Chisel sharpening

[Wend]

Apologies for yet another thread on everyone's favourite topic! But I've been trying to master the art of sharpening chisels, and I don't think I've quite got the hang of it yet.

I'm starting off by trying to work on the back of an old 1/2" chisel. I figure that the back ought to be the easiest bit to do, as I don't have to worry about bevel angles or anything. The chisel isn't in great shape, but I figure that shouldn't matter much for just sharpening practice.

So here's what I started with:

Unfortunately that photo's a little blurry, but hopefully you can tell that the scratches nearest the tip are vertical.

So I started on a coarse diamond stone, with horizontal movements, so I could see what was happening. This felt like it went well, with horizontal scratches soon appearing across the whole end:

(in the photo it seems to have more pronounced vertical scratches still, but in person I'm sure that horizontal appeared to be much more dominant).

Then I went on to the fine diamond stone, with vertical movements. Again, this seemed to go fine, with vertical scratches reappearing.

The extra-fine diamond stone is where it started to feel like it went wrong. I went back to horizontal movements, but there was a triangle (bottom left of the photo) where vertical scratches remained:

(in fact, in this photo, the triangle also seems to have horizontal scratches in, but in person it looked like vertical dominated. It depends a bit on how the light catches it, I think).

I kept going on the extra fine, and the triangle gradually shrunk:

And shrunk more:

At this point I thought I would move on to the strop (leather + Chromium Oxide), to see what effect it would have on the part outside of the triangle. However, it appeared to have no visible effect whatsoever:

I thought that I was meant to be left with something with a mirror-like finish, but this very much still has visible scratch marks on it.

So, do these photos give any hints as to where I might be going wrong?

Thanks!

 

[D_W]

Mirror only happens if the abrasive is capable of it (and uncontaminated) and the steel is hard enough to not be cut too deeply by the abrasive (mild steel polishes at a higher grit than hardened steel).

Strops are notorious for harboring contamination (grit or coarse particles) and spider webbing is the result.

I'd start with the coarse grit again and work that corner off, but if you don't, you'll still probably be able to use it.

Pressure with your finger where you want metal to be removed (so toward the end of the chisel) and pretty much just keep rubbing it and don't let it rock on the abrasive surface.

 

[Jacob]

Didn't seem to be anything wrong with your chisel in the first pic, except it needs sharpening. This means taking material off the bevel, not the face as you have done.
Then a tiny bit of face down burr removal is enough to polish your face and reduce friction.
There's a strong fashion for flattening/polishing/mirror finishes etc but if you just want to use the chisel for woodwork you really don't need to waste your time on these processes.
PS I forgot to say - your first photo shows a typical very slight convexity behind the edge. This is very common with a newish chisel. I'm not sure if this is a deliberate design feature or not, but it makes a chisel very easy to sharpen as less material needs to be taken off to remove the burr. This advantage is slowly lost with further sharpenings. A chisel is never so easy to sharpen as when it's brand new; 1 minute max.
Your flattening exercise merely speeds up the rate of wear on the chisel and ages it, equivalent to many years of use. Old tools get polished with use, not because somebody has set about purposely polishing them!

 

[John15]

Hi Wend,

Not sure where you are in Oxfordshire but I live about 10 miles north of Oxford and would be happy to demonstrate my method for sharpening chisels. PM me if you think I can help.

John

 

[essexalan]

I would grind that chip out and clean the edge up roughly on the bevel side before doing anything further. Often found a void in old chisel blades in that area no idea why.

 

[Racers]

Looks like your coarse diamond stone isn't flat or you where rocking/putting to much pressure on one side.
As the others have said you need a finer grit to get a mirror finish.


Pete

 

[nabs]

I'd say the corner you could not reach with the diamond stone was probably not flat in the first place, which is quite common on old chisels (presumably because they have been sharpened on stones that were not flat).

In that case I would have flattened it too, as it will make subsequent sharpening easier (it is harder to remove the all the burr that will form if the face is not flat). Per other comments above, I would just go back to the coarse diamond stone until you are working on the whole area at the tip of the tool.

You can get a polished face by spending more time on the finer grits and strop, but I am not sure it makes a big difference as the face will get gradually polished during normal sharpening.

 

[Phil Pascoe]

If you have a lathe, glue some 80 or 100grit on some scrap ply or mdf on as large a disc as it'll handle - you can flatten anything in seconds.

