What is the theory behind a galley hatch

[Ron Dickey]

I have made but not attached the frame around the outsides of the hatch and am about to cut more. back is 4 tall 4 wide I am thinking of only adding 2 more rigs but I see some people with 6. I also see cross ribs all over the place.

I am thinking of the two center ones being skinned on both side and the left and right ones only skinned on the outside. Any cross ribs would be at the top or bottom of the frame. The center ribs will have cross ribs and the outside skin would support them.
L&R ribs are made of pine about 1 inch thick but the inner ones will be made of plywood maybe double thickness on each. I am planing of putting the plates on the hatch and the outside frame would also support the center ribs.

But is there a rule of thumb for A Galley hatch and it's ribs.

The ribs will be held in place by triangular pc's at all upper and lower corners so they are less likely to move. Plus being attached to the outside skin

Or is the ribbing on the left to right cross ribs to give the outside skin more support?

Ron

[citylights]

The theory behind the galley hatch is to make it lightweight but ridged and strong enough to lift without racking. Another issue is spring back from the bent plywood making the hatch not fit right.

So it is a balancing act. Light enough to lift. Strong enough to maintain shape.

Mine, like the rest of my tear I guess, is a heavy beast! I used four 1/2 inch ribs with blocking that triples the thickness of each.



After I did mine, I saw a really neat tip from Grant. He uses a sandwich of aluminum skin between the ribs. He did not use blocking. He says the aluminum sandwich stops spring back and makes the ribs much strongest without adding a lot of weight. Check it out here

https://www.facebook.com/teardrops.net

[Ron Dickey]

The theory behind the galley hatch is to make it lightweight but ridged and strong enough to lift without racking. Another issue is spring back from the bent plywood making the hatch not fit right.

So it is a balancing act. Light enough to lift. Strong enough to maintain shape.

Mine, like the rest of my tear I guess, is a heavy beast! I used four 1/2 inch ribs with blocking that triples the thickness of each.



After I did mine, I saw a really neat tip from Grant. He uses a sandwich of aluminum skin between the ribs. He did not use blocking. He says the aluminum sandwich stops spring back and makes the ribs much strongest without adding a lot of weight. Check it out here

https://www.facebook.com/teardrops.net

What do you mean by spring back?

Ron

[doug hodder]

Spring back is what happens after you have the skin all glued to the ribs and you remove it from the jig, assuming you built one...the arch actually flattens out a bit and doesn't fit the profile of what you originally designed because the skin material pulled on the frame assembly. At least that's what I call it. Doug

[citylights]

What do you mean by spring back?

Ron

When you bend a flat piece of plywood in a curve, it really doesn't want to be bent. I wants to spring back to its original shape... Thus spring back. Over time, the plywood will get trained to the curve shape and stay that way on its own, but it takes years. In the mean time, the relatively thin ribs in the hatch have to withstand that spring back in addition to any force you put on it by lifting the galley lid.

Some people make a jig to train the plywood for the galley hatch over several weeks or months while they are building the rest of the tear. This enables them to keep the hatch lighter as the ribs don't have to be as large with the plywood pre trained. My hatch skeleton was my jig, and it stayed in and heavy. Some people build with finesse... I guess I just build with brute force.





By the way, in my very dry desert climate, it helped to wet the plywood when bending. I kept these towels damp while I was bending the plywood around my hatch. Aka... Mr Incredible and Scooby team up to bend my hatch! Over a day or two, I tightened the straps until the plywood took the shape of the hatch. Then I let the towels dry and left it that way for a week. After that week, I until-clamped, removed the towels, applied liberal amounts of glue to the partially trained plywood and re clamped for another week. Ofter that... Rock solid. I can lift it pretty easy. My 15 year old boy can lift it. My wife doesn't try. You can put in gas struts to help or totally compensate for the weight. Mine doesn't have gas struts, just sliding prop bars that latch open.



See the black dots on the lower part of the hatch? Those are screws from when I glued and screwed on the lower flat piece. The upper portion has no black dots. That is because it was clamped until the glue dried, no screws. Most f my teardrop was built with glue and screw. The screws provided the hold and clamp while the glue dried. I did not use external clamps hardly at all. This results in a lot of screws left in the teardop. While not a horrible thing, it is not exactly the finesse or master craftsman way to do things.

[Esteban]

Ron, if you are very worried about spring back you can buy bendy plywood from Mayan Hardwood in Paso Robles. Bendy plywood has all the grain going in one direction so it does not resist staying bent.

SLO County:
Mayan Hardwood
2501 Oakwood Drive
Paso Robles, CA 93446
(805) 238-0038

mayanhardwood.com
mayanhardwood.com/sheet_goods/plywoods

[3nero]

Or just soak the plywood in a pool of water. I hour per 1mm of thickness

[tony.latham]

I've built two hatches now using the method Steve Fredrick suggests in his teardrop Shop Manual. No hint of springback. It relies on 4" thick gussets reinforcing the two ribs on the sides of the hatch. With both my builds, I used 1/8" plywood inside and outside the hatch and covered with .040 aluminum. If I wasn't going to sheath in aluminum, I'd glue on a second layer of 1/8" ply. Plenty of strength.






Tony

[citylights]

I've built two hatches now using the method Steve Fredrick suggests in his teardrop Shop Manual.


Tony

Wow, nicely done. Beautiful result.

[KCStudly]

I just don't understand why more people don't go deeper with their hatch ribs. It doesn't have to be heavier, just separate the outer fibers of the ribs further.

Tony's deep side ribs, a la the Fredrick's method, are the perfect example.

I'm using four 3-1/2 inch deep 1x exposed ribs with 5 mm ply, and I really don't expect to have much, if any spring back. Time will tell the outcome.

[KennethW]

I don't understand why people don't just build the hatch so part of the main camper then use a router to cut the hatch off.

[grant whipp]

Ron!

I don't have time to search your build thread to see what your hatch profile will look like ... post up or send me a drawing or picture and I'll be happy to make some suggestions. In case you've forgotten, my e-mail is [email protected] ... ...!

CHEERS!

[finleycraft]

Just my 2 cents, I went and got some bending birch. comes in 4/8 sheets and its very light weight. down side is not every hardwood store carries it and you need to make sure to carry it on its side when moving it a around so it doesn't collapse on you. My Trailer is 6'6" wide so I have 7 ribs that are 1 1/2" "tall". with the bending birch I have zero spring back and the hatch fits like I want. also on the end of the hatch I only get about 12 lbs of downward pressure. very easy for the wife to even lift. Obviously the closer to the hinge the more downward pressure I get maxing out at about 112 lbs about a foot from the hinge. All that being said, give grant a buzz. he will instill confidence in you from his experience and you will be happy!

Keep it up the end is near and camping season is here!

[hiker]

I don't understand why people don't just build the hatch so part of the main camper then use a router to cut the hatch off.

That is a good question, I should have a vertical door. Since its not built yet, it could change.

[jss06]

That is exactly what I did with mine.