Embarrassing question about plane blade cambers.....

[Kalimna]

Greetings,
Having recently taken delivery of a jig that simplifies the honing of a camber on a blade (for me at any rate, this isnt meant to be a jig vs handheld question), and put a nice gentle camber on a couple of blades, I have a query regarding said blades.

Apologies if this is as daft a newbie question as it sounds in my head, but what is the suggested technique for squaring up an edge with one?
With the flat blades, I just did sequential shavings to square up an edge, which took me a bit of time, but got there in the end. However, using the cambered blade, it seems that I am getting very large swings in off-squareness from one edge to the other with this technique. I still seem to get there in the end, but lose a significant portion of board width doing so.

Having said that, track-free surfaces when smoothing are rather wonderful. I may not need so much sandpaper now

Thanks for any help offered,
Adam

 

[Paul Chapman]

This, from Chris Schwarz, might be helpful http://blog.woodworking-magazine.com/bl ... Guide.aspx

Cheers :wink:

Paul

 

[bugbear]

However, using the cambered blade, it seems that I am getting very large swings in off-squareness from one edge to the other with this technique.

Sounds like you've got quite a big camber.

EDIT: here's a repost from another forum:

In an attempt to clarify recent comments, and stop a useful discussion being side tracked by disputes over jargon, I'm made a diagram.

This shows 3 techniques which can be used to make the edge of a board square to its face.

The leftmost image shows a straight blade, set to take a uniform shaving. The board is made squarer by taking a partial width shaving. The plane is kept stable by being seated firmly on the edge of the board. Multiple shavings using this technique will eventually make a square edge with "steps" which can be made into a smooth, square edge with a finishing pass.

The centre image uses a cambered blade. Again the plane is seated firmly on the edge, and the geometry of the camber allows a tapered shaving to be taken, again bringing the edge closer to square. Sucessive shavings are taken so that the successive tapers can out the error, leaving a square edge.

The rightmost image shows what may be the most obvious technique; the plane is held perpendicular to the edge of the board (i.e. with the sole at the desired angle for the edge) and a shaving taken. This makes a small surface at the correct angle; successive shavings will make the surface larger until it is full width.

I have attempted to make no comment on the relative merits or properties of these techniques; I've merely trying to present some kind of agreed jargon for a helpful discussion.

BugBear

 

[mr grimsdale]

Apologies if this is as daft a newbie question as it sounds in my head, but what is the suggested technique for squaring up an edge with one?
With the flat blades, I just did sequential shavings to square up an edge, which took me a bit of time, but got there in the end. However, using the cambered blade, it seems that I am getting very large swings in off-squareness from one edge to the other with this technique. I still seem to get there in the end, but lose a significant portion of board width doing so....

Shouldn't make much difference if you plane square down the middle. The cambered blade will in theory leave a slightly hollow footprint, but the camber is usually so small that you wouldn't notice.
But if the edge is a bit off square, with a cambered blade you can take off a tapered shavings by doing it off central, to bring it back to square. You can even take out a twist by planing diagonally from one corner to the opposite so that the tapered shaving is lifted first on one side and then on the other.

 

[Philly]

I still seem to get there in the end, but lose a significant portion of board width doing so.

Sounds like you may be taking off too thick a shaving - aim for around a 4 thou shaving when jointing. Its thick enough to remove material and leave a nice surface but not so thick that you seem to lose half a board when jointing.

There's some very useful info in David Charlesworths first book on this subject - worth checking out!

Hope this helps,
Philly

 

[Kalimna]

Thanks for the replies folks.
At least I think I am doing roughly the right thing, even if a little heavy handedly, which would explain the swings Im getting.

I don't think the camber is too much, as I am using the (ahem) veritas jig. And to my eye, the camber is all but invisible.

I have also read the DC book, and found much of value within, but I always like to get further opinions, hence the posting.

