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Cannot make flat edge with a cambered blade

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JoshD

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I'm no expert on this, very much on a learning curve myself, but the guys who taught me advocated way less camber: 0.25-0.5mm (that's slightly more than the 5 thou, ie, 0.125mm mentioned above). At 0.25mm, with the plane adjusted to take a fine shaving there's no visible scallop. Btw I use a #6, again that's what I was taught.
 

JoshD

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Btw I don't actually measure the camber, I just sharpen the iron applying pressure from side to side, then when I'm reattaching the cap iron it gives me an opportunity to see roughly what I've got by way of camber.
 

JoshD

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Just thinking about it if you have 1.5mm camber then you can't really have a closely fitting cap iron----unless that's cambered as well.
 

GerryT

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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.

Agreed.

As others have said: why use a cambered iron in the first place ?
Swap out for a straight iron or regrind your existing iron straight and knock off the edges .

Like others have also commented, it‘s all too easy to get carried away but getting a flat/square edge should be uncomplicated.
David Charlesworth is superb craftsman but I feel that he often unnecessarily complicates things.
Why would you try and get a square edge with a clambered iron in the first
place ?
 

Jacob

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Maybe over thinking it but I always feel a cambered blade gives you much more control - you've got the choice of planing centrally or at a shallow angle away from the centre without even adjusting the tilt. Then you have automatically adjustable blade width - as you reduce the set you are also reducing the width of the cut. The edge of the cut tapers to nothing and leaves less of a mark than a flat blade with sharp or even rounded corner.
On the other hand the more the camber the more material you can remove - a little scrub blade only 32mm wide but with a 25mm radius camber removes material faster than anything.
 

Fitzroy

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Heavily cambered old woodie scrub plane and straight sharpened No 4 and No 5 is what I use. I do like the idea of a slight camber on a blade so that you can control the shaving thickness across the width of the plane, I've just never made the leap to reshape an iron and I don't have a spare to practice with., one day I'll try.
 

jcassidy

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So I'm recovering long-suppressed practical skills from technical school, but i do remember the application. We never measured the camber, always sharpened by hand and eye, and definately more concerned with the reference faces being at the correct angle to each other (usually 90°) and flat from edge to edge. A slight hollow in the middle across the edge (a teeny bit of light visible under the square) was a good result.

You keep pulling the iron back to reduce the shavings the closer to flatness you get. Adjust the blade using the lateral lever and depth adjustment.

I've never used a flat iron cos, as above, I've never reshaped and iron and don't have any spares to practise with...
 

Jacob

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So I'm recovering long-suppressed practical skills from technical school, but i do remember the application. We never measured the camber, always sharpened by hand and eye, and definately more concerned with the reference faces being at the correct angle to each other (usually 90°) and flat from edge to edge. A slight hollow in the middle across the edge (a teeny bit of light visible under the square) was a good result.

You keep pulling the iron back to reduce the shavings the closer to flatness you get. Adjust the blade using the lateral lever and depth adjustment.

I've never used a flat iron cos, as above, I've never reshaped and iron and don't have any spares to practise with...
All my blades were nicely cambered due to hollow stone and I never gave it a thought until one day I decided to flatten the stone - following the bad advice generally given by sharpening maniacs. Was never the same again - I have to think about it and work at it! It helped in the old days having only one combi stone but now I've got several and sharpening has become more difficult.
 

David C

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Many interesting points here!

Providing the camber is not excessive, the edge will be minutely hollow. This does not seem to affect gluing, I suspect some compression takes place.

I like to demonstrate that we can see light of as little as 0.0003 " with a good light and set square. We can see much smaller errors than we can correct.

Every craftsman I have consulted over the years say that they use a slight camber. If this does not work for you, a straight blade and long shooting board will get the job done.

Best wishes,
David Charlesworth
 

rafezetter

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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
I've been known to do something similar and bought a wooden badger plane for the task and then added a wide HDPE strip to the "bottom" plane side to act as a rubbing strip and to lift the blade edge off the workbench. (a badger plane blade goes right to the very edge of the body like a rebate plane and with the added advantage that the blade itself is set diagonally in the plane body for a better shear cut - works very well indeed)

At the risk of sounding above my experience I would have to agree with David C's last comment above - the camber should be minimal and the OP's complaint of seeing a 0.25mm hollow is just overthinking it considerably, and to my mind this slight hollow would have the same effect as adding "spring" to the joint along the board - "some compression" as David C stated - would help to keep the joint lines tight.

The only way I can think a cambered blade would be detrimental would be if some eejit was using a scrub blade!
 
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mark w

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Totally agree with Jacob, I think the only time a straight cutting edge comes onto play is when edge planing two boards back to back, the error in "out of square" is cancelled out.
 

tibi

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Well, I have practiced both techniques, and now I can get reasonably square edges with both techniques.

What I have found out is:

1. Blade needs to be really sharp. Today I have built a tool rest for my new bench grinder and hollow-ground all my plane blades. Sharpening on stones is now much quicker and not torturous anymore. It took ages to remove bellied bevels on stones.

2. When I have my stock in the vise and I use a cambered/straight blade, I can make a square edge, unless ...

3. I pick the stock from the vice and look into a strong light. After some minute adjustments, I can even make this look square, unless

4. I angle my small square so the beam rests on its edge (like a knife square), then the new world of light gaps appear. I have never even tried to correct this.

knife square for illustration. This one has a precision of 0.003 mm per 100 mm (0.00012 inches).
1633117845162.png


If I ever managed to get no light under the knife square across the full length, it would definitely be high in the middle lengthwise and I would have to start over again :)
 

Ttrees

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Many would go bananas at the thought, but for precision dimensioning work, the following just makes sense to me.

Do you have a flat bench to check against?
There could be twist, I often use the square and the calipers when wanting that precision,
a feel thing not any measurements taken, and is an asset to back up gut feeling.
Pulling the square off of the edge a few times I find better than always sticking it tight against the work, should you have a bench that will be dependable to use in such a fashion,
The lamp must be where you want it.

Along with sighting with a long reach angle poise lamp, at least a 7.5" shade, see if gap appears in terms of flatness of the face or edge,
Seeing where the work pivots about, has a knock when pressed corner to corner, and on wider or more precise work burnishing or even graphite marking can be used.

Always looking at the ends of the timber, especially if you use the cap iron.
It comes into play here IMO even though more difficult for myself,
the fact that one can turn the timber around and not be worried about reversing grain
makes things less faffing about.

My 2 cents
Tom
 
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