Spring Back Hatch

[madjack]

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.

CHEERS!

Grant

a damn fine suggestion from "them what's done it".................................................

[doug hodder]

I agree with Grant on this....1/8" is all that is needed...I just happened to have a lot of leftover materials from other projects that I wanted to use up so it ended up being heavier that I really wanted...I just can't seem to make my projects end up using all the materials that I may have at hand..and Grant...after opening up the windows...I see that they aren't tinted...but laying against the wall in the living room...the screen sure made it appear so...added a lot more darkness than I remember on the first one....I'll radius the corners on this pair like you mentioned to me earlier...hopefully I won't drop them and cut a divot out of my shin on them this time.... Doug

[bdosborn]

You might try clamping the hatch down while the glue for the skin dries. I pulled the top and bottom of the the hatch together about a 1/2" while it was drying and had minimal springback. My hatch will try and straighten out if I leave it open a long time (like all week in the garage). I have draw latches on the side to pull it in when closed and it goes back to the proper shape after a day or two. Not shown in the picture is the pipe clamp I used to pull it into a tighter radius.

[Chris C]

I've tried not to interject any of my opinions on the subject of hatch "springback" because I've not actually built one. But..............I've built a lot of things in my life out of wood which were cylindrical or curved and can offer an experienced opinion here. If the builder will take the full sheet of plywood and coil it to the desired circumference with ratchet straps and leave it for a week or two in the corner of the shop, the rachet straps will likely fall off, leaving the plywood in the shape it was with the straps holding it. Patience is the key here. Why fight the wood? Then build your hatch frame and apply the already bent plywood to it. It shouldn't spring back if it's fastened securely. In fact, I've over-bent sheets before and had almost as much trouble flattening them out as I would have had in bending them if I hadn't done it. As Doug always say, "just my humble opinion".

[doug hodder]

You're right Chris...I just didn't have enough forthought to do it like that, just grapped a piece that was going to fit and screwed and glued it up...and then had to deal with it.."Humble" don't think I ever used that one? maybe I should...check my Avatar...is this guy humble or full of excrement? Doug

[Chris C]

Sorry if I misquoted you, Doug. But hard as it may be, you do need to try desperately to be humble ocassionally. I know it must be hard when your image is "hooded and gold-chained".

[doug hodder]

I am now officially "humbled" and full of excrement! Doug

[Kevin A]

Humble you say?, there ain't nuttin humble about those pants,
BTW, that's a GREAT idea Grant shared about keepin a hatch from springing back, it also adds a lot of strength to the outer ribs.

[madjack]

I am now officially "humbled" and full of excrement! Doug

humbled??? ...full of it...oh yeah .........................

[doug hodder]

guilty as charged... oh well...guess I'll have to get over it doug

[Tim Greiner]

Hey Boys-

Just a little information that could prove useful- there is also a product called bendable plywood. It has all the plies arranged in the same direction. Bends quite a bit easier than the regular stuff but of course doesn't have the strength of regular ply in that direction, either. I don't know how many woods it's available in, so if you want to made it pretty an overlay might be required. It can be found more easily at specialty plywood stores. Remember to figure out ahead of time which way you want it bendable, it comes both ways. I've used it on boats with success.

Tim Greiner

[john]

Chris C,

I did exactly that with my second hatch. The first was lost to springback. I left my skin curled with load straps for over a month (other things got my attention). When I went to apply it I had to flatten the skin to follow the curve of the hatch frame.

I still get sringback in the winter, though. I applied the aluminum in the summer. During every cold spell the aluminum shrinks enough to pull one bottom corner away from the side by about 1/8". When it warms up the gap goes away.

[Gage]

I didn't read all the post but I did read the first one and what Grant had to say, and a couple others. And like Grant says, you don't need to skin with 1/4" ply. Your just going to have problems. The way I built mine was locating the frame work (3/4" birch ply and the trim was matched to the sides, no spring back figured in) to the tear and then I located the outside skin (1/8"birch ply) with about 6 screws and then took it to the bench and applied all the rest of the screws. After that was finished I laid it in place and wala, it fit and matched the contour perfect. The bottom pic is of the hatch just laying in place with no clamps or anything else to hold it in place. Looks pretty good. Several months later I removed the hatch from the tear, laid it on the work bench and clamped another sheet of 1/8" birch ply to the interior. Added glue and more clamps and I was finished with the hatch. And still no spring back. It was no harder building my hatch than it was building the complete teardrop, mater of fact it was easier. It's just the way I did it. I'm not saying it's the way you should do it.




Have a good day.

[John6012]

Yoy all have great input but the glue is set and I figure I have no choice but to start another hatch. Instead of two ribs (one on each side), I'll plan on at least four oak veneer that I have leftover. Then I'll glue horizontal pieces at random. After that sets, I;m going to have to try and find some 1/8" water resistant plywood-maybe special order from alocal lumber company. Then the rest "should" be easy with the proper application of clamps. Or if I can't get the 1/8" ply use the 1/4" after kerfing.... By the way, how does one treat the underside of the hatch cover preventing water damage? Poly and then the weather striping does the job? Thanks, Juan

[Nitetimes]

I used 5 ribs of 3/4" ply, wrapped it with 1/8" twice. Never even tried to spring back. If you can find some cheap wood paneling (read: sale or clearance) that stuff works great, very flexible and you can usually get it for less tha 10 bucks a sheet. I got some of mine from Builders surplus when the stuff that was on sale went on sale, 3 bucks a sheet!! If I'd have had the room to store it I'd have bought it all.