Back Flattening

[mudman]

Right, whilst Mr G.'s at the beach, I feel safe enough to post on this subject. :wink: :wink:

I have a load of pig-sticker mortice chisels that I got from ebay and by heck the backs are bad! A couple appear to have been taken to a grinder and most are approximating a banana shape.

Before going on holiday, I spent a load of time trying various metal removal devices to flatten these but wasn't getting very far very fast.

On holiday I bought a DMT x-coarse/coarse stone for $94 (£42 in our money ) and was very impressed with the results. Really fast and I found myself actually starting to get somewhere. Finally finished flattening the one I'd started before holiday a lot faster than I would have hoped before. Then I finally got around to watching DC's video on chisel prep. Looked good I thought, completely different to what I had been doing so I tried it out. Heck of a difference. It seems to me that you need to combine the right equipment with the right techniques. Without this combination you can reach your goal but it may get a bit long-winded.

Only problem I do have is with the heavy thumb pressure, my thumbs are a bit knackered and I get a lot of pain doing that sort of thing for too long, but that's just me. Anyone else get this problem?

Anyway, I'd thoroughly recommend DC's approach. (That doesn't make me sound too much like an acolyte does it? :? )

 

[mr]

Anyway, I'd thoroughly recommend DC's approach. (That doesn't make me sound too much like an acolyte does it? :? )

Senseless guru worship.

Cheers Mike

 

[Vormulac]

Doesn't mean he's wrong! :lol:

V.


"He *is* the Messiah, I should know, I've followed a few..."

Sorry.

 

[dunbarhamlin]

Way to go! Had a few test wacks with a newly arrived OBMC just last night - I'm hooked. This style feels much more comfortable/controllable to me. (Happily almost flat back though)

Last joints of index fingers worse for me. Had a monster flattening session earlier this year and found a long stick on top of the blade helped - let me use different parts of my hand as a pressure applicator. Of course, this might be a really bad idea results-wise, but seemed to help after several hours of finger abuse

Mr C's vids are on my list.

Cheers

 

[mudman]

Way to go! Had a few test wacks with a newly arrived OBMC just last night - I'm hooked. This style feels much more comfortable/controllable to me. (Happily almost flat back though)

Last joints of index fingers worse for me. Had a monster flattening session earlier this year and found a long stick on top of the blade helped - let me use different parts of my hand as a pressure applicator. Of course, this might be a really bad idea results-wise, but seemed to help after several hours of finger abuse

Mr C's vids are on my list.

Cheers

I might try the stick idea, thanks for the tip.
I agree about the feel, you can tell that whacking out rectangular holes in wood is what these tools were created for.

 

[engineer one]

these days flattening definately makes my fingers hurt. not sure whether that is the long term problem, or just that holding small things so tight for so long was the reason.

paul :wink:

 

[JesseM]

Way to go! Had a few test wacks with a newly arrived OBMC just last night - I'm hooked. This style feels much more comfortable/controllable to me. (Happily almost flat back though)
Cheers

I'm glad your happy with them as I am mine. OBMC's are not common here, and this was my first introduction to them. It makes mortise chopping very enjoyable

 

[MarcW]

Hi all,

I do not recommend putting a stick on a chisel in order to flatten the face, commonly called back. I did this to a 2 inch Robert Sorby - which I bought for paring - and actually did not flatten the face but put a low spot on the area near the edge. The stick provides much pressure just over the edge. That and the long lever arm lift the back on the other side of the stone a tad and will cause you much more worry. DC's method works fine putting your fingertips on the chisel, no stick :wink:

 

[bugbear]

I will point out that flattening the back of a 1/8" wide 1/2" deep mortise chisel is "tricky"

DAMHIKT.

BugBear

 

[ByronBlack]

Is it really that beneficial to have a really flat back on a mortice chisel? It's a fairly rough/simple operation, and I would have thought a strong sharp edge is more important than a flat back - as opposed to paring/bench chisels where I can obviously see the benefits. But a mortice chisel? I'm not sure it makes a huge differece.. i'm happy to be corrected if there is something i'm missing here

 

[mudman]

Is it really that beneficial to have a really flat back on a mortice chisel? It's a fairly rough/simple operation, and I would have thought a strong sharp edge is more important than a flat back - as opposed to paring/bench chisels where I can obviously see the benefits. But a mortice chisel? I'm not sure it makes a huge differece.. i'm happy to be corrected if there is something i'm missing here

I can see what you mean and I expect that there is some truth in this. My thinking was that you need them to be reasonably flat and definitely without a belly across the width. This way the chisel itself will help to keep the mortice square and well formed. I suppose that the ends can be finished off with a paring chisel but if the mortice has been accurately prepared, then the whole mortice could be chopped out in one operation.

Anyway, my ones were/are waaaaaay out of flat. One looks like it has been attacked with a bench grinder by someone with a severe case of hiccups.

 

[MrJay]

Ni hao

Pig-stickers are tapered in cross section, so if you remove material from the face you also lose width. Not necessarily the end of the world, but worth keeping in mind.

Zaijien

 

[mudman]

Pig-stickers are tapered in cross section, so if you remove material from the face you also lose width. Not necessarily the end of the world, but worth keeping in mind.

Yep, I'm aware of this as you say, I don't think it is the end of the world and unfortunately unavoidable in this case.

 

[David C]

Without flatness of back adjacent to the cutting edge, good sharpening, i.e. honing/polishing away the wire edge , is going to be difficult.

1/8" and under, chisels are very difficult indeed. Back or flat side much more crucial than the bevel. I use movement 2 only to try and avoid rocking thin chisels.

