Building a trailer

Whatswrong · Nov 19, 2011

,I m in the process of building a trailer from scap parts from work. The hubs are +/-3600 x4 on axles designed to carry 7000lbs minus hitch weight which I can't remember.I plan to buy 4 PR5 springs from e-trailer (5800lb axles rated) .The tires are trailer type I think about 3200lb. capacity .My frame is built out of 3x3x3/16 tubing for cross member as well as long ,8x16. It isn't a tilt bed,hitch is A frame style with a tongue to about 2 feet in front of front axle.8000lb jack,seems the tires are the weakest link ,I think my welding is average at least. As near as I can tell when the bed is completthe tires will only be about two -three inches above bed so will require about a 6" fender. This will be my first flatbed trailer.My main concern is if I will max out my pickup before I ever load the trailer.
Any comments will be appreciated

Diamondpilot · Nov 19, 2011

Tough to tell without detailed pics. Easier to fix now then later.

Chris

sandman2234 · Nov 19, 2011

You can make or break it by how you use the metal. I have a trailer that is twice as heavy as it should have been simply because of the selection of metal and how it was applied and just how much bracing was added. The 3x3 tubing isn't ideal for typical trailer building, as the horizontal 3" is usually a little overkill for the 3" vertical capacities. A few ideas might be to purchase a channel of more depth (4, 5, 6 etc) to increase capacity for the same weight for the two main frame beams. You will be much happier with the trailer if you do! If you really want to cut the weight, and the 3x3 is free, consider setting up a sawing or cutting guide and make 3x3 angle out of it, but it would have to be free for me to want to spend the time/effort to do this. Use the 3x3 sq tube or angle if you do cut them as cross braces.
David from jax

Whatswrong · Nov 19, 2011

Sandman, in your reference to cross brace are you meaning diagonal bracing as I haven't done any of that?It was free but I still wouldn't put the energy into ripping them that sounds like a huge job ,it is already welded together ,will attempt some pictures soon.I have a vision of only needing to weld on spring hangers which I haven't purchased yet and fabricate fenders and ramps.

sandman2234 · Nov 22, 2011

Very few people put diagonal bracing in trailers, though some incorporate it into the ends. The fifth wheel flatbed I just acquired has diagonal bracing on it around the neck, but that is almost a requirement on a fifth wheel trailer.
I was thinking that your two 8x16 runners would be best as a taller channel. There are going to be some weight concerns, compared to typical channel/angle iron construction trailers.
Before you start cutting up a bunch of metal, have you drawn out a plan of attack? If you have scribbled a drawing of this trailer on the nearest tabletop or scrap piece of paper, then figure out just how many pieces of metal, their lengths, and take that much metal and throw it in the back of your trailer and run down and weigh it. (before you cut it up). If the truck won't haul that much metal, then there is a good chance your going to be over weight for that truck. (Not always true, but a good discussion point). If you don't have all the parts to the trailer, figure out what the missing parts weigh and add them to your total. Check online for the weights of a 16 foot trailer and compare it to what your total is. Don't forget to add in the decking, screws, fenders, tires and axles, tongue jack, etc.
Adding up all of this is a lot of trouble, but nowhere near as much as building a trailer that is TOO HEAVY for you to use, so you just cut it up for scrap metal, or sell it cheap to somebody who hasn't figured out what a TOO HEAVY TRAILER looks like. Plan it out and see what happens.
David from jax

Iplayfarmer · Nov 22, 2011

Here's a chart from my local steel supplier that I use often for similar figuring on my own build ideas...
Vernon Steel

They have lbs./ft. information for most typical sizes of steel.

Using their numbers for 3X3X0.188 tube I get a frame weight of just under 500 pounds assuming you have three cross members in addition to the front and back. You can keep calculating to include the tongue and whatever other weight you have like decking, etc.

Just by way of reference, the channel that is the nearest in lbs./ft. to 3" square tube is 5" channel at 6.7 lbs./ft. 4" channel is 5.4 lbs./ft. You'll be about 20% heavier than a typical trailer made from 4" channel. Assuming the typical trailer is about 1500 lbs. That's an extra 300 pounds. I think you'll be alright.

Whatswrong · Nov 22, 2011

Thanks guys, at 6.87 lb /ft frame will weigh about 725lbs,maybe 75lbs for fenders,300lbs minimum for floor plank guessing 300lbs for suspension,even with under estimating the tongue weight shouldn't be very high.Appears it will be a fairly typical weight for 16' tandem axle trailer.
I saw a bunch of drops OR mistakes today that may make ramps ,not sure if it is heavey enough ,but think I will pick some up anyway.

sandman2234 · Nov 23, 2011

Free steel is always worth hauling home!
David from jax

Reg · Nov 24, 2011

Whatswrong said:
,I m in the process of building a trailer from scap parts from work. The hubs are +/-3600 x4 on axles designed to carry 7000lbs minus hitch weight which I can't remember.I plan to buy 4 PR5 springs from e-trailer (5800lb axles rated) .The tires are trailer type I think about 3200lb. capacity .My frame is built out of 3x3x3/16 tubing for cross member as well as long ,8x16. It isn't a tilt bed,hitch is A frame style with a tongue to about 2 feet in front of front axle.8000lb jack,seems the tires are the weakest link ,I think my welding is average at least. As near as I can tell when the bed is completthe tires will only be about two -three inches above bed so will require about a 6" fender. This will be my first flatbed trailer.My main concern is if I will max out my pickup before I ever load the trailer.
Any comments will be appreciated

If I read that right... You are putting 5800 (or so) lb rated springs on 3500 (or so) rated axles.
I question the wisdom of that - even though I have a STRONG tendency myself to over spec things.

EDIT:
Sorry, I just re-read it.
The AXLES are 7,000 lb., I was confusing the hub rating with the axle rating.
:END EDIT

I think you should spring it according to what the limiting factor will be, i.e. the axles.
If you "over spring" it you will have a very bouncy/jouncy trailer leaping around back there.
It will not be a trailer that you could ever load down to where the springs settle into their designed working range.

LD1 · Nov 26, 2011

Any pics of this thing yet????

3x3x3/16 isnt going to make a very strong trailer IMO, and as others have suggested.

You really need something with more depth. That is where the strength is. I would be scared to load much over 3000-4000 lbs on that trailer with only a single 3x3x3/16 down each side:confused2: And considering you are using a pair of axles that will net 14k, or springs that put you over the 10k mark, kinda sounds like a waste of some good heavy duty axles to me. Kinda like putting a pair of 7k axles under a utility trailer:confused2:

Just to give an example, my homemade trailer (built in the 80's NOT by me) has 2x4x1/4 wall tubing down the sides and a 4x4x1/4 down the middle, And I wouldnt want to put more than 7k on it. And 2x4x1/4 is about 82% STRONGER than that 3x3x3/16

Even standard 4 " channel @ 5.4lbs/ft is going to be 56% stronger than what you have got. And a 5" @ 6.7lb/ft is going to be almost 3x's stronger.

Pound for pound, square box tubing is about the worst for deflection and strength when used as a beam. IT excells at torsional strength, but that isnt going to be needed as much for your trailer.

Conclusion: Personally, I would use all your free steel for crossmembers, supports, etc. But get a couple of 20' sticks of 5" channel. Otherwise, IMO those axles are about a waste on a trailer built like that. Unless you can get really creative on strengethening it up some.

Again, any pics yet??