Flattening, polishing and friction.

[Random Orbital Bob]

In my experience all the real sharpening gurus say the same thing which is simply to flatten that part of the chisel that contributes to the edge that will be cutting. Ie the little "coastline" that is within 1,2,3 mm from the edge

Any more than that is just masochism. The only value of flattening more than that is to save time in the future when you've reground the bevel so many times that you've shortened it's length beyond your flat "coastline"

The sharpening principle is simple, a scratch free edge created by both mating surfaces is sharper. Both bevel and back need be scratch free but 1mm back from the back.....who cares

 

[Jacob]

In my experience all the real sharpening gurus say the same thing which is simply to flatten that part of the chisel that contributes to the edge that will be cutting. Ie the little "coastline" that is within 1,2,3 mm from the edge

"coastline" - well described!

.......The only value of flattening more than that is to save time in the future .....

Except you remove that little trace of concavity (which most chisels old and new all seem to have) and actually make future sharpening more difficult. So it really is worse than useless!

 

[Tom K]

In my experience all the real sharpening gurus say the same thing which is simply to flatten that part of the chisel that contributes to the edge that will be cutting. Ie the little "coastline" that is within 1,2,3 mm from the edge

"coastline" - well described!

.......The only value of flattening more than that is to save time in the future .....

Except you remove that little trace of concavity (which most chisels old and new all seem to have) and actually make future sharpening more difficult. So it really is worse than useless!

No it isn't removed the tide is just slightly further out. On subsequent honing the "coastline" is maintained by removing the burr.

 

[Random Orbital Bob]

Ha....like it....tide

 

[bugbear]

http://logancabinetshoppe.com/blog/2011 ... p-lapping/

His justfication for a non flat back is based on his analysis of paring, which is ... poor.

The bevel of a chisel is a wedge. The action of a wedge is such that the direction of travel as the wedge is driven is along a path that bisects the angle of the wedge.

That would only be true if driving the chisel into the middle of a piece of wood. If the workpiece is (in fact) thinner on one side than the other, the difference in material resistance will also play a part.

Now, in paring, one side of the cut is a shaving, and the other side is the pretty much the whole workpiece.

The resistance of the shaving will not drive the chisel into the workpiece. Obviously.

BugBear

 

[Dangermouse]

My take on this is that you need the plane sole to be a total mirror finish. Other wise I cant use it to shave with, using my rounded bevel 2 inch chisel. I thought that was why every one needed a shinny bottom. :lol: :deer

 

[Jacob]

.....
The resistance of the shaving will not drive the chisel into the workpiece. Obviously.

BugBear

Except (obviously) it's not a shaving until it's been cut . Chicken & egg innit!
I'm always impressed by the struggle to make simple woodworky things complicated and incomprehensible.

 

[bugbear]

.....
The resistance of the shaving will not drive the chisel into the workpiece. Obviously.

BugBear

Except (obviously) it's not a shaving until it's been cut . Chicken & egg innit!

At the risk the being philosophical, the uncut shaving is just as thin as the cut shaving, and just as flexible.

BugBear

 

[Jacob]

.....
The resistance of the shaving will not drive the chisel into the workpiece. Obviously.

BugBear

Except (obviously) it's not a shaving until it's been cut . Chicken & egg innit!

At the risk the being philosophical, the uncut shaving is just as thin as the cut shaving, and just as flexible.

BugBear

No it isn't, it's firmly attached to the wood beneath. :roll:

 

[bugbear]

No it isn't, it's firmly attached to the wood beneath. :roll:

Take two 1" thick planks. Drive a chisel horizontally into the middle of one of them, and 1/64" below the top of the other. Observe what happens. See if there's any difference. Try to work out why.

You do make difficulties where there aren't any.

BugBear

 

[Jacob]

Nah can't be bothered.

 

[GazPal]

.....
The resistance of the shaving will not drive the chisel into the workpiece. Obviously.

Except (obviously) it's not a shaving until it's been cut . Chicken & egg innit!

At the risk the being philosophical, the uncut shaving is just as thin as the cut shaving, and just as flexible.

In reality, an uncut shaving remains as inflexible as the timber in which it rests.

No it isn't, it's firmly attached to the wood beneath. :roll:

Take two 1" thick planks. Drive a chisel horizontally into the middle of one of them, and 1/64" below the top of the other. Observe what happens. See if there's any difference. Try to work out why.

You do make difficulties where there aren't any.

Grain run, edge bevel orientation and driving force dictate the direction of split unless controlled by similar means to a plane or steered via varying degrees of vertical pressure on the chisel handle. An upward facing bevel will tend to cause a chisel to disregard grain direction and dig in more than if the bevel faces downward. End grain paring is pretty much the same, as bevel direction tends to dictate paring performance.

Enhanced control in the cut is much the reason behind the invention of the hand plane - as it's construction sets cut depth and helps avoid the inclination for a wedge shaped edge to dive into the workpiece - and why we choose tooling to suit the work in hand.

Axe, froe, adze, plane/chisel, scraper, sandpaper.

 

[bugbear]

Grain run, edge bevel orientation and driving force dictate the direction of split unless controlled by similar means to a plane or steered via varying degrees of vertical pressure on the chisel handle. An upward facing bevel will tend to cause a chisel to disregard grain direction and dig in more than if the bevel faces downward. End grain paring is pretty much the same, as bevel direction tends to dictate paring performance.

Enhanced control in the cut is much the reason behind the invention of the hand plane - as it's construction sets cut depth and helps avoid the inclination for a wedge shaped edge to dive into the workpiece - and why we choose tooling to suit the work in hand.

Axe, froe, adze, plane/chisel, scraper, sandpaper.

