Sash construction - joints

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rich3911
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Sash construction - joints

Postby rich3911 » Mon Feb 04, 2019 10:11 am

I thought this was an interesting blog of sash window contruction.

http://customfurniture.us/index.php/furniture-blog/82-making-furniture/103-replicating-historic-window-sash

They use a haunched mortise and tenon with nails going through.

I have read some posts about just gluing scribed joints, which sounds like a recipie for disaster down the line...

The classic joinery books show a dovetail, saying it's better that haunched mortise and tenon. I've seen that some windows use a m&t with a dowel through. Does the presence of sash horns make the m&t the joint to use there and for dovetail for the upper sash top rail and lower sash bottom rail?

A thin rail make m&t less of an option too... Our middle bay lower sash has a pane of glass thats 42"x38" and the meeting rail is only 1¼" high. The bottom rail is about 2½" high.

Another option is m&t with wedges, which I guess could be done foxtail style or just wedged either side of the tenon? This does mean having to taper the mortise but I guess that's done by hand with a chesil or can you angle the stile on the mortiser?

Is there a prefered method these days, or would it be better to follow whatever was done on the original window?

If using Accoya, for instance, does this dictate a particular joint type?

That's a lot of questions! :roll: Sorry!

Just trying to get a thorough understanding of sash construction.

Leveller2911
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Re: Sash construction - joints

Postby Leveller2911 » Mon Feb 04, 2019 12:43 pm

rich3911 wrote:I thought this was an interesting blog of sash window contruction.

http://customfurniture.us/index.php/furniture-blog/82-making-furniture/103-replicating-historic-window-sash


I would ignore the blog to be honest. The order of processes are not great and in fact create more work so for instance every single Joiner I know will plane up the timber, set out the sashes, mortice the mortices, tenon the rails,glazing bars etc and then finally mould,rebate and groove the sash members. In the blog he moulds the timbers firstly (which creates more work) and then sets out ,mortices,tenons......


They use a haunched mortise and tenon with nails going through.


The only nails you really need to use is the joint between the stiles and meeting rails if there are no horns .If the sashes have horns (as in your case) then glued wedges are by far the best method of fixing a joint. Others may disagree but it my opinion.

I have read some posts about just gluing scribed joints, which sounds like a recipie for disaster down the line...

The classic joinery books show a dovetail, saying it's better that haunched mortise and tenon. I've seen that some windows use a m&t with a dowel through.
I'm not sure what you mean by "a dovetail"....


A thin rail make m&t less of an option too... Our middle bay lower sash has a pane of glass thats 42"x38" and the meeting rail is only 1¼" high. The bottom rail is about 2½" high.


The meeting rails can be any width you like, they tend to be slim because its then less visible to the eye. I think a 2 1/2" bottom rail is a bit narrow because I always fit sash lifts to assist opening the sashes and you need a wider bottom rail to fit them on..

Another option is m&t with wedges, which I guess could be done foxtail style or just wedged either side of the tenon? This does mean having to taper the mortise but I guess that's done by hand with a chesil or can you angle the stile on the mortiser?


When you set out the sashes and mortices ,set out the mortice width and then just mortice 6mm or so outside of the mortice lines and as the chisel moves down just move the motrice bed which creates a tapered mortice for the wedge to fit into..

Is there a prefered method these days, or would it be better to follow whatever was done on the original window?


Wedged and glued mortice and tenon, been around for centuries and ist still good today..

If using Accoya, for instance, does this dictate a particular joint type?


No but using accoya restricts the types of glues,paints you can use and also ironmongery fittings ,screws and pins because the Acetic Acid will eat away certain metals..So when you pin on the staff beads you need to use stainless steel pins...

rich3911
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Re: Sash construction - joints

Postby rich3911 » Mon Feb 04, 2019 1:04 pm

Leveller2911 wrote:
rich3911 wrote:I thought this was an interesting blog of sash window contruction.

http://customfurniture.us/index.php/furniture-blog/82-making-furniture/103-replicating-historic-window-sash


I would ignore the blog to be honest. The order of processes are not great and in fact create more work so for instance every single Joiner I know will plane up the timber, set out the sashes, mortice the mortices, tenon the rails,glazing bars etc and then finally mould,rebate and groove the sash members. In the blog he moulds the timbers firstly (which creates more work) and then sets out ,mortices,tenons......


They use a haunched mortise and tenon with nails going through.


The only nails you really need to use is the joint between the stiles and meeting rails if there are no horns .If the sashes have horns (as in your case) then glued wedges are by far the best method of fixing a joint. Others may disagree but it my opinion.

I have read some posts about just gluing scribed joints, which sounds like a recipie for disaster down the line...

The classic joinery books show a dovetail, saying it's better that haunched mortise and tenon. I've seen that some windows use a m&t with a dowel through.
I'm not sure what you mean by "a dovetail"....


A thin rail make m&t less of an option too... Our middle bay lower sash has a pane of glass thats 42"x38" and the meeting rail is only 1¼" high. The bottom rail is about 2½" high.


The meeting rails can be any width you like, they tend to be slim because its then less visible to the eye. I think a 2 1/2" bottom rail is a bit narrow because I always fit sash lifts to assist opening the sashes and you need a wider bottom rail to fit them on..

Another option is m&t with wedges, which I guess could be done foxtail style or just wedged either side of the tenon? This does mean having to taper the mortise but I guess that's done by hand with a chesil or can you angle the stile on the mortiser?


