When to use a cambered edge and for which plane
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- This topic has 3 replies, 4 voices, and was last updated 3 years, 9 months ago by Ed.
11 June 2019 at 10:33 am #579957
Hi all. First time poster and beginner woodworker here.
Firstly. Is a cambered edge an edge anything other than square? Or is there a difference between cambered edges and slightly rounded corners?
Secondly. When to use a cambered blade over a straight blade? I have a #4, #4 1/2 and a #5 1/2 and slightly rounded the corners on each. But wouldn’t a straight edge help for flattening something square or for use on a shooting board? Surely a curved blade will produced dished out shapes as opposed to straight ones?
Thanks for any help!27 August 2019 at 7:18 am #603108
Welcome to the forum Bobby.
Cambered edge is usually the edge that has a slight curve throughout the edge of the iron. Typically it’s anywhere from 0.1 to ⅛”ish deep, if you took a square edge and placed it along the edges of the iron, you should see a slight curve sticking out in the middle. The way I achieve this is by starting on one side of the blade tilted up and as if I’m sharpening as usual, incrementally bring the iron down to the centre and then I start from the other edge, again tilted up and go down toward the centre. For me it’s never an exact science…so I go by the feel.
As for the plane selection, it depends on what you’re working on. If you have to deal with straightening a huge piece of board, then probably #5 would be ideal. However, if you are planing to clean up a rough sawn stock, then a narrower plane will be ideal, because with heavy camber, you want the sole of your plane to not skip the “groovy” planes surface that your cambered iron creates.
As for the dished out aspect left from a cambered irons…sometimes these can be beneficial too. It’s an old trick…if you want to edge join laminate two boards, then dish out the middle part and you’ll get a really tightly closed glue join line.
Here’s my take, for what it’s worth. First, be a little careful because there are two curves, one along the bevel (thickness of blade) and one across the bevel (width of blade). Paul is somewhat unique in using a curve in the thickness of the blade, and this is what he calls a cambered edge. The curve across the width of the blade is what I think you’re talking about, and is sometimes called a camber, sometimes a crown. For that curve, here’s what I do:
1. Joinery tools like rabbet planes, shoulder planes, and plow / grooving planes are always dead straight.
2. On a bench plane planing with the grain, more crown means that you sever the fibers better when planing. For perfectly straight grained wood, there aren’t any fibers to sever, but with more difficult wood, the fibers go hither and yon willy nilly. The crown helps sever the fibers and facilitates getting a cleaner shaving. The extreme of this is a scrub plane, and this is why they can take such heavy shavings. But, as you increase the crown, you get a narrower shaving, which becomes frustrating for leveling a surface because it is like trying to color in a sheet of paper using a crayon point rather than using the wide side of the crayon. Also, more crown means more of a scalloped appearance. So, think about what you want, and use that to decide how much crown. Some advocate for smoothers to be flat with just rounded corners so that they take the widest, thinnest shaving possible, yet don’t leave track marks from the corners. This has never worked well for me, and I always want just the smallest amount of crown. For smoothing, I try to have a wide flat area in the middle and then a little curve of one to a few thousandths in the outer 1/4 of the blade. It’s just by eye.
3. I think a crown can help adjust the squareness of an edge. Usually, I can adjust with a flat blade, but sometimes it’s too much and I grab a blade with more crown. If I want to keep what I have, I’ll reach for a plane that is flatter.
4. For the shooting board, I like a flat blade.
I have a couple #4, a couple #5, and one #8 and try to have one of each on the flat side and one of each on the crowned side, but honestly they each are however I last sharpened them. You don’t need multiple planes if you are using old Stanley’s and Baileys since the thin irons are easy to add, or remove, the small amounts of crown we are talking about, but I’m glad I have multiple planes (or at least multiple blades). On modern planes with thick blades, the amount of work to adjust the crown is much, much higher. One or two of my planes have thick blades and I like them for a few things, but overall I do my best to avoid them because they are so hard for me to adjust the sharpening in these subtle ways.
By the way, I’ve never had luck using Paul’s method of lifting the edge to round off the corner. It is quite easy to just make an angle or otherwise have a sharp transition. For most of what I described, it is just a matter of adding a little pressure on one side or the other or letting an edge hang off the stone.
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