Do you (and Jacob) really think that a chisel driven horizontally, taking a 1/64" paring cut is really driven into the solid body of the workpiece by the tiny amount of wood above the edge?

In many accounts of dovetail waste clearance (both old and new), there is clear acknowledgement that trying to remove too much waste with the chisel on the scribed line will indeed drive the chisel below the scribe line, due to the wedging action.

It is precisely for this reason that it is recommended to remove the bulk of the waste with heavy cuts (or a coping saw) above the scribe line, only placing the chisel in the scribe line to remove the last of the waste accurately.

BugBear

 

[GazPal]

Grain run, edge bevel orientation and driving force dictate the direction of split unless controlled by similar means to a plane or steered via varying degrees of vertical pressure on the chisel handle. An upward facing bevel will tend to cause a chisel to disregard grain direction and dig in more than if the bevel faces downward. End grain paring is pretty much the same, as bevel direction tends to dictate paring performance.

Enhanced control in the cut is much the reason behind the invention of the hand plane - as it's construction sets cut depth and helps avoid the inclination for a wedge shaped edge to dive into the workpiece - and why we choose tooling to suit the work in hand.

Axe, froe, adze, plane/chisel, scraper, sandpaper.

Do you (and Jacob) really think that a chisel driven horizontally, taking a 1/64" paring cut is really driven into the solid body of the workpiece by the tiny amount of wood above the edge?

In many accounts of dovetail waste clearance (both old and new), there is clear acknowledgement that trying to remove too much waste with the chisel on the scribed line will indeed drive the chisel below the scribe line, due to the wedging action.

It is precisely for this reason that it is recommended to remove the bulk of the waste with heavy cuts (or a coping saw) above the scribe line, only placing the chisel in the scribe line to remove the last of the waste accurately.

BugBear

No. Wedging action and grain directly influence the cut and it will deepen unless guided. Timber is seldom perfectly grained or amenable to being tooled...... Hence the need for craftsmen to manipulate hand tools and wood machinists to control machinery.

I tend toward the view that an outcome cannot be predetermined unless an edged hand tool is adequately guided. Regardless of shaving thickness, a single bevel is steered by whether it faces upward or is inverted. A fairly good example of the manner by which a paring blade can nose-dive into one's work is if you consider the way a flush plane reacts during a cut. With bevel facing upward and the main blade body resting on the workpiece, it has the propensity to nose dive into the work unless one exerts downward pressure upon the rear of the blade.

While unable to speak for Jacob, I base my views upon extensive long-term workshop experience as a professional cabinetmaker and not solely from book reading or classroom theory. I don't doubt Jacob's experience and knowledge. You can re-program my computer and I can advise you on woodworking. :wink:

A chisel's driving force is provided - during a cut - by pressure from behind the blade, whilst bevel and grain direction influence the route taken by an edge, unless your guiding hand steers the blade and holds it flat to the work. Blade bias is toward the edge and is the reason we need to steer a cut as it progresses.

 

[Jacob]

You are being trolled Gary! These sorts of ramblings can go on and on and obfuscate the real practical issues.

 

[GazPal]

You are being trolled Gary! These sorts of ramblings can go on and on and obfuscate the real practical issues.

I agree, but he's your stalker Jacob. :lol: :wink:

It's much like having an apprentice return from a two week block release and trying to tell you how this book says this or that book says that, or "but my instructor told us to....". Only to discover he's gotten nowhere in terms of hands-on, real time experience without realising you've earned your stripes through hard work and shook more saw dust out of your socks after work than he's ever made.

 

[bugbear]

A fairly good example of the manner by which a paring blade can nose-dive into one's work is if you consider the way a flush plane reacts during a cut. With bevel facing upward and the main blade body resting on the workpiece, it has the propensity to nose dive into the work unless one exerts downward pressure upon the rear of the blade.

Absolutely! And in a horizontal paring cut, the same applies - the flat back of the chisel, on the already cut flat surface provides the support - and if the cut is reasonably shallow, this support is normally sufficient to guide the chisel as one intends.

But if one takes a too-deep-cut, the wedging effect is too great, and the chisel cannot be stopped from diving, hence the dovetail technique previously described.

Edit; just to add; I really like fully understanding stuff. Wax on - Wax off might get the job done, but I want more than that. I can catch a thrown ball, but I learnt the laws of motion and quite a bit about the human visual cortex too.

BugBear

 

[GazPal]

The chisel back simply braces against the workpiece, whilst control is obtained via good technique.

Depth could equate to a gnat's whisker in thickness and you'd still find the blade's bevel meets resistance forcing the edge downward as it's driven forward in the cut. Direction of travel is governed by the single bevel as it wedges itself into the cut. Reducing the bevel angle below 20 deg greatly improves control when paring and lessens this downward trend, but - again - technique plays a massive part in end results.

IMHO cranked paring chisels work best, as you can flex the blade in the cut.

 

[Jacob]

......I can catch a thrown ball, but I learnt the laws of motion and quite a bit about the human visual cortex too.

BugBear

No amount of knowledge about laws of motion and brain activity would be the slightest help in catching a ball. Similarly being skilful catching a ball is possible with zero knowledge of laws of motion and brain activity, though the practice might help towards the knowledge, if that was what you wanted.
Craft work is very similar.

 

[David C]

I don't know what I'm missing here, but if a fine enough cut, is taken with a sharp enough chisel, with good technique and a nice flat back, it will not dive.

This applies to end grain, and cross grain. Long grain will depend on fibre orientation,

Simple eh? I have been doing this for 40 years, though it might not always have gone quite right in the beginning!.....

David Charlesworth