Weird sharpening issue

[JWD]

Hi all, slightly embarrassing issue -

Apparently one jpeg is too big an upload size :roll: , I am having trouble keeping the back of this chisel perfectly flat, I don’t really understand how it’s happened but could really do with some constructive advice on how to fix it up
It seems that where the flat of the back meets the blade, both 90’ corners roll slightly off flat, so if you put it on a flat surface bevel up, the two corners where the back meets the surface would not be touching

Please excuse my terrible explanation and skills of sharpening...

I tend to use a 1200g eze lap stone then a new 10000g water stone. I’m confident the water stone is flat. I’ve never had this issue with the bevels of blades and I don’t think I’ve had issues with the back of plane blades either but it’s been a while since I flattened one.

I feel terrible as my angel of a girlfriend brought me the most incredible jap chisels and I’m kind of falling at the first hurdle before even using them!

Any and all constructive advice will be gratefully received

Cheers!

 

[Derek Cohen (Perth Oz)]

The back of the blade is dubbed, that is it is curved behind the blade. This is usually a result of poor grinding or polishing at manufacture (Two Cherries chisels are notorious for this) or poor sharpening technique (using unflat media, or rocking the blade).

While the back of a chisel blade does not need to be polished its full length, it does need this behind the bevel. Therefore the back here must be flat. Mark the back of the blade with a sharpie to monitor progress. If the blade is domed, you are better off hollowing the centre slightly, and then flattening it on a stone or sandpaper. Ensure that the media is flat - that is also a way to create this situation in the first place!

Regards from Perth

Derek

 

[MikeG.]

.....Apparently one jpeg is too big an upload size......

Pixresizer, a freebie download. Does images individually, or by the folder. Size the bigger dimension to 800 to 1000 pixels and you'll be fine.

 

[tony_s]

JWD, it sounds to me that assuming your technique is correct, you may need something a little more aggressive than a 1200g stone

 

[thetyreman]

maybe you are slightly raising the chisel? you have to be very aware of how your are holding it, also why not start at a lower grit? 1200 is usually what I finish on then go to a strop, but generally I only flatten it once, then it stays flat. It's usually 250, 600 then 1200 on diamond stones, and if it's really not working, go to a piece of float glass with abrasive paper through the grits.

 

[Woody2Shoes]

Hi - my tuppence-worth:

- as said above, 1200 grit is probably too fine to remove enough material from the back to get the back flat (again) without a lot of work. 300-400 grit (wet'n'dry paper on a bit of float glass or on top of your diamond stone, or another stone) would get you where you want to be quicker.

- also technique - I don't know how you're doing it but I'd put about 20mm of the pointy end on the edge of the stone back down and then place a single finger on top of the blade near the bevel to provide downward pressure, while using the other hand to slide the blade along the length of the stone, being very careful not to let the sideways force lift or drop the blade from flat.

Other techniques and ideas are available...

Cheers, W2S

 

[D_W]

We'll need a picture to be sure. Japanese chisels usually have a crisp junction where the sides meet the bottom, but there's always a first.

What Derek describes is very common on machine buffed chisels, and for some reason, especially chisels from continental Europe. Here in the states, we've been pumped full of two-cherries chisels for as long as I've been in this hobby, as if they are something spectacular. I bought the hirsch branded chisels of the same type years ago and never really saw the draw since they were rounded over, and still really don't see the draw to them. Bulky sides, rounded backs - can be corrected, of course, but there's always been something better available for less - "better" just has less savvy distributors, I guess.

Anyway, nobody will have good advice unless we can see a picture.

 

[Limey Lurker]

Are these the TRUE Japanese chisels, with the deep dish in the back? Have you been sharpening them in the European way?

 

[David C]

Many Japanese chisels are not remotely flat when new.

A problem I describe in my first book is that the shaft can cause the chisel to lift on the stone, causing dubbing. I usually solve this by grinding a little from the side of the shaft. This problem is not universal, tends to appear on about 50% of my chisels.

