New (to me) trailer option from Westbrook Trailers

[TimC]

I recently ordered a 4x8 flatbed trailer from Tractor Supply (currently on sale for $675 shipped to store from Ontario). It is a Sterling brand (aka Marathon) kit trailer. I've received the trailer and plan to assemble it in the next week or so if the temperatures warm up a bit; 4" of snow the last two mornings. It is sold by a number of US stores such as Home Depot, Tractor Supply and Northern Tool but I don't think they stock them.

This particular one is an all galvanized frame and fasteners and seems to be of very good quality. 1230# capacity with 1000# payload (230# dry weight). Just what I wanted to build a new foamie benroy to pull with my EV. It comes with 8" wheels which I will upgrade to 12" radials. I'll use an eight inch for a spare. I chose the 4x8 because it will be just me on trips.

What I like so far prior to assembly...
Dexter axle with solid tubing unlike the Harbor Freight and Northern Tool kits with C channel axle
Galvanized frame
Heavy duty fenders unlike the HF and NT trailers with cheap sheet metal fenders


https://www.westbrooktrailers.com/product/4x8-kit-trailer/?variant=4x8-Kit-TrailerModel-48-096-K08

[twisted lines]

looks like a good start
Bit tiny but here we are

[TimC]

...
Bit tiny but here we are

Tiny it is. Just what I was looking for.

Finished assembly and wheel/tire upgrade. Will adapt the stock fenders to the "moved back" axle. The TD wall will partially support the fender.

In case you haven't seen this model of trailer the side frame members on the eight foot version are three pieces. They are spliced together in the center and doubled up where the spring hangers are mounted.

I managed to mount the axle at almost 60% from the front of the frame by using only the back holes in the frame for each spring hanger. Then i only had to drill four additional holes for the spring hangers. The two rear most holes for the slipper spring hanger ended up where the frame members weren't double thickness so i added a galvanized 90 degree mending plate for a couple bucks. I added the mending brackets on the back half of the back mounting plate where it transitions to a single frame member. I may add an additional bolt on the side of the frame there to beef it up a bit.

I don't want to drill too many new holes in this very light frame. An engineer once told me that as long as you fill that hole with a bolt and an overlapping chunk of metal the integrity of the frame will not be diminished much. An open hole is another matter.

[featherliteCT1]

Looking good!

[kennyrayandersen]

An engineer once told me that as long as you fill that hole with a bolt and an overlapping chunk of metal the integrity of the frame will not be diminished much. An open hole is another matter.

That depends. The fastener needs to fill up the whole hole -- with a tight fit, otherwise it's really the same as an open hole.
Also, from one hole to another you should have a minimum spacing of 4 times the bolt diameter as a minimum (unless you can actually do some stress calculations). It does look like they put a hole right in the middle of the intersection of the tongue and the first cross member. That's the highest stress area of the tongue and the highest stress in the section. It's steel, and you're making a foamy, so it's probably OK.

[TimC]

... It does look like they put a hole right in the middle of the intersection of the tongue and the first cross member. That's the highest stress area of the tongue and the highest stress in the section. It's steel, and you're making a foamy, so it's probably OK.

I'll have to check that out. Not sure where you are referring to but I'll look it over.

[kennyrayandersen]

... It does look like they put a hole right in the middle of the intersection of the tongue and the first cross member. That's the highest stress area of the tongue and the highest stress in the section. It's steel, and you're making a foamy, so it's probably OK.

I'll have to check that out. Not sure where you are referring to but I'll look it over.

Right where the tongue (A-frame) runs into the rectangular part of the trailer. Usually the cabin (box) starts right there. That means the moment starts at zero at the ball and builds up until the tongue part intersects with the rectangular part (cabin). The moment (and thus stress) is highest right there. It looks like they put a bolt right exactly there. Now, having said that, it's probably oversized (stronger than it needs to be) and made out of steel (usually not a fatigue problem), so ultimately it will be ok. It's just bad design practice. It's likely they don't have any actual engineers working on it...

If you see the other aluminum trailer thread, someone posted a trailer and they put all of the joining fasteners through the middle of the beam (where the stress is low) rather than in the upper flange (where the stress is high). That was actually done correctly (at least following good design practice. In this case they gave it no consideration (but again, probably OK).

[TimC]

KRA, I see what you are referring to now. The frame bolts holes will be tightened up so not worried about that. The area is real close to the stake pocket holes which I can remedy with a simple backing plate and bolts. The real concern is the wire cut-out. It is large and aligned with the frame bolt holes. Not sure how I'll beef that up but I'll address it. And I am going to bring this to the manufacturers attention. That hole can easily be positioned in another spot, if it's needed at all.

Even though it will be a lightweight foamie I will be bouncing down highways and that will fatigue that area over years. I appreciate you spotting this as a concern.

[kennyrayandersen]

KRA, I see what you are referring to now. The frame bolts holes will be tightened up so not worried about that. The area is real close to the stake pocket holes which I can remedy with a simple backing plate and bolts. The real concern is the wire cut-out. It is large and aligned with the frame bolt holes. Not sure how I'll beef that up but I'll address it. And I am going to bring this to the manufacturers attention. That hole can easily be positioned in another spot, if it's needed at all.

Even though it will be a lightweight foamie I will be bouncing down highways and that will fatigue that area over years. I appreciate you spotting this as a concern.

The wire cutout is nothing -- (well, not nothing) it is in a low stress area (middle of the beam). Whether the bolt is tight or not doesn't matter -- there's a hole there. Holes = stress concentrations. When the hole is in a low stress area, then the field stress times the Kt from the hole isn't a big concern. What stresses most in a beam that is bending is the top and bottom flange. So, rather than make a clip that attaches at the beam center, they put it smack dab in the highest stressed area the beam has. It's very likely over-sized (heavier than it has to be), and you are building a light cabin so it's likely just fine. It's just that those kind of details kind of poke me in the eye. The other concern is that they completely removed the web from one of the beams as they crossed. Usually this would require a bolted on fitting of some kind to add back the shear stiffness remove by cutting out the entire web. The sharp corner of the cutout next to the upper flange will make a high stress concentration area as well. the way to do that is to but the cross bean attach the webs with shear clips and then put a strap across the upper and lower flanges. That way there are no peaks and it's all tied together. These are just engineering nits that if you aren't shooting for something right-sized may not matter much because the loads are getting spread around in less efficient ways, but because it's oversized it likely wont break. At least they didn't cut the web out of the tongue!!

[kennyrayandersen]

you could add a shear clip to the webs on the corner kitty-corner to the wire cutout hole (2 fasteners on each side of the angle) that tied the two webs together. with that gap I don't see what prevents the inside beam from jiggling up and down. The upper and lower flanges do that (sort of), but that puts the flanges in bending which is atypical. A shear clip maintains shear continuity between the two beam webs. That would fix 'er good!