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Cannot make flat edge with a cambered blade

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tibi

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I have been using the technique that David Charlesworth describes in his video for squaring an edge with a cambered blade.

He has an animation that shows how to cut a slanted edge straight with a cambered blade here:

After the piece is being cut the line is perfectly straight. I cannot get this in reality, so I tried to model myself this situation.

My stock is 25 mm wide (1"). My blade is 50 mm wide (2"). My blade has a radius of 300 mm (12"). So the distance between edge and center of the blade is vertically 1,5 mm (1/16th). The situation is simplified so that you plane perfectly straight along the length of the stock with no deviation and no tilting the blade.

The premise is that the plane has to touch two highest points of the previously cut stock to form a plane on which the sole rests before the cutter engages into the wood and forms a new shape of the stock edge.

1. Initial state. One edge is 1 mm lower than the other.
1632302818784.png


2. I place the center of the blade (the most protruding part) above the highest edge and the plane of the sole touches the two high points of the current shape of the edge.
1632303061883.png

3. After the cut, we have 0,256 mm hollow in the center. Light will shine through under the try square
1632303128901.png

4. I try another cut where I move the center of the blade towards one of the edges
1632303479298.png

5. This cut made the situation worse
1632303576848.png


To conclude I can never get a truly flat edge (in theory) by this method, and I need to accept a hollow in the middle that is directly proportional to the camber size.

After retracting the blade and cutting both high ends off, I got this profile. (number 37.5 is just a canvas number and has nothing to do with the drawing)
1632304846023.png


However, if you have a straight edge on your blade, then you would just copy the original angle of the stock and you would not make it straight. Pivoting on the high side of the edge and trying to keep the plane perpendicular to the face in the air is not an option, too. So I do not have a solution for this with a straight blade, either.

I just want to know your thoughts on this and if I made an error in my methodology.

Thank you.
 
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Ttrees

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On really narrow stock, I overhang the plane off the edge, rather than keeping all of the plane
on the stock.
I notice I have to overhang the plane over the edge more so with a flatter camber, especially with a wee
narrow a piece like that.

Keep an eye on both ends of the timber, especially with a flatter camber.
Tom
 

tibi

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On really narrow stock, I overhang the plane off the edge, rather than keeping all of the plane
on the stock.
I notice I have to overhang the plane over the edge more so with a flatter camber, especially with a wee
narrow a piece like that.

Keep an eye on both ends of the timber, especially with a flatter camber.
Tom
I was planing some 15 mm boards yesterday and I did the same as you. I overhang the plane and it made it flatter, but I had less registration area that way, so I could easily tilt the plane one way or the other.
 

Ttrees

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I'd rig up a long edge planing setup for that if I'd much of it to do.
Pinching @custard piccy for you
(Hope you don't mind Mr Custard.)
Bench,-Edge-Shooting-06.jpg
 

Argus

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Getting a slight tilt out of what will become the face side by adjusting the presentation angle of the blade is one way of doing it.......but as you have found out it's a never-ending fiddle made to appear easy.

Personally, I think that the pursuit of a straight edge starts with a straight line marked on what was marked up as a face side. Then plane-and-check, check-and-plane down to that.

The other, more traditional way way is to present your plane at a right angle to the edge, start at the far end, check it and adjust, achieve a square edge then the work gradually backwards, resting the toe of your plane on the square part that you have just created. This should present your plane blade at the correct attitude without adjusting the tilt of the cutting edge.

At the end of all this you'll have a reasonably square edge that may have some highs and lows - you can than attack each of these in turn to get the thing onto or parallel with, your original line.

Unless you are going to glue two parts together, one rule often overlooked by 'Professional Designer/Makers' is that the eye is extremely forgiving. Basically, if it looks right, then it is right..... even with a slight imperfection.

Another thing, is to keep your plane hardware at a manageable level..... in other words, avoid super long planes.... about a number 4 is as big as you need - not more than a number 5. Otherwise you'll end up spending as much time fighting the plane as you will the angles!

There will be plenty of different techniques along before this topic goes off at a tangent!

Good luck
 

tibi

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Getting a slight tilt out of what will become the face side by adjusting the presentation angle of the blade is one way of doing it.......but as you have found out it's a never-ending fiddle made to appear easy.

Personally, I think that the pursuit of a straight edge starts with a straight line marked on what was marked up as a face side. Then plane-and-check, check-and-plane down to that.

The other, more traditional way way is to present your plane at a right angle to the edge, start at the far end, check it and adjust, achieve a square edge then the work gradually backwards, resting the toe of your plane on the square part that you have just created. This should present your plane blade at the correct attitude without adjusting the tilt of the cutting edge.

