Hatch Braces - Is this Overkill

[ukuleleblues]

My hatch will be is 60" wide and about 60" tall. https://picasaweb.google.com/lh/photo/MDplHUN4yBPzYWslv9eR0dMTjNZETYmyPJy0liipFm0?feat=directlink I was going to make 5 braces out of 3/4 plywood 2.5 inches wide.
See Diagram https://picasaweb.google.com/lh/photo/Vm4GI9p6Ihx2YDwQcSrBzdMTjNZETYmyPJy0liipFm0?feat=directlink

Is the 3/4 x 2.5 overkill?

I was also wondering where I could get some of the locking latches that mound on the sides and pull it tight? What is the hot set up for hatch latches?

[bc toys]

the 2 on outside you might want to double up and glue really good cause you will be screweing in to them thats my .02$

[steve cowan]

According to your sketch you are using 1/4" to skin the hatch so you need it to be stout to avoid spring back .

Steve

[Wolfgang92025]

I don't think its overbuilt. The only thing I would do different is use two 1/8" skins to avoid spring back.

Here you can see my hatch build, about the same size. I doubled up in the center for skinning the inside of the hatch.



You can find a few more pictures in my album about page 22.
Just my thoughts...... for what it's worth.

[Kody]

When I get to the part where I build the hatch, I will be laminating the curved spars from 1/4" x 1" They will be only 2" deep. The spars will be covered with 4mm plywood on both sides. This will produce a very strong frame and hatch. Yeah, I know it's a lot of work to laminate but the finished result will be worth it all. I might even cover just the outside of the frame, it depends how stiff the frame finishes up with the lamination's. With the lamination's showing it would look really great and reflect the work that's gone into it. More on this later when I get to build the hatch. I drew up the spars with the CAD program thinking I could use a thick sheet of plywood to cut them from. I gave this idea away as the expense of the plywood was simply horrendous and there was far too much waste left over. I am looking forward to laminating the spars and the cost is much cheaper by far. Photos will come eventually. I have just about finished making all the studs/bolts for fastening the wooden bearers to the frame. Again, photos will come soon.

Kody

[woodywrkng]

I agree with Wolfgang. Two layers of 1/8 will be much better than one piece of 1/4 inch plywood. The main problem I had with my build was using 1/4 inch plywood on the hatch. I used 6 spars, each made from 1/2 inch plywood, and the 1/4 plywood exterior changed the radius by around one half inch.

[grantstew8]

I've used 3.6mm ply 1/8" and I'm going to coat it with epoxy and the thinnest fibreglass material I can find.
The 6mm 1/4" ply I've used for the walls and it's not really bendy at all....
Here are a few videos of my build
Cutting ribs http://youtu.be/o9vGok3tN0M
Assembling the ribs http://youtu.be/GxAGYafOxYs
Skinning the hatch http://youtu.be/zDw12lsKeWo

[planovet]

I just used one layer of 1/8" birch and covered that with an aluminum skin. If you want 1/4", I would suggest using two 1/8" pieces like stated above.

I'm not sure what kind of locking latches you are looking for. If you are looking for some like mine, I got mine at http://www.mcmaster.com

[Gage]

The two teardrops that I have built I skined them with 1/8" birch and have had no problems. I wonder why being how every one else either uses two sheets of 1/8" or one sheet of 1/4". My teardrop is 11 years old and has been in all kinds of weather and no major problems.

[woodywrkng]

I wanted 1/4" for the hatch because I would be pushing it closed against the weatherstripping and wanted the extra rigidity. The top and front are 1/8". I guess 1/8' would have been fine for the hatch, but I wanted to err on the side of strength.

[KCStudly]

Hatch strength comes from the ribs and superstructure. The deeper the ribs and the more solidly the frame is built (tight fitting joints and gusseting) the more stable the shape will be. The structure is what holds the ply into it's unnatural bent position. The rigidity comes from the framework and curvature, not so much from the thickness of the ply.

I will shout it from the mountain tops. I believe in deep hatch ribs. 3 inch deep ribs are quadruple the strength of 1.5 inch deep ribs.

[eamarquardt]

Hatch strength comes from the ribs and superstructure. The deeper the ribs and the more solidly the frame is built (tight fitting joints and gusseting) the more stable the shape will be. The structure is what holds the ply into it's unnatural bent position. The rigidity comes from the framework and curvature, not so much from the thickness of the ply.

I will shout it from the mountain tops. I believe in deep hatch ribs. 3 inch deep ribs are quadruple the strength of 1.5 inch deep ribs.

Actually, unless I'm mistaken, the strength goes up with the cube of the height. So, 3 inch ribs are 8 times stronger than 1.5" ribs.

Cheers,

Gus

[eamarquardt]

I cut some 1/8 BB ply into strips and laminated a test rib.

I preformed the pieces into a tight circle to reduce springback when I glued them up. I clamped them to short pieces of angle iron screwed to plywood as a form. Preforming them was unnecessary. When I did the actual gluing up of the rib I used c-clamps as they worked better than the spring clamps.


Here is a picture of the finished laminate.


Here is a picture of the finished rib. There was no springback when I removed it from my jig and it is exceptionally stiff. The advantage of this technique is that a lot of the grain is parallel the entire length of the rib which makes it far stiffer than a rib cut out of plywood.


Actually, I think laminating the rib was easier than cutting a bunch of pieces out of plywood and gluing them all together. In addition, the only wasted material was that which was lost from the saw kerfs. Minimal. Also I really like the side view of all the laminations.

Just my two cents.

Cheers,

Gus

[KCStudly]

Well Gus, technically we are both wrong.

The formula for a rectangular shape rib is: Moment = (width x height^3 (cubed)) / 12

So the answer is, "it depends". I may have exaggerated, but it is more than double.

[Larry C]

Actually, I think laminating the rib was easier than cutting a bunch of pieces out of plywood and gluing them all together. In addition, the only wasted material was that which was lost from the saw kerfs. Minimal. Also I really like the side view of all the laminations.

Just my two cents.

Cheers,

Gus

Gus,
Your plywood lamination's look great. Did you run them through a thickness planer or were you able to keep everything level during glue-up? I had to run mine through my planer. I agree this method is MUCH easier, and cost effective over cutting from plywood. I will be using it for my hatch as I did for my perimeter profile.