Philly - what you suggest of the 4-thou thickness for truing is probably a fair bit thinner than what I have been 'achieving'. I shall check it out next time im out in the workshop/garage, and adjust accordingly.
I wonder if I could also ask a completely unrelated question, but still with planes? I have glued up a plane blank according to Fincks book, and am wanting to make it a round-bottom longitudinally as well as widthways. How do you suggest I proceed with the marking up of the mouth and subsequent opening up? I imagine it to be slightly different to a flat bottomed plane - so should I open it up a little then shape the bottom? Or shape first? I am just using up a couple of spare bits o' wood and will post piccies when finished....

Cheers
Adam

 

[Philly]

Adam
The camber needs to be as scaled to match the shaving you expect to take - too tight a camber and you will only use a small portion of the iron on a finer shaving.

As for the plane sole - leave the mouth too tight. Curve the sole, then when you are happy with it open the mouth to allow the iron to project.
When you mark out the mouths position you'll need to move its "virtual" position up the side of the plane a few mm - make it so the mouth is the width of the iron at its highest point. As you shape the sole the mouth will open up at its sides, so by making the mouth tight at the high spots you end up with the mouth too tight at the middle - something you is easy to tweak and desirable.

Hope this makes sense,
Philly

 

[David C]

When planing edges I consider a 4 thou shaving to be rather heavy and would suggest 2 thou. Your board will disappear less fast!

David

 

[NickUrquhart]

Hi Adam,
If it helps, i've found that a two plane method is a much quicker and less 'board hungry' way of squaring an edge. A cambered jack will get you within say 5 thou of your final measurement, but often if you try to make fine adjustments with an inappropriately coarsely set plane, you'll end up alternately overshooting. If you are 3 thou off square and your plane is set at 6 thou, you'll take off the 3 error and add more on the opposite side, hence just changing the problem to the other edge.

This is a common problem when jointing with old jacks with a high center of gravity. They tend to rock more easily than the Bailey types, the low posture of which, really helps with watching the shaving come through the mouth, helping you to keep things level. If you get the edge close to what you want with the cambered blade, and then switch to a square finely set Bailey, you can mark the high spots with pencil and selectively remove it. A fine set smoother could be set for 1/2 a thou, which makes it easier to 'creep up' on the final square edged measurement.

I've also found that if a board is dangerously close to what you need, and you are bricking it, in case the next pass takes you undersize, find a very small plane and take off only the high spots. I have a 4" long by 20mm wide dovetailed bu mitre plane, made a few years back especially for fishing rod building, which is ideal for very fine tweaking of peaks. It can be much easier with a 20mm wide plane to deal with those annoying humps in a thin board, which often lead you to rock and take off yet more where you didn't intend to.

Some people prefer a 4 1/2 or no.7 for final jointing because the extra width seems to make it easier to judge when you're level. I've often tried taping a mini spirit level to the front of Mathieson jack, just to see if it helps with shaving economy. In practice after a while you'll get a feel for it just by the way it feels in the hands.

Hope that helps and best of luck with the boards.
cheers, Nick.

 

[Kalimna]

Again, thanks for all the advice so far!

Philly - yep, that does all make sense, so I now have, sitting on the kitchen worktop, a maple/padauk glued up body with a 30cm radius roughly bandsawn base... Tomorrow I shall smooth it off and attack the rest!

David - I did a quick micrometer measurement, and found the shavings I had been taking were around 4-6thou. So probably a little thick! However, the planes I have been using were also happy taking 1-2thou, so perhaps thats where I should be?

Nick - Your suggestion of differently set planes makes sense too, and I sortof have that setup, but not as regimented as perhaps I could make it. Similarly, I may also try using a smaller plane to remove the high spots.


Out of interest, is there a situation whereby having a camber on a blade is a disadvantage (Im talking about 4-5-6-7 size planes)?

Cheers again,
Adam

 

[Paul Chapman]

Out of interest, is there a situation whereby having a camber on a blade is a disadvantage (Im talking about 4-5-6-7 size planes)?

One situation where a straight blade would be better is when jointing boards by planing two boards together. I like this technique because it doesn't matter if the edges are not planed at exactly 90 degrees - when you put the boards together, any discrepancy in one board is cancelled out by the other. I find the technique very fast and virtually foolproof and I'm surprised that more people don't seem to use it (provided the boards aren't too thick, of course).

