(Mitred) Joints!

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(Mitred) Joints!

Postby Benhen » Sun Mar 19, 2017 11:32 am

Can anyone advise? At the end of the day, well, 20 years of days, is the mitred spline as strong as the traditional cross-keyed sliding dovetail joint?

I read the previous thread on the Forum with great interest. I have frames made by two leading framers (Martin Turner and Giaccherini). The frames have been subjected to great climatic variations, from damp Argyll to relatively dry London. There is not so much as a hairline crack in the critters despite, in some cases, being over 15 years old. However they are all sliding dovetails.

I would rather go down the table saw path, but is the mitred spline really as strong.

Anyone with long term experience? Be much appreciated....
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Re: (Mitred) Joints!

Postby prospero » Sun Mar 19, 2017 2:05 pm

Depends on the shape of the moulding. Splines are better suited to deep, narrow sections where it is
impractical to insert biscuits. Sliding dovetails for wide, relatively flat shapes. On wide mouldings there
is a greater tendency for the joints to crack. Wood expends/shrinks across the grain rather than lengthwise
and the bridging piece on a sliding dovetail helps prevent this.

I use a lot of biscuits. :D Typically on 3" ish wide mouldings. On more chunky stuff, two in each corner.

If we are talking about cracks due to shrinkage, the best way to prevent them is to let the wood 'normalise' in
a inside living room environment for a few days before chopping and joining. Especially if it's been stored in a
shed in winter or straight off the lorry.
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Re: (Mitred) Joints!

Postby Benhen » Sun Mar 19, 2017 2:38 pm

Good point re. damp shed. One loose link and pop, there's that crack.
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Re: (Mitred) Joints!

Postby Benhen » Sun Mar 19, 2017 2:52 pm

I also wondered if the rabbits have developed tougher skins since HS2 got the go ahead through their beloved Downs..... it seems somewhat too strong at 11:1
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Re: (Mitred) Joints!

Postby Not your average framer » Mon Mar 20, 2017 12:04 am

There is a lot to consider when trying to answer this question. The whole subject is not necessarily straightforward at all. There are some who like make the splines (also called feathers) using a contrasting wood type to visually highlight the splines when in place. Also if the splines are the main strength of the joint apart from the glue in the mitres, then it follows that the wood used for the splines needs to be chosen for the right physical properties.

I don't claim to be an expert on this, but I have repaired items of antique furniture (not frames) and in doing so have replaced sliding dovetailed splines (or keys as I have also heard them called), although not necessarily with the exact same wood type. However furniture makers do have various different opinions about the best ways of making keys and splines, some recommend particular wood type and some recommend drying out the wood for these keys / splines before cutting and inserting them so that they will expand slightly after being inserted and tightened as they absorb atmospheric humidity.

You may be surprised to hear that in traditional furniture making the sliding dovetail splines are not always glue in place, but are just a very good tight fit.
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Re: (Mitred) Joints!

Postby Jamesnkr » Mon Mar 20, 2017 11:48 am

I think you know the answer anyway. A mitred joint is the weakest possible joint as it relies solely on the glue on two facing surfaces. Which is why it is underpinned or splined or biscuited - as these give additional surface area for the glue to attach. A sliding dovetail, on the other hand, is a mechanical solution, the glue being just a bonus.

I'm not quite sure what you mean though. I can't quite see how a sliding dovetail joint fits into a normal picture frame?

dovetail.jpg
dovetail.jpg (62.54 KiB) Viewed 245 times


Unless this is for the flat part of a cassetta* frame - with mitred inner and outer bits attached? If that's what you mean, and you've a workshop and a decent router, then why wouldn't you. Probably takes less time than putting a spline or biscuit in. I guess this could well have been made that way:

cassetta.JPG
cassetta.JPG (91.27 KiB) Viewed 245 times


Or maybe if making a Nicholson Frame (and I mean a Nicholson Frame, not a bog-standard cassetta 'St Ives' frame). Or perhaps for a sub-frame.

This is a cool idea for using a biscuit cutter to make splined joints: http://www.woodmagazine.com/woodworking ... rced-miter

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Re: (Mitred) Joints!

