Octagonal table - advice on type of joint to use?

[Col]

Hi,
Having been distracted by a couple of projects for my daughter I'm now back to building my oak octagonal table and have a 'joint' question.

The style I'm looking at is like the 'Mouseman' coffee table with cross rails - see second image on this old ebay listing : http://www.ebay.co.uk/itm/Robert-Thomps ... 7675.l2557

The legs are 75mm by 75mm square (from an oak worktop offcut ripped and glued) and I'm looking for some advice on the best type of joint between the legs and the top/bottom cross rails (which are 75mm wide to match the legs). I was planning on mortice and through tenon, but the tenon would look oversized in the square stock - so would a double tenon be right for this or is there something better?

Thanks for any advice, Colin

 

[Mattty]

I'd be just putting a single 25mm wide tenon in. I't doesn't need a double tenon.

 

[Col]

I'd be just putting a single 25mm wide tenon in. I't doesn't need a double tenon.

Sounds good - much less work - I was a litttle concerned about getting double tenons at each end of the legs perfectly aligned given my level of skills

 

[Mattty]

I'd be just putting a single 25mm wide tenon in. I't doesn't need a double tenon.

Sounds good - much less work - I was a litttle concerned about getting double tenons at each end of the legs perfectly aligned given my level of skills

Completely unnecessary mate. Take some pictures of your progress!

 

[marcus]

I was taught that max shoulder width on a tenon should be 5/8", and if it is going to be more than that with a single tenon you should do a double. That's what I stick to.

The reasoning behind this is that on thick stock a double is stronger and longer lasting. The combined tenon width is greater and there is a much larger area for glue: even at only three inches wide the timber can cup ever so slightly across the width with changes in humidity — only a tiny bit, but enough to open the joint slightly round the shoulders, or apply pressure against them. Over a long period of time this can weaken the joint. Double tenons ameliorate the effects because the timber (ie the component with the mortise in it) is secured nearer to it's edges helping to reduce movement, and the joint is intrinsically stronger. On narrower components none of this matters because any movement will be too small to have an effect.

If you do single tenons it will be OK for a good while, possibly for ever, but if you want to do the best job possible I would do double tenons on that. Have a go — they're not so hard and you will feel proud of yourself afterwards!

 

[Col]

I was taught that max shoulder width on a tenon should be 5/8", and if it is going to be more than that with a single tenon you should do a double. That's what I stick to.

The reasoning behind this is that on thick stock a double is stronger and longer lasting. The combined tenon width is greater and there is a much larger area for glue: even at only three inches wide the timber can cup ever so slightly across the width with changes in humidity — only a tiny bit, but enough to open the joint slightly round the shoulders, or apply pressure against them. Over a long period of time this can weaken the joint. Double tenons ameliorate the effects because the timber (ie the component with the mortise in it) is secured nearer to it's edges helping to reduce movement, and the joint is intrinsically stronger. On narrower components none of this matters because any movement will be too small to have an effect.

If you do single tenons it will be OK for a good while, possibly for ever, but if you want to do the best job possible I would do double tenons on that. Have a go — they're not so hard and you will feel proud of yourself afterwards!

thanks Marcus - good explanation - that's a vote either way!

I think I will at least try a double tenon in some scrap and see how it goes.

I've looked through a couple of books that I have (and some available online) but cannot find useful references as to when to use such a double tenon. Can anyone point me at a reference book that has this type of detail please?

Thx

 

[Steve Maskery]

My take is this:
The twin tenon (I think a double tenon is two in line rather than two side-by-side, is it not?) is the best for the shrinkage issues discussed above. It is totally unnecessary from a strength point of view, there is very little stress on those joints.

A single tenon would do. Loose tenons would also do and if the legs and feet are machine to exactly the same width, you could easily rout mortices from each side and there would be a very good chance of them lining up. This would be a good home-workshop solution.

You could also turn a spiggot on the ends of the legs and drill a corresponding hole in the feet. Wedged it would be very strong.

If you go the twin tenon rout, you have already worked out that it is not enough for the tenons to be a good fit in their respective mortices, they also have to be exactly the right distance apart, otherwise each will foul the other as you try to put them together. If you have a bandsaw or a tablesaw, you can cut this joint easily with 100% accuracy (yes, Right First Time Every Time) with my Ultimate Tenon Jig. There are no test cuts for fit and only one for alignment to ensure that the sides end up flush.

You have lots of very good options.
HTH
Steve

 

[Sgian Dubh]

I think a double tenon is two in line rather than two side-by-side, is it not?) Steve

It might be, but I've always known those as forked tenons, eg two forked, three forked, four forked, etc-- narrow edges parallel. Double or twin tenons are the form where the wide faces are parallel with each other, and triple, etc tenons are triple, quadruple, etc. You don't see many triple, quadruple and above jobbies around. Slainte.

 

[Steve Maskery]

Forked is not a term I've come across before. But then I've never had any formal training in woodwork.
You learn something new every day.
S

 

[Col]

My take is this:
The twin tenon (I think a double tenon is two in line rather than two side-by-side, is it not?)

