Frame overkill and other Q's

[Ben W]

Hi all,

Below is my first frame drawing for a 5x10 Benroy style. Steel only, not including the frame is weighing in around 220lbs. Have I completely overkilled this thing? I'd like to get it lighter, but I have the following caveats.

1. I'm in Colorado so this will see some dirt and washboard roads.
2. Body construction will be 3/4 solid ply (no frame and foam)
3. I'd like to keep the angles for a tongue box.

My initial thoughts to lighten it up are any/all of the following:
a. remove the 2x2 running down the center.
b. cut the inside cross-members down to 1x2.
c. bring the 3x2 tongue back to the second crossmember instead of the third.

Of course it needs to be safe...I'm a worry wort.

I'll be using Andrews balance and tongue weight spreadsheets, but need to finalize the overall design first.

On other fronts I also have some general questions related to weights.

1. Any idea what I should estimate the weight of a 2000lb torsion axle w/brakes/wheels and tires to be? I've checked Dexter info, but it wasn't readily available.

2. In estimating plywood weight I'm using 75lbs for a 4x8 3/4 inch sheet. Am I in the ballpark?

Thanks in advance for any and all replies!

-Ben

[mikeschn]

Hey Ben,

That certainly looks plenty strong to me.

To lighten it up I would go with a 2x2 tongue x 3/16 or 1/4 wall.

I would probably eliminate the center member running to the back of the trailer.

And yes, I would consider 1x2 cross members on the inside of the frame. But take the tongue back to the 3rd member, to give you enough places to weld it to.

Just my $.02

Mike...

[Guest]

Ben,
At 220 lbs. you are lighter than me...
I too live in an area where roads to where I camp, are sometimes more like trails...

[asianflava]

You can probably get rid of the first crossmember. With the diagonals connected to both the front and sides, it will be plenty strong and prevent racking.

[Ben W]

Okay,

Cutting out the 2x2 down the middle and reducing the 3 inside crossmembers down to 1x2's gets me down to 187lbs - a nice drop.

I spoke to engineering at Dexter and they said a #9 is gonna be right around a 100-110 lbs, depending on final dimmensions.

Add 35lbs per wheel/tire and I'm looking at 367lbs for the whole frame. That still seems pretty heavy.

[mikeschn]

The only way to make it lighter is to build your teardrop in Unibody fashion, and then attach a couple of tubes to the underside of the body.

Andrew's Superleggra design does it that way...
http://www.angib.pwp.blueyonder.co.uk/t ... tear32.htm

Mike...

[asianflava]

This is the estimate for my frame which is a pretty minimalist design.

Dexter axle 77lbs
Wheels & tires 70lbs
Tongue Jack
Coupler
Tongue Handle 20lbs
Estimated weight of steel (37.23ft X 3.05 lbs/ft) 113lbs

Grand total= 280lbs!

That includes everything except for lugnuts, safety chains, hubcaps, lights, paint.

[angib]

Ben,

I'd go with the frame-lightening suggestions you've already received and add some more:

- A 3x2 tongue seems excessive, seeing you've also got two 2x2 stays. I'd go to 2x2x3/16 for the tongue. If you stay at 3x2 it would be logical to make it 2 wide and 3 high, not the other way as you have it now - the big loads are vertical and so you want the greatest depth in that direction.

- How about 2x2 angle for the internals? It's 2/3rds the weight of 1x2 box and you get a flange to bolt the floor to. I'd stay with 2x2 box for the front and back frames and the one under the back of the tongue.

- How about eliminating all the internals except for the one under the back of the tongue? You're not going to be holding barn dances in there, are you? Rmember that the floor can be supported by things above it, as well as below - if you make a strong joint from the floor to the galley bulkhead, that will support the floor in that area.

Andrew

[Ben W]

Thanks guys,

I think we're there. I've mixed all your suggestions in to the pot and come out with this.

The whole body will be built out of 3/4 ply so, it should be pretty sturdy. I've left one internal 2x2 for the tongue to latch on too, and one 2x2 angle to provide floor support in the large sleeping area. The galley bulkhead will get a strong joint as Andrew suggested and that should take care of the floor in the rear. Also went down to 2x2 x 3/16 tongue.

The weight, with axle and tires is 340lbs

Thanks again!

-Ben

[JunkMan]

Ben, It looks great to me. You have a couple of cross braces in the door area, which is where most of your weight will be when entering and exiting. The diagonals on the tounge will take a lot of the flex out of the frame, and the 3/4" sides will take care of the rest (if there is any). I believe that the 3/16" tounge is plenty, especially with the braces (that's what I am using on mine, and have had on several other small trailers).

I think your axel might be a bit too far forward, but without knowing what you plan for the back, it's hard to say. It will also act as an additional cross member (although it will be lower than the rest).

The only place that I can see where you might trim a bit more weight is by making the diagonal tounge braces out of angle instead of square tubing.

[bledsoe3]

I used angle for the diagonal braces. It worked fine.... unless you plan to have a swivel tongue jack. The problem is you have to leave enough space between the hitch and where the angle attaches to the tongue for the jack to swivel up. I don't think 36" is enough. So I attached the jack to the angle after I welded in a piece of 2" sq. tubing so it had something to secure to. The angle then flexed under the weight of just the frame. So I had to weld a piece of 2" sq. tube from the tongue to the angle to take the flex out of the angle. What a pain.

This is before I welded the extra piece from the tongue to the angle.

[Guy]

Dear Ben,

I believe you have lightened your frame too much in the rear.

The rear (aft of the axle) is the place where the most weight and bending forces will be placed and therefore needs the most support. Your axle is not a support, however, it does creat a bending moment one additional angle support under the galley and gussets at your axle will provide the additional support necessary. You have properly supported for the door, even though it is not as important as the rear. In the rear you are actually cantilevered from the axle and the whiplash from the bumps will cause greater stress in that region.