 

[Jacob]

If you have a lathe, glue some 80 or 100grit on some scrap ply or mdf on as large a disc as it'll handle - you can flatten anything in seconds.

Yes that's the way to finish it off! I suppose it couldn't make it much worse than it is already.
Pity to see a perfectly good chisel being wrecked in the cause of fashion!

 

[Cheshirechappie]

One factor may be the nature of the abrasives used. Diamonds as used in sharpening stones have something of a reputation for being quite 'pointy', and being firmly held, tend to leave deepish scratches compared to other abrasives of similar grit size.

There may be two solutions to the problem. The first is not to worry about the scratches too much. Just sharpen the bevel up as usual, back off as usual, and put the chisel to work. See how it performs - it may be perfectly adequate. The second solution, if performance turns out to be less than that desired, is to do the bulk of the sharpening on the diamond stones, but finish on a fine abrasive of some other sort; for example, waterstones give a good polish, but can be messy to use, fine oilstones work well on simpler steels (less well on the fancy ones) but can be pricey to buy, Welsh Slate gives an excellent finish, but cut very slowly.

In general, most experienced craftsmen tend to gravitate towards a fairly simple honing regime with a maximum of two stones; a coarse-ish one to hone away wear and damage to the edge, and a fine one to impart the final polish. There's no law that says they have to be the same medium.

Unfortunately, there's no perfect sharpening medium that does everything really well. If there was, we'd all be using it. Most of us eventually find a way that works for us, though - so keep going, and you'll get there!

 

[Ttrees]

Your not trying to flatten you chisel on one of those DMD whetstones that sell for about 2 quid a pop, by any chance ?
I use wet and dry 400 sandpaper on a flat surface plate, Use float glass has a green tinge to it(not plate glass) a broken granite plate from a stove or tile place or other similar thing or machine table
Then I have a good diamond stone really worn 1800grit for the rest from Stu-Mac, I can't remember brand,
but its one of the good brands
This produces a mirror polish just about ...with a strange techinque you may have found aswell ?,
By lapping on a stone drying out it gives a better polish, and you get a feel for the perfect time to take the iron off before the lubrication is gone.
I spent waaaaaay to long lapping all my irons on this stone
And I don't use this technique, so I have a smeared kind of mirrored back on all tools now.
A 4000 grit waterstone gives me a scratch pattern like in your pics

I could do with a rougher grit whetstone as the cheap sandpaper doesn't go very far
You need quite a bit more than you think sometimes.

I wonder if the Ultex whetstones are up to the task?

Tom

 

[nabs]

it is not (only) a fashion Jacob! having a reasonably flat face/back is one less thing to worry about when learning to sharpen - particularly if you are using old tools - because once it is flat it is easy to remove the bur and you can always be confident that the edge has been finished to a good standard on at least one side (and can thus just concentrate on the bevel).

 

[Ttrees]

A chisel is never so easy to sharpen as when it's brand new; 1 minute max.


Your flattening exercise merely speeds up the rate of wear on the chisel and ages it, equivalent to many years of use. Old tools get polished with use, not because somebody has set about purposely polishing them!

I have never heard anyone saying your easy when new statement Jacob, would you say the same for a plane iron?

I can't say flattening the back on a chisel is as sure of a thing as its made out to be, maybe in some scenarios it may work, I might have to look to those videos again with skeptical eyes.

I'm doing a pig of a job at the moment widening deep mortises, and finding I'm having to lift the chisel excessively long grain paring down to the line.
I was thinking of making an adjustable jig for resting my chisel on to go halfway through, so I can pare cross grain instead of long grain....
Maybe this is a scenario in which the flattened back is where it shines, I wonder

Tom

 

[Phil Pascoe]

I assume all the people who don't flatten chisels and irons sharpen tools such as carving tools, knives, axes etc. on one side only? If not why not?

 

[Jacob]

it is not (only) a fashion Jacob! having a reasonably flat face/back is one less thing to worry about when learning to sharpen - ...

Really? It seems to me to be exactly the opposite. Thread after thread with people spending hours flattening and polishing, usually with great difficulty, as per our OP. Top photo shows chisel in ideal shape for easy sharpening in one minute or so (very slight hollow behind the edge).
It's a just a modern fashion; old tools were polished by use. I think this is where the idea was born but it wasn't achieved by purposeful polishing. An easy mistake!!

