Joints for stretcher bars for canvases

[brianhabby]

Does anyone know the best or easiest way to cut the joints for canvas stretcher bars please?

Like this:

regards

Brian

 

[SPSlick]

I would use a tenoning jig on the table saw.

 

[brianhabby]

Okay, thanks for that

regards

Brian

 

[Steve Maskery]

It pretty much has to be a two-part process, cutting the tenons and open mortices first and them the mitres.
I'd do it all on the tablesaw, although I guess you could do it on the spindle moulder.

 

[ColeyS1]

I wonder whether just a simple glued mitre with those v nails would suffice...?

 

[Steve Maskery]

I think that the point of this joint is that it can easily be used to stretch the canvas once it has been tacked into place. A wedge (or is it two?) gets inserted in each corner to enlarge the frame. It pushes the frame members apart and thus keeps the canvas tight.
S

 

[Chrispy]

The best and easiest way for me would be with a tenoner, in two goes as Steve said one for the slot and one for the mitre.

 

[Argus]

I think that the point of this joint is that it can easily be used to stretch the canvas once it has been tacked into place. A wedge (or is it two?) gets inserted in each corner to enlarge the frame. It pushes the frame members apart and thus keeps the canvas tight.
S

I agree with Steve.

The point of a picture stretcher joint is that it allows stretching, not when made, but when put into use. Canvas is a moisture absorbing material and these things can be made well in advance and stored for acclimatisation - a bit like timber.

As I recall, the joint is a wide slot, about 1/3 the thickness of the material in the end of each side. Assembled, the slots align and the corner of each piece accommodates a wide wedge. The canvas is then fixed in place by staples along the edges and the wedges tightened to tension the canvas uniformly.

Next, before use, the cloth is wet primed, which allows the canvas to soften; the wedges are tightened again when wet which makes the whole thing is rigid when dry. There are variations for larger pieces, cross braces for monumental paintings etc, but that's the basic construction.

Hope this helps.

 

[brianhabby]

Thanks for all the replies, I think I will have a go using the tenon jig on the table saw as suggested.

I understand about the wedges for tightening the frame but does anyone have a picture from inside the mitre showing how the wedges work please?

regards

Brian

 

[AndyT]

This could be the picture you want

It's from a useful old book on joints, available online here and elsewhere:

http://chestofbooks.com/home-improv...ts/Frames-For-Oil-Paintings.html#.U9UzhI7TVYk

It's actually a slightly different joint - though doing the job you want - which should be quite a bit easier to cut.

 

[Steve Maskery]

Good picture.
I'm not sure it is easier to cut, though. In Brian's original the shoulders are square, in that pic the shoulders are angled to match the wedge.
S

 

[dickm]

Isn't there another problem with that suggested wedge arrangement, in that the wedges would surely be covered by the canvas in use, and therefore inaccessible for adjustment?

 

[Steve Maskery]

No, the canvas is just over the front, the wedges are accessible from the back.
S

 

[Argus]

Isn't there another problem with that suggested wedge arrangement, in that the wedges would surely be covered by the canvas in use, and therefore inaccessible for adjustment?

You can't 'adjust' a stretched canvas when it's complete and dry - the paint coating is semi-rigid and it will crack.
Any tightening is done after the priming stage, before the artist applies paints .... at this point I'd pin the wedges.

 

[Benchwayze]

Brian,

The wedges are meant to allow for returning a canvas to its original tightness, when the canvas becomes slack after a few years. This isn't to be confused with over stretching, which as Argus said, can crack the paint film. Some paints are more flexible than others though, and I've never had these problems with Winsor and Newton's paints. (This is one reason I have gone over to painting on canvas, glued onto a fixed support such as plywood. This re-stretching problem doesn't exist.

Canvases are stretched because when the idea of painting on canvas first emerged, no one thought to simply glue canvas to a solid ground. Stretching seemed to be the best way. Over the years it's become standard, and is reckoned to be 'best', because it's traditional. These days we have better adhesives, and if you think of all the problems stretching has, it clearly isn't the best option! That's a personal opinion BTW!

If you are making just one frame I would suggest looking at the joint closely and figuring out the marking, before cutting it by hand . By the time you've messed about setting a machine, you'll be golden.

HTH Brian.


Regards
John

 

[AndyT]

Good picture.
I'm not sure it is easier to cut, though. In Brian's original the shoulders are square, in that pic the shoulders are angled to match the wedge.
S

I think it would be easier as you don't need to cut tenons. You plough or saw two grooves, mitre across the full width at the corners then cut the angled ends of the grooves with a narrow chisel.
The wedges work as loose tenons as well as opening the corners to give tension.