Low angle, 5 or 5 ½ jack plane for a beginner?
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Jacob
New Luddism. Wake up and resist.
What is it you don't understand Pete?
G S Haydon
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Dead right Pete. As Andy said, it's more than likely they would be. But, the two winding sticks need only be parallel and close in width, not sure I'd want a 20mm tall and a 150mm tall 
Jacob, Pete,
In an attempt to bring this discussion to a conclusion... It's easy to describe something as parallel to something else and overlook the fact that there are three different planes (X, Y and Z) to think about. If you don't draw a diagram or write very carefully, you can be thinking of one relationship in which a surface or edge is parallel to another but your audience can be thinking of different surfaces or edges which are not parallel.
In use, the sticks are placed parallel to the ends of the board when viewed from above.
They are then looked at horizontally.
Provided that both sticks are parallel to each other when viewed from above, they could be different heights. In this case, their upper surfaces would not be parallel with the top surface of the board. That wouldn't matter, as you would actually be looking at their top front edges, which would lie on a plane, if the board was flat. This plane would be sloping, relative to the board surface.
If the sticks are the same height, it still works, and the imagined plane on which the top front edges lie is parallel to the board. The upper surfaces of the sticks are also on this plane.
Having them the same height means that if you place them slightly out of parallel to each other when seen from above, it doesn't matter. They will still look parallel. They aren't, but the effect of one end being nearer and the other end being further away is trivial on the scale of a normal workpiece.
So, mismatched sticks could work but would be harder to use.
I hope that helps. It took a long time to type and I want to go and do some woodwork now.
In an attempt to bring this discussion to a conclusion... It's easy to describe something as parallel to something else and overlook the fact that there are three different planes (X, Y and Z) to think about. If you don't draw a diagram or write very carefully, you can be thinking of one relationship in which a surface or edge is parallel to another but your audience can be thinking of different surfaces or edges which are not parallel.
In use, the sticks are placed parallel to the ends of the board when viewed from above.
They are then looked at horizontally.
Provided that both sticks are parallel to each other when viewed from above, they could be different heights. In this case, their upper surfaces would not be parallel with the top surface of the board. That wouldn't matter, as you would actually be looking at their top front edges, which would lie on a plane, if the board was flat. This plane would be sloping, relative to the board surface.
If the sticks are the same height, it still works, and the imagined plane on which the top front edges lie is parallel to the board. The upper surfaces of the sticks are also on this plane.
Having them the same height means that if you place them slightly out of parallel to each other when seen from above, it doesn't matter. They will still look parallel. They aren't, but the effect of one end being nearer and the other end being further away is trivial on the scale of a normal workpiece.
So, mismatched sticks could work but would be harder to use.
I hope that helps. It took a long time to type and I want to go and do some woodwork now.
Jacob
New Luddism. Wake up and resist.
I'm afraid you are wrong. Try it with two different height sticks. They will align if parallel but not otherwise.custard":3np8ydmi said:
Jacob
New Luddism. Wake up and resist.
That means you are working with an acceptable degree of error for you. The bigger the difference between the sticks and the more they are out of parallel, the greater the error.custard":2yd6tc20 said:
Might as well make them identical to start with!
Sgian Dubh
Established Member
Here's a situation where I agree with ... er ... both you and Jacob. Andy seemed to do a good job of describing various issues. From a practical point of view winding sticks of different heights are fine assuming they're set up parallel to each other, or at least pretty close to parallel. If they're set up on the tested surface out of parallel to each other, then the greater the difference in thickness between them, the greater the error.custard":2kturafr said:
But Jacob makes a fair point in that winding sticks are best if they're the same thickness so that setting them up parallel on a surface under inspection isn't required. I think the phenomenon Jacob's alluding to is parallax causing displacement of an object depending on the sight line, or at least a variation of parallax. A tip for avoiding potential parallax error I give to learners is to hold a rule on its edge when measuring between two points rather than holding it on one of the wide flat sides. In the latter case the thickness of the rule can lead to misreading the measurement through the effect of parallax. Slainte.