At the end of all this you'll have a reasonably square edge that may have some highs and lows - you can than attack each of these in turn to get the thing onto or parallel with, your original line.

Unless you are going to glue two parts together, one rule often overlooked by 'Professional Designer/Makers' is that the eye is extremely forgiving. Basically, if it looks right, then it is right..... even with a slight imperfection.

Another thing, is to keep your plane hardware at a manageable level..... in other words, avoid super long planes.... about a number 4 is as big as you need - not more than a number 5. Otherwise you'll end up spending as much time fighting the plane as you will the angles!

There will be plenty of different techniques along before this topic goes off at a tangent!

Good luck
Thank you very much Argus for your reply.

Can you please explain how do you mean present your plane at right angle to the edge? If the stock is narrow, I cannot plane it transversely. Maybe I did not get it right.

Also if you want to joint very long edges or plane faces and you want to do it in sections, do you always start at the far end and go backwards? I have already heard it twice (with your mention). What is the reason behind this?

Thanks.
 

Argus

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Can you please explain how do you mean present your plane at right angle to the edge? If the stock is narrow, I cannot plane it transversely. Maybe I did not get it right.
Hello, tibi..... What I meant by 'at right angles' was to say that, if you are planing a board's edge to create a face-edge that is at a right angle to its face side, I would expect it to clamped with the edge uppermost. The plane is then presented with its length aligned with the board, (Not with the plane at right angles to the board!) but the bed at right angles to the side in the way you would start a cut. This means that as you lay a correctly aligned blade edge to the wood it will start by taking a cut that is at right angles to the face of the board. If the board's edge is at an angle, repeated cuts starting from the far end, about 6 to 8 inches each time (15 to 200 mm) will cut away the misalignment and you can then progress backwards, each time resting the toe-end of the plane-bed on the previously cut piece, advancing to the far edge of the board, when it will be reasonably square.
You can then go to the next part, which is checking and adjusting and removing any obvious hollows or high parts.

I think that it consists of two elements:
First, judgement, secondly building that into skill and experience.
Finally, knowing when to stop!

This method here is good for a single board.

Preparing two boards to be glue-jointed is another, slightly different technique..... a different approach, but as with anything else wood-work oriented, there are several way to do it.
 

Jacob

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A lot of over thinking going on here!
Basically just plane the edge as well as you can.
Then check with a square and squint along it for straight.
If it helps - pencil mark the bits which are too high, side to side and/or end to end, and then plane off the marks.
Repeat this with progressively finer set of the plane.
 

tibi

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A lot of over thinking going on here!
Basically just plane the edge as well as you can.
Then check with a square and squint along it for straight.
If it helps - pencil mark the bits which are too high, side to side and/or end to end, and then plane off the marks.
Repeat this with progressively finer set of the plane.
This is what I am currently doing. I can get decent results with very slight deviations, but I cannot achieve the theorem given by any random youtube woodworking teacher : THE EDGE IS FLAT AND PERPENDICULAR TO THE FACE IF AND ONLY IF NO LIGHT UNDER ANY CIRCUMSTANCES PENETRATES UNDER YOUR FINEST STRAIGHTEDGE WHEN CHECKING AT ANY POINT ALONG STOCK'S LENGTH.

Maybe I just have very good eyes.

I have started this thread with David Charlesworth and I will conclude it with his golden advice: "Do not chase errors that exceed your skill level." :)
 

Jacob

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This is what I am currently doing. I can get decent results with very slight deviations, but I cannot achieve the theorem given by any random youtube woodworking teacher : THE EDGE IS FLAT AND PERPENDICULAR TO THE FACE IF AND ONLY IF NO LIGHT UNDER ANY CIRCUMSTANCES PENETRATES UNDER YOUR FINEST STRAIGHTEDGE WHEN CHECKING AT ANY POINT ALONG STOCK'S LENGTH.

Maybe I just have very good eyes.

I have started this thread with David Charlesworth and I will conclude it with his golden advice: "Do not chase errors that exceed your skill level." :)
Don't use a straightedge.* If it looks straight enough, it is straight.
One obvious exception is when matching board edges to join, e.g. table top. Plane one to fit the other for each joint, without trying to get them all perfect so they all fit each other. Mark them so you know which edges pair together.
*Short straight edges like a combi square or ruler are useful but long ones are no use for woodworkers.
Whatever you do don't check anything with feeler gauges - that way madness lies!
PS and ignore all "the theorems given by any random youtube woodworking teacher" 90% are complete nonsense., particularly sharpening advice which can be insane.
PPS forgot to add - a slightly cambered blade makes everything easier as you can virtually scoop material up from where it is not wanted, instead of having to use the whole width of the blade. The end result with most hand planing is finer and finer scallops until sufficiently invisible. They can often be seen on older work if you focus a torch light across the surface, if it hasn't been sanded.
Forgot to say - woodworkers do of course make their own straightedges such as this one which is also a plumb level. Perfect for door frame fitting. Add a perpendicular arm like a T square and it works for horizontal levels too
It is as accurate as the eye can judge and precise as a piece of string. Good enough!

