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By GrahamF
#1246192
Why are blind mortise and tenons used when a dowel joint is quicker and easier to cut and possibly stronger?

To keep it simple, if we look at the one thirds rule for joining two pieces of 3" x 1 1/2", the tenon would be 2" x 1", giving a glue area of 6" x whatever depth. If 2 x 1" dowels are used (same depth/length) then the glue area will be 6.28" - theoretically stronger.

Am I missing something?
By Jacob
#1246194
the 1/3rd rule is a rule of thumb just a rough guide, but useful.
In your example a 1" dowel in 1 1/2" wood would be 2/3rds of the width with 1/4" thin walls to the "mortice" and weak.
Dowels in general are weaker.
By Mike Jordan
#1246195
My preference would be for through wedged m & t followed in decending order by blind m & t and in desperate times dowel construction. The dowelled are the cheap end of the market and at one time also featured finger jointed stiles and rails. Like most tradesmen of my aquaintance, I would never buy the finger jointed stock.
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By CHJ
#1246197
GrahamF wrote:Am I missing something?


Cross sectional area of Dowel versus Tenon, relative to shear strength of Tenon wood species versus Dowel

Don't think the glue area to hold them in place is really relevant.
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By Pete Maddex
#1246201
Don't forget that end grain dosn't glue very well so half of the circumference of the dowel can be discounted, unless you are using epoxy.


Pete
By phil.p
#1246206
:? You wouldn't have end grain on the circumference.
edit - sorry, yes, you've little long grain in a round mortice.
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By woodbloke66
#1246211
Jacob wrote:Dowels in general are weaker.

I used to think so too, but it's a commonly held misconception. When the Dowelmax jig came to the UK, Derek Jones tested it for F&C and stated that it was the best dowel jig he'd ever come across. I subsequently bought one and it is a superb bit of kit.
In a subsequent article, he was then loaned the Dowelmax hydraulic rig which they used to test joints of various sorts to destruction. I can't remember the exact joints that were on test, but a fairly standard m/t joint was one of them (amongst others) which was compared to one made with a Dowelmax jig (not sure how many dowels/size either). To cut a long story sideways, the dowel joint proved to be the strongest of all those on test, much to Derek's amazement. It's all written up in one of the F&C articles from a few years ago, a copy of which I've got somewhere but I can't be faffed to go and dig it out :lol: I think the caveat is that the dowel joint has to be made properly with decent, high quality, close fitting dowels...not the Silverline things :( they supply with it - Rob
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By custard
#1246213
There's nothing wrong with dowel joints, but a problem you may well encounter is sourcing good enough quality dowels to make a decent dowel joint. You need a dowel where the grain doesn't run out, and one that delivers a snug fit without any "ovalling". Find those and you're laughing, without them it's a case of rubbish dowels = rubbish joints.
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By thetyreman
#1246218
I'd go with motise and tenon over a dowel in terms of strength, in theory the dowel can shrink once it's inside, the mortise and tenon was designed to expand and contract together, if something works don't try and fix it, the M&T worked for thousands of years.
By Jacob
#1246219
woodbloke66 wrote:
Jacob wrote:Dowels in general are weaker.

I used to think so too, but it's a commonly held misconception. When the Dowelmax jig came to the UK, Derek Jones tested it for F&C and stated that it was the best dowel jig he'd ever come across. I subsequently bought one and it is a superb bit of kit.
In a subsequent article, he was then loaned the Dowelmax hydraulic rig which they used to test joints of various sorts to destruction. I can't remember the exact joints that were on test, but a fairly standard m/t joint was one of them (amongst others) which was compared to one made with a Dowelmax jig (not sure how many dowels/size either). To cut a long story sideways, the dowel joint proved to be the strongest of all those on test, much to Derek's amazement. It's all written up in one of the F&C articles from a few years ago, a copy of which I've got somewhere but I can't be faffed to go and dig it out :lol: I think the caveat is that the dowel joint has to be made properly with decent, high quality, close fitting dowels...not the Silverline things :( they supply with it - Rob
Nearly all the chairs I've had to repair have had failed dowel joints.
You don't find them at all in old joinery - they weren't used a joint (with odd exception - non stressed decorative add on bits) but were used as pins through M&Ts.
By phil.p
#1246220
Likewise - scores of them. But they invariably failed because the glue failed, not because the dowels themselves did.
Any purposeful testing of course would have to be perfect m&ts against perfect dowel joints, both of which are probably quite rare. :D
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By GrahamF
#1246232
thetyreman wrote:I'd go with motise and tenon over a dowel in terms of strength, in theory the dowel can shrink once it's inside, the mortise and tenon was designed to expand and contract together, if something works don't try and fix it, the M&T worked for thousands of years.


Obviously, strength in a joint depends on fit and strength of glue used but surely the same arguments can also be made for loose tenons and dominoes where different materials and possibly grain differs?
By phil.p
#1246234
thetyreman wrote: ... the M&T worked for thousands of years.


Yes. Picks and shovels worked for thousands of years, but I'd sooner use a JCB. :D
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By woodbloke66
#1246240
custard wrote:There's nothing wrong with dowel joints, but a problem you may well encounter is sourcing good enough quality dowels to make a decent dowel joint. You need a dowel where the grain doesn't run out, and one that delivers a snug fit without any "ovalling". Find those and you're laughing, without them it's a case of rubbish dowels = rubbish joints.

Agreed, as I said above

Jacob wrote:Nearly all the chairs I've had to repair have had failed dowel joints.
You don't find them at all in old joinery - they weren't used a joint (with odd exception - non stressed decorative add on bits) but were used as pins through M&Ts.


That may so Jacob, but it doesn't alter the proven, systematic test done by F&C that a correctly made dowel joint, with properly fitting dowels is actually stronger than a m/t - Rob