Why can't I flatten the back of my mortice chisel?

[Jacob]

It’s an interesting idea @Jacob. I will give it a go. In the past I’ve used sticky sandpaper stuck to my table saw table, or spray glue on an old cast iron surface plate that I never really managed to get off. Sticky sandpaper is expensive and remarkably hard to find (when I looked).

Wet n dry paper is really cheap and available everywhere.

The downside I can see, is you don’t want any sparks.

It's not a new idea - it's how DIY engineers did things in the old days like flattening cylinder heads for new gaskets on their Ford Prefects etc etc and is designed for the job.
Sparks totally improbable! It's all wet surfaces to start with and you could do it with water if you are really anxious!

 

[Adam W.]

I tried the paper stuck to glass method and other less modern ones and now I have one of these if I want to sharpen dull/damaged stuff in a hurry.

https://www.dmtsharp.com/sharpeners...duosharp-bench-stone-coarse-extra-coarse.html

Seems to work a treat and I got it for a reduced price at Amazon warehouse.

Now, I know some will say that I don't need it or that there are other better/cheaper/traditional options, but nevertheless, it's what I have and if your mileage varies, so be it.

 

[Fergie 307]

I am with Jacob on this one. Whole sheet on a suitable glass or other flat surface. Wet the plate and the paper will stick to it perfectly flat, then wet the paper and off you go. Less likely to roll if you just draw it towards you, rather than pushing to and fro. Personally I use two hands, a finger on top of the tip to keep it flat, and a very light grip on the other end to pull it across the paper. On the granite plate I use I find good old water works best.

 

[worn thumbs]

I do possess a few mortise chisels and have never felt the need to flatten any of them,in fact I would be rather surprised if something so narrow wasn't flat enough without making a big effort.Not entirely to be contrarian,I will mention that I hardly ever use them for cutting mortises.After I first got a bench drill I found it more convenient to chain drill the mortises and clean out the residue with an ordinary chisel.A few years later I bought a very basic mortiser and now only use the chisels if I have to clean out a mortise in situ.

 

[Agent_zed]

Pour a pool of white spirit on to your glass

That would make your hands stink and you'd be breathing in VOCs. I'd much rather use water and just make sure I dry my tools properly afterwards.

 

[Jacob]

That would make your hands stink and you'd be breathing in VOCs. I'd much rather use water and just make sure I dry my tools properly afterwards.

Well yes, but I don't do it very often, just the occasional remedial job. Perhaps I'd set it up to use water if I started making a habit of it. Couldn't use my combi outfeed table with water.
Normal sharpening for me is just oil stone

 

[spanner48]

So what is wrong with using an 8" diamond-grit flat stone? It's always worked for me, and the diamond-grit stones are not epensive nowadays.

 

[Jacob]

So what is wrong with using an 8" diamond-grit flat stone?

Nothing wrong except limited for size and larger granite stone etc is probably going to be flatter. You can do the sole of a No8 with two sheets of wet n dry

It's always worked for me, and the diamond-grit stones are not epensive nowadays.

 

[Phil Pascoe]

Normal sharpening for me is just oil stone

Negative excrement, Sherlock!

 

[donturner]

All rejoice, my mortice chisel back is now flat and sharp. To be clear, the end goal here was not just to make the back of the chisel flat, it was to make it sharp all the way across the cutting edge.

Thanks for all the suggestions. In particular, to @Peter Sefton who pointed me to his excellent 2hr video tutorial on sharpening (£19 well spent imo). As many have mentioned the key problems were:

- Using too coarse wet/dry sandpaper
- Not sticking the sandpaper down completely flat
- Inefficient/poor technique - dragging the whole chisel back over the abrasive is not efficient or required - only the first 30mm or so from the cutting edge needs to be flat

Here's what I did (or stopped doing):

- Stopped using sandpaper on glass and moved back to using diamond stones: coarse, fine and extra fine. I appreciate that using sandpaper is cheaper, but a number of people have said this approach is suboptimal.
- Starting with the coarse stone, moved it out of its plywood holder (which inhibited access to the stone's long sides) and into a rubber holder (this one) which holds just a single stone which allows access to all sides of the stone (see photo)
- Positioned the chisel at 45 degrees to the side of the stone and moved it forward and back along the whole length, this seemed to be a lot more efficient at cutting
- Didn't push too hard downwards, just tried to keep the chisel back absolutely flat against the stone at all times
- Worked my way up through the stones, regularly marking the edge with a sharpie, made sure that all the sharpie marks were completely gone before moving to the next grit
- Did not use a strop

Less relevant but still helped:

- Cleaning up my diamond stones with a pencil eraser seemed to improve the cutting action quite a bit

Whole process took about 30 mins.

