also influences the direction the vector will take. One may change the vector using the same handle - the Stanley is an example of this: push from high or push from low. Comfort or ergonomics (when holding the plane) is not the issue here (although is an important consideration when choosing a handle). The Veritas LAJ and BUS handles, for example, are handles that offer a single vector - pushing forward only.

One may use muscle power to overcome extra effort. Or one may, in lacking muscle power, find that helpful vectors are not enough. The person plays a part, but there are too many variables in the "guy holding on" to quantify and thereby to conclude that this is the deciding factor in planing efficiency.

Regards from Perth

Derek

[David Weaver]

So,Jim,you seem to be using the web of the thumb to push the plane,but don't have the side of the plane to rest your fingers on.

By the way: EGAD!!!!! Not another of these threads!!!!!!!!

Finally found a good picture.I wonder if this was one that you made, George.

http://anthonyhaycabinetmaker.files....5/scan0011.jpg

[bill howes]

Mechanics will come into it, however the shape of the handle also influences the direction the vector will take. One may change the vector using the same handle - the Stanley is an example of this: push from high or push from low. Comfort or ergonomics (when holding the plane) is not the issue here (although is an important consideration when choosing a handle). The Veritas LAJ and BUS handles, for example, are handles that offer a single vector - pushing forward only.

One may use muscle power to overcome extra effort. Or one may, in lacking muscle power, find that helpful vectors are not enough. The person plays a part, but there are too many variables in the "guy holding on" to quantify and thereby to conclude that this is the deciding factor in planing efficiency.

Derek,
We are probably of the same mind. I agree each plane will have a line or vector along which if force is applied it is most efficient and a change in that line requires extra (and wasteful) effort.
My thought is that the tote should allow you to apply the force along that line such that your wrist is neutral and your forearm directed in that same line. I think that is why you are happy with your new tote.
I suspect the people at Veritas take all of this into consideration with their designs.
Bill

[Jim Matthews]

I love the "Period Authentic" photocopy in the background...

[David Weaver]

Sometimes you gotta carve, sometimes you gotta sharpen, sometimes you gotta chisel, sometimes you gotta plane....

.. and sometimes you gotta photocopy a design

I'm glad just to see a picture of the planes - the handle is further back on the plane than I'd have guessed and even further to the side than I'd have guessed.

[Derek Cohen]

I'm curious how that offset handle improves ergonomics? Logically it should unbalance the plane. What gives?

Regards from Perth

Derek

[george wilson]

Yes,David,that is one of the jack planes we made. Looking well used!! These were the bench planes they used in the Historic Area after Jon and I issued them.

Derek,Have you read the other posts I made about the offset handle? Kees also posted an even earlier Dutch plane which had the handle very close to the user's right side,in the LAST thread about this same subject. And,as I mentioned before,the planes from the Mary Rose,Henry VIII's ship,the handle was completely ON the right side,dovetailed into the side of the plane with a wide dovetail. Apparently,old time users felt the most important thing was to use the web of the thumb to avoid carpal tunnel. It does seem that the plane would be unbalanced by the offset handle,but that is the way they did it. I cannot be certain how they balanced the plane. Possibly the other hand aided in balancing it. At least,that's how I would have to do it if I were using such offset handle planes. My other hand would be coming down on the plane from the opposite side. I'd likely use the meat of the thumb to hold it down on the opposite side. Food for thought. When I was working in the Historic area,we did not yet have these authentic offset handle planes to use. I made them years later as toolmaker,when I was behind the scenes. But,we were issued original planes to copy. They were made with offset handles,if they were handled planes.

I just hope we all learn how to hold our planes so we can get some work going!! Somehow we muddle through. We weren't alive in the 18th. C. to know some things for sure,but,there are only so many ways to hold onto a simple block of wood when pushing it. The handle,being so short,and to the side,lends itself to using the web of the thumb. The other hand SEEMINGLY would aid in holding the plane down. A sharp blade would also help SUCK the plane down,as was mentioned above.

It was Mack Headley who developed the hypothesis of using the we of the thumb to push the plane. He was using one every day for many years.

About the photo copy: Keep in mind that we were not supposed to be actually living in the 18th. C.. Our shops were also labs where we studied original work and reproduced it. Photo copies were an aid to doing that,though It would have been better for Mack to keep it in a less obvious place. People were always snapping pictures,and it was easy to be caught off guard.

[David Weaver]

It seems to me that any amount of offset would just cause the user to skew the plane a little bit in use and user their left hand a little more, which isn't bad given that it's not like the handle is off to the side a foot, it's just an inch or two. that's probably something some of us do already, just not with a plane that was designed specifically to be used like that.

Mack's jack looks well used enough you could probably convince someone that it was an old plane, but I know they don't like to use original tools there.

[george wilson]

It was against museum policy to use original tools. That is why us toolmakers reproduced them. Original tools would obviously be worn out if used enough.Especially the blades. And,you only had a few inches of actual steel in an old plane blade.

[Kees Heiden]

When you are standing to the left of your work (as usually for a right handed woodworker) a plane with centrally placed tote is more unbalanced I think. With the offset tote to the right, your offset position to the left is compensated.