flattening the back of a chisel

[matjos26]

How important is it to flatten the back of a new chisel ive been watching a few you tube videos and allot of them put allot of time in to this more than the beveled angle itself

 

[Kalimna]

I think that the general consensus on here is that, unless you are doing the finest of cabinetry, that absolute flatness is not necessary.
Removal of machining marks will ensure an edge of the finest nature, but it's probably unlikely that you would notice.
An exception to this might be use of a paring chisel, where you may want a greater degree of flatness to improve the 'self jigging' effect.

You will also find that several polar opinions are likely to be offered. Try and read between the lines and analyse the advice. If it makes sense, then follow it. If not, then don't.

Cheers.
Adam

 

[tobytools]

As stated it depend what you want to use your chisel for, if it to open a tin of pair then a bend wouldn't matter. For a carving chisel not a problem, for a paring chisel a bigger problem.
At the end if the day there isn't a right or wrong, this sort of question falls behind the "sharpening" debate.
That being said it's better to have a true chisel in my eyes.

Japanese chisels have a hollow/belly on there backs.

TT

 

[Jacob]

It's a completely pointless waste of time in my opinion.

Honing and turning to remove the burr will leave you with a polished area behind the edge without you having to do anything special.
Removing the slight concavity found with most new chisels will just make subsequent sharpenings slightly more difficult.
It takes 20 seconds or so to get a new chisel working.

 

[AndyT]

The forum software automatically searches for similar posts. If you want to see how this question has been answered before, look down the page at the links, especially the first one,if you have time to spare.

https://www.ukworkshop.co.uk/forums/topic68506.html

 

[Corneel]

A NEW chisel shouldn't require any special attention. Polish it up a bit. If it happens to have a belly, so you can't reach the edge: send it back.

OLD chisels are another matter. You'll have to remove the pitting, because it interfere's with the edge. If it is severely bellied like a lot of them are, the you'd better only pay attention to the last 1/2" or so. Too much bother to adress that belly. And the chisel will cut nonetheless. If the belly is slight you might want to try to remove it first on very coarse sandpaper on a flat surface, but it is a lot of work.

 

[bugbear]

How important is it to flatten the back of a new chisel ive been watching a few you tube videos and allot of them put allot of time in to this more than the beveled angle itself

That's because the back is much larger than the bevel.

But it only needs doing once in the lifetime of a chisel. Back flattening isn't sharpening, it's "prep" or "fettling"

BugBear

 

[RossJarvis]

How important is it to flatten the back of a new chisel ive been watching a few you tube videos and allot of them put allot of time in to this more than the beveled angle itself

I have a set of Bahco chisels I've had for five years, every time I sharpen the chisels I spend some time trying to flatten the backs, I believe some of the thinner ones might have flat backs by now, the 36mm which I use most, after 5 years, is approaching having a flat back nearly up to the cutting edge. Generally they're fairly sharp in use, I'll tell you if they're any better with flat backs, but it could take another 5 years!

 

[Scouse]

If you have spent a few happy minutes on the forum, you will have gathered by now that there is more than one way to skin a cat when it comes to sharpening...

I flatten the backs of new chisels. I look at it like this; I'm going to spend the next however many years sharpening the tool, so I like to start from a known baseline on one of the two surfaces which will intersect to form a sharp edge. I'm not saying I'm right and everyone else is wrong, indeed I might be wrong, and wasting my time. It's my time, I don't mind.

In the past few weeks I have bought 5 Ashley Iles dovetail chisels (Workshop Heaven, great service, great chisels), 3 Narex mortise chisels (Classic Handtools, great service, great chisels) and a couple of sets of Aldi bevel edge chisels (again, great chisels...).

They would probably have all been fine straight out of the box, but I wouldn't regard any new tool to be ready to use immediately, and as I said I like to check. No harm, no foul.

None of them required more than a couple of swipes on 800 and a couple on 4000, a minute or two per chisel, and all were very slightly hollow, which was nice.

I'm not sure if it is a new fad, I was tought to check new blades twenty-five years ago; anyhow it is a one time only operation, removing the wire burr after sharpening the bevel each time keeps them flat.

It does no harm, and it's a nice hour or two dodging 'Professional Masterchef'.

But if you don't want to flatten, that's ok too.

 

[David C]

Convexity or concavity ?

I know which one is preferable.

David

 

[G S Haydon]

I would personally not flatten the whole back. I would work the back on you chosen medium until you have a 1/4" of honed metal behind the bevel. Other options are available.

 

[Jason]

Flat backs are probably no great advantage for chopping. But an advantage for pairing.

I suppose I'd inspect the back and see how much work I was looking at. If it's not going to be arduous and it's a chisel that'd be good for pairing then I'd go the extra distance. Otherwise, I might think better of it and do what's needed to get it chopping quickly or think better of it and spend my time elsewhere.

Haydon's suggestion will get you chopping and cutting quickly. But the down side is that you start giving your chisel an upturned nose - which is where it starts going wrong if you want the chisel to be good at pairing (though you'd still be fine for chamfers and some other things) - so I think it's worth taking a moment before you commit.

