Posted: 8/31/2011 6:34:11 PM EDT
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.....and capacity.
I've been working on this off and on for a while.... 
I picked this up for $100.00 a while back.....with the intentions of making a small camping mule.... 
Here is the issue....I built the trailer frame with just the work body in mind. The side rails are 3" x 1 1/2" x 1/8"wall Rectangle tube steel....with 2" x 2" x 1/8"wall square tube steel. and the axle is 3500#....I have a extra leaf to install later when finishing the frame. 
The tongue is 3" x 3" x 3/16".....and goes back to the center cross member over the axle.... 
The trailer mounts in 6 spots with 3/8" angle iron about 3" to 4" wide...and is held on by 5/8" grade 8 bolts.( the gap allows for a 3' x 8' folding table to be carried underneath.) The weight of the utility body is at best guess.....400#s....the frame is about 200#s.....and the topper is about 350#s.....totaling about 1000#s (that's a bit heavy...but let us err to the side of caution.) Now figure that I'll probably have about 500 to 700 pounds of gear on there for our usual Scouting event....not as much with just the family. Once I install a bunch of 1/4" gusset plates at the corners and over the shock mounts.....and weld solid the mounts for the bed.... Is the frame strong enough for hauling that?....I would have probably used 3/16" wall tube on everything...If I had planned on the topper. Or am I just being my usual "Overkill" self....and should worry about it??? BTW....I have 60 linear ft of 2" x 4" x 3/16"wall tube....and could just go with a heavier axle....maybe brakes....not sure if necessary. What says the hive? |
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A flat bed trailer is made of similar construction, though the floor adds considerable strength to the frame. They also have side rails to prevent the frame flopping at the ends. I don't know how your body is tied to the frame, but it can't add much structural strength to the frame. Stiffeners lengthwise might help. Some type of ladder arrangement. I tend to over build too. For some reason I keep thinking it needs a diagonal brace to keep the frame square.
You might load the frame with dead weight at the attachment points for the body and have someone pull it around the neighborhood while you observe for flexing. A little is OK. The rectangular tubing might have a tall enough cross section for the weight you have in mind. Commandeer your kid's bike to keep up. If I notice anything else I will add below. Good idea BTW. ETA: On seconed look the diagonal bracing is not necessary. The tongue covers it well. You may have a winner like it is. If the frame rails are tall enough extra stiffeners won't be needed. It isn't like you will tow this around daily. I still recommend the load testing. |
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A flat bed trailer is made of similar construction, though the floor adds considerable strength to the frame. They also have side rails to prevent the frame flopping at the ends. I don't know how your body is tied to the frame, but it can't add much structural strength to the frame. Stiffeners lengthwise might help. Some type of ladder arrangement. I tend to over build too. For some reason I keep thinking it needs a diagonal brace to keep the frame square. You might load the frame with dead weight at the attachment points for the body and have someone pull it around the neighborhood while you observe for flexing. A little is OK. The rectangular tubing might have a tall enough cross section for the weight you have in mind. Commandeer your kid's bike to keep up. If I notice anything else I will add below. Good idea BTW. Gregg, I beg to differ. Those tool boxes are tall, and have a nice flat sheet of metal top and bottom. Like C channel 3 ft tall. There is a lot of load bearing capacity in the shape of the structure of the tool bed. |
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Now you got me to thinking about that engineering class I took.... How far from the axle to the hitch? 8 foot tool box bed right? So we have 4 ft in front of the axle and 4 ft aft of the axle? OH and by the way...luv the street drag tires.  the tongue is long now.....haven't trimmed it to length.....may get a spare tire carrier up there.... I'd say it will be between 3.5 and 4 ft. the tires make it go faster.... 
