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How would you do this?

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How would you do this?

Postby 9fingers » 27 Aug 2018, 11:28

I've not been posting much as the last few weeks has seen me stripping armchairs back to bare wood, staining them mid oak, varnishing and shipping them off to a local upholsterer for completion. So no woodwork and lots of my least favoured activities, sanding and finishing. There are 8 of the blasted things to do counting a 2 seater sofa as two and it has been rather tedious

Like this

chair.jpg
(346.16 KiB)


Note the curved front rail which is the reason for this query.


Management wants a footstool in the same design so I have an excuse for real woodwork. Here is the design I am copying.

footstool.jpg
(5.21 KiB)


The frame is easy M&T joinery with a bit of interest in the form of curved long rails (the short ones will be straight) The radius of the curve is about 1metre and I need to make a firm curved plywood base to give the upholsterer to do here work on. It needs to take staples from underneath so I'm thinking 1/2"- 12mm finished thickness but how best to form the curve so it keeps the radius when detached from the frame so she can form the cushion and get the top fabric wrinkle free when it becomes attached.

My thoughts so far are to use two pieces of 1/4" ply with numerous kerf cuts along the short axis, to make it more flexible, and glue those in a set of curved cauls with the kerf cuts facing each other.

My everyday goto glue is Everbuild D4 pva/eva stuff which I have heard will creep under continual stress. Is this correct? If so maybe I should use cascamite type glues.

I'd welcome all input especially from the pro's that we have here regarding methods. The upholstery is costing multiple arms and legs so I need to get this right first time if at all possible.

TIA

Bob
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Email:motors@minchin.org.uk
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Re: How would you do this?

Postby Robert » 27 Aug 2018, 13:36

Took me quite a while to work out what the question was all about. Think we are talking about formed plywood that has a curve to it like it was cut from a large cylinder.

In which case I'd start with 1/8"ply and use 4 layers for your 1/2" then glue the layers together in a form of some kind. Maybe use vacuum. Can't see the glue being a problem as there is no strength in 1/8 ply and in use it just gets pressed again anyway.

If it's not that then maybe some more explanation needed :)

Hard to tell from the little picture what curves where.
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Re: How would you do this?

Postby 9fingers » 27 Aug 2018, 14:09

Thanks Robert,
You have manage to capture the requirement exactly from my deeply coded question. :lol:

Here is a bit larger photo I found online.

footstool2.jpg
(42.36 KiB)


The curve on the underside of the long rails are duplicated on the top surface so the seat base also has a curve of about 1m radius.

I like the idea of 1/8" ply because as you rightly say this won't put up much of a fight. I'll have think about cauls vs vacuum clamping form. I've only got one to make so as I'll have a template for routing the hardwood frame curves, I can easily knock up a few softwood cauls

Bob
Information on induction motors here
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Email:motors@minchin.org.uk
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Re: How would you do this?

Postby Stargazer » 27 Aug 2018, 23:12

Bob,
This seems a very similar manufacturing problem to the curved kite shields we make for re-enactments, these are the familiar kite shape but with a cylindrical curvature. We make then by laminating upto 3 pieces of thin (4mm) ply together with titebond and clamping around a cylindrical former using straps until dry, typical radius is 0.5-0.75m. Former can be specially made from ply and solid wood or a spare oil barrel.

Our shields get painted and edged in leather and get abused and used in all sorts of weather outside, never seen one delaminate, get completely smashed yes, but not lose its shape and delaminate.

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Re: How would you do this?

Postby Mike G » 28 Aug 2018, 07:21

Your question has been answered, but let me ask another one. Why? Why does the base need to be curved? If you want the top of the cushion to have a camber, then get them to cut the foam like that.
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Re: How would you do this?

Postby Woodbloke » 28 Aug 2018, 08:52

Robert wrote:In which case I'd start with 1/8"ply and use 4 layers for your 1/2" then glue the layers together in a form of some kind. Maybe use vacuum. Can't see the glue being a problem as there is no strength in 1/8 ply and in use it just gets pressed again anyway.



I'd probably do it that way as well but use a 2mm oak face show veneer. Everbuild D4 is wunderbar but to go full 'belt n'braces' with minimal risk of spring back or delamination, I''d use Cascamite between formers with plenty of G clamps - Rob
I no longer work for Axminster Tools & Machinery.
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Re: How would you do this?

Postby Rod » 28 Aug 2018, 09:06

How does the top attach to the base?

My father made loads of foot stools and the ply was thin. The supporting area is very small.
Is the ½” just for the upholstery?

Rod
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Re: How would you do this?

Postby 9fingers » 28 Aug 2018, 09:09

Mike G wrote:Your question has been answered, but let me ask another one. Why? Why does the base need to be curved? If you want the top of the cushion to have a camber, then get them to cut the foam like that.

Basically the rail is curved on both top and bottom edges on the chairs and I'm copying that detail.
Having discussed it with swmbo I have now approval to make the top flat which does make the job a whole lot simpler both for me and the upholsterer. Yes she could cut the foam to give a concave top but would have to button the top to pull the fabric to follow the curve.

Thanks for the question Mike and stimulating the design change :D

Bob
Information on induction motors here
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Email:motors@minchin.org.uk
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Re: How would you do this?

Postby 9fingers » 28 Aug 2018, 09:12

Rod wrote:How does the top attach to the base?

My father made loads of foot stools and the ply was thin. The supporting area is very small.
Is the ½” just for the upholstery?

Rod

Now that I'm not curving the top, I will probably use traditional buttons to attach it to the frame
The 1/2" ply is to give plenty of meat for the upholstery staples to go into.
Bob
Information on induction motors here
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Email:motors@minchin.org.uk
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