This summer I'm going to tear down a 2-horse trailer and rebuild it into a small
heavy flatbed/stakeside (5½x9½'). My design goal is to be able to carry 3500#
loads. What I need to do is to choose the lightest steel pieces which will take
the load. Unfortunately, my intuition was developed building large oceangoing
ships, and I tend to massively overdesign every steel structure I make. If I'm
making a surface plate stand for example, there is little penalty, but on a
hitch-mounted trailer, every pound you put into the trailer subtracts from the
payload. This isn't a standard trailer design as far as I can tell, so I can't
just buy some plans and order steel.

I plan to use steel channel for the frame box, angle for the stringers, and use
2x6" tongue-and-groove fir for the deck. I'm leaning towards 4" steel channel
and 2x2x1/4" angle.

Ideas? Comments? Suggestions? All welcome ..

Grant Erwin
Kirkland, Washington

By steel channel, do you mean the stuff that looks more or less like an
I beam that only has flanges on one side? That sounds very heavy to
me.

I would go down to you auto wrecking yard and see how cheap you can get
steel from a truck frame. The frame will be a lot stiffer for torsion
if you box the frame. I would not use any angle. See if you can find
some small channel that was used for industrial shelving. You could
also see if you can find some pieces for pallet racking. A couple of
10 foot beams might work real well for the long frame pieces. They
would already be boxed. According to my Grainger catalog , the heavy "
seismic " 9 foot beams are good for 7,000 lbs. I assume that is for a
pair, but it does not say.

Dan

The problem with trailers is that you have all sorts of momentum loads
that completely screw up normal beam calculation formulas or tables.
Technically you can still do the calcs but you need to take into account
the mass of the load, mass of the trailer, spring rates, yada, yada.

I'd suggest stopping by a few of your local rental places as well as any
utility trailer places and have a look. bring your caliper and take some
notes. One of my local places has some heavy duty trailers similar to
what you are thinking about.

If you plan on just 2 stringers front to back, 4" just "feels" too small
for a 3500# load. You could go from a 4" to a 6" channel, double the
strength, and add only 50 pounds. When you buy channel, get the lightest
weight (thinnest web) channel in each size. Heavier channel in the same
size just has a thicker web, the extra steel doesn't do you much good.

My local steel yard has some "Z" shapes done in a press brake. This lets
you mount the springs to the top of the "Z", drop the deck onto the
bottom of the "Z"

Grant Erwin wrote:
This summer I'm going to tear down a 2-horse trailer and rebuild it into
a small heavy flatbed/stakeside (5½x9½'). My design goal is to be able
to carry 3500# loads. What I need to do is to choose the lightest steel
pieces which will take the load. Unfortunately, my intuition was
developed building large oceangoing ships, and I tend to massively
overdesign every steel structure I make. If I'm making a surface plate
stand for example, there is little penalty, but on a hitch-mounted
trailer, every pound you put into the trailer subtracts from the
payload. This isn't a standard trailer design as far as I can tell, so I
can't just buy some plans and order steel.

I plan to use steel channel for the frame box, angle for the stringers,
and use 2x6" tongue-and-groove fir for the deck. I'm leaning towards 4"
steel channel and 2x2x1/4" angle.

Ideas? Comments? Suggestions? All welcome ..

Grant Erwin
Kirkland, Washington

I second the visit to the rental place.

Rental equipment usually gets abused severely and the trailers they use
have been tested under fire.

Take a good look at how the understructure of these trailers are laid
out.

A couple of points..

Use open members...any closed member will collect moisture and salt and
will rust faster than you will believe.

Use similar metals....I have seen different metals combined
(steel/aluminum) and unless you properly insulate them you will see
corrosion occur.

Every pound counts...as you have noted, every pound in the trailer
detacts from what you can haul.

Over build for capacity...it is human nature to overload a
trailer...allow for it.

Avoid unnecessary addons...a spare tire, a tool box, an end gate, heavy
side walls...they all add unnecessary weight. Most can either be built
of lighweight materials or the items can be detached and stored in the
towing vehicle.

Welding versus fasteners for joints....trailers are subject to
incredible vibrational and torisonal stresses. Bear this in mind when
connecting the members together.

