Large oval top doorway

[Tim Nott]

Anyone ever made anything to fit a hole like this?

(alt+p)

It's 2.7m wide by 2.5m high. Thew bottom half should be straightforward enough with double doors and fixed lights to each side, but the top????
My tiny bandsaw only cuts 70mm deep, and I don't have room for a bigger one. I did something similar once, but that was smaller and internal, and had a rectangular outer frame, concealed in the partition, and the lining was kerfed to get the curve

(alt+p)

 

[Chems]

Thats a job for a router, jig saw and some MDF templates.

 

[MikeG.]

Tim,

I'd take a close look at the opening if I were you. That is essentially a "flat arch", with rounder corners. Flat arches don't exist.......it is really a segmented lintel, and as such is liable to sag over time, or indeed fail completely.

My instinct would be to re-build the arch to a proper shape in stone, but if that is not on then get a piece of steel made up to support it. Don't, whatever you do, use the window frame to hold it up!

Mike

 

[xy mosian]

Hi, Photograph it, square on, print out full size, stick the print to a big piece of wood and cut around the outline of the arch :lol: :lol:

Seriously, it may be possible to get accurate dimensional details from an image on the pc. Start off with a 'square on' photograph. Import it into some graphics program, scale to a known size then take graph plotting type co-ordinates. Using a graphics program you may well be able to find a 'good fit' radius for the curved sections which would make life a little easier.

For manufacture I would consider building the frame up in a way similar to a segmented bowl, as found in turning.

xy

 

[FatFreddysCat]

Anyone ever made anything to fit a hole like this?

Yes. It's large, but that's the only real issue, I'd say. Only thing I'd avoid is kerfing any external structure such as this because that is always going to be where terminal rot starts no matter how well you seal it.

That is essentially a "flat arch", with rounder corners. Flat arches don't exist.......it is really a segmented lintel, and as such is liable to sag over time, or indeed fail completely.

You must be a structural engineer! :roll: Looks fairly old to me, and yet it's still standing........ We do see sectional flattened arches in some of the old stone buildings round here. If you try dismantling them you sometimes find that they are held together with iron keys and are quite stable even after several centuries. Not sure I'd try to change a historical detail such as that.

Thats a job for a router, jig saw and some MDF templates.

Really? We are talking building sections here, something like 5in x 3in solid timbers (not built-up) or bigger, especially in softwood. Any smaller and the whole plot will just flex. For that a bandsaw and spindle moulder with a ring fence would be the best (only?) approach. Trying to saw that sort of size in hardwood with a jigsaw is just begging for problems as the blades will flex and give an inconsistent cut, even on a Festool. In the absence of a large enough bandsaw the traditional approach would be to cut out the curved sections using a frame saw with a turning blade. Once the sections of the head have been roughed out the old fashioned approach would have been to work the curves with a compass plane although an 1800 watt 1/2in router could also be used to do the rest of the work. Working it from scratch with the router seems like another exercise in futility. In the absence of specialised equipment it may well be worth making a plain (i.e. rectangular x-section) frame with separate lightweight glazing frames held inside. That would simplify construction somewhat

 

[MooreToolsPlease]

I've built a dummy vented window to this, similar dimensions too.
What I did was to make radiused corners, and then spliced them into the head and the jamb. The curved templates were all done with a router and trammel, but the template following was done with a ring fence on the spindle.
I think what I would try and do in this instance would be to make the side lights take up as much of the curve as possible, so that the main doors are essentially straight topped.

The key to doign a job such as this, is a full size pattern of what you are going to be making, with all of the radius' drawn on it and numbered.

To get a rough idea of the radius, I would measure a chord rom 2 points, and then measure the projection square to the chord, whis will be able to tell you the radius with some maths.
Apart from that, enjoy it! I would love to get a job like that at the moment.

 

[Russ]

Tim,

I'd take a close look at the opening if I were you. That is essentially a "flat arch", with rounder corners. Flat arches don't exist.......it is really a segmented lintel, and as such is liable to sag over time, or indeed fail completely.

My instinct would be to re-build the arch to a proper shape in stone, but if that is not on then get a piece of steel made up to support it. Don't, whatever you do, use the window frame to hold it up!

Mike

Mike, I reckon that solid stone opening is over 400 years old and around 60cm thick... And will certainly last another 400 years. Looks pretty solid to me.

Tim, I have a customer in le Gers with a similar problem, if you find a solution I'd be interested.

Russ

 

[Chems]

Thats a job for a router, jig saw and some MDF templates.

Really? We are talking building sections here, something like 5in x 3in solid timbers (not built-up) or bigger, especially in softwood. Any smaller and the whole plot will just flex. For that a bandsaw and spindle moulder with a ring fence would be the best (only?) approach. Trying to saw that sort of size in hardwood with a jigsaw is just begging for problems as the blades will flex and give an inconsistent cut, even on a Festool. In the absence of a large enough bandsaw the traditional approach would be to cut out the curved sections using a frame saw with a turning blade. Once the sections of the head have been roughed out the old fashioned approach would have been to work the curves with a compass plane although an 1800 watt 1/2in router could also be used to do the rest of the work. Working it from scratch with the router seems like another exercise in futility. In the absence of specialised equipment it may well be worth making a plain (i.e. rectangular x-section) frame with separate lightweight glazing frames held inside. That would simplify construction somewhat

5x3" doesn't seem huge to me. I don't know really I've never worked with anything that large, it was just that I saw Norm make a huge arch in one episode with those methods. His router didn't have the depth of cut so he'd make one cut with a guide bush on his template then cut the other side with a bottom bearing guided cutter for the rest of the thickness.

 

[ferdinand]

Anyone ever made anything to fit a hole like this?

This may be a silly question, but there are hinge pins in the pic. Is there a chance that the old doors are lying around somewhere?

We had a pair of antique room dividing doors which fitted a Georgian arch about that size which were being used as a workbench in the attic. It took a few months to notice.

I'm tempted to say get a full size template by setting up your base line, offering up a pair of 8x4 sheets of whatever, tacking them to the wall, and drawing round the arch carefully with a pencil.

Or you could treat it as a ground survey and do multiple diagonal dimensions to give an accurate plan.

Ferdinand

 

[Tim Nott]

Thank you all for your input.
With regard to the sectional lintel/arch I'm not too worried. It has stayed up for several hundred years, it's not my place and I think it will continue to stay up. At least till the cheque clears.
Jigsaw and router? Don't think so - did make an oval bulls-eye window once with a router, but that was fairly small sections.
I love xy mosian's suggestion about photos, but the template isn't a prob - can do that with sheets of ply or MDF on site. As per Ferdinand's suggestion.
The segmented approach seems the way to go, though. Can you still get Cascamite?
I've got a ring fence for my spindle - never used it as it frightens the dung out of me. But you can get a spindle equiv of a bearing-guided router bit like this thing http://tinyurl.com/y8udn2j
I've got a similar opening at my place - tho a lot samller, and the builders (employed by the previous owner) made a rectangular oak frame and stuck a curved piece of glass straight to the stone above


Later...
Don't you just love clients? I talked this over today, and explained that it was going to be challengingly expensive

"Oh no - we just want it rectangular- we'll fill in the top with cladding."

Profound aplogies for wasting everyone's time. Good fun though.