 

[Jacob]

....
Haydon's suggestion will get you chopping and cutting quickly. But the down side is that you start giving your chisel an upturned nose - which is where it starts going wrong if you want the chisel to be good at pairing .....

Well yes possibly, but in fact the slight upturn you find on most well used chisels (which haven't been repeatedly flattened) doesn't make any difference - or if it does you just use it slightly differently, probably without even being aware of it.
I feel that the general anxiety about "flatness" (bellied! :shock: ) is exaggerated and if your attention isn't drawn to it in practice you wouldn't notice it.
I'm slightly irritated by the flatness panic in that some years ago I sold on some perfectly OK chisels in the mistaken belief that they were unusable unless given hours of flattening attention. Just another woodworking myth.
I'm also puzzled by the notion that chisels need "prepping" any more than saws, screwdrivers, hammers etc. It's just another myth. People launch these redundant ideas and they float around, getting in everybodys way, unsinkable, for years!

 

[G S Haydon]

Hi Jason that is a valid point, mainly down to my poor explanation :lol:. I will put my money where my mouth is on this when I do a video review on the Narex chisels and bring some clarity to my point.
From the OP's point of view and for any one looking for advice on the subject you will find collision with this issue very quickly

http://www.youtube.com/watch?v=9Wl_uQOABxg (I include myself within the group discussed in the video)

The key thing is finding a system that works for the type of work you do.

 

[Scouse]

I'm slightly irritated by the flatness panic in that some years ago I sold on some perfectly OK chisels in the mistaken belief that they were unusable unless given hours of flattening attention. Just another woodworking myth.

I wonder if there is a discrepancy between an idea of flattening the backs to an engineering tolerance and 90 seconds on a couple of stones to provide a corresponding polished surface to the bevel? I've not come across a chisel which needs hours of attention myself, but...

I'm also puzzled by the notion that chisels need "prepping" any more than saws, screwdrivers, hammers etc. It's just another myth. People launch these redundant ideas and they float around, getting in everybodys way, unsinkable, for years!

I thought you were a Sellers groupie? They're all at it :lol:

http://www.youtube.com/watch?v=Ki8tt-VjwqI

 

[Jacob]

......
I thought you were a Sellers groupie? ....

Not at all. I like most of what he says but nobody is perfect!

We had flattening ad nauseum back here post759803.html

To save you the bother I've copied and pasted my contribution here. Wouldn't change a word, except I'd add that you don't have to remove machine marks to reduce friction.

Here's jh's chisel before and after. Old stock but unsharpened and with a cap to keep it in good nick. Ground at 25º

Distinctly concave along the length and slightly across the face so a paring cut will dive in a bit. It's not sharp so the result is more of a scrape

The kit; 2 oil stones and one strop;

The pink stone and 15 seconds later it's sharpish and machine marks almost gone (from the edge). Rounded bevel started so it's caught at the heel as well as the edge. Eventually after many sharpenings the whole bevel will be rounded with an edge at 30º;

The face near the edge is flattening out and shows up;

Another 30 seconds on beige stone and strop and it is sharp with machine marks gone (from the edge);

A planing/paring cut will pass over the surface without diving, unless you press it down near the edge and it will take off fine parings;

That's it. Say one minute in all, not counting getting the kit out and cleaning up. If you wanted it extremely sharp another 30 secs on a finer stone would do it. As the rounded bevel extends it will take a bit longer to hone which means spending longer on the coarser stones to back off the bevel.

It's self flattening - every time it is honed the flat area gets extended a touch and there's certainly no need to deliberately flatten or polish

Perfectly good chisel, well worth £1 + postage! Thanks jh.

 

[Cheshirechappie]

Jacob - I'm terribly sorry to be the one who has to break this news to you, but - what you've just done with that chisel is EXACTLY what the rest of us advocate when we talk about 'flattening the back of a new chisel'. We DON'T mean obtaining optical flatness and a deep chrome-like polish across the entire width and length back to the shoulder. We DO mean taking out the grinding marks just behind the cutting edge - just as you've done to that green-handled chisel!

Jacob - I'm so sorry. This probably means we now have much less to argue about....though no doubt you'll find something.

 

[Jacob]

Brilliant! Glad to hear it. :lol:
But there is no "flattening" involved - just normal honing and turning to remove the burr. No "prepping" (stupid word); just sharpening. No removing of machine marks (except incidentally).

"Obtaining optical flatness" seems to have been the objective in earlier posts and people have talked of hours of work involved, working their way through grits etc. etc. and (see matjos26's OP) there are videos! (I name no names :roll: ).

OK so what do you want to argue about next?

 

[Corneel]

So, the new chisels are clear.

Now the old ones. I have a very nice old chisel here, Nooitgedagt, late 19th century, laminated blade, 4 cm wide. I've got some work to the back allready, but the left edge in this picture is still pitted and just a tad lower then the rest. In this condition I can't get the corner sharp. So either I leave it as is and don't use that corner, or I put more work into it.

 

[Jacob]

Depends what you want to do with it and whether or not you have an alternative.
Personally I'd leave it as it is (but aim to correct it over time with each sharpening) and use another chisel if I wanted one sharp right to the edge