Help there must be an answer

[newt]

This is a serious post.
I was reading an article on snipe and how to overcome the problem and it got me thinking. If we take a planner/jointer the out-feed table in theory should be level with the cutting blades when they are at top dead centre however we normally set the blades a fraction higher. Therefore if we lower the in-feed table by say 1 mm, 1 mm should be taken of the stock and the planed face should rest on the out feed table as the stock passes over the cutter. The same applies to a router table if the stock has to be planed eg the out-feed fence is shimmed out by the depth of cut required and made level with the cutter. Also the same applies to power planes the in-feed sole (the part in front of the rotating cuters) is raised to the required depth of cut and the out-feed (the sole behind the cutters) remains level with the blades. What has this to do with snipe well it does have an effect but it got me thinking of something far more interesting, please read on.

If all the above is true, how does a normal hand plane work? we know it does but how. The sole of the plane is fixed over its length and the blade projects to set the depth of cut. So into the workshop I go, I rub some engineers blue over the length of the sole, set the depth of cut to about 1mm, put some soft wood in the vice, applied downward pressure to the front of the plane, pushed forwards about 100mm then stopped, removed the plane and guess what, the sole of the plane behind the blade had not been touched. Repeated several times keeping downward pressure on the front of the plane same result. Then I relaxed the front pressure and operated the plane normally moving the downward pressure to the rear at the end of the stroke, only the very back of the sole near the handle had made contact. This indicates to me that the plane is operating at an angle eg both parts of the sole can never all be in contact with the wood. Anyway I can still plane quite flat but I am now confused about the physics and why we spend so much time making the whole sole flat.

 

[Anonymous]

You must enter a message when posting

 

[Bean]

Newt
It Sound confusing. When the planes sole is not flat and you start a cut the front of the plane is in contact only, the iron then goes into contact and starts to cut. this leaves no surface for the tail of the plane to sit on as the projection of the iron has cut it away.
Now if the tail of the plane was not flat to the toe or front it could have one of two effects. It could deepen the cut if it was convex or make the cut shallower if it was concave.

In general terms the plane can only sit on a couple of points in use. But by flattening the sole you can help to make the cut even across the board. With a sole which is not flat you will have little or no control over the depth of the cut, hence the cut will vary in depth across or along the the board. So the flatness of the sole will have an impact upon the flatness of the board you are planing with it.

Candle wax is a good lubricator for planes and helps to minimise friction but it will not make up for a plane sole in need of flattening

Hope that helps

 

[Anonymous]

You must enter a message when posting

 

[newt]

NORMANWISDOM

All I am saying is that all forms of power planers as far am I am aware have two parts the in-feed and the out-feed, the in-feed part is adjustable to set the depth of cut as I described. The perfect hand plane is dead flat over the whole of the sole and the depth of cut is determined by how much the blade protrudes through the sole. However as I described in my crude experiment the plane sole can never be in contact over its whole length. I am not saying that a hand plane does not function I am just saying that I do not fully understand how it works when the majority of the sole behind the blade cannot be in complete contact no matter how small the depth of cut. BEAN has perhaps pointed me in the the right direction, this is all academic but it would be nice to know why a hand plane differs fundamentally in its operation to power planners, both types in principle should produce a flat surface.

 

[George_N]

Isn't the technique in hand planing to apply the pressure on the front of the plane at the start of the cut, when the rear is projecting off the end and to transfer the weight to the rear as the front of the plane clears the other end. That way the whole length of the sole will have been in contact with the surface being planed, just not all at the same time. I suspect, though, the physics of this simple sounding action are really quite complicated, which is probably why novices like me find it difficult to master.

cheers

George

 

[Anonymous]

You must enter a message when posting

 

[Philly]

Newt
Well done-you've spotted something which has always got me thinking (a potentially dangerous experience :lol: )
As you say, how can a hand plane cut a flat surface when it has a sole where the infeed and out feed "tables" are in alignment, not shifted by the thickness of a shaving.
I believe this is why hand planes (even with "perfectly" flat soles) will always cut a convex surfave (to a small degree). If you watch David Charlesworth's DVD on hand planing you will see that he attempts to plane each surface to a slight hollow (i.e. concave) as it is an easily achieved result. If you continue to take full length shavings from a board (edge or face side) you will not end up with a flat surface.
Why is this not a huge problem to woodworkers??? And why aren't we all asking the tool manufactorers to make an improved "Wonder PLane"??
Because the amount of "snipe" is so small. And because, as planes are "hand" tools, there is always a certain amount of human variation in its use.
Hope this is some help,
Philly
Who's head is hurting...

 

[newt]

Philly that does help thanks. It is quite sad really I spent the best part of my time in bed last night thinking through this issue, as an engineer I should have been able resist the dangerous temptation to think about something that has been perfectly ok for centuries. However I cant help thinking what if a hand plane had the same features as a power plane with a variable hight in-feed sole, would it work? The clue in your response is the convex surface produced by a flat plane, actually you can mimic this effect if you mis-align the in -feed and out-feed tables on a planner.

