A quick question on skew chisels

[Jacob]

Hi Jacob

Personally, I see no issue with the way anyone wants to cut dovetails. I agree with you and I agree with BB - see, I am flexible!

Glad to hear it!

If one wants to replicate the dovetails that were used by those in past centuries, then do so. I suspect that you will find that they varied, however. I'm not a historian, so am open to correction (hey, I'm always being corrected!).

You don't have to be a historian you just need to look at stuff. It's a habit well worth adopting.

..
The slim "London" style dovetails (where on Earth did that name come from - is there a more appropriate name?)

I think of them as "single kerf" dovetails. The position of each pin hole is marked up freehand with a single saw cut freehand, and the saw dropped into the same kerf to cut the 2 sides. It's quick, easy, and very common in items where strength isn't a big issue, such as lightly loaded drawers.

DTs are used for two principle reasons - they are self locating so clamps are not necessary, and they divide up the joint so that any movement won't necessarily translate itself to the whole joint. A sort of "stitching" - you get a similar effect with glue blocks, where a lot of short ones makes a stronger joint than one long one. Or a lot of small nails is stronger than one large one etc.

My theory is that one draws attention to workmanship either through attention to details such as mouldings and other intricate carvings such as ball-and-claw feet, which were more prominent 100 years ago, or we find some other focus. The current zeitgeist appears to have been influenced by the Shakers, Danish and other contemporary stylings which seem to be dominated by their silhouette instead.

Or workmanship as opposed to design. A good point - there's a lot of stuff out there which is beautifully made but still very boring. And vice versa - good design with poor workmanship. Personally I rate design above all. If it's well made that's a bonus!

 

[Cheshirechappie]

.....
IMO Dovetails in hardwood should be fine and slender 1:7 to 1:9 to look right 1:8 as a standard, I feel 1:6 and 1:5 are for softwoods and I see no merit in cutting one of our most expensive joints in the cheapest timbers. .....

Historically they weren't "our most expensive joints" but were merely the normal way to join drawer fronts to sides, or box corners, etc. in cheap or expensive timbers. There weren't many alternatives.
All the waffling about angles is just a modern affectation - you will find many variations in old furniture - especially the hand made "production line" stuff where the makers were under pressure to be cost effective.
You can find out a lot about how to do things by looking at stuff - IMO people don't look at stuff enough, and it really shows - the difference between 1:6 and 1:5 is so little as to be meaningless. If you take the trouble to actually look you will find DTs varying from 1:2 through the whole range to to straight "box" joints.
Give yourself a break - start looking at stuff! You have nothing to lose!
Also try thinking about it - logically hardwoods being generally stronger could take a steeper DT angle than weaker softwoods. The popular view is quite opposite, and basically nonsense.
Suggestion for new years resolution - in 2014 make more effort to look at things and think about them!

Imagine pulling a drawer front off the sides. For this to happen, the dovetails must fail. There are (at least) two failure mechanisms. The first is by shearing off the angled part of each tail - long-grain failure of the wood. That's more likely if the wood is hard and brittle, or if the dovetail angles are steep leaving short-grain. The second is failure by crushing wood fibres allowing the tail to pass the pins, a failure more likely in softer wood and with shallower dovetail angles.

I think there are good pragmatic reasons for softwood dovetails to be cut at a steeper angle than hardwood ones, and the 1:6 (or thereabouts) angle is a good compromise between insurance against failure by crushing and failure by short-grain breakage. In hardwoods, failure by crushing is less likely, but failure by short-grain breakage is possible so a shallower 1:8 (or thereabouts) angle is a pragmatic one. I think it's taken a long time and much experience for craftsmen to settle to those angles as about the best compromises, and they've done so for good reason - a lot of collective experience over several generations.

Looking at old work can be very instructive, but one has to be careful not to regard everything done in the old days as automatically right or best practice. Anybody involved in the restoration of old buildings, machinery or whatever will be well aware of examples of what would not be regarded as best practice nowadays. Sure, some old examples of poor practice have survived, but we don't always know how many examples didn't survive, because they were poor practice!

 

[Jacob]

........
Looking at old work can be very instructive, but one has to be careful not to regard everything done in the old days as automatically right or best practice. Anybody involved in the restoration of old buildings, machinery or whatever will be well aware of examples of what would not be regarded as best practice nowadays. Sure, some old examples of poor practice have survived, but we don't always know how many examples didn't survive, because they were poor practice!