Any other suggestions for Grant anyone?

TMT

Any other suggestions for Grant anyone?

TMT

Google for trailer plans.
I found loads of sites.
This looks good.
http://www.trailerplans.com/site_map.htm

John

Another thought.
If you are stripping the trailer frame, consider having it galvanised. It
lasts a whole lot longer.

John

"John Manders" wrote in message
...
Another thought.
If you are stripping the trailer frame, consider having it galvanised. It
lasts a whole lot longer.

John



If you have the math skills the book
How to Design and Build Trailers - Vol. 2

by M.M. Smith is a great book. Northern tool carries it.
It tells you how to design your own trailer . It is not a set of plans for a
trailer. But has all the info for stresses moments, inertia etc etc.

Hi, Grant.
Several years ago I bought 2 books on trailer design and building from
Northern Hydrolics, or what ever their name is. They send catalogs
about every 3 months and usually they go into the recycle bin. Can't
find them now to see if the books are still offered. I just glanced
through the books and they look like what you want. I never did build
the trailer. Too easy to go rent what I need.

Paul
Redmond, OR

On Sat, 04 Jun 2005 06:56:41 -0700, Grant Erwin
wrote:

...., and use
2x6" tongue-and-groove fir for the deck.

I can't offer much wisdom with respect to the frame but I'd suggest
not using tongue and groove for the deck. Moisture and dirt get
trapped in the joints and you get a rotted out bed in no time flat.
Better to use just plain 2x6 and a wood preservative for some degree
of longevity. If you intend on hauling dirt, sand or gravel, stuff
that might fall through the cracks (I'd also suggest spacing the deck
boards about 1/4" apart for drainage), invest in some sacrificial OSB
to cover the deck whilst hauling the loose stuff.

Dennis brings up a good issue....what does one use for a trailer floor?

In my trailers, I haul dirt, gravel, machine tools, metal stock,
lumber, more machine tools, lawn/tree waste, building debris...just
about anything.

What does one use for flooring that can stand the weather but keep on
working with MINIMUM upkeep?

TMT

"Too_Many_Tools" wrote in message
oups.com...
Dennis brings up a good issue....what does one use for a trailer floor?

In my trailers, I haul dirt, gravel, machine tools, metal stock,
lumber, more machine tools, lawn/tree waste, building debris...just
about anything.

What does one use for flooring that can stand the weather but keep on
working with MINIMUM upkeep?

TMT


Thin steel over 3/4" or 1" marine plywood works pretty well.

Thin steel over pressure-treated 2"x6" works better, especially for heavy
loads.

The wood supports the load while the steel provides an easy-sliding surface
for ease in unloading/cleaning.

Too_Many_Tools wrote:

Dennis brings up a good issue....what does one use for a trailer floor?

In my trailers, I haul dirt, gravel, machine tools, metal stock,
lumber, more machine tools, lawn/tree waste, building debris...just
about anything.

What does one use for flooring that can stand the weather but keep on
working with MINIMUM upkeep?

Aluminum, of course. Ideal in all respects except cost.

Guys I know figure you just have to replace the decking every few years. I think
most of them just use 2x6 treated fir T&G flooring. The US Navy, on its LSDs
(essentially ships which are floating drydocks) uses ironwood decking. Real
spendy. - GWE

With the new treatment for pressure treated wood in place, doesn't this
lumber corrode metal?

TMT

What does one use for flooring that can stand the weather but keep on
working with MINIMUM upkeep?

I brought up the point about T&G decking because that's how I built
the floor of the first trailer I had. It took very little time for the
deck to rot out. But I'm here in the Pacific Northwest and in the
foothills of the North Cascades to boot. So, your mileage might vary.

As for how to haul loose material like gravel and dirt, I'd just throw
a cheap tarp over the bed before loading. Or buy some cheap OSP to
cover the bed and stash it out of the weather when not in use.

A wood deck on a trailer that sits outside in an area that gets plenty
of rain will, by all means eventually rot out. But if you space the
deck boards so water can't get trapped and the wood stays moist, you
can get quite a few years out of plain old rough cut lumber.

Oh, by the way, that first T&G deck trailer I built- yes I had treated
the wood with a preservative.