How do you flatten chisel backs?

[snafuspyramid]

I've been working my way through a bunch of Titan registered firmers, most of which have had backs which are VERY far from being flat.

While the smaller sizes haven't caused too much trouble, I'm now getting to the biggies, and this is starting to take me AGES.

So far, I've tried using the 120 grit Sigma Power SiC stone, as well as using silicon carbide lapping grit on glass. The stone works much faster. I then move on to 240, 1000 and 6000 grit stones.

But the work is painfully slow, and this is coming from a man who just entirely reground fifteen ancient, much-abused bevels on bench stones by hand.

Is there a quicker, non-mechanised way? What do you guys use to flatten chisel backs?

[Skew ChiDAMN!!]

Non-mechanised?

That rules out 120-180grit on a belt-sander then.

[derekcohen]

...Is there a quicker, non-mechanised way? What do you guys use to flatten chisel backs?

It depends how much you want to flatten.

I suspect that you are confusing "flat" with "shiny". Ideally the back needs to be flat (and some will argue even that). It does not need to be honed to the level of the bevel except for directly behind the bevel. I aim for 1/2" - 1" (max). But even a couple of mm behind the bevel is enough. The rest of the back can be flat and dull.

So that should cut out a LOT of honing!

Regards from Perth

Derek

[snafuspyramid]

No, I haven't even got around to honing anything yet.

I'm just trying to take it one step at a time, and get everything into its basic form - my smoothing plane beds flat (can't see the point of doing the others), all the planes clean, de-rusted and tuned, all my old chisels re-ground to get a good bevel, and all my chisel backs flat.

Since I'm doing all this entirely by hand for six planes and fifteen Titans - that is, a huge heap of rust - you'll appreciate it's teaching me patience.

When I was buying an eccentric honing guide roller at Carbatec the other day, the guy at the counter pointed out that, in the past, apprentices spent between three and five years doing almost nothing except learning sharpening and watching the master. I have to say, I'm starting to feel like that. It's been around five months and I've not built a single thing

But I am learning things in the right order. In my case, that's tool collecting and sharpening first. (Workbench next, then on to making some of my own tools). The upside is, once you've spent hours and hours on a single tool, you start to feel like it's actually yours.

Anyway, to get back to the point, I'm still trying to flatten, not hone, the backs. I agree that there's no point in honing (polishing) the whole back. But, it's necessary to flatten a good section of the back because otherwise the end of the chisel forms a noticeable crown.

I'm just wondering what methods others use. Is sandpaper quicker than stones?

[Bernt]

I must say I mainly buy new tools, so tuning is not a huge job but still makes all the difference. For initial flattening and squaring I use wet and dry sandpaper (when a lot of work to do on some tools even started at 80 grid) on table saw or planer bed. Make sure to clean, dry and oil the machines after doing this. If no machine beds available, a piece of glass on your bench is fine to tape your sandpaper to. Stones work very well for maintenance and sharpening but when you have that much to do the won't stay flat enough during the process and you keep having to flatten them or will never get your surface flat. I know good professional woodworkers who do all their sharpening with sandpaper on a piece of glass. I prefer water stones.
good luck with it!

[AlexS]

I use a diamond plate for initial flattening. As Derek says, it's only the last 1/2" or so that needs to be flattened on chisels.

[rsser]

Have tried a range of manual methods. Diamond plates, ceramic stones, 'Scary Sharp' etc.

I like the Woodpeckers Honing Plates for their length and flatness and convenience, and pray that coarse 3M Imperial lapping film will become available in retail quantities ...

Next experiment will be with Worksharp tempered glass discs with PSA abrasive sheet mounted on the lathe or drill press. OK, not manual, but where's the virtue in not using a machine for this purpose?

[snafuspyramid]

OK, not manual, but where's the virtue in not using a machine for this purpose?

In my case, because I don't own any

I've tried courser grades of silicon carbide paper on glass with much more success. Not fantastic fun, still, but at least satisfyingly measurable results

[rsser]

Yeah, SiC sheet on glass, regularly changed when it's blunted, will give you a result but not in my experience a reliably flat one.

Your mileage may vary.

[mic-d]

does it really need to be flat?

[rsser]

Good question.

Put a back bevel on a bevel-down plane iron, registration is not an issue.

With a chisel, following the pack, I've flattened and polished the back to about 30mm from the edge, assuming that user compensation and the rest of the shaft were within bounds.

Sometimes the chisels I look to rehab have a serious shaft bend so are not worth the effort and get tossed.

You have a diff. view Michael?

[derekcohen]

does it really need to be flat?

That article of Bob's has flaws. Read it cautiously.

The need for "flat" at the back of a blade - plane or chisel - is to achieve a sharp edge. As I pointed out earlier, one only needs to flatten the area immediately behind the bevel (about 1/2" or so) to create the flat/honed area.

So what about a flat (not honed) back of a chisel being used for registration - the point that Bob disagrees on? Bob is correct in saying that a wedge will move when driven into wood. It does not go straight in. However it moves in the direction of the flat, and if the flat is registered against a fence (such as a block of wood when chopping dovetails) it will be held by this and move in a straight line. Then a straight cut depends on the straightness of the back of the blade. If you attempted to chop down without the wooden fence, then the chisel would move back (and over the baseline). The thinner the section of wood to pare, however, the less the chisel will be influenced by the wedge.

Regards from Perth

Derek

[snafuspyramid]

Personally, I am inclined to flatten the backs of chisels.

Plane irons too.

The whole point of this, for me, is to do everything by hand, everything to the best of my ability, and to take no shortcuts. So far I've not departed from any of those ideas, much to my satisfaction, and against most sensible advice (especially with the no powered grinder thing).

Might sound strange, but for me this is a hobby not a profession.

[mic-d]

Good question, but not my question. I found that blog and immediately posted the link here for anyone interested - bit of food for thought. That's not my view though, I still think at least a paring chisel needs to be flat some distance back from the edge. If I see empirical evidence otherwise I'll reconsider.

Good question.

Put a back bevel on a bevel-down plane iron, registration is not an issue.

With a chisel, following the pack, I've flattened and polished the back to about 30mm from the edge, assuming that user compensation and the rest of the shaft were within bounds.

Sometimes the chisels I look to rehab have a serious shaft bend so are not worth the effort and get tossed.

You have a diff. view Michael?

[snafuspyramid]

Well, I've flattened quite a few chisels now, but I'm running into problems.

They're all flat side to side. I stopped flattening when I saw no more crown in the edge - and even grind marks along the back edge.

However, they still aren't flat from back to front, if that makes sense.

To illustrate what I mean, I just did two sketchup models. I did these quickly, so I hope it's clear what I mean. The red and pink areas are the surfaces that I consider to be flat (in that, when applied to a perfectly flat waterstone, these were the areas that became immediately polished).

These are thumping chisels, not for paring (registered Titans).

Both chisels are flat and "polishable" immediately behind the edge, which is really what I want. But are these shapes an issue?