There are often bumps in the back where the hard layer meets the soft shaft.

I agree that 1200 stone is not coarse enough to initially flatten. I use 600, 700, or 800grit.

You say your waterstone is flat, but how many strokes till a hollow develops. I certainly flatten after approx. 50 to & fro strokes.

It is worth examining the shape of the back very carefully. If one is not careful metal will be removed much faster from the top, where the area of hard steel is smaller than at the edge. The aim is to remove as little metal from the top as possible, so careful use of downward force is required.

Hope this helps,
David Charlesworth

 

[Dangermouse 2nd]

Grind that boy on some course grit....

 

[matthewwh]

Applying pressure here rather than directly over the bevel will stabilise the ura over the stone, so it is 'self jigging' and creates a continuous planar surface. Pinch the neck with the other hand but avoid touching the handle with your palm.

A coarse diamond stone with plenty of soapy water or window cleaner would be an appropriate starting point for fixing the problem, don't use diamond plates for the bevels of laminated blades though - the softer backing material will clog up the surface.

 

[D_W]

Many Japanese chisels are not remotely flat when new.

A problem I describe in my first book is that the shaft can cause the chisel to lift on the stone, causing dubbing. I usually solve this by grinding a little from the side of the shaft. This problem is not universal, tends to appear on about 50% of my chisels.

There are often bumps in the back where the hard layer meets the soft shaft.

I agree that 1200 stone is not coarse enough to initially flatten. I use 600, 700, or 800grit.

You say your waterstone is flat, but how many strokes till a hollow develops. I certainly flatten after approx. 50 to & fro strokes.

It is worth examining the shape of the back very carefully. If one is not careful metal will be removed much faster from the top, where the area of hard steel is smaller than at the edge. The aim is to remove as little metal from the top as possible, so careful use of downward force is required.

Hope this helps,
David Charlesworth

The coarse work to flatten an entire back is the job of something like 100 grit PSA roll on a long run of glass, but most people don't have a long run of glass like that. In the states, it cost me $20 to buy a "replacement shelf" at a glass store, 8x42 and 3/8ths thick (which means the supporting surface below the glass must be flat - which we can easily conjure up by planing a bench dead flat and marking the area where it is).

the trouble with flattening the whole back of a japanese chisel is that some are not made with intentional convexity on the back. The user of the chisel should be aware that in that case, only the first 1/2 inch or less of the chisel should ever be worked on the stone on the back (both to avoid flattening the whole ura off of the stone, which makes the chisel less easy to sharpen, and also to avoid the mortal sin of leaving a japanese chisel halfway off of a stone and grinding deeply at the thinnest part of the ura, permanently marring the back of the chisel (unless the ura is removed).

It's important to look at a japanese chisel and see if it has that mild convexity along its length - if it does, it shouldn't be worked flat from end to end.

I have seen some very cheap chisels that are concave along their length - those are just defective.

In western woodworking, I guess we have this notion that the entire back of the chisel needs to be flat, but there is little we do (unless we're using a paring reference) where the direction of cut of the chisel hasn't been determined 1/4 inch into the cut. My first set was convex on the back, and I sold them to a friend. Then I got more convex chisels later and realized it's no impediment to work at all, and wish I'd have kept the first set.

I have also bought about 50 older japanese chisels over the years, and have never seen one concave along its length. I don't believe a user would've tolerated such a thing before white collar buyers became the main market.

(also have seen very little difference in edge holding - or, i should say none - between a $10 used chisel off of the japanese auction site - not a new cheap one, but a relatively older chisel that's seen professional use and is well finished - and the myriad of newer showy chisels that are $100-$200 each. the only requirement to get those older chisels in shape is the glass lap. A user would give up if they were using a stone for that).

 

[D_W]

the softer backing material will clog up the surface.

It (the soft metal) will also literally pull diamonds out of the electroplate layer. The harder the steel, the better the diamond plate will fare.