 

[Jacob]

......

I have never heard anyone saying your easy when new statement Jacob, would you say the same for a plane iron?.....

I blame the mags etc. There's a huge vested interest in telling everybody these things are difficult. It sells gadgets, jigs , stones, DVDs , courses, people make a living by it!

Modern plane irons are always dead flat already.
Ancient or modern they all need to have a good tight fit of cap iron to face, not necessarily flat along the length of the face, but just the last few mm, which is what you get anyway after a few sharpenings and removing the burr.

All the new chisels I've ever had have had that very slight concavity on the face, just like the OPs above, which doesn't look as though it had had much use. This makes them very easy to sharpen in seconds. I don't know if this is a deliberate maker's intention, or just a by product of the usual processes.

 

[Jacob]

....
I'm doing a pig of a job at the moment widening deep mortises, and finding I'm having to lift the chisel excessively long grain paring down to the line.
I was thinking of making an adjustable jig for resting my chisel on to go halfway through, so I can pare cross grain instead of long grain....
Maybe this is a scenario in which the flattened back is where it shines, I wonder

Tom

A concave back (face) wouldn't help but flat or convex would be OK. Slightly convex is giving more control perhaps - you can lift or dip the edge to guide it?

 

[ED65]

There's a strong fashion for flattening/polishing/mirror finishes etc but if you just want to use the chisel for woodwork you really don't need to waste your time on these processes.

All woodwork is the same is it Jacob? Everyone needs chisels prepped to only the level you require, is that the claim you're making? :roll:

A chisel is never so easy to sharpen as when it's brand new; 1 minute max.

Firstly, that statement is utter tosh. It's wrong in principle and conveniently ignores some variables.

Everyone here with a good many chisels under their belt knows that how long it takes will always come down to the individual chisel. I haven't had the dozens of chisels pass through my hands that some have but I've already seen firsthand all the usual suspects: flat at the edge with a hollow back a bit from it (yay), slightly crowned or bellied (ugh), uneven left to right at the edge (double ugh), and much more rarely, very flat all the way back as far as you care to check. It does nobody any favours to 'suggest' that every one of those is equally quick to deal with.

Now what about taking into account steel type (exotics, hello?) and relatively speed of honing surface?

Secondly, and perhaps most importantly, Wend specifically said "an old 1/2" chisel" and we can clearly see both corners are dinged or worn. So any supposed golden rule for prep time for new chisels isn't relevant anyway!

 

[ED65]

At this point I thought I would move on to the strop (leather + Chromium Oxide), to see what effect it would have on the part outside of the triangle. However, it appeared to have no visible effect whatsoever:
...
I thought that I was meant to be left with something with a mirror-like finish, but this very much still has visible scratch marks on it.

Taking a small leap here without knowing what your green compound is really like but there's a very good chance that if you persevered it could give you a mirror polish or very close to it. Some green honing blocks just use CrO the way they used to, some are a mix and some are just dyed green so they are very much not all the same. But it seems all will work and raise a polish of some degree or another.

But it's difficult to get this on a large area of the flat of a chisel by hand stropping, much much easier on the bevel. My stropped bevels are all mirrors but the backs vary. This isn't so much to do with differences in steel or in technique, it's merely that I no longer strop to make things nice and shiny (the novelty wears off ). I strop until I think the edge can't get any better and then stop, so how many strokes this takes varies significantly. Depending on a few factors including chisel width and how the sharpening went this time or the last few times some are properly reflective, some are a "hazy mirror" as it's sometimes referred to.

There's an additional contributing factor to scratches in a brighter area of polished steel that I'll just mention briefly as it may or may not relate to your finer diamond plates. These can be quite notorious for having clumps of diamond sitting well proud of the surface and only when well broken in will they be giving more consistently fine results somewhat in line with a stone of similar grit size. This break-in period is claimed by the makers to take just a few minutes but user feedback tells us it can unfortunately take weeks or months of use.

 

[D_W]

Don't get fascinated with needing a cosmetic mirror polish on the back of a chisel. It'll have little to do with sharpness if the back is flat to start.

That is, unless there are out of flat spots on the back of a chisel or deep scratches that get to the edge and form a nick, there's little to be gained by trying to make the back jewelry. I don't personally like completely polished chisel backs, they've got significant grip on end grain. Is it a practical problem? No, but it's something you can feel on a parer, etc, and it's annoying.