It has always seemed to me that some tools are in too bad a state to warrant the huge time and effort required to rescue them.
Deep rust pitting is such a case. (always wanted a nice surface grinder, but can't really justify the space).

The only thing that I have found so far which helps, is something like masking tape to afford better friction, on the the top of the blade.

David Charlesworth

 

[bugbear]

Without flatness of back adjacent to the cutting edge, good sharpening, i.e. honing/polishing away the wire edge , is going to be difficult.

1/8" and under, chisels are very difficult indeed. Back or flat side much more crucial than the bevel. I use movement 2 only to try and avoid rocking thin chisels.

Agreed, in respect of "normal" 1/8" chisels. But 1/8" pig stickers are in a league of their own! They just want to "flop" over, since the driving surface is 4x as far from the worked surface as the work surface is wide.

(I jigged the pipper in my ludicrous honing guide to get the job done).
http://www.geocities.com/plybench/tour. ... pening_jig

The only thing that I have found so far which helps, is something like masking tape to afford better friction, on the the top of the blade.

For plane blades and wide chisels, a simple dado'd bit o' scrap works well.

http://www.geocities.com/plybench/scrub.html#blade
(second photo, which needed a darker background)

BugBear

 

[mudman]

It has always seemed to me that some tools are in too bad a state to warrant the huge time and effort required to rescue them.
Deep rust pitting is such a case. (always wanted a nice surface grinder, but can't really justify the space).

David Charlesworth

I have been thinking that as well in the last couple of days. I gave up buying old carving tools as I was getting too many that had been ruined by grinding not just rust.

I think it is the deep rust that is the killer. The back can be brought to a level of flatness within a reasonable amount of time, but when you have to take metal off of the entire surface just to remove the pitting that always seems to occur close to the edge, that is when it gets tedious. I thought I'd give myself a break from mortice chisels and sort out an old Isaac Greaves drawknife that had been languishing in a drawer for a year or so. Even worse! The pitting here is quite severe but I'm getting through it and it shouldn't take much longer to produce a usable tool. Luckily it had originally been hollow ground.

If you consider the amount of time and effort, I admit that it does seem to be a bit nonsensical. However, I really enjoy bringing these old ruins back to life and when I finally get to using them, it will give me immense pleasure just to pick it up and remember its original state.

 

[mudman]

Is it really that beneficial to have a really flat back on a mortice chisel? It's a fairly rough/simple operation, and I would have thought a strong sharp edge is more important than a flat back - as opposed to paring/bench chisels where I can obviously see the benefits. But a mortice chisel? I'm not sure it makes a huge differece.. i'm happy to be corrected if there is something i'm missing here

Funnily enough I've been reading an article on FWW (thanks for the tip Alf) about morticing methods. In it, Brian Boggs says:

The
quality of the mortise depends largely on how the chisel is tuned.
Boggs told of the occasion when a student who could not chop a
good mortise borrowed his chisel and had no further problems.
Mortising chisels generally have long, stout blades as thick or
thicker than they are wide. This allows them to be hammered aggressively
and deeply into hard woods without breaking. Unlike
most power tools, few chisels arrive from the factory ready to go.
To tune one, use an engineer's square to check the surfaces and a
benchstone to make them true. The bottom and sides of the blade
must be flat and square (the top of the blade is irrelevant). The cutting
edge must be both razor sharp, straight and perpendicular to
the sides. If not, the chisel will wander no matter how hard you try
to keep it going straight down.

This sort of makes me feel happier and a bit vindicated about the quest for flatness.

 

[ByronBlack]

mudman - that does make sense (the second part of your quote) as i've noticed that a certain mortice chisel I have seems to always twist in the cut, which can get quite annoying - despite it being razor sharp. I can certainly see the appeal of LN chisels - no hassle

 

[David C]

BugBear,
That's quite a feat, here's an alternative suggestion, for working up the backs of old mis-shapen OBMs

It occured to me some time last night that a good option would be to hold a narrow mortice chisel in a machine vice or equivalent with the flat side uppermost and horizontal. Some shims may be required if the chisel has tapered crossection.

Measure height of flat side from bench surface.

Then create a pyramidal wooden prop, with a smooth slightly domed "point" i.e.not pointed at all!

The base of this pyramid is about the width of a large benchstone.

This prop is used upside down, i.e. domed head running on bench top, with the broad end supporting one end of bench stone, (preferably diamond to start with).

One can then hone away to one's hearts content, with the opposite end of the stone working the back of the chisel, knowing that the bench stone is moving in a fixed plane. ~;-)#

I like this set up and have used it before for bevelling the long edges of Japanese chisels, for getting into corners of dovetails.

What do you think?

David Charlesworth

 

[Anonymous]

"Tune" an OBM? :lol: :lol:
Just needs to be sharp. Doesn't matter about flat face, although needs to be geometrically regular in section as someone pointed out, otherwise it could twist I suppose.
I find all this tuning stuff a bit odd, it's as though every newly aquired tool should be re-machined as though it's just an unformed bit of steel.
In reality most things just need a quick sharpen and you are off. Rust and pitting disappear with use unless extreme.
PS

Boggs: The bottom and sides of the blade
must be flat and square (the top of the blade is irrelevant).

He's wrong, ideally the side are tapered, so not sqaure with the face, the back matters too i.e. has to be parallel to the face as the face/back wedging action is essential part of using an OBM, unlike most other chisels.
I am a bit mystified by the new Ray Iles OBM design with a rounded back. Can't be a good idea IMHO.

cheers
Jacob