Thread: Big circles

Tricky. It depends on what tools, timber and equipment you have. Are you going to use these to stretch the canvas for painting and then release it? My limited understanding of the art world was that distorts and damages your piece.

As per the curves... a few options spring to mind.
1. Make a many sided polygon using straight timber and half lap joints. Then use a jigsaw/bandsaw to cut the curve into the polygon. Finishing with a sander or spoke shave.

2. Make a mould with MDF (cut to shape with a jigsaw/bandsaw, then layered and a flush cut router) then thin strips of any timber (inc. hard wood) bent by clamp and glue to the mould.

3. Use a giant piece of ply, cut with a jigsaw.

The painting wouldn't be removed from the stretcher, for exactly the reasons you suggested.

I like the idea of Jigsawing ply, I just didnt realize the sheets came over a metre and a half wide. I thought the biggest you could get them was 1.2 x 2.4

Ive been considering the polygon idea too. My thinking regarding making the many sided Polygon was that, because all the force of the canvas would be pulling forward it wouldnt be strong enough unless it was 2 circles of thinner ply glued over each other. I made a stretcher of this size using a similar idea, and it weighed a tonne and also took a really long time.

I think if I were to do it now I could do a much better and quicker job, but given that I'd be looking to make a few stretchers, in your experience would it save time to create moulds and do the gluing and bending or quicker to just cut ply circles?

Fitting one circle exactly within the other wiil be a challenge. If the circles can also serve as the frame of the finished work, four identical half-rings of plywood, with each pair offset 90 degrees and the canvas between the pairs before assembly, would eliminate the need for the outer band. Also, the drying shrinkage would occur at the mid-plane of the donut so as to resist "dishing." By addressing the dishing problem this way, it could weigh much less than the tonne of your previous effort.

If you have a lot of these to do, some experiments would be in order to establish minimum requirements.

The many-sided polygons would incorporate much less waste than the plywood. I would offset the two full rings by half a segment, but otherwise as above with the plywood.

The ring fastenings could be all from the back, or included as a design feature of the frame.

Cheers,
Joe

astojkovich

Take two sheets of 18 mm ply and but them edge to edge. Scab some boards across the joint tio hold them together.

Mark out your circle and drill 18 mm holes in the circumference about every 100 to 150 mm. Set hard wood dowels in the holes and let them stick up 75 mm to 150 mm.

Cut strips of wood say 100 mm x what ever length you can get and about 2mm to 4 mm thick. Depending on your skill and equipment level. Glue the strips but end to but end with a scarf joint until they are long enough to go around and lap over the ends.

You can dry bend or steam bend thin wood quite easily. Clamp one end of the strip to a dowel and using a heavy duty heat gun (hair dryer) slowly heat the wood and bend if around frame. Overlap the ends and clamp. let cool, make a scarf joit and glue in place. Use two ro three layers to make the inside hoop.

Leave the hoop in place and build a second hoop over the outside of the first hoop. Put a filler piece between the two for the canvas. Instead of a scarf joint where the ends com together put a wooden block on each end and leave a 12mm gap. Run a long bolt through both blocks of wood so you can tighten the outer hoop onto the inner.
Regards
the other Joe