How many bolts?

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How many bolts?

Postby dio449 » Wed Jul 04, 2018 6:40 am

I have searched through the forums to determine the best way to attach my cabin to the trailer frame, and I've seen many discussions comparing bolts to screws. I have decided that I am going to use bolts however I would like to know how many bolts I would need to make a solid connection. I am planning to weld tabs along the two main rails and then some more on the cross members. I was then going to put 3/8 inch carriage bolts through the tabs with a large washer on top and a lock washer underneath. The floor is going to be 3/4" plywood. The question I have is how many do I need, I was planning on 12, 4 along each side and 4 down the middle.

here's a pic of the frame

IMG_20180704_075022.jpg
IMG_20180704_075022.jpg (375.81 KiB) Viewed 1745 times


I that enough?
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Re: How many bolts?

Postby coyote » Wed Jul 04, 2018 7:00 am

I used 6 or 8- 3/8 grade 8 on mine, it has worked well for me. I have to be careful; 42 years at a "Cat" dealer; I want everything stronger, heavier. I have to remember, I'm not building a house, just a place I can wander and sleep in. Coyote
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Re: How many bolts?

Postby greygoos » Wed Jul 04, 2018 7:05 am

I have used 6 to 8 bolts grade 8 depending on the length of the trailer.
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Re: How many bolts?

Postby noseoil » Wed Jul 04, 2018 7:15 am

Grade 5 or 8 isn't really necessary for a light trailer & is a waste of money. The single-shear value of a single 3/8" grade 2 bolt is over 4000#, so one bolt would be fine...

https://www.nucor-fastener.com/Files/PD ... rength.pdf
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Re: How many bolts?

Postby dio449 » Wed Jul 04, 2018 7:43 am

Ok, thanks everyone for the quick replies.

I think I can match the consensus with 4 tabs along each side rail, with regular carriage bolts. So a total of 8. I may consider a higher grade bolt as the cost difference for eight can't be that significant in the grand scheme of things.

Thanks
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Re: How many bolts?

Postby working on it » Wed Jul 04, 2018 9:22 am

noseoil wrote:Grade 5 or 8 isn't really necessary for a light trailer & is a waste of money. The single-shear value of a single 3/8" grade 2 bolt is over 4000#, so one bolt would be fine...

https://www.nucor-fastener.com/Files/PD ... rength.pdf
  • I used eight 3/8" carriage bolts to attach my initial 1/2" floor (12 year-seasoned Birch plywood) to the crossmembers of my trailer, countersinking the heads a bit, but still leaving sufficient plywood underneath, for strength, while using PL adhesive between frame and plywood.
  • Then, I covered that with 1/4" Luan, glued on with Titebond 2, and used small Tek screws thru both layers of wood, and into the metal frame itself, around the perimeter, to ensure that the edges would never lift up from the frame (if I had a delay before building the upper structure). I see no way that the frame and cabin will ever part! http://www.tnttt.com/viewtopic.php?f=35&t=68349&hilit=tek#p1202710
  • carriage and teks.png
    carriage and teks.png (337.88 KiB) Viewed 1695 times
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  • *extended-run, on-board, 2500w generator *Coleman dual-fuel stove & lantern, Ikea grill, vintage skillet
  • *zinc/stainless front & side racks *98"L x 6" diameter rod & reel carrier tube on roof
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Re: How many bolts?

Postby tony.latham » Wed Jul 04, 2018 10:55 am

If your using carriage bolts, see if you can't find some proper torque washers:

Image

I think they help strengthen the connection.

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Re: How many bolts?

Postby Sparksalot » Wed Jul 04, 2018 3:20 pm

I used 13 on Rose, for several reasons. I had the bolts already. The holes in the frames were already there, so I used them. The way I extended the frame I wanted to be sure all was tight, so the cabin is really a part of the structure.
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Re: How many bolts?

Postby halfdome, Danny » Thu Jul 05, 2018 12:40 pm

I use 24 elevator bolts.
I weld a 45 deg. gussett at every corner and bolt it down and one in the center of each cross member.
It may seem an over kill to some but I sleep well knowing it won't come off or shift.
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Re: How many bolts?

Postby lfhoward » Thu Jul 05, 2018 2:37 pm

I used 24 grade 5 with washers and lock nuts. Probably overkill, but peace of mind.

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Re: How many bolts?

Postby working on it » Thu Jul 05, 2018 4:43 pm

tony.latham wrote:If your using carriage bolts, see if you can't find some proper torque washers:

Image

I think they help strengthen the connection.

