Spring Back Hatch

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Spring Back Hatch

Postby John6012 » Sat Jan 28, 2006 11:03 pm

I had one hatch built with 4 verticals and it fit ok, I just didn't like the way it turned out. Then I built another with 2 verticals and horizontals-about 5 -6 of them Fit good before I put the luan on then it turned south. I put a ratchet strap on both sides tonight to maybe pull it down but I don't know that is a lot of pressure. If I can't make the new one do, I will have to go back to the old one even though the luan doesn't extend beyond the floor at the bottom. Any suggestions as to how I can use my new hatch?
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Postby SteveH » Sat Jan 28, 2006 11:35 pm

John,

You might be able to warp the new hatch into shape with pressure and dampening the wood with amonia.
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Postby doug hodder » Sun Jan 29, 2006 12:08 am

John...I had the same issue on my hatch...but I don't know if my answer is going to help as I don't know exactly how you are going to seal your hatch....I skinned the inside of mine first, used 1/4 maple panel...I lost the arc that I had in it from spring back....I laminated up enough material on the outer portion to build back in the curve I wanted and then shaped it down...I'm going to do the new one in a jig this time...and maybe only skin it in 1/8" as I'm wanting to go lighter...live and learn..Doug
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Postby Micro469 » Sun Jan 29, 2006 12:58 am

Not really sure what you guys mean by spring back... If your ribs are cut out of ply, or solid wood, aren't they strong enough to stay in shape? Or are you not using enough ribs?
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Postby doug hodder » Sun Jan 29, 2006 1:06 am

You'd be surprised at the strength of 1/4" ply wanting to stay flat....my outer ribs on my first tear were laminated up of 2 pieces of dry 3/4 material, each side and 1.5 inches thick in profile...they spread...I didn't use ply as I was wanting to shoot some screws into it on the outer trim and didn't think the ply would hold the screws...doug
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Postby DrJerry » Sun Jan 29, 2006 1:19 am

Old boatbuilders trick: Use 1/8" plywood, score it every inch or so..shallow sawcuts will do. Screw and glue it to ribs. Then do same trick with a second sheet of 1/8" ply using a thin coat of 2-part epoxy all over between the two sheets. Clamp everything together well. Once that sets up, Superman won't be able to straighten it out. :D
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Postby mikeschn » Sun Jan 29, 2006 1:26 am

John,

Hatchspring back is a problem if your vertical ribs are not stiff enough, or if you try to bend too stiff a piece of plywood around it.

I used 3/4" baltic birch for the ribs, and made them as wide as I could. I even doubled up the two outside ribs on the baja benroy. Then I used 1/8" plywood, but I bent the 4' side around the ribs. (It bends much easier that way).

For the Generic Benroy which was 5' rather than 6' wide, I didn't make it quite as heavy. You shouldn't have a problem with this design as long as you use 1/8" luan on the outside, and bend the wood along the 4' side.
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Postby fornesto » Sun Jan 29, 2006 1:57 am

Worst Case Scenario - Start looking for some T-shaped trim with an extra wide fin to cover the gap. I got some from So-Cal tears. Maybe leave the 1/4" outside laying over a trash can during the rain....It might take some of the life out of it. I used the Kuffel Creek method on my first two hatches :? and finally figured it out. They recommend making gussets for the outsides. I put in lots of blocking and used lots of screws to hold everything in place. I aluminumed over the screws (stainless). In the interim, you might want to temporarily screw some additional 1x4 struts from the top to the bottom of the outside spars, creating a triangle, to give the frame support while you're tweaking it to get the siding on. Once the siding quits pulling up, you can remove the struts. Ideas from one tinkerer to another...
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Postby doug hodder » Sun Jan 29, 2006 2:03 am

DrJerry wrote:Old boatbuilders trick: Use 1/8" plywood, score it every inch or so..shallow sawcuts will do.


I was able to just bend the marine ply to fit the frames on my boats without kerfing them...but I had a lot more frame to attach to...good idea though...I think I'll do it on #2 using a straight edge and a knife....I just don't trust not cutting through thin material with a saw blade...I don't have a really good flat bench and may have problems...on 1/8" material I don't use the saw...just a knife and a couple of passes....I'll bet the kerf thing will do the trick..PS on my first hatch...I only did the 2 outer pieces curved...everything else was just a horizontal rib....thanks!! :thumbsup: doug
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Postby John6012 » Sun Jan 29, 2006 9:05 am

I think my big mistake was going for the easy work. I saw a picture of a hatch that someone had built with only two verticals -one on each side with horizontals and I thought, that's the way to go. Maybe if I'd kerfed the 1/4" luan it'd have worked. I think I'll try and kerf the inside and if it works, cover the kerfs with moulding trim. Anyone who believes in evolujtion has NEVER built a teardrop. These thing don't just materialize, it takes patience, time, and repeated effors to get it near acceptable. I've gone thru a couple of hinges so far because I cut the notch out of the hinge. :cry:
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hatch

Postby oklahomajewel » Sun Jan 29, 2006 9:18 am

Now I'm scared !!! :shock:

Is the hatch always this hard, have this many problems?
I'm starting to wonder if I should get a contractor.....
Some things are way over my head !! ...but it keeps me looking UP!
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Re: hatch

Postby toypusher » Sun Jan 29, 2006 9:26 am

oklahomajewel wrote:Now I'm scared !!! :shock:

Is the hatch always this hard, have this many problems?
I'm starting to wonder if I should get a contractor.....


I built mine of 1 1/4" spars and covered with 18" luan on the outside and 1/8" birch ply on the inside. Aluminum over the luan. No problems and no 'springback'!! Check my build photos:Build Photos Here
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Re: hatch

Postby mikeschn » Sun Jan 29, 2006 9:58 am

oklahomajewel wrote:Now I'm scared !!! :shock:

Is the hatch always this hard, have this many problems?
I'm starting to wonder if I should get a contractor.....


The hatch is not hard. But if you cheat you may run into problems. Use a robust design and the right materials, and it'll be easy as pie!

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Re: hatch

Postby madjack » Sun Jan 29, 2006 11:32 am

mikeschn wrote:
oklahomajewel wrote:Now I'm scared !!! :shock:

Is the hatch always this hard, have this many problems?
I'm starting to wonder if I should get a contractor.....


The hatch is not hard. But if you cheat you may run into problems. Use a robust design and the right materials, and it'll be easy as pie!

Mike...


I agree...we used ribs in the vertical position that were 3" at the bottom and tapered to 2 5/8 at the top...using robust ribs in the vertical position is much better than running them in the horizontal plane...IMNSHO
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Postby grant whipp » Sun Jan 29, 2006 1:19 pm

Suggestion:

Cut a pair of "rib partners" out of 1/8" or 1/4" aluminum sheet scrap. Glue & screw to the outside of the framework before you add the 1/8" inner and 1/8" outer sheathing (believe me, guys & gals, you don't NEED anything thicker than 1/8" sheathing). Of course, you'll have to adjust the overall frame width to accomodate for the rib partners. Viola! - no springback, guaranteed.

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