Hatch, just starting

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Hatch, just starting

Postby Arne » Mon Sep 12, 2005 7:40 am

I'm going to be starting my hatch. I have a pretty good idea about how to do it, but am concerned about the 1/8 th ply 'springing' the ribs out of shape causing the hatch to fit poorly.

I plan on using Steve Fredericks as a guide, but will not have an interior skin, so the ribs will be exposed..

First, is 1/8" ply thick enough for a hatch, or do I need 1/4".? I'd like to use 1/8th is possible for lightness.... I'll probably insert blocks between the ribs for torsional strength.

How many ribs and what dimension (x-section) is needed for strength?

What material is best? I'm thinking of cutting them out of 1x6 pine and gluing sections together to get the curve....

Right now, I'm guessing the hatch will be less than 4 feet from top to bottom, and I'm going to make the curve as slight as possible to reduce springing mentioned above.

Any do's and don'ts are appreciated......
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hatch skinning

Postby goldcoop » Mon Sep 12, 2005 10:04 am

Arne-

I used a combo of 1" x 3" oak and 3/4" plywood for my 5' long x 6' wide hatch's framing.

The oak for the 3 straight horizontal members.

The ply for the four curved vertical members.

I used half-lapped joints at the intersections and gusseted every intersection with either metal L brackets or ply for stength (be careful here not to interfere with any latching mechanism).

I skinned both inside and outside and DID have spring back!

Best to either tighten the curve on the verticals a certain percentage and to clamp the whole mess into the curve whilst the glue drys OR make your hatch, let it dry and do what it is going to do and then scribe and sand the ends of your tear to fit the hatch!

I believe if you follow Steve's advice here you should have no problems!

Let us know how it goes!

Cheers,

Coop
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Postby Ken A Hood » Mon Sep 12, 2005 10:11 am

I remember someone who used a lamination of wood and aluminum. They sandwiched a strip of aluminum between the 2 layers of wood; which they said reduced the "spring" back since the bottom side of the aluminum is glued and in tension. I think they used gorilla glue.........
they might be a member here, or on the "old" board but I remember seeing there construction pages.
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Postby IraRat » Mon Sep 12, 2005 1:17 pm

Me, and some others, doubled up on the 3/4 ply for the gussets--making for 1 and 1/2" thick gussets. Only two gussets though, not three, and springback wasn't an issue at all.

And it especially won't be an issue for 1/8th, which I think is too thin if you're not covering with alumunum. (We went 1/4" for the skin.)

As far as the hatch spars...1 by 2 poplar, although you could probably get away with pine.
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Postby asianflava » Mon Sep 12, 2005 1:22 pm

Here is a pic of my frame, it is made up of 3/4ply ribs with 1X2 and 1X4 poplar in between. Even on the tight curve of the modernistic profile, I had minimal springback. I was only going to use one layer but since I'm using the edge of the skin as the sealing lip for the hatch, I went with 2 layers of 1/8in ply.
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Postby Arne » Mon Sep 12, 2005 4:22 pm

Thank you for all the information... very helpful... I may double up the 1/8"... a single layer seems a bit flimsy...
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Postby SteveH » Mon Sep 12, 2005 4:31 pm

Arne,

I built mine like asianflava's, except I doubled the end pieced (laminated 2 3/4" ply), and sheeted with 1/4" ply with the grain ran from side to side, and had no springback.
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Postby Arne » Mon Sep 12, 2005 4:46 pm

One thing I'm going to do is try and design it with as little bend as possible... trying to keep my ever mounting problems to a minimum.

Am surprised 1/4 could be bent that easily. Did you steam it? Was it the cheap luan, or real plywood?
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Postby SteveH » Mon Sep 12, 2005 4:54 pm

It was just regular plywood, and I didn't wet it or anything. Just started at the top and worked it around glueing and screwing it as I went.
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Postby asianflava » Mon Sep 12, 2005 6:50 pm

One trick I learned was to anchor one end, then after it is dry, bend it over and clamp down the other side putting screws in the sides as you go along. I used polyurethane caulk to hold mine down. It was strong enough to hold it's own after a few hours. Just check some parts that ooze out. If it's not dry, you'll know real quick.
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Postby Arne » Mon Sep 12, 2005 7:14 pm

I'm really impressed with that 1/4" bend. I've been using doubled up 1/8" and always have trouble with getting a slight space between some portions between the sheets... makes me wish I'd bought a sheet of 1/4in to experiment with the first time around.... would have been much nicer.. and neater.
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Postby norm perkiss » Mon Sep 12, 2005 8:06 pm

If you haven't aready built your hatch, you could use "bendy" ply. It's 1/4" and will not spring back. I bends like a wet noodle, I rolled it up to haul it home. I found it at a specialty lumber store here in Portland Or. It is about $30 a 4x8 sheet.
I used 1/2" cabinet grade ply for the curved pieces on each side of the hatch and 1x2 poplar for the horizontal structural members.
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Postby Arne » Mon Sep 12, 2005 11:37 pm

I'd forgotten all about bendy ply.... I'll see if I can locate some locally.
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Postby bledsoe3 » Tue Sep 13, 2005 12:54 am

norm perkiss wrote: I found it at a specialty lumber store here in Portland Or. It is about $30 a 4x8 sheet.


Norm, Where did you get it? My hatch hinge came today and I'll be needing to build my hatch soon. :frightened: Jim
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Postby Geron » Tue Sep 13, 2005 6:32 am

IraRat wrote:Me, and some others, doubled up on the 3/4 ply for the gussets--making for 1 and 1/2" thick gussets. Only two gussets though, not three, and springback wasn't an issue at all.

And it especially won't be an issue for 1/8th, which I think is too thin if you're not covering with alumunum. (We went 1/4" for the skin.)

As far as the hatch spars...1 by 2 poplar, although you could probably get away with pine.


That's what I did and so far, no problem. I used 1/8" Luan outside covered with aluminum and 1/8" bendable birch plywood on the inside.

I used 3/4" plywood as gussets because it's laminated and I feel gives better resistance to spring back bending than natural grained wood. I doubled the gussets on both sides using only those two gussets both doubled to make them 1 1/2" thick.

After building the doors, the hatch was so easy I wouldn't worry about having to do a "do over" on it -- except for the expense.

Be careful to keep the hatch braced, level and square as the skins are applied, glued and dry. It has a tendency to shape itself to any uneven surface it may be lying on. Experience talking here. I got a slight warp in mine but the securing clasps pull it in tight and snug.

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