Moon gate arch

[jim shula]

I have to estimate the building of a moon gate arch for a sign customer. The shape will be a half circle with a diameter of 48", and the section of the half circle will be approx 6"x6". This will sit on top of two 6x6 posts, and the swinging part of the gate has a corresponding half circle shape to create a full circle opening when the gate is closed. It is located in a garden fence.

The old arch was built up from several layers of 3/4" cdx plywood, then fiberglassed with polyester resin. I could use this same strategy to build the new one except I would use epoxy resin (I've built several boats with it), but I'm wondering about other ways to build it so it won't be so heavy.

One approach would be to have a continuous piece of 1/2" marine ply as each outer piece with scraps of 2" hdu sign foam glued in as filler material, then glass the structure with 4oz fiberglass and epoxy resin.

The other thought I had is to use the same continuous outer layers held apart by blocks every 12" or so, then bend 3mm marine ply around the top and bottom of the shape to close it in, then glass it with 4 ox glass. If I did this, it would weigh the least of the three options, but I wonder if I would need to drill breather holes so it wouldn't blow apart?

[bleeth]

Since in your area this is going to go through some real weather extremes if you do opt to have it hollow inside I would definitely drill a drain/relief hole at the bottom. Remember that the epoxy/cloth system will require good UV protection in a well maintained topcoat.

If you use the right hinges and they are well blocked as well as balanced the weight shouldn't be much of a factor.

A different look and longlasting results could also be had by building the gates out of T & G red cedar sandwiched up with ribs inside. Then finishing is with something like sikkens.

For outdoor gates built that way don't forget to allow for seasonal expansion and contraction.

[scottp55]

Jim, I have no idea what the posts and door are,or their style. But a Salem style arch made of cedar, with arches glued into dadoed roof panels with a custom shaped keystone(perhaps engraved or symbolized) it would minimize end grain exposure and would look nice with a snowdrift on top. customizable to the n'th and just oil finish. Not mine I just liked it when I searched,I like the second door myself. I don't know if it helps. When I worked at The Boatyard in Manset I saw something like your third option and the guy used brass window screen stapled and glued on the interior side in routed slots for ventilation and to keep carpenter ant out. Scott17844

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[jim shula]

Scott, your bottom image is similar to what I have to quote. I only have to build the fixed arch, not the whole gate. The arch I build will basically be a solid 6"x6" in section. I could build it from solid plywood or make it hollow.

Below is a google image of what I have to build - the arch only, not the whole swinging gate.

http://www.exteriorspecialtyconstruction.com/images/moon_gate_Los_Angeles.jpg

[scottp55]

Jim, How does the arch mount to the post? Any idea why and where the old arch failed? No experience with hdu,does it react with resin?I slapped together 3x8' pocket doors of 1/4" birch ply and celotex core red birch spline,they were temporary and were going to taken out of the house and into workshop after the real doors were done,19 YEARS AGO. 1/8" deflection in winter is my only gripe. Anyways, a triple lam of 1/2" / full foam/1/2"/ full foam/ 1/2" wrapped in 3mm. with a solidly(SOLIDLY) integrally mounted base plate. Just a thought. I would cedar glue lam,or look for the right shaped tree and let the next generation worry bout it. BEWARE I answered this before my coffee.

[bleeth]

Jim, If you built it out of layered up solid western red cedar and staggered the joints on the laminations it would last forever.

[scottp55]

SOMEBODY WITH EXTERIOR EXPERIENCE PLEASE SHOOT HOLES IN THIS! Jim, the closest I came to doing this was an end-grain balsa and teak composite 30 years ago for a 8' commercial tanning drum( like the vanes in a dryer). I haven't blown gel coat and dust out of my nose for the same amount of time. Jim, the temp pocket doors I mentioned are way tougher than I thought they would be( for 15 years they have locked each other in the bedroom by clamping the grabs with the big 12" quick-grip,and they have thrown themselves full length at it sometimes 2 of them at a time- and the boy(180 lbs. now) finally managed to bend the johnson hardware but not the door). Will the 3 mm take the 4' curve without kerfing? black flies-it was so nice working with the garage doors open. Darn! I had to throw that caveat in there. Scott Oh, heres the doors.

[scottp55]

Dave, I entirely agree,but whats the matter with eastern red,I mean we are in Maine.

[bleeth]

The Eastern is actually a fast growing Juniper also known as Aromatic Cedar (As in line a closet with it and keep the moths away). It is rot and insect resistant. Here is a bit about it:

http://cedarusa.com/newpage2.htm

Western Red is a true cedar and is generally straight grain and more uniform in color. Also rot and insect resistant

Google it for images and you can see the difference.

[scottp55]

Jim, just a thought,don,t know where you are in state,but this one is near August. solid cedar would be arrogant(japanese for elegant). don't know how to web link yet but www.mainetimberworks.com/beams

[jim shula]

The old arch failed because the glass is delaminating from the plywood. They used polyester resin, and as any boat builder will tell you: "polyester and wood, no frigging good".

I'm in Buxton.