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Woodworking/Mortise and tenon jointing on sofa frame

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Wood Jointing
Wood Jointing  
QUESTION: Hi Stuart.  Could you pleae pass an opinion on the mortise and tenon joint in the images attached.  I have other pictures that I can send, do you have a direct email address that I could send them to at all? Many thanks in advance for your response.
Regards,
Stephen.
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ANSWER: Hi Stephen

A well proportioned wedged haunched mortice and tenon joint is one the strongest woodworking joints forward two reasons. One being that it has a large glueing surface area and secondly, by wedging you are trying to create a dovetail shape, preventing the joint coming apart. From the photo I find it hard to determine fully what is going on with the mortice and tenon joint. I would have used a haunched mortice and tenon joint. There are a couple of rules of thumbs which need to be observed. The tenon thickness should be around a third of the rail thickness. The tenon is too thick in the photo so it could be a problem with the morticed timber piece. It's going to have a weakness. Can't make out whether the thin timber pieces are wedges or infill pieces. I would use a ratio of 1:7 for my wedges. It is hard to comment further, generally everything else looks ok.

I am happy to respond to any further questions should you have any but I am unable to tell you my email.

Hope this has help you with what you wanted to know.

Stuart

---------- FOLLOW-UP ----------

Sofa frame rail
Sofa frame rail  
Sofa arm
Sofa arm  
QUESTION: Hi again Stuart.  Thank you for the previous comments.

Please see a couple more images attached - one of the images attached is where the mortise and tenon joint in the previous image I sent you has been dressed up.  The other image is of the sofa arm - again if you could pass an opinion on the jointing and also give me your opinion on what look to be saw marks that have been made from sawing the excess timber off the tenon that would be grand.  Maybe I'm just being over critical and what you can see is acceptable for the most part these days, granted it won't be seen when it's been upholstered, but is that a good enough reason?  I just don't like to see what I believe to be rough work carried out, whether it's seen or unseen, particularly when it's on a costly high end made piece of furniture.

Thank you in advance for your further comments Stuart.  

Regards,
Stephen.

ANSWER: Hi Stephen

The photos given are more helpful. I didn't get the sofa arm photo in your orginal question.

My background is do the best work, quality job in all aspects whether seen or hidden. Workmanship says a lot about the skills and care of the craft person or organisation. If I go to IKEA store as a customer then I know what my expectations should be. If I commission or go to a high end store then my expectation should be higher that I am getting better made, higher quality product.

From a joinery point of view: (Upholstery trade may have a different view)

Sofa arm: I would have cut the tenons close to within 2mm then use my Mirka sander to smooth them flush with the sofa arm. It is going to take some work to remove all those marks by hand planing or power sanding. Every component is rough which may be acceptable in the upholstery trade. For me personally I wouldn't be happy with this and the corners need the arris removing or the corners  slightly rounded over. There is evidence in the photo that timber components corners could be a problem.

Sofa frame rail: it's basically a repair job, There is nothing wrong with the repair itself but will effect the visual quality of the product. I couldn't give a quality product to a paying customer with this kind of workmanship defect. The upholstery trade may say that the strength isn't affected and it's not the finished item.

Hope this helps you.

Stuart


---------- FOLLOW-UP ----------

Freshly cut frame pieces
Freshly cut frame piec  

Sam_0367.JPG
Sam_0367.JPG  
QUESTION: Dear Stuart,
 
I hope all is well with you.  I have finally received some picture images through of a freshly made and constructed sofa frame - this one I have been assured has been made and constructed by a professional cabinet maker.  

I have attached one or two of the most pertinent images for you to have a look at and evaluate the work that's been done if you wouldn't mind.  In general, to the untrained but very interested eye it appears to be considerably better than the first attempt; however, I would like your opinion on the images attached.  

In the image of the frame the jointing of the upper back horizontal frame cross member and the centre vertical post doesn't look quite right to me.  I'm sure there should not be any gaps whatsoever between these two pieces of wood but they are visible in the middle and on the outside as you can see.  Also, I would have thought that the mortise and tenons in the other picture image attached should be dressed up before they get assembled and glued together - could the gaps that are visible between the upper back cross member, the side piece and verticle center post be a result of bad preparation before assembling and glueing?  When you zoom in it looks quite rough both in the middle and on the outside - in my humble opinion it looks like it requires further attention before the upholstery stage begins.

Also, you will notice what looks to be a screw holding the cross member in the middle to the verticle centre post - would a screw be a common way to fix/secure such a joint in preference to a wooden dowel?   

As already mentioned, I believe it's a much better job than before, but would you class this as a good standard of woodworking craftsmanship based on present day standards?  I am a bit limited as to how many images I can attach at one time.

As always thank you in advance for getting back to me Stuart.  

Kind regards,
Stephen Austwick.

Answer
Hi Stephen

From the pictures you can see that it a good build. I share your view on the gaps between the horizontal and vertical components though I can't really tell how big they are. Ideally gaps shouldn't exceed 0.5mm. Like you I can't understand why they are not fitting better. I don't have any issues with using screws in my joinery. There are used where they are hidden from view.

The tenons have been cut out using a bandsaw, nothing wrong with that. It's more to do with the tightness of the joint. You can't beat a tight mortice and tenon joint glued with PVA glue. If the surfaces are a little rough then that will help increase the bond. What I am concerned about is the taper shape to the tenons, it wouldn't be something I would do or have ever seen before. I wonder if it is a shortcut on the wedging. Traditionally tenon are straight and the taper wedges transform it into a dovetail shape. This creates joint that doesn't come apart in service. Referring back to what done in the photo, with the wedging the tenon will just create a straight joint.

I'm a joiner by trade not a cabinetmaker so I would do the job differently. It's hard to give an opinion on what goes on or acceptable by present day methods. In principle I am prepared to say that it is a good build. I would want that horizontal component to fitter better with out the gaps. Don't like what I think is going on with the tenons and it's a cheats way of creating a wedged mortice and tenon joint.

Hope this helps you.

Stuart

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Stuart Mawle

Expertise

Now been a carpenter & joiner for the past twenty years in the UK. I can give avice / help on carpentry & joinery, health & safety, woodworking machinery, power tools and suppliers.

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I have served an indentured carpentry apprenticeship with a medium sized building contractor doing a wide range of domestic and commercial work. This has included office buildings, barn conversions, building extensions and renovations. During my career, I spent over three years as a wood trades technician at a college. My job involved joinery work, wood maching and helping CITB carpentry & joinery students` pratical projects. Spent three years as a accredited NVQ assessor covering site carpentry and bench joinery. Now I teach my skills to others.

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I have city and guild qualifications in site carpentry and purpose made joinery. An indentured apprenticeship Hold the equivalent of a master craftsman status.

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