Tony
  • Torque washers make a very strong connection, but I was using materials and methods I was used to in assembling my trailer. As a mechanical troubleshooter at work for many years, lifelong automotive enthusiast/car builder/racer, and self-proclaimed redneck engineer, I trusted bolt-together construction, using steel hardware everywhere. Bolted, of course, functional, and exposed as a sign of the hardware's strengthening presence.
  • I believe in over-kill construction: why use a # 6 or #8 woodscrew to fasten a critical area, where 1/4" or 3/8" bolts could do a better job, with no chance of being pulled or shaken apart? Doubling-up on fasteners, and using twice the normal amount of adhesives and caulks, too, became my method of joinery, except where disassembly might be needed (I.e., for removal and replacement of A/C unit, or a broken window), might be needed...otherwise, it was built to never come apart.
  • I used 8 carriage bolts w/o washers (or torque washers) to fasten the sub-floor to the frame, but topped that with the Luan floor, whereupon I used 36 or 38 flathead Tek screws thru both flooring layers, directly into the frame perimeter, to do the real work of securing the floor to the frame; the carriage bolts were just an intermediate step, PL adhesive under the sub-floor, on every underlying metal portion of the frame, was the first step. Once the floor was finished, the upper structure also was built using PL everywhere wood was joined to wood, and alas mechanically held together with steel angles (gusseted), and heavy corner plates. Instead of using torque washers (or threaded inserts, which could get pulled through), I used oversized stainless fender washers under both carriage bolt heads (with a few exceptions, in non-critical areas), and/or the loctited acorn nuts (or ny-locks, where their use was indicated). PL adhesive was also used inside the bolt holes, and under the washers, for added strength and waterproofing. I can't see where any part of the TTT can ever come loose, unless forcefully, intentionally, disassembled.
2013 HHRv "squareback/squaredrop", rugged, 4x8 TTT, 2150+ lbs
  • *3500 lb Dexter EZ-Lube braked axle, 3000 lb.springs, active-progressive bumpstop suspension
  • *27 x 8.5-14LT AT tires (x 3) *Weight Distribution system for single-beam tongue
  • *100% LED's & GFCI outlets, 3x fans, AM/FM/CD/Aux. *A/C & heat, Optima AGM, inverter & charger(s)
  • *extended-run, on-board, 2500w generator *Coleman dual-fuel stove & lantern, Ikea grill, vintage skillet
  • *zinc/stainless front & side racks *98"L x 6" diameter rod & reel carrier tube on roof
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Re: How many bolts?

Postby KCStudly » Tue Jul 31, 2018 8:34 am

I did four (4) 3/8-16UNC bolts at each xmbr, kind of equally spread across the floor area. In retrospect, I would have omitted all of the ones 'in the field' and just gone with the ones around the perimeter. Four up each side and two more each along front and rear xmbr.

Some people will feel this is excessive, but the box is where the stiffness comes from and I want my trailer frame to stay with the box to avoid any relative motion (flexing, chaffing) that might otherwise cause wear through the moisture barrier.
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Re: How many bolts?

Postby Aguyfromohio » Tue Jul 31, 2018 12:37 pm

Your plan to weld on tabs for bolts made me think of our build. We thought up an even more time-consuming and difficult approach. We drilled smaller clearance holes up through the frame tubes going through both both top and bottom, and them came back and enlarged just the bottom holes with a Unibit to be about an inch so we could get the lag screw heads through them plus the socket to tighten them. It worked great but wasted a ton of time. Awful job that filled my shop with metal chips.

Later we screwed on a small floor for the galley, and just used self-drill, self-tap sheet metal deck screws with wafer heads. You can find them on the web or at a hardware store, sometimes called deck screws. Worked great, and they were so easy to install we put in a few extra just to be sure. Next time we'll screw down the main deck to the frame with these.

The two little tabs above the drill point clear away wood but shear off when they hit the steel, so you get a perfect clearance hole in the wood automatically. The low profile wafer head pulls down flush into the plywood then stops without pulling clear through. Drive them straight down through the plywood into the steel tube, no drilling required. Quick, easy, cheap, strong.

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Re: How many bolts?

Postby Billinthedesert » Mon Jul 15, 2019 2:46 pm

Need a like button for this.
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Re: How many bolts?

Postby Aguyfromohio » Mon Jul 15, 2019 7:21 pm

Billinthedesert wrote:Need a like button for this.

+1
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