Thread: Which Dovetail Marker?

Peteman,

There's a myth perpetuated on US woodworking sites about the slope of the dovetail vs the timber type.

The timber type's irrelevant to the slope. If it wasn't then there are weak hardwoods and stronger softwoods -> why stop there.

In trade:.....

Dovetails for show are cut at a slope of about 1:8, both in hardwood and softwood.

Carcase dovetails are cut at a slope of about 1:6 for strength, both in hardwood and softwood.
Sorry for rushed answer, have got to do a thousand things before midnight.

Cheers,

eddie


edit: Just read Ian and Derek's responses.

Trade training is 1:8. The dovetail bits are indeed ground at 1:7 to give a middle value.

I can only agree with the comments on the thin dovetails. They tend to snap off when the drawer racks a bit in the frame - essentially, they're much the same as having a drawer side held on by a skinny dowel. In situations where the drawer will rack, then cut the tails a bit thicker. A good rule of thumb is to cut the tail in its thickest point about 2/3 of the thickness of the drawer side, and space the tails about three times as far apart as they are wide.

Good stuff, Eddie - like the way you cut through to the heart of the matter!

Hadn't thought of wracking as the cause of pin snapping - had assumed it was just rough tratment, like jerking on tight, heavily-laden drawers, but that makes sense, too. The piece I was talking about has solid sides with the dividers dovetailed into them. The back is just boards nailed on, so plenty of scope for movement, & no bracing. One of the reasons I like (decent quality) ply backs glued & tacked into a rebate. May not be 'authentic', but more than enough sheer-bracing.

Cheers,

There's a myth perpetuated on US woodworking sites about the slope of the dovetail vs the timber type.

I have a textbook which mentions this rule here that pre-dates the world wide web, so I doubt it has anything to do with myths on US woodworking sites:

The pitch of the sloping sides of the dovetails varies from 1 in 4 for softwoods to 1 in 8 in hardwoods.

The book is "Woodwork in theory and practice" by John A. Walton first published in 1947. It was the textbook for high school woodworking in Australian schools for many years.

I don't know whether there is any proof that it makes a difference, I usually use 1:8 more for looks than anything else, however it's more than just a myth perpetrated in the US.

Originally Posted by silentC

I have a textbook which mentions this rule here that pre-dates the world wide web, so I doubt it has anything to do with myths on US woodworking sites:



The book is "Woodwork in theory and practice" by John A. Walton first published in 1947. It was the textbook for high school woodworking in Australian schools for many years.

I don't know whether there is any proof that it makes a difference, I usually use 1:8 more for looks than anything else, however it's more than just a myth perpetrated in the US.

great research, SilentC.

I knew that there was a reputable source for the 1:6 /1:8 difference.

Walton is a very good book and only I disagree with the statements made in it when forced to by overwhelming evidence (usually where the text has not been updated to deal with modern developments).

I should also note that the Lion marking gauge that i posted about earlier was made in Swindon UK and has 1:6 and 1:8 elements. So someone there thought it was appropriate.

Originally Posted by silentC

I have a textbook which mentions this rule here that pre-dates the world wide web, so I doubt it has anything to do with myths on US woodworking sites:

Silent - I know Eddie can speak very clearly for himself, but the word he used is PERPETUATED - ie carrying on, not originating. Ther are an awful lot of myths perpetuated in 'reputable' textbooks - they bled people for thousands of years as a treatment for disease (a more counter-productive treatment for most conditions could hardly be imagined). It was still advocated in 'reputable' textbooks up til relatively recently!

Any information not backed up with rational argument or convincing evidence is worth very little, and declarations on what ought to be the slope of a dovetail like Mr. Walton's are very much in that category, IMO. For starters, I reckon it's A##e about face - if you have ever tried cutting & fitting tight 1:4 dovetails on soft wood, you'll know the edges are very fragile. And what advantage is this supposed to confer? There is probably no addition in structural strength beyond a few degrees of slope, in most instances, so the slope of a dovetail is really a matter of taste & convenience.

Just an opinion - I don't write those sorts of textbooks.

Cheers,

I used the word perpetrated deliberately. I know he said perpetuated, I'm just pointing out that it didn't originate on US woodworking sites and that there are published authors who mention the practice.

Now, just because myths have been perpetrated and/or perpetuated by textbooks in the past, it does not follow that all "facts" expressed in them are based on myth. The two arguments cancel each other out. You cannot use that as a basis for saying that Mr Walton has it wrong. It is obviously his opinion (or was because I fear he is no longer with us) that different slopes are required for different timbers. Whether it was based on experience or whether he was just passing on the opinion of his trade teacher (much like Eddie is doing), we will never know. However I don't believe it can be ruled out simply because people have been wrong before. I do know it is an opinion shared by other authors.

Just being published does not make a person right about everything they put down on paper, but it does place them in the spotlight where all and sundry can challenge their views. I suppose it depends on whether you choose to believe what they say - and that probably comes as much from your own prejudices and experiences as from anywhere else. Nobody is suggesting you should believe everything you read, but then it's usually a good starting point in practical subjects I find.

The fact that the book was retained as a textbook for so many years might simply be down to the fact that there was a dearth of Australian material around at the time. It's not the greatest book I have ever flipped through, being like a lot of textbooks - very dry and prescriptive.

I'm not going to sit here and say that he was right beyond all doubt. I'm simply saying that here at least is one published, and presumably respected author, who believed it to be true. It is more than a myth perpetuated on US forums, it is a published rule of thumb.