MattRoberts
Established Member
Jacob, have you been on the sauce? Talk us through it then.Jacob":1r279hh2 said:
The height of a stick simply determines how far your winding stick edge is from the actual surface it's representing, nothing else. Assuming that all four edges of a stick are parallel to each other, it makes zero difference how high either stick is*
*Unless you're taking into account the curvature of the earth in your calculations, in which case I defer to your obviously superior standards of accuracy and would suggest you compare sticks at a distance of less than a few miles.
I'm back, I hope this will do:
When the surface under test is flat, and the sticks (viewed from above) are parallel, the edges line up ok, even if the sticks are of different heights.
Starting from that case, imagine twisting one of the sticks a little bit so it is not quite parallel to the other. Think about the edges which you are sighting - they won't lie on a plane any more.
BUT, if the surface of the board is twisted, it could compensate for that effect, by tilting one or both sticks end to end, and make the edges line up ok. It would look as if everything was ok when it wasn't.
To avoid the necessity of always getting the sticks parallel, it's common to use matched pairs.
When the surface under test is flat, and the sticks (viewed from above) are parallel, the edges line up ok, even if the sticks are of different heights.
Starting from that case, imagine twisting one of the sticks a little bit so it is not quite parallel to the other. Think about the edges which you are sighting - they won't lie on a plane any more.
BUT, if the surface of the board is twisted, it could compensate for that effect, by tilting one or both sticks end to end, and make the edges line up ok. It would look as if everything was ok when it wasn't.
To avoid the necessity of always getting the sticks parallel, it's common to use matched pairs.
Jacob
New Luddism. Wake up and resist.
Two (nicely made etc) winding sticks of different sizes on a flat surface will have their top edges in the same plane only when they are parallel to each other. If you turn one of the sticks away from parallel (still on the flat surface) the top edges won't be in the same plane. It's just simple geometry - nothing to do with parallax, curvature of the earth, or effects of alcohol. :roll:
If the difference isn't great then neither will be the error, so you can get away with it within reason.
If the difference isn't great then neither will be the error, so you can get away with it within reason.
A quick note to the original poster - I hope you are still reading this stuff. We often go wildly off-piste on a topic like this. Sometimes the discussion will throw up interesting nuggets of information, sometimes not. It's nothing personal - we just like to carry on chatting long after your question has been answered, even if nobody else is listening!
Jacob
New Luddism. Wake up and resist.
Exactly! Congratulations!AndyT":1610hp02 said:
(hammer)
PS or if the board is flat it will look as though it isn't.
Well, it took a while, but I think we have collectively got from
Winding sticks have to be straight obviously but also parallel top and bottom and both exactly same height.
to
Winding sticks have to be straight, with top and bottom edges parallel. They are better if they are the same height, so are generally made that way.
Phew!
Winding sticks have to be straight obviously but also parallel top and bottom and both exactly same height.
to
Winding sticks have to be straight, with top and bottom edges parallel. They are better if they are the same height, so are generally made that way.
Phew!
Jacob
New Luddism. Wake up and resist.
We got from "any old straight off-cuts will do. They don't have to be the same. The only thing they need to be is straight."AndyT":1507vbzl said:
via Pete's doubtful wibbling,
finally to
Winding sticks have to be straight obviously but also parallel top and bottom and both exactly same height.
:lol:
Jacob
New Luddism. Wake up and resist.
Dunno, you tell me Pete. I wouldn't worry about it if I was you.Racers":3rfqnl7w said:
PS just wondering - on the one hand you have people going on about 'reference planes' and high precision, on the other being very casual about a simple but very precise trad technique actually involving a reference plane. Is there a connection?
So I assume that if the two strips are exactly the same width they won't work if the bench isn't dead horizontal, or if you're testing the side of a tapered workpiece for flatness?