Note: in this photo you can still see some very slight differences at the corners, however, these were removed when honing the bevelled edge

Thanks again to everyone to posted.

 

[Adam W.]

Now you need to only get the back shiny like a mirror for part 2.

 

[donturner]

Now you need to only get the back shiny like a mirror for part 2.

Haha, I don't have a diamond stone fine enough for a mirrored finish and I'm scared to use a strop in case of rounding the corners again! I've ordered some "scary sharp" supplies so hopefully I'll be able to see my face in it soon. Or maybe I'll just get back to chopping mortices and not worry about it.

 

[okeydokey]

Glad you have it sorted, I use water as a lubricant when using my diamond stone it helps, about a leather strop -imo leather is softer than steel so I think you will be ok using one.
I have seen others use a spray bottle of window/glass cleaner instead of plain water.

 

[Fred48]

Haha, I don't have a diamond stone fine enough for a mirrored finish and I'm scared to use a strop in case of rounding the corners again! I've ordered some "scary sharp" supplies so hopefully I'll be able to see my face in it soon. Or maybe I'll just get back to chopping mortices and not worry about it.

 

[Fred48]

Glad you have it sorted, I use water as a lubricant when using my diamond stone it helps, about a leather strop -imo leather is softer than steel so I think you will be ok using one.
I have seen others use a spray bottle of window/glass cleaner instead of plain water.

Don't know what happened there. Adam's recommendation in an excellent idea
Fred

 

[Adam W.]

Thank you @Fred48.


@donturner

Currently your mortice chisel edge resembles a saw.
If you want it properly sharp, you need to go all the way and get rid of those scratches and shine it up. And you don't need a micro bevel on it, because all it does is increase the angle of the cutting edge, ask @Jacob about that he's a fan of the single bevel too.

 

[--Tom--]

Go get mortising - what’re you making?

 

[spanner48]

Nothing wrong except limited for size and larger granite stone etc is probably going to be flatter. You can do the sole of a No8 with two sheets of wet n dry

The question was about a mortice chisel. An 8" diamond stone is plenty big enough for any such. And the point about diamond stones is that they DON'T wear hollow - as granite stones do. I've spent too many hours using corundum grit and water on a steel plate, trying to flatten hollowed sharpening stones, to ever want to do it again . . .

 

[Jacob]

The question was about a mortice chisel. An 8" diamond stone is plenty big enough for any such.

Yebbut one system suits all, i.e. full sheets of wet n dry on a big enough plate. This for remedial work only not for routine sharpening.

And the point about diamond stones is that they DON'T wear hollow - as granite stones do.

But they do wear out, as oil stones don't, which typically can last for life, as long as you don't spend hours pointlessly flattening them.

I've spent too many hours using corundum grit and water on a steel plate, trying to flatten hollowed sharpening stones, to ever want to do it again . . .

Waste of time. I never flatten sharpening stones - if you spread the work they stay flat enough for life. A bit of a dip length-ways is no problem and a hollow across is OK as most plane blades need a camber anyway.
I occasionally freshen one up with a 3m diapad to remove clogged up surface, embedded wire edges etc.
I had one 2nd hand Norton "0" combination stone with a deep hollow lengthways on the coarse side which must have been done with regular axe sharpening or similar, and in fact I found perfect for axe sharpening! The fine side was rounded over very slightly which made a change from hollowed out. Didn't realise this at first until it started showing up on plane blades. No prob, just have to change the technique slightly to get a camber instead.
My basic opinion of modern sharpening is that it is grossly over thought and is much easier done almost head-down-brain-off, with no fancy gear

 

[Adam W.]

I flatten my oil stones regularly with a diamond plate, it keeps them in good condition, flat and cutting nicely.

Other than that, I'm old skool with a red India and a piece of slate.

¡Olé!