Screenshot 2021-09-22 at 14.11.01.png
 
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Fitzroy

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Correct, with a curved edge you can never get a perfectly flat surface, that's just geometry. However, your 300mm radius camber is not quite correct as the bed angle of the blade will result in a larger effective radius at the contact point, it will also no longer be a circle it will be a parabola. At a bed angle of 45degrees your 0.26mm dip in the board reduces to a 0.18mm dip, and the lower the bed angle the smaller the dip.
 

tibi

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Correct, with a curved edge you can never get a perfectly flat surface, that's just geometry. However, your 300mm radius camber is not quite correct as the bed angle of the blade will result in a larger effective radius at the contact point, it will also no longer be a circle it will be a parabola. At a bed angle of 45degrees your 0.26mm dip in the board reduces to a 0.18mm dip, and the lower the bed angle the smaller the dip.
Fitzroy, yes you are correct. I did not take bed angle into account. So the hollow will be definitely less pronounced.
 

D_W

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If there's enough camber to see a relatively large gap through the middle of wide stock, then there's too much camber. Jointer camber around 5 thousandths or so is kind of nice, but with less of the camber in the center and just gradual bits going off at the edge. That should leave you with an ideal center cap of "not enough for a sheet of paper to get through"

Otherwise, when the left or right of a board is high, plane it toward square while you're refining the edge. If it gets out of square, then just move the plane left or right, wherever you need to plane the high spot off, and if you're still not getting satisfaction, check lateral adjustment on the plane as it's a pretty good way (out of whack lateral adjustment) to get something you don't expect.

If you do a lot of hand tool work, within less than a year, you'll feel vertical to a very square degree and your eyes will see a couple of thousandths of out of squareness unless there is confusing grain on the wood creating an illusion that it's going the other way.

Long story short, just work through this and don't worry too much - you're building skills and think will change to feel pretty soon (leaving less to check with a square at the end).
 

Jacob

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Correct, with a curved edge you can never get a perfectly flat surface, that's just geometry. However, your 300mm radius camber is not quite correct as the bed angle of the blade will result in a larger effective radius at the contact point, it will also no longer be a circle it will be a parabola. At a bed angle of 45degrees your 0.26mm dip in the board reduces to a 0.18mm dip, and the lower the bed angle the smaller the dip.
If you know the radius of your camber you are over thinking it.
 
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Cabinetman

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Never had a camber on a blade and never missed it, I just take the corners off a bit.
Sacrilege I hear you cry, tramlines will no doubt be mentioned, I finish off on a very fine cut set up properly, and I don’t have a problem even on tabletops, and no I hardly ever use sandpaper.
Suggest you get yourself another blade and keep it straight for edges.
 

TheTiddles

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Yep, that’s a curved blade for you.
Depends what you’re making, rough stuff you’ll never notice the error, fine things you will never be free from it.
 

deema

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Now not opening the sharpening Pandora box, if you sharpen your plane blade straight, and them as Cabinetman suggests just take the edges off by sharpening so that more pressure is applied to the outside edges you end up with a nice very slight curve in the blade. With a slightly curved blade you just keep the centre of the blade or in other words the plane directly on top of the high spot. Often a high edge will move from one side of a board along its length to the other so you follow it with the plane after working out what’s happening with a square. There will always be a slight hollow, it’s actually desirable if your gluing up boards, the outside edge is slightly more compressed than the centre to create a nice tight joint. Clamp force will pull the edges fully together.
 

Jacob

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Now not opening the sharpening Pandora box, if you sharpen your plane blade straight, and them as Cabinetman suggests just take the edges off by sharpening so that more pressure is applied to the outside edges you end up with a nice very slight curve in the blade. With a slightly curved blade you just keep the centre of the blade or in other words the plane directly on top of the high spot. Often a high edge will move from one side of a board along its length to the other so you follow it with the plane after working out what’s happening with a square. There will always be a slight hollow, it’s actually desirable if your gluing up boards, the outside edge is slightly more compressed than the centre to create a nice tight joint. Clamp force will pull the edges fully together.
You can see what happens if you keep the throat clear and simply watch shavings emerge as you go.
 

hlvd

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Just grind a flat edge on your blade and forget about cambered edges, you're making this way more complicated for yourself.

If you need to take some off the left side, hold the plane more to the left and vice versa.

What's with the fascination with the No4 on this forum, if you want to shoot an edge use the longest plane you've got, a No7 or even better a No8.
 
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