Teardrops n Tiny Travel Trailers

Alrighty ...

I'd love to replace traditional wooden hatch ribs with bent pieces of aluminum tubing or channel. Problem is, for most builds, that rib is an elliptical arc - sometimes even a composite of two or three arcs - and so far, no mom n' pop machine shops around me can do the job.

Any ideas? Do I need to shell out for a hydraulic pipe/tube bender, and if so, how easy is it to conform to an elliptical arc?'

Thanks!

Not suggesting buying one - since they seem to cost in the $10-20k range - but it seems a CNC bender will do this. But there are services.

PS - template and router and cut rubs from aluminum plate. Lots of ways to connect them across depending on other materials involved.

QueticoBill wrote:Not suggesting buying one - since they seem to cost in the $10-20k range - but it seems a CNC bender will do this. But there are services.

PS - template and router and cut rubs from aluminum plate. Lots of ways to connect them across depending on other materials involved.

QueticoBill, you wouldn't happen to know any Midwestern services of CNC bending, would you?

I've considered the use of aluminum ribs ... but boy, does it get pricey for 1/4-inch aluminum sheet. I don't mind paying more for the ribs ... but not 20x more :/

This would do it for the arch your looking at.

https://www.zoro.com/heck-industries-tu ... /G6154251/

You would need to have a set of dies made for the type or metal you want to use. If it wasn't a square type of tube or flat bar.

Philip wrote:This would do it for the arch your looking at.

https://www.zoro.com/heck-industries-tu ... /G6154251/

You would need to have a set of dies made for the type or metal you want to use. If it wasn't a square type of tube or flat bar.

Thanks for the info, Philip. If I had a template to which I could compare my tube-in-progress, I guess I would form the ribs iteratively by hand using the tube roller ... Once you figured out the pattern, though, you might be able to crank through the ribs pretty quickly.

It happened I found one not far from me in Lisle IL.
http://www.zemanmfg.com/cnc-tube-bending.html

I have bent metal like this with a manual machine -a 50s era Hossfeld - one of the neatest coolest pieces of machinery I've ever worked with - but no way I was good enough to make a group of matching ellipses.

Please report what you discover. I can't help but think the most expensive marine ply cut on a CNC router table won't be much less expensive but bent aluminum tube with an aluminum skin welded on would be really cool and very light and last a very long time.

I'm curious why you want to move away from aluminum ribs. Is the reason to save weight? Or to have a thinner profile?

I'd echo previous posters, in that I consider a sandwich of 1/8" aluminum plate, 3/4" plywood, and 1/8" aluminum plate if you're wanting to do something different. If you're looking to do volume, you could have the aluminum sides CNC laser or water-jet cut.

aggie79 wrote:I'm curious why you want to move away from aluminum ribs. Is the reason to save weight? Or to have a thinner profile?

I'd echo previous posters, in that I consider a sandwich of 1/8" aluminum plate, 3/4" plywood, and 1/8" aluminum plate if you're wanting to do something different. If you're looking to do volume, you could have the aluminum sides CNC laser or water-jet cut.

I may have mis-stated my last post. I don't want to move away from aluminum ribs ... I want to move towards them! I meant that I'd prefer bent aluminum tubing over routed/milled aluminum sheet. Your idea of a metal-wood sandwich is great, Aggie79, because it overcomes the issue with mere sheeting: It's too thin. It doesn't give me the torsional or transverse rigidity I need. A sandwich does solve that problem, though, but finishing three or four sides with aluminum sheeting sounds very labor-intensive.

Now, if you mean why move away from wooden ribs, that's for several reasons: No springback, no water damage, no finishing, no maintenance. I know a good quality wood and finish can solve all those issues, but bent tubing just sounds so much more ... elegant?

QueticoBill wrote:It happened I found one not far from me in Lisle IL.
http://www.zemanmfg.com/cnc-tube-bending.html

I have bent metal like this with a manual machine -a 50s era Hossfeld - one of the neatest coolest pieces of machinery I've ever worked with - but no way I was good enough to make a group of matching ellipses.

Thanks for the link, Bill. They make some pretty cool stuff!

IIRC, somewhere on here member alaska teardrop had pics of how he hand forms steel box tube over a jig. Probably could do the same with aluminum.

Also, capnTelescope (Brad) used his cnc router to let aluminum sheet inserts into the sides of his hatch spars.

Just curious - with aluminum ribs, how are you going to attach the hatch skin and hardware (hinge, latch, trailer lighting, etc.)? I can see maybe top and bottom aluminum tubing, but then how do you connect these to the ribs?

I think all aluminum is very cool. I assume welded. I don't know how you weld the skin without it showing but suspect there is a technique. Tiny gas shocks to raise and hold open. A strong gust of wind could be a problem when open would be my worry.

Personally, I'm OK with some adhesive products. Maybe filon with double faced super tape (does the adhesive telegraph through?) But I still like aluminum. Go heavier gauge for skin, have it rolled, and you could get away with just a perimeter tube frame - or aluminum angle even, maybe with the vertical leg overlapping wall for that ideal weathertight hatch edge. The perimeter would allow welding with some thought or trim. With the angle, the frame could be on the outside, and weld to inside of horizontal leg unseen.

What I'm envisioning is a hatch lid made very similarly to the standard style - ribs on the side, cross members between, skin on top - but with aluminum tubing substituted for the wood. The geometry of the design doesn't change, just the materials. Depending on the thickness of the aluminum tubing, KC, you could just substitute wood screws with sheet metal screws (with threadlocker, if you wanted), or you could substitute rivets for wood screws. So the latch, hinge, and any lighting would all be assembled in the same way, just with slightly different fasteners. Does that help? I think we're on the same track ...

Ideally, the galley lid would be made super strong and maintenance-free.

If I was going to use adhesive rather than rivets, screws or welding to attach the aluminum skin to the aluminum frame, I'd probably pick a 3M VHB tape.

I'm not much help answering your questions about welding, Bill I'm an armchair welder, myself. I know TIG is recommended for aluminum. I don't know how thin of sheet metal you can go and get adequate penetration without the weld telegraphing through the back. I'm sure it's bigger than 18-gauge aluminum, though! Beyond my skill level.

You might want to take a look at one of the vintage trailers from the late 40's, which were made out of aluminum & built by the guys who made the fighters & bombers during WWII. If it was good enough for then, it would work for you as well.

Personally, I think it might be overthinking the traditional hatch design a bit. Aluminum is light, strong, compact & certainly very solid once it's done, but it doesn't lend itself very well to what you're doing with it since the shape is, as you have said, a compound curve. As a one-off design it will be a lot of work. In a production run it would be pretty good, since it would pay back the rib setup in terms of labor costs spread out over the run.

A more "conventional" hatch done with lighter wood parts & a well-thought-out design still has a lot going for it in terms of convenience, since there are a lot of things which make it work (skins, weather strip, wiring, latch assembly, etc.). It is, without a doubt, the most complex part of a teardrop & requires more thought, fit & finish than any other single part of the build, at least IMO. Cutting out wood ribs with a router & pattern is a pretty basic woodworking chore & takes very little time.

Would like to see what you come up with for the design & materials!

It sounds like your proposed hatch framing is similar to how Little Guy does (or used to do) their hatch framing:



It looks like they used light gauge steel tubing instead of aluminum but either should work. I think the key to this design is that the framing forms a truss with the lower chord helping keep the geometry of the curb (no spring-back).

The way that Little Guy does its hatch seal is less apparent but I believe they did something similar to how Len does his hatches:
http://www.tnttt.com/viewtopic.php?p=1166704#p1166704