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Quoted:
A flat bed trailer is made of similar construction, though the floor adds considerable strength to the frame. They also have side rails to prevent the frame flopping at the ends. I don't know how your body is tied to the frame, but it can't add much structural strength to the frame. Stiffeners lengthwise might help. Some type of ladder arrangement. I tend to over build too. For some reason I keep thinking it needs a diagonal brace to keep the frame square. You might load the frame with dead weight at the attachment points for the body and have someone pull it around the neighborhood while you observe for flexing. A little is OK. The rectangular tubing might have a tall enough cross section for the weight you have in mind. Commandeer your kid's bike to keep up. If I notice anything else I will add below. Good idea BTW. ETA: On seconed look the diagonal bracing is not necessary. The tongue covers it well. You may have a winner like it is. If the frame rails are tall enough extra stiffeners won't be needed. It isn't like you will tow this around daily. I still recommend the load testing. If you look in the bottom pic....you can see the front mounts....there are 2 more sets...and they will be gusseted. |
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A flat bed trailer is made of similar construction, though the floor adds considerable strength to the frame. They also have side rails to prevent the frame flopping at the ends. I don't know how your body is tied to the frame, but it can't add much structural strength to the frame. Stiffeners lengthwise might help. Some type of ladder arrangement. I tend to over build too. For some reason I keep thinking it needs a diagonal brace to keep the frame square. You might load the frame with dead weight at the attachment points for the body and have someone pull it around the neighborhood while you observe for flexing. A little is OK. The rectangular tubing might have a tall enough cross section for the weight you have in mind. Commandeer your kid's bike to keep up. If I notice anything else I will add below. Good idea BTW. Gregg, I beg to differ. Those tool boxes are tall, and have a nice flat sheet of metal top and bottom. Like C channel 3 ft tall. There is a lot of load bearing capacity in the shape of the structure of the tool bed. I would have to see how the box attaches to the frame. Those bodies are meant to sit on frame rails and carry a lot of weight. IDK if it could absorb the flexing moment as it is light gauge steel or aluminum. I can't remember seeing what the underpinnings look like. It migh be enough. I don't think it is meant to add rigidity to the truck chassis. A pic of the mounting arrangement would be helpful. |
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I see room on the tongue for a small box or propane or fuel tank. Nothing too wide. How is the clearance when backing in a turn? Haven't cut to length yet... Length on a short coupled trailer is a good thing. Keep it as long as practical. Short trailers suck when backing up. |
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Mmmmk S W e G
@400# tool bed @350# topper 1000# Scout gear.....You know somebody is gonna pack heavy 1750# total on frame Now to make the math easier I hereby declare this horse to be a sphere.....  .....inside joke....
I am declaring the load to be balanced over the axle and vertically centered 1 ft above the trailer frame. 1750# X 1ft = 1750 ftlb torque on the frame in a 1G stop. If the frame were bent in this It would look like the banana in a DQ Sundae. 1750ftlb / 3.5ft = 500 lb load on the ball hitch of the Suburban in a 1G stop. I would need to get some books and look up the flex of the tubing, but really the numbers do not look too bad. |
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A flat bed trailer is made of similar construction, though the floor adds considerable strength to the frame. They also have side rails to prevent the frame flopping at the ends. I don't know how your body is tied to the frame, but it can't add much structural strength to the frame. Stiffeners lengthwise might help. Some type of ladder arrangement. I tend to over build too. For some reason I keep thinking it needs a diagonal brace to keep the frame square. You might load the frame with dead weight at the attachment points for the body and have someone pull it around the neighborhood while you observe for flexing. A little is OK. The rectangular tubing might have a tall enough cross section for the weight you have in mind. Commandeer your kid's bike to keep up. If I notice anything else I will add below. Good idea BTW. Gregg, I beg to differ. Those tool boxes are tall, and have a nice flat sheet of metal top and bottom. Like C channel 3 ft tall. There is a lot of load bearing capacity in the shape of the structure of the tool bed. I would have to see how the box attaches to the frame. Those bodies are meant to sit on frame rails and carry a lot of weight. IDK if it could absorb the flexing moment as it is light gauge steel or aluminum. I can't remember seeing what the underpinnings look like. It migh be enough. I don't think it is meant to add rigidity to the truck chassis. A pic of the mounting arrangement would be helpful. Agreed....I was just thinking of the fore-n-aft flex. Diagonal rigidity...welcome to a whole new world 
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Another factor is how far from the spring hanger brackets the body is attached to the frame. The farther away the greater the force trying to bend the frame. The tongue really doesn't (or shouldn't) carry that much vertical load. If the body has stiffeners on the bottom and that translates into greater rigidity of the structure that is a plus.
The design of the tongue is good. The diagonal sections stiffen the frame longitudinally. This will keep the frame from folding fore and aft during a turn. The more I think about it the only question is the vertical flexing. The frame may be to short to worry about. Good exercise in understanding the forces applied to a frame. |
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The body attaches to the frame.....6 points total.
in the front of the body...2 points about 3" away from the bend of the frame rails. in the rear in pretty much the same manor. and off the center frame cross member to the cross member under the sheeting on the bed. the front and rear anchor points are 1/4" plate from one side to the other of the body. the center is going to a cross member that IIRC is 1/8" bent into a "C" channel. |
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That tool box body is fairly rigid by it self, I think you've done a good job on it. The body will be your traingulation.
I built myself a trailer 15 years ago, using 2" x2" x 11 guage (think 1/16") with a 2" x 3" x 1/8" tongue. I hauled half of this house over some incredibly rough roads with it, and no problems. AFAIK the guy I sold it to still has it. Ops |
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I need to look closer at the pics. I didn't look close enough at the pictures last night. That side rail tubing should be plenty strong to hold that much weight. I was driving all day and was tired sitting in a truck stop when I posted. Your trailer design looks good and you didn't build it out of I beams.
I would still keep the tongue as long as practical.( I hate SHORT trailers.) We want pics after you get it painted and wired and put together. |
I set the shell on the body to see how much it would squat it with the springs the way they are......dropped about 1/2"
The extra leafs will take that away for sure..... I was trying to figure out how to do the tailgate..... I'm just going to build up to the doors. I'll have to do a bit of fabricating to make it work....but I think it will be worth it when it is done.... 
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