Cross Beams or Ribs Question

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Cross Beams or Ribs Question

Postby Classic Finn » Mon May 08, 2006 4:31 pm

Can I use 1 x 2,s for the ribs or cross sections or do they have to be 2 x 2,s?

I was just curious to find out... I understand that the portion or section where the galley hinge will mount should be a stronger form of wood as well?

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Postby Chris C » Mon May 08, 2006 4:38 pm

Heikki,

1x2's are okay if your trailer is 4' wide. If you're going 5' wide, you might want to glue up two 1x2's with growth rings opposing so you have a very rigid 2x2. Just my opinion, though. Maybe others will disagree.
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Postby Classic Finn » Mon May 08, 2006 4:42 pm

I found some real nicely pre sanded 2 x 2,s which then are under the 2 x 2 in reality....

quite nice...

just wanted to make sure...

Thank You Chris :thumbsup:

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Postby Chris C » Mon May 08, 2006 4:56 pm

Heikki,

A 2x2 in the store won't be nearly as strong as a 2x2 made by you. Just get some good straight lumber and machine 1x2's (actual dimensions) and glue two either face to face or back to back to make a real 2x2. It will be considerably more rigid..............it'll take more work, but will make a better build. And be sure to mount them so the seam runs perpendicular to the trailer body.
Last edited by Chris C on Mon May 08, 2006 4:58 pm, edited 1 time in total.
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Postby Classic Finn » Mon May 08, 2006 4:58 pm

:thumbsup: :thumbsup: okidoki

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Postby asianflava » Mon May 08, 2006 5:59 pm

I used 1X2 Poplar, face down (wide side) 12in on center. With 2 layers of 1/8 ply, it is plenty strong enough. I think Gage did his like that too.
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Postby madjack » Mon May 08, 2006 6:03 pm

we used 1x1.25(actual) with no problems...those really nice 2x2 you spoke of will probably do just fine...you are sandwiching them between 2 flexed sheets of ply and should be PLENTY strong enough...maybe even dance on 'em(very carefully)...
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Postby oklahomajewel » Mon May 08, 2006 6:18 pm

The Kuffel Creek plans have double spars at about three or four locations... in the front, about where the gust of wind will hit and then up top then at the galley point.

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Postby Sonetpro » Mon May 08, 2006 6:24 pm

Chris C wrote:Heikki,

1If you're going 5' wide, you might want to glue up two 1x2's with growth rings opposing so you have a very rigid 2x2. Just my opinion, though. Maybe others will disagree.

Thats how I did mine. edge up. I used poplar except where the hatch hinge is, I used oak there.
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Postby Chris C » Mon May 08, 2006 6:38 pm

I've been thinking about making some sample 2" "I" beams out of 1/4" plywood......to see if it would save some weight over the 2x2's. Anyone done that yet? Maybe Andrew could save me doing it and just calculate the advantage/disadvantage. :lol:
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Postby Gerald_G » Mon May 08, 2006 6:54 pm

I've been wondering about I beams too. Maybe even 3" ones for a larger trailer ?

I wonder about the weight to strength ratios. However, I had not considered sandwiching plywood with dimensional wood. This should make pretty strong spars in farily small (hence light) dimenssion.

Or OSB instead of ply like the housing floor trusts.
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Postby Dewayne_Mellen » Mon May 08, 2006 7:14 pm

I was thinking of making a 2x2 frame for my trailer. Would the trailer be stronger by using 3/4" plywood that is cut to 1 1/2" and then glued together? :thinking:
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Postby cracker39 » Tue May 09, 2006 7:03 am

Plywood tends to resist flexing in two directions. Once you bend it in a curve from front to back, it would be difficult to make it bend down from side to side, so I don't believe that the cross members (spars) have to be overbuilt. For my 5' roof spars, I used 1" wide by 1 1/2" inside to outside. There are wider spars where two pieces of skin join, and those are 1 1/2" x 1 1/2".

Mose TDs won't have corner spars like I do, where the front and back sections join and where the front or back joins the top. Those are all 2-piece lanimated spars ripped at the required angles and glued together. These are even wider than the others for strength at the joints. Most of them measure about 2" width in either direction from the corner and are all 1 1/2" thick.
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Postby Arne » Tue May 09, 2006 8:12 am

This has caused me to give some amateur engineering thought to this topic. Essentially the roof system becomes one big beam, with a plywood top and a plywood bottom. with a 1.5" spread, the roof probably does not need much in the middle, as the tension and compression strength is provided by full coverage plywood to accept those strains. If the ribs are 3/4 wide by 1.5 inches tall, it seems the major concern is that they be true when installed, and they should remain that way.

And, the only reason I would use 3/4 wide is so I could hit them with a brad nailer... otherwise, 1/4" ply every 6 inches would probably work. This thinking is based on the cardboard interior of those cheap doors that are very rigid. The only real load on the roof is snow in the northern areas.

And one of those cheap doors spans more than 5 feet. If I was not building a conventiional curved tear, but something like a weekender, I might even consider using those doors as a roof system. Put some cpes on each side, and it would make a very rigid roof.... but, no standing on it.
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Postby asianflava » Tue May 09, 2006 5:33 pm

Eh, I posted to this when the board went down then it got lost. I'll make a short version:

Argeed with Arne, you don't need a super duper roof.

Put spars wide side down for 3 reasons:
1. easier to hit with the brad nailer (like Arne)
2. easier to butt plywood on a spar
3. more surface area for glue
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