Cheers :wink:

Paul

 

[Kalimna]

Paul - yes, I have tried that method too (initially on front and back plates for an acoustic guitar), and I understand the theory behind it, but sometimes I still end up with two boards not perfectly aligned. So I reckon my technique is at fault there too

Cheers,
Adam

 

[bugbear]

Out of interest, is there a situation whereby having a camber on a blade is a disadvantage (Im talking about 4-5-6-7 size planes)?

Adam

I think if one were jointing a very wide edge (i.e. 2 3/8") the camber might plane a deep enough hollow to adversely influence the glueing process.

BugBear

 

[mr grimsdale]

Paul - yes, I have tried that method too (initially on front and back plates for an acoustic guitar), and I understand the theory behind it, but sometimes I still end up with two boards not perfectly aligned. So I reckon my technique is at fault there too

Cheers,
Adam

Practice, practice! That's the answer to most woodwork problems and questions .
With the proviso that you also look closely at what you are doing and think about why it is/isn't working.

 

[woodbloke]

I've used both methods to edge joint and now just use a straight blade to plane the pieces individually, taking a couple of 'stop' shavings to get each board slightly concave.
It's not a difficult process with a decent, well set up plane taking fine shavings (mine is a LV LA jack or try) but it does take a bit of practice. The critical thing is to ensure that the side of the timber is dead vertical...it's then easy to judge when the edge is at 90deg - Rob

 

[bugbear]

Paul - yes, I have tried that method too (initially on front and back plates for an acoustic guitar), and I understand the theory behind it, but sometimes I still end up with two boards not perfectly aligned. So I reckon my technique is at fault there too

Cheers,
Adam

Practice, practice! That's the answer to most woodwork problems and questions .
With the proviso that you also look closely at what you are doing and think about why it is/isn't working.

I think initial advice on what to do, and subsequent advice on fault analysis can both be helpful.

But, yes, practice is neccessary for muscle memory.

BugBear

 

[mr grimsdale]

....yes, practice is neccessary for muscle memory.

BugBear

And perhaps more importantly; conscious memory. If you look closely at what you are doing (bright light helps) you can often see what is going wrong and take measures to avoid it. Frinstance you can look down the mouth of a plane, at the wood just in front of the blade.

 

[bugbear]

....yes, practice is neccessary for muscle memory.

BugBear

And perhaps more importantly; conscious memory. If you look closely at what you are doing (bright light helps) you can often see what is going wrong and take measures to avoid it. Frinstance you can look down the mouth of a plane, at the wood just in front of the blade.

Well, on a plane set with a narrow mouth to reduce tear out, you can't. But that's a minor point.

Moving on...

If things are going wrong, and you're analysing and correcting them, you're not "practising", you're "learning", or "researching" or something like that.

Which is a perfectly sensible thing to do, but not the same as practice.

Practice is what happens when a master shows an apprentice how to cut a mortice, then tells him to cut 500 of 'em.

BugBear

 

[mr grimsdale]

....
Practice is what happens when a master shows an apprentice how to cut a mortice, then tells him to cut 500 of 'em.

BugBear

By which time he will have learned how to do them pretty well, better than by any amount of instruction.
Same with splitting 500 hairs!

 

[Kalimna]

Mr Grim and BugBear - As a general rule with any skill, I find the learn a bit, practice, ask some advice, practice some more, ask some advice routine works very well.
Practicing is only useful if you are practicing 'correctly'. I find it emminently useful to have someone say "that's not quite how it should be done, try this instead" or "yes, that's the correct way, keep practicing". Whichever statement is the advice given is immaterial, if the advice is heeded then an improvement in technique should be the result.

Thanks to everyone (again) for their helpful suggestions. I think I have enough advice to go and practice some more now Though perhaps not at ten thirty in the evening, as even the gentle swish of shavings from a 5 1/2 can be noisy for the neighbours

Cheers,
Adam