Here's what Ernest Joyce has to say about it:

For carcass-work where strength is necessary and appearance of little consequence the slope can correspond to a slope of 1 in 5 or 1 in 6; while for show-work, drawer sides, etc., 1 in 7, and for very fine decorative dovetailing 1 in 8, can be used, always bearing in mind that the rake must not be too course, i.e. much below 1 in 5, or the short grain will be too weak, while too fine a pin, i.e. over 1 in 8, will have no real holding power.

Despite being written in a textbook, I find that makes a lot of sense.

So perhaps what Mr Walton was suggesting was that softwood, being softer, requires the steeper angle for the extra strength. I suppose that softwood pins and tails are more likely to compress and work lose? Could that be the basis for his comments?

Silent - this is fun! I love a good debate with a worthy adversary!

First up, I agree with virtually everything you say. I was simply pointing out that totally erroneous myths DO get published (ad nauseum, in many cases) as an example that we should always evaluate any statement not supported by good reasons or clear evidence; not as proof that all published statements are myths. And likewise, that reputation is by no means a gaurantee of infallibility, unless you happen to belong to certain religious orders....

Being published most certainly does not mean you are right about everything, and let's be reasonable - who would have had the oportunity or desire to challenge a few minor contentious statements in a school textbook in 1947? So I rather suspect that your diagnosis is quite correct - that the reason Mr. Walton stipulated 1:8 for dovetails was because that's what HIS teacher told him, and not based on a body of empirical or theoretical work.

So here's the challenge - can anyone come up with some convincing evidence that there is any significant difernce in the structural properties of (well-made) dovetails ranging from 1:5 to 1:9.......?

Originally Posted by silentC

So perhaps what Mr Walton was suggesting was that softwood, being softer, requires the steeper angle for the extra strength. I suppose that softwood pins and tails are more likely to compress and work lose? Could that be the basis for his comments?

We crossed over - .
Yes, that's the reason for the steeper angles on softer woods that I've read. But to me it doesn't make a lot of sense, because you are trading off on the weaker short-grain in the steeper tails, so anything gained by one is lost to the other. They are also a PITA to cut & fit as I keep saying - try it!

Gotta run...

who would have had the oportunity or desire to challenge a few minor contentious statements in a school textbook in 1947?

This is true, but it has been revised a number of times, the most recent being 1979 (seems like only yesterday). Since my edition is a reprint of the 1979 revision, I have no way of knowing whether that nugget of information was included from the outset, or added at a later date. I would assume that plenty of people have passed their eyes over it since then - but the great majority of them would have been school boys I suppose and the teacher would not appreciate anyone challenging the notion in class.

I don't work with softwood generally, or when I do it's glue and screw time, so haven't had the opportunity to test the theory. So I'm happy to take the consensus of opinion of those who have as a starting point. Like Jeremy, I do tend to give credence to guys like Mr Walton, I mean you don't just sit down and write a textbook on woodworking without having a considerable amount of experience behind you. But if you're telling me that your experience runs counter to his advice, who am I to argue?

Originally Posted by silentC

But if you're telling me that your experience runs counter to his advice, who am I to argue?

Someone who likes a bit of a debate?

Silent - I'm not trying to set myself up as an authority by any means, but my temperament & professional training leads me to question something I find runs counter to both experience & intuition.

But my experience is not in the same league as Eddie's or Whatsisname Walton. What we all lack is the sort of evidence I would consider crucial to the whole debate. So we're dealing with opinions here, and yours is as good as mine.
However, if someone out there pops out of the woodwork (so to speak!) and assails us with overwhelming evidence or incontestable reasoning to support Walton, I'll be the first to embrace it.

It would be far from the first time in my life that I had my ignorance enlightened...

Cheers,

So we're dealing with opinions here, and yours is as good as mine.

I think you're selling yourself short there.

Actually I don't really have an opinion on it, because I've got nothing to base one on. Having no reason to doubt it, I've always believed the 1:6 for softwood to be a rule of thumb but one which I've never had the occasion to apply. I'm not attached to it and will happily discard or embrace it, if as you say someone comes along with evidence, or even a convincing argument (I'm willing to risk it) one way or the other. But until I actually make a dovetail in softwood, it is academic.

It's like the 1/3 rule of thumb for tenons, and I already know what you think of that one. I stick with it because 1/4" works very nicely with 3/4" rails but I understand and appreciate your point of view.

Rules are made for the guidance of wise men and the obedience of fools (Douglas Bader?). I guess if you are teaching woodwork to school children, rules are useful also. Once we grow up and make our own way in the world, we're free to keep or discard them. I still remember the number of days in a month with that little jingle.

I'll pull my head in now

Originally Posted by silentC

Rules are made for the guidance of wise men and the obedience of fools (Douglas Bader?).

Nope, not Bader, but his squadron commander. It's been my mantra all my life, & the reason I've gotten into some trouble. Had lots of fun, though.

Originally Posted by silentC

I'll pull my head in now

Aww, c'mon - you're one of the more cogent respondents out there!

I can't help kicking the odd sacred cow, Silent. I have the privilege of teaching some rather bright young people, & I'm very conscious that many of today's truths are going to be heresy tomorrow. I keep telling them that it's their job to find out where our generation is wrong & the next generation's job to find out where THEY'RE wrong.....

Avagoodone - gotta get back to the paying job.
Cheers,

Rules are made for the guidance of wise men and the obedience of fools (Douglas Bader?).

[quote=IanW;807807]Nope, not Bader, but his squadron commander. It's been my mantra all my life, & the reason I've gotten into some trouble. Had lots of fun, though.
/quote]


Also Winston Churchill, but the original quote is much older than any of these - possibly Lord Nelson.

Cheers

Graeme