If it has survived that's one indication of good practice. Not reliable of course; the Georgians were notorious for cheapskate buildings which are still with us because maintenance is cheaper than replacement.

I think there are good pragmatic reasons for softwood dovetails to be cut at a steeper angle than hardwood ones, and the 1:6 (or thereabouts) angle is a good compromise between insurance against failure by crushing and failure by short-grain breakage.

Sounds logical, but as I say - if you look at stuff you find that it's not that simple. I have some old pine drawers with DT gradients approaching 1:2 and they have survived intact for 100 or more years, even though this particular chest of drawers was left out in an open sided shed for many years .

 

[xy mosian]

As the conversation has drifted to Dovetail angles.
Here we have the largest collection of dovetails I have in any one piece. My Grandfather's Chest. Made, most likely, in the last few years of the 1800's. The height of the corner, of the chest, is 19", 480mm.
As you can see there is some variation in both the angle of the Dovetails and the mean angle of the tails to the edge.
xy

 

[Jacob]

Brilliant! Instead of theorising actually looking at stuff is really interesting and informative!
Every DT freehand I guess.

 

[Trafalgar]

As the conversation has drifted to Dovetail angles.
Here we have the largest collection of dovetails I have in any one piece. My Grandfather's Chest. Made, most likely, in the last few years of the 1800's. The height of the corner, of the chest, is 19", 480mm.
As you can see there is some variation in both the angle of the Dovetails and the mean angle of the tails to the edge.
xy

They certainly have a lot more verve than today's dovetails that strive for so much precision and regularity they may as well have been cut by machine.

 

[Cheshirechappie]

Jacob - a great many modern 'authorities' suggest that dovetail angles of about 1:6 for softwoods and about 1:8 for hardwoods are regarded as good practice. Now, I'm not saying they're 'right' or 'wrong', but those two approximate angles do seem to crop up quite regularly. Why has this become so, do you suggest?

 

[Jacob]

Jacob - a great many modern 'authorities' suggest that dovetail angles of about 1:6 for softwoods and about 1:8 for hardwoods are regarded as good practice. Now, I'm not saying they're 'right' or 'wrong', but those two approximate angles do seem to crop up quite regularly. Why has this become so, do you suggest?

Good question. I think the answer may be that someone was asked to be definitive about it at some point, a teacher or a writer perhaps, and his arbitrary suggestion went viral and has been repeated ever since. It'll do as an answer and there is a sort of logic to it, but there is no reason to stick to it. Slightly mad in fact - would it make the slightest difference if everyone did 1/7 instead? Of course not.

 

[Cheshirechappie]

Jacob - a great many modern 'authorities' suggest that dovetail angles of about 1:6 for softwoods and about 1:8 for hardwoods are regarded as good practice. Now, I'm not saying they're 'right' or 'wrong', but those two approximate angles do seem to crop up quite regularly. Why has this become so, do you suggest?

Good question. I think the answer may be that someone was asked to be definitive about it at some point, a teacher or a writer perhaps, and his arbitrary suggestion went viral and has been repeated ever since. It'll do as an answer and there is a sort of logic to it, but there is no reason to stick to it. Slightly mad in fact - would it make the slightest difference if everyone did 1/7 instead? Of course not.

In other words, you haven't a clue why.

I think I'll stick to my theory (I don't have a problem with theorising - it's what sets humankind apart intellectually from all other species) that over several centuries of collective and accumulative experience of using dovetail joints in wood, those are roughly the angles that work best for strong, lasting joints.

 

[bugbear]

Some research reveals that the January 1958 issue of Woodworker published the results of actual experiments at the Forest Products Research Laboratory, by K.S.Walker on dovetail angle versus joint strength.

http://www.amgron.clara.net/dtailtest32.html

BugBear

 

[Jacob]

......
I think I'll stick to my theory (I don't have a problem with theorising - it's what sets humankind apart intellectually from all other species) that over several centuries of collective and accumulative experience of using dovetail joints in wood, those are roughly the angles that work best for strong, lasting joints.

If they are the best angles then why did so many people not use them and produce furniture which survives still?
BBs article is interesting. A completely unrealistic test of DTs. As anybody who has looked at old furniture can tell you - DTs fail by being forced outwards sideways when glue fails or there is too much stuff packed in the box/ drawer etc. I doubt many ever fail by being pulled in the way shown. In any case the tests were on machine made DTs which are particularly weak in the sideways way, which wasn't tested.
People like definitive answers to questions. The choice of 1/6 or 1/8 gives the illusion of precision. People like appearing to be authoritative by quoting particular figures - just think of all the sharpening bevel discussions!
PS As for theorising - you don't need to theorise if you can look at stuff instead.
Failing DTs usually by spreading (see above) in which case the angle isn't going to make the slightest difference. But the number of DTs presumably would - the more there are the more the glued surface area.