When you set out the sashes and mortices ,set out the mortice width and then just mortice 6mm or so outside of the mortice lines and as the chisel moves down just move the motrice bed which creates a tapered mortice for the wedge to fit into..

Is there a prefered method these days, or would it be better to follow whatever was done on the original window?


Wedged and glued mortice and tenon, been around for centuries and ist still good today..

If using Accoya, for instance, does this dictate a particular joint type?


No but using accoya restricts the types of glues,paints you can use and also ironmongery fittings ,screws and pins because the Acetic Acid will eat away certain metals..So when you pin on the staff beads you need to use stainless steel pins...


Thanks muchly for the speedy replies!

Re Accoya, I know all about waht it does to plated steel! A joinery company we used fitted a plated multipoint lock to an Accoya patio door and didn't seal the pocket. The lock looked like it had been in the sea after just a month or two. You could clearly see that the corrosion started from the inside and was working it's way outwards. They denied it was anythnig to do with the wood and said it was due to the salt air... (we are 4 miles from the sea). Likewise with screws holding in the window locks... and the panel pins in the beading...

Re dovetail. I might have used the wrong terminology, but Cassells Carpentry and Joinery shows this:

sash dovetail.jpg


It also shows a m&t joint though...
(Edit: I'm lying. It shows m&t on the top/bottom rail to stile and dovetail on meeting rails to stiles)

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Re: Sash construction - joints

Postby thatsnotafestool » Wed Feb 06, 2019 5:12 pm

The reason for the dovetail is to maintain the integrity of the joint in case of glue failure ie if the glue fails, the meeting rail isn;t going to pull out when you shut the window. With modern glues I think that is less of a problem.

I like thin meeting rails for the reason that Leveller says. The timber to glass ratio of most modern 'off-the-shelf' window is appalling. There was one house near us with a tiny window in the downstairs loo where they had used the same standard profiles as they'd use on really large windows elsewhere. It was all frame and a tiny pane of glass in the middle and looked really naff.

It's the one negative comment I have re your existing windows..those two massive frames between the two outer windows. Do you have to keep the same design? Could you not go for something else to avoid those chunks of wood ? Or if you are tied to the design, make the two outers fixed or the middle one fixed? Or even to what IIRC Ellis did in one of his windows which was fly all the weights to the outer boxes thus reducing those two central timber chunks.
The advantage of a bad memory is that one enjoys several times the same good things for the first time.
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Leveller2911
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Re: Sash construction - joints

Postby Leveller2911 » Wed Feb 06, 2019 6:20 pm

thatsnotafestool wrote:
It's the one negative comment I have re your existing windows..those two massive frames between the two outer windows. Do you have to keep the same design? Could you not go for something else to avoid those chunks of wood ? Or if you are tied to the design, make the two outers fixed or the middle one fixed? Or even to what IIRC Ellis did in one of his windows which was fly all the weights to the outer boxes thus reducing those two central timber chunks.



I was gonna say the same thing.... The current window is a triple but may well look better as either a venetian (wider centre sashes with narrow outside sashes) which would mean those central boxes which are currently hollow to allow for the weights could be much slimmer (75mm) and the weights can be housed in the outside boxes or just make the central sashes wider and keep the weights in those central hollow boxes. Currently the window looks a bit bland and would look like more of a feature with either a venetian or just wider centre sashes.

Those centre boxes look so wide they look like they would house weights for all 6 sashes but personally I would re design it , have a venetian with wider sashes to the centre, slim centre mullions and have fixed sashes to the outside. I would also machine a staff bead moulding to the ouside linings and head linings and it would look a lot better aesthetically..

I pretty much always make my sashes with horns because it allows me to secure the joint with glued wedges , without them it relies on glue and pins because I don't know anyone who makes a "dovetail " meeting rail joint. I've seen 100's of meeting rails that have bowed over the years because when the sahes bind up and difficult to open people tend to force them and then the joints pull apart so I always fit sash lifts to the bottom rails and sash pulls/rings to the underside of the top sash meeting rail to assist opening rather than forcing the sashes open..

I'm rubbish as uploading pix .............. https://www.flickr.com/photos/55385455@ ... ed-public/

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Re: Sash construction - joints

Postby Meccarroll » Wed Feb 06, 2019 7:09 pm

Leveller2911 wrote: I'm rubbish as uploading pix .............. https://www.flickr.com/photos/55385455@ ... ed-public/


But obviously very knowledgable when it counts..............Joinery!

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Re: Sash construction - joints

Postby Leveller2911 » Wed Feb 06, 2019 7:11 pm

Duplicate post..........PC going wonky. :lol:

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Re: Sash construction - joints

Postby Leveller2911 » Wed Feb 06, 2019 7:14 pm

Meccarroll wrote:
But obviously very knowledgable when it counts..............Joinery!


I'm very weak on stairs and would love to be taught more about making staircases. I know the basics but don't that many enquiries and when I do I tend to shy away a bit ..........Lack of confidence I guess. :roll:

rich3911
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Re: Sash construction - joints

Postby rich3911 » Wed Feb 06, 2019 10:36 pm

I agree the mullions are big and seeing as I only want the middle sash to open, I could run the sash cords along the top of the head and into the outside sash boxes.

Can't do venetian, even though I like the look of them as our Orangery has equal size triples too. (but not sashes, just fixed casements)


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