Bending skirting board to fit a bay window.

Hi All
Sorry to be asking for advice again, but I would rather ask a stupid question than make a stupid mistake!
I have a bay which has been plastered to a smooth curve, which I need to bend skirting board to fit. The bay is about 8' across and 3' deep, either side finishes nearly 90 to the back. In the rest of the property I have used MDF for the skirting but I can get the same profile in pine, the finish will be painted. The skirting is 3/8'' by 4 1/2'', I have thought of a few options outlined below but I am not really keen on any of them.
Option one, kerfing the back and or front. Option two, building the molding up in situ (not sure this would be practical though. Option three steaming a length to shape, I have only ever helped a friend repair boats with this technique and seem to recall it does not work so well with pine.
Any Insights would be gratefully received, I am leaning to option one at the moment.
Cheers,
Stuart
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On 4/10/2010 10:57 AM, Stuart Pearson wrote:

Obviously off-the-shelf molding?
If so, I would sacrifice a few pieces to option one. One trick, if the kerfs will be visible from the top, is to set your kerfing saw to 45 degrees so that your bending kerfs will have a "v" shape.
I would want the wooden molding to be rather thin and flexible to start with, so if it is the usual 3/4" thick molding, you may want to do a combination of resawing/planing/jointing the actual trim to a thinner thickness before kerfing, then using a more flexible piece (layers of 1/8" to 1/4" material; mdf, plywood, etc) beneath it to make up the thickness.
I've bent plywood into some pretty tight curves with kerfing, but unless the wood trim very flexible to start with, the thinner the better, IME.
Steam bending is best with green wood, cut specifically with long grain in mind.
Then, there are plenty of architectural flexible moldings available from many different sources. DAGS ... Here's a starter:
http://www.flexiblemoulding.com/products.html
In any event, interesting project, so let us know how it works out.
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Option four: rip the decorative top section from your board, back-kerf the bottom section, and bend or steam-bend only the thin top section (which will be nailed to the kerfed bottom section).
If you have the right router bits, you can make a glue-joint seam with the top section and the bottom, which might be preferable. You might also consider a 45 degree slant cut when parting the decorative top, then the bent top slips behind the kerfed stuff and can easily be pinned through the flat.
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I would use 1/8" masonite in layers to match the finish of the MDF. The material will make the curve with little or no struggle and is easy to glue. I do think 1/4" MDF would make the curve, but you would need to experiment.
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On Sat, 10 Apr 2010 16:57:44 +0100, the infamous "Stuart Pearson"

There are polyester moulding boards available now which are very flexible, Stuart. Since you'll be painting it, it should work perfectly for you.
http://www.flexiblemoulding.com / http://www.resinart.com / http://www.flextrim.com http://fwd4.me/L7U Outwater, where I learned this stuff existed. The catalog was late getting to me so I lost out on bidding for that contract. (standard disclaimer applies)
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snipped-for-privacy@diversify.invalid wrote:

That's option four. Here's option five (which I did a few years ago in exactly the same situation): bent laminations. You'll need to make a bending form, and use several thin layers of a wood that bends easily -- I used 1/8" ash. It's also imperative to use a glue that dries rigid. Titebond won't do (it creeps under that kind of stress). You'll want a urea-formaldehyde glue. Glue, clamp, wait for glue to cure, trim, install.
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Have a job coming up where the customer wants to encase his coved doorways that separate one room from another. The doorways are already coved in drywall and measure about 8' across, the radius is fairly large. What would you guys use to encase this upper section of the doorway. Plywood kerf in back or bent 1/8 - 1/4" Masonite? The encasement will be painted..
Thanks, Rich
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IMO kerfing works much better when the kerfs are on the inside of the curve. The remaining material pushes against each other to keep the piece from breaking at the kerfs. Since your openings have a pretty large radius and assuming the radius on the sheetrock is round enough, I would use two or three layers of 1/4" fiber filled plywood. It will make the bend easily. I would install the round first and then you can cut the angle on your legs. This will give you 3/4" material to cover the ends so the round piece doesn't really have to be fit very closely. Having been down this road before, I would also suggest removing the existing drywall corners if the new casing will cover. Usually there is so much mud build-up that it can be difficult to get the new casing to lay down.
Mike O.
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Mike O. wrote:

suggestion. Thanks
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In forth:

I'd use3/8" bendable plywood and add a 1/8 birch door skin for paint
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Simply use bending Luan, or look at some other methods: http://www.woodweb.com/knowledge_base/Best_material_for_bent_lamination.html
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| Have a job coming up where the customer wants to encase his coved doorways | that separate one room from another. The doorways are already coved in | drywall and measure about 8' across, the radius is fairly large. What would | you guys use to encase this upper section of the doorway. Plywood kerf in | back or bent 1/8 - 1/4" Masonite? The encasement will be painted.. | | Thanks, | Rich | | -- | You can lead them to LINUX | but you can't make them THINK ! | Mandriva 2010 using KDE 4.3 | Website: www.rentmyhusband.biz
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On Sat, 10 Apr 2010 16:57:44 +0100, "Stuart Pearson"

Have you tried just pushing the MDF in there to see if it will go? I haven't used the 3/8 but the 5/8 I have used is pretty darn flexible. I would think the 3/8 would make the bend. If it won't go, I'd use two pieces and just rip them to make a back side and a front side. You need to use two pieces to make up for the loss of the saw blade width. Surely 3/16 of mdf will make the bend.
Mike O.
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Mike O. wrote:

Soak the mdf , prop the ends betwwen chairs anf place a weight on the centre
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