Steve

Steve - I've found several references that are the other way round:

"There are other variations of the mortise and tenon joint, two of which are the double tenon and the twin tenon. The double tenon is used on timbers that are wide. This variation features two or more tenons next to each other and a mortise cut to receive them. A twin tenon is used when the tenon rail is comparatively wider than its thickness. This variation has two tenons attached by a haunch that is inserted into a mortise cut accordingly to receive it"

However, I also found the following:

"The terms double and twin tenon are often confused. A double tenon is as shown above whereas a twin tenon has two tows of tenons and are used on say the middle rail of a door to allow a lock to be fitted without destroying the joint. You may well find that a number of text books get mixed up from time to time and this author is no exception"


Maybe I should start a new thread on whether it is double or twin or forked as an alternative to sharpening discussions :roll:

...
A single tenon would do. Loose tenons would also do and if the legs and feet are machine to exactly the same width, you could easily rout mortices from each side and there would be a very good chance of them lining up. This would be a good home-workshop solution.

You could also turn a spiggot on the ends of the legs and drill a corresponding hole in the feet. Wedged it would be very strong.

If you go the twin tenon rout, you have already worked out that it is not enough for the tenons to be a good fit in their respective mortices, they also have to be exactly the right distance apart, otherwise each will foul the other as you try to put them together. If you have a bandsaw or a tablesaw, you can cut this joint easily with 100% accuracy (yes, Right First Time Every Time) with my Ultimate Tenon Jig. There are no test cuts for fit and only one for alignment to ensure that the sides end up flush.

You have lots of very good options.
HTH
Steve

thanks for these options - I don't have a router or lathe (yet) so will be cutting this by hand. Will try out a double (or twin) on some scrap and see how accurate my measuring/making is - you never know! I have already watched your youtube video advertising the bandsaw jig and it looks good. However, at the moment I'm still learning and it will do me good to practice these skills (I may change my opinion when I see my results ).

 

[marcus]

I think a double tenon is two in line rather than two side-by-side, is it not?) Steve

Yes it depends entirely on which book you read!

 

[Col]

ok - so tried my first double/twin in scrap (and first mortice/tenon in hardwood)

Result looks OK but it failed the 'should not use unreasonable force to fit' test (I didn't want to over trim the tenon to fit) and learnt a couple of lessons on the way. I deliberately didn't show a picture of the underside showing the through tenons where I had over cut the mortice by chiseling all the way from the top

I'm sure that after the next eight they will be looking better with even less adjustment!

 

[marcus]

Looking good!

 

[Steve Maskery]

That looks good from the camera view
You have learned a lot, I am sure. Have another go, this time chopping in from both sides. Perhaps invest in a float, it will be a lot cheaper than a Domino XL

Well done that man.
S

 

[Col]

Looking good!

That looks good from the camera view
You have learned a lot, I am sure. Have another go, this time chopping in from both sides. Perhaps invest in a float, it will be a lot cheaper than a Domino XL

Well done that man.
S

thanks guys - there was no airbrushing - honest - though I did take the 'best' angle

Steve - I'd never heard of a woodworking float (plastering float - yes). So I now know there are two types of woodworking float - edge and flat sided - guess you were recommending flat sided to adjust the tenon sides (rather than edge to bottom out between the tenons)?

 

[Steve Maskery]

Never used one myself, this is far too manual for my lazy approach...
But yes, I gather it's what the neanderthal cognocenti (if that is not an oxymoron) use to perfect their tenons. If you have a visa to visit the Hand Tool forum, I bet there are many people more knowledgeable over there to advise you.
S

 

[Sgian Dubh]

I think a double tenon is two in line rather than two side-by-side, is it not?) Steve

Yes it depends entirely on which book you read!

Or where you trained perhaps which is where I learned the term forked tenon for two tenons narrow edge to narrow edge on a wide board, eg the middle rail of a frame and panel architectural door. Twin or double tenons were used, and still are in my usage mostly on the end of chunky posts and rails, and the like, although they're also used in more delicate work, eg, drawer divider rails into the carcase sides (or gable ends (sic) as I learnt them). I suppose there are numerous regional variations in terminology. For instance, I've been calling hand drills 'wheelies' just about all my working life, an Edinburgh thing I imagine, but I'm also aware that many Americans call them egg beaters! Slainte.

 

[Dangermouse]

I restore a fair bit of antique furniture, and this type of table in Edwardian times would have had a spigot turned on the legs, a hole drilled in the cross pieces and then glued and wedged. This lasts for a hundred years, so is pretty tough and easy to make.

 

[Col]

I restore a fair bit of antique furniture, and this type of table in Edwardian times would have had a spigot turned on the legs, a hole drilled in the cross pieces and then glued and wedged. This lasts for a hundred years, so is pretty tough and easy to make.

Thanks - sounds like another good reason to get a lathe (it is the next major tool on my long wish list ) . For this project though I've just finished cutting all (8) double tenons. I'll post some pictures after a bit more progress ...

 

[marcus]

I restore a fair bit of antique furniture, and this type of table in Edwardian times would have had a spigot turned on the legs, a hole drilled in the cross pieces and then glued and wedged. This lasts for a hundred years, so is pretty tough and easy to make.

It will probably last, but at that thickness it will leave scope for the shoulders to open over time, which is unsightly if nothing else. Most antique furniture (and I speak as a fan) was built to fairly indifferent standards, same as today, and for the same reasons — cabinet makers wanted to make money, and most customers had other things to spend their money on and were more interested in being fashionable than in quality. Everyday antique furniture in no way represents some sort of golden age of quality.

So yes, it will probably stay together like that (as it would if it were a single tenon), and that may be fine for your purposes, but if you want to do the best quality job, double tenons are the way to go....

Looking forward to seeing the pics...