 

[MMUK]

Don't mention the S word Jacob!

 

[Cheshirechappie]

......
I think I'll stick to my theory (I don't have a problem with theorising - it's what sets humankind apart intellectually from all other species) that over several centuries of collective and accumulative experience of using dovetail joints in wood, those are roughly the angles that work best for strong, lasting joints.

If they are the best angles then why did so many people not use them and produce furniture which survives still?
BBs article is interesting. A completely unrealistic test of DTs. As anybody who has looked at old furniture can tell you - DTs fail by being forced outwards sideways when glue fails or there is too much stuff packed in the box/ drawer etc. I doubt many ever fail by being pulled in the way shown. In any case the tests were on machine made DTs which are particularly weak in the sideways way, which wasn't tested.
People like definitive answers to questions. The choice of 1/6 or 1/8 gives the illusion of precision. People like appearing to be authoritative by quoting particular figures - just think of all the sharpening bevel discussions!
PS As for theorising - you don't need to theorise if you can look at stuff instead.
Failing DTs usually by spreading (see above) in which case the angle isn't going to make the slightest difference. But the number of DTs presumably would - the more there are the more the glued surface area.

I did think about doing a full, point-by-point answer, but since most of the points you raised in this post have been dealt with earlier in the thread or by the research presented in Bugbear's link, to do so would just be going round in circles having an argument for the sake of it, and frankly I can't be bothered with that.

One point raised was not dealt with earlier. It's quite true that most dovetail joints are likely to fail by coming apart the way they went together, but as the discussion was about dovetail angles, it's irrelevant anyway.

 

[Peter Sefton]

.....
IMO Dovetails in hardwood should be fine and slender 1:7 to 1:9 to look right 1:8 as a standard, I feel 1:6 and 1:5 are for softwoods and I see no merit in cutting one of our most expensive joints in the cheapest timbers. .....

Historically they weren't "our most expensive joints" but were merely the normal way to join drawer fronts to sides, or box corners, etc. in cheap or expensive timbers. There weren't many alternatives.
All the waffling about angles is just a modern affectation - you will find many variations in old furniture - especially the hand made "production line" stuff where the makers were under pressure to be cost effective.
You can find out a lot about how to do things by looking at stuff - IMO people don't look at stuff enough, and it really shows - the difference between 1:6 and 1:5 is so little as to be meaningless. If you take the trouble to actually look you will find DTs varying from 1:2 through the whole range to to straight "box" joints.
Give yourself a break - start looking at stuff! You have nothing to lose!
Also try thinking about it - logically hardwoods being generally stronger could take a steeper DT angle than weaker softwoods. The popular view is quite opposite, and basically nonsense.
Suggestion for new years resolution - in 2014 make more effort to look at things and think about them!

Jacob you do make me laugh - your comedic value is worth so much. I may put the idea of "looking and thinking" to others who teach just incase they had never considered that as a learning opportunity :lol:
I may borrow your idea if I may about using our past masters work to see if we can learn any thing and I will inform my students that they may cut dovetails at any ratio between 1:2 up to 1:8 it doesn't matter its all been done before so there is no best practice. :roll:

Now I have "looked" at my collection of drawers I did notice that the lap Dovetails tend to be slender 1:8 and fine whist the back through Dovetails tend to be steeper 1:6, a cheaper quicker joint never really seen and a of course not requiring a Fishtail or Skew chisel. The carcass Dovetails do also tend to be steeper 1:6 but again are constructional not not to be seen or judged by the customer or used as a factor in the perceived value of a finished item, this is a factor that has not changed with history unlike our craftsman's wage packet and expected standard of living.
You may wish to hand cut your Dovetails at a steep angle but feel you will struggle to find your customer base within the fine furniture market, but possibly this is my historic customer base not yours.
I look forward to your next gems of wisdom Cheers Peter (with tongue severely in cheek)

 

[Jacob]

.....
IMO Dovetails in hardwood should be fine and slender 1:7 to 1:9 to look right 1:8 as a standard, I feel 1:6 and 1:5 are for softwoods and I see no merit in cutting one of our most expensive joints in the cheapest timbers. .....