Postby Benhen » Mon Mar 20, 2017 11:56 am

Thanks, Mark.
All makes complete sense to me. The no glue bit calls to mind Stevenson's lighthouse, Skerryvore, 100 miles west of here. The masonary was cut with such precision and no cement was needed.
Thanks, James.
Yes, I must get the router onto it. But am slightly nervous of breaking the joints with too much pressure (I don't possess mitre clamps, which seem rather expensive for four.
(Sorry about the website, I've slightky given up on that as social media seems to be where it's at. Hope you are well)
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Re: (Mitred) Joints!

Postby Benhen » Mon Mar 20, 2017 12:03 pm

Or am I being dim, the table mounted router is best?
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Re: (Mitred) Joints!

Postby Jamesnkr » Mon Mar 20, 2017 12:09 pm

You can't come up with £7.50?! Brilliant piece of kit:

https://www.amazon.co.uk/Wolfcraft-3441 ... band+clamp

Don't be tempted by the ones that look like this as the nylon slips if you try to get it properly tight:

https://www.amazon.co.uk/BRAND-CLAMP-LE ... band+clamp

Lion sell one for about £50 with a metal band. You can get that really tight, but it's jolly expensive and it's a right faff to use.

Or you could buy these and knock something up for the corners.
http://www.pritchardtyrite.co.uk/cargo- ... AsVq8P8HAQ
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Re: (Mitred) Joints!

Postby Not your average framer » Mon Mar 20, 2017 8:33 pm

The sliding dovetail key goes across the mitre joint at 45 degrees at the rear of the frame.

When this method of locking joints is used on the top and bottom corners of the carcass on antique furniture these sliding dovetail keys are cut off flush and then hidden by means of decorative trim mouldings. The trim moulding is pinned in place and usually is also fixed with scotch glue.

Scotch glue has limited strength and is easy to loosen and break the bond to enable repairs and whatever dismantling required to effect repairs. These days little regard is given to repair, probably as modern items are not intended to last.
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Re: (Mitred) Joints!

Postby IFGL » Mon Mar 20, 2017 9:21 pm

Jamesnkr wrote:I think you know the answer anyway. A mitred joint is the weakest possible joint as it relies solely on the glue on two facing surfaces. Which is why it is underpinned or splined or biscuited - as these give additional surface area for the glue to attach. A sliding dovetail, on the other hand, is a mechanical solution, the glue being just a bonus.

I'm not quite sure what you mean though. I can't quite see how a sliding dovetail joint fits into a normal picture frame?

dovetail.jpg


Unless this is for the flat part of a cassetta* frame - with mitred inner and outer bits attached? If that's what you mean, and you've a workshop and a decent router, then why wouldn't you. Probably takes less time than putting a spline or biscuit in. I guess this could well have been made that way:

cassetta.JPG


Or maybe if making a Nicholson Frame (and I mean a Nicholson Frame, not a bog-standard cassetta 'St Ives' frame). Or perhaps for a sub-frame.

This is a cool idea for using a biscuit cutter to make splined joints: http://www.woodmagazine.com/woodworking ... rced-miter

__________________________
*I see you've a couple of these on Instagram. BTW the link to Instagram from your website doesn't work.


Wow
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Re: (Mitred) Joints!

Postby Benhen » Mon Mar 20, 2017 10:16 pm

A bit off topic; But Richard (if you see this), thanks for the 'follow' on IG -- by way of thanks, check this awesome piece of fluid chasteness at Tate Mod, on a Giaccometti if memory serves correctly.
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Re: (Mitred) Joints!

Postby Jamesnkr » Tue Mar 21, 2017 10:40 am

Oh, I see, I completely misunderstood what you were getting at with the sliding dovetail key; I thought it was a sliding dovetail joint - which would, as mentioned, be great on the flat part of a cassetta.
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Re: (Mitred) Joints!

Postby Framemaker Richard » Tue Mar 21, 2017 12:25 pm

Nice one Ben :yes: Lovely looking frames
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