 

[engineer one]

newt you must be careful, or they will truly ban us engineers from the site.

power planes do not actually cut, they chip, and give you a kind
of scalloped surface, although it is very slight.

in my view, hand planes work in a slightly different way.
the important thing to think about is that in most cases, the blade does
not go to the side of the tool. so the whole plane is kind of tilted to one side.

when you get long shavings, in the middle of the plane, it is still
riding along the other side of the sole where the blade is not. that's
why so many of us when we start. or re-start hand planing, have
a problem. i also think as well as grain, it is why so many people
suggest planing wide boards with the plane at an angle.

in most cases, we tend to only plane narrow boards by hand,
and so i do not think it is too relevant.

anyway properly sharpened(whoops )
a hand plane gives a really nice finish.

personally i think the major problem with pt's and hand power planers
is the way in which you put the board through. i can now plane
by hand at least the width of a door, quite well, but do the same with
a power planer, always get the groove/snipe.

when you feed the wood into a pt, the rollers can tend to snatch, and in
general, we do not have proper support at the infeed edge, which is why
you get leading edge snipe, at least on my ad160. maybe i should build a
sled for feeding in :?

outfeed snipe is also to do with the board tipping, not proper support.

anyway just use the thing, and get some sensible sleep. in this weather it
is difficult enough to sleep anyway without trying to understand why
thousands of years of hand planes actually works.

paul :wink:

 

[Bean]

Jacob

Strangely a perfectly flat hand plane used perfectly on a board wider than the plane CAN"T possibly plane a flat surface - it can only cut a trough - which has the same profile as the bit of blade protruding below the sole

I seem to think that i disagree, your statement above assumes that the plane travels in one direction only and then parallel to its sides. Infact by skewing the plane you gain ,in effect an infinity long trench, by keeping the toe of the plane on the uncut surface you also keep the same relationship between the blade and the surface as you did on the first cut. So instead of making a series of shallow trenches you make a trench and then widen that trench until you get to the otherside of the board. Also i believe that the flatness of the sole contributes to keeping the relationship between the iron board and sole consistent, on its own it will not contribute to the flatness of anything

 

[Scrit]

Outfeed snipe is also to do with the board tipping, not proper support.

On cheaper thicknessers snipe is actually down (at least in part) to the fact that as the rear edge of the workpiece clears the infeed roller the entire infeed/outfeed roller - cutter assembly tends to drop towards the rear of the machine exacerbating snipe. This is also true of infeed snipe. Industrial machines use separate nose or pressure bars to minimise and even they suffer from snipe. The solution is to butt a piece of scrap up against the end of the board as you feed through work (or just cut the snipe end off). You're right about longer infeed/outfeed tables making the snipe less evident, though

Scrit

 

[Anonymous]

You must enter a message when posting

 

[Anonymous]

What I don't understand is where you get the not-flat planes from. I've never had one or seen one, or are you talking tenths of a mm?
Re viewing the plane 'scoops' another way is to draw in the blade on your smallest plane, then 2b pencil over plane sole, and then slide it about over the sample. It'll show up all the highlights. A well planed piece done by an expert will have a regular pattern of even scoops - a bit like a carved surface as finished with a shallow gouge, but of course much longer, shallower and barely visible.

cheers
Jacob

Jacob, this is a really interesting idea. Do you have any photos showing the effect at all?

I am not sure that this effect will be seen if you plane with most pressure on the front of the plane during the stoke until the front clears the end of the wood; this will leave the front supported on wood above the level of the cut and result in no scalloping action. I would expect a flat even cut along the full length with possibly some variation near the end as pressure is moved to the rear.

By the way, I just visited your website and am very impressed.

 

[Anonymous]

You must enter a message when posting

 

[Bean]

Jacob

I think we are agreeing aren't we? That planing a board flat consists of joining up a series of trenches. You start on a very un-straight piece of wood with short trenches or scoops on the high points and progress towards your long trench i.e. as long as the board, when the board is straight.
PS not sure about holding the plane skewed - it's not something I conciously do - I'll think about it while I take the dog for a walk.

Yes I think we are, possibly just looking from different angles.

 

[newt]

In my second post I asked if a hand plane with an adjustable front shoe which would set the depth of cut, thus providing intimate contact for both the in-feed and out-feed during the planning process, would work. If there is genuine support for this idea I may have a go at making a prototype.

 

[Paul Chapman]

In my second post I asked if a hand plane with an adjustable front shoe which would set the depth of cut, thus providing intimate contact for both the in-feed and out-feed during the planning process, would work.

I remember that when I was a child we had a book at home which had an illustrated article about just such a plane, so the idea has been tried before - but I'm not sure how successful it was. I'm afraid I can't remember any details of the book but I'm talking of about 50 years ago.

Paul

 

[Anonymous]

You must enter a message when posting

 

[Alf]

This wondering about why hand planes work at all has cropped up periodically amongst Galoots for years and years. Trouble is finding the threads that discuss it #-o , but here's one that might be helpful. Way over my head mind you...

Cheers, Alf