Historically they weren't "our most expensive joints" but were merely the normal way to join drawer fronts to sides, or box corners, etc. in cheap or expensive timbers. There weren't many alternatives.
All the waffling about angles is just a modern affectation - you will find many variations in old furniture - especially the hand made "production line" stuff where the makers were under pressure to be cost effective.
You can find out a lot about how to do things by looking at stuff - IMO people don't look at stuff enough, and it really shows - the difference between 1:6 and 1:5 is so little as to be meaningless. If you take the trouble to actually look you will find DTs varying from 1:2 through the whole range to to straight "box" joints.
Give yourself a break - start looking at stuff! You have nothing to lose!
Also try thinking about it - logically hardwoods being generally stronger could take a steeper DT angle than weaker softwoods. The popular view is quite opposite, and basically nonsense.
Suggestion for new years resolution - in 2014 make more effort to look at things and think about them!

Jacob you do make me laugh - your comedic value is worth so much. I may put the idea of "looking and thinking" to others who teach just incase they had never considered that as a learning opportunity :lol:
I may borrow your idea if I may about using our past masters work to see if we can learn any thing and I will inform my students that they may cut dovetails at any ratio between 1:2 up to 1:8 it doesn't matter its all been done before so there is no best practice. :roll:

Now I have "looked" at my collection of drawers I did notice that the lap Dovetails tend to be slender 1:8 and fine whist the back through Dovetails tend to be steeper 1:6, a cheaper quicker joint never really seen and a of course not requiring a Fishtail or Skew chisel. The carcass Dovetails do also tend to be steeper 1:6 but again are constructional not not to be seen or judged by the customer or used as a factor in the perceived value of a finished item, this is a factor that has not changed with history unlike our craftsman's wage packet and expected standard of living.
You may wish to hand cut your Dovetails at a steep angle but feel you will struggle to find your customer base within the fine furniture market, but possibly this is my historic customer base not yours.
I look forward to your next gems of wisdom Cheers Peter (with tongue severely in cheek)

What makes me laugh is the cautious, conservative, timid, idea of best practice which is just made up with no relationship to practical needs. The craft woodworking "establishment" is a very closed and inward looking world.
Yes you should tell your students to experiment with different angles, and experiment in general. They might come up with something interesting. You should also tell them to look at stuff and not take anything for granted.
Your "customer base" is what you choose it to be. It seems that a lot of our cautious arts n crafts followers end up having to teach, or desperately sell people tools they don't really need. :lol:

 

[bugbear]

Yes you should tell your students to experiment with different angles, and experiment in general. They might come up with something interesting.

More likely they'll waste a lot of time reinventing the wheel. I would not look kindly on a teacher who led me down such a garden path.

Surely students should carefully copy historic best practice before inventing their own ideas...

BugBear

 

[Jacob]

Yes you should tell your students to experiment with different angles, and experiment in general. They might come up with something interesting.

More likely they'll waste a lot of time reinventing the wheel. I would not look kindly on a teacher who led me down such a garden path.


BugBear

Basic principle of good design education and practice is to diverge and consider all possibilities and then converge on the end product, which may take you back to the idea you first thought of, or on the other hand perhaps to pastures new.
The term "best practice" is another of those odd viral ideas which get kicked about and probably gets in the way more often than not. As though there is holy text of "best practice".

 

[bugbear]

Yes you should tell your students to experiment with different angles, and experiment in general. They might come up with something interesting.

More likely they'll waste a lot of time reinventing the wheel. I would not look kindly on a teacher who led me down such a garden path.


BugBear

Basic principle of good design education and practice is to diverge and consider all possibilities and then converge on the end product, which may take you back to the idea you first thought of, or on the other hand perhaps to pastures new.
The term "best practice" is another of those odd viral ideas which get kicked about and probably gets in the way more often than not. As though there is holy text of "best practice".

I find standing on the shoulders of giants a good route to getting things done without flailing around in blind alleys

Perhaps you think maths students should discover calculus for themselves, instead of blindly following Newton/Leibniz?

BugBear

 

[Peter Sefton]

I think I recall a C&G multi guess question
What is the preferred angle for Dovetails in deciduous timber?

1. 1:5
2. 1:8
3. 1:2
4. Whatever

 

[Jacob]

......
I find standing on the shoulders of giants a good route to getting things done without flailing around in blind alleys./...

Yebbut which giants? Old Jim Krenov? IKEA? Come to think IKEA would be better for design than St Jim.
If people didn't bravely flail around in apparently blind alleys (including Newton) there would be no progress at all.