attaching deck to trailer, bolts or screw?

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attaching deck to trailer, bolts or screw?

Postby nemoskull » Thu Apr 20, 2017 12:49 am

im leaning towards screwing down the deck to the frame. is there any reason to not screw down the deck? id be using stainless screws.
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Re: attaching deck to trailer, bolts or screw?

Postby Tigris99 » Thu Apr 20, 2017 1:40 am

Not a good idea, everything you build will be attached to the deck which is attached to the trailer.

Little screws will come loose, corrode, break off or pull out when ran through stamp steel. Likely to snap a few off just trying to get them to cut through to thread the holes you drill. If you drill them bigger they will literally start coming loose slowly as you start towing it.

All your saving is a few bucks and a few minutes to use bolts with nuts/washers.

That's always the one place not to be cheap or lazy, that's the foundation on which everything else is built.

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Re: attaching deck to trailer, bolts or screw?

Postby daveesl77 » Thu Apr 20, 2017 7:08 am

Use bolts. The very few dollars you save and the minor amount of time (when considering the total time investment in the build) is, to me, not worth the probable future aggravation and safety factors. I also used nyloks. Just my opinion.

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Re: attaching deck to trailer, bolts or screw?

Postby QueticoBill » Thu Apr 20, 2017 7:33 am

Well, clearly I'm odd man out but plan to use Tek screws. I was thinking #12 or #14, but available to 3/8" I see. I'm sure I'll drive in a few more Tek screws than bolts needed.

Pretty good data on these products so easy to calculate. And I'm reminded of how many times something set on a car roof and forgotten is still there after highway and rush hour driving.

But then I believe in designing to be strong enough, not as strong as possible.
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Re: attaching deck to trailer, bolts or screw?

Postby absolutsnwbrdr » Thu Apr 20, 2017 9:35 am

Bolts. Plain and simple. No worries.

Aren't tek screws designed for light gauge cold-formed steel construction, rather than heavier gauge hot-rolled steel??

In the long haul, I dont think I could trust 40 of them vs 8 carriage bolts.
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Re: attaching deck to trailer, bolts or screw?

Postby aggie79 » Thu Apr 20, 2017 9:39 am

I used SS trailer deck screws installed 6" on center along the outer frame rails. I also used the same to mount my tongue box.

Many people go way overboard attaching the deck/shell to frame. Remember that there is only one 1/2" or 5/8" pin holding your trailer to your vehicle.


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Re: attaching deck to trailer, bolts or screw?

Postby QueticoBill » Thu Apr 20, 2017 7:01 pm

absolutsnwbrdr wrote:Bolts. Plain and simple. No worries.

Aren't tek screws designed for light gauge cold-formed steel construction, rather than heavier gauge hot-rolled steel??

In the long haul, I dont think I could trust 40 of them vs 8 carriage bolts.


Tek screws is one brand of self drilling self tapping machine screws. Aggie's trailer deck screws are basically the same. Used for a lot more than light guage steel framing.
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Re: attaching deck to trailer, bolts or screw?

Postby Tigris99 » Thu Apr 20, 2017 7:57 pm

aggie79 wrote:I used SS trailer deck screws installed 6" on center along the outer frame rails. I also used the same to mount my tongue box.

Many people go way overboard attaching the deck/shell to frame. Remember that there is only one 1/2" or 5/8" pin holding your trailer to your vehicle.


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That would work when you have that many screwed in. Curious as to their long term durability. I've already bought carriage bolts as I prefer the piece of mind.

Comparing to a hitch pin though is a bit strange. The amount of force to sheer those pins is extreme (5/8s pin takes about 24000 lbs of force in this application). You'll tear up a lot before that pin sheers.

Problem with self tapping screws is they can and WILL work loose. Expansion and contraction due to temperature change is drastically different between wood and steel. Combine that with vibrations of being towed and it'll happen.

Not saying "OMG your trailer will fall apart tomorrow" but understand that screws will fail years before carriage bolts will. Problem won't be breakage to start, it will be them coming loose from the frame first.

Longer Screws through pre drilled holes into wood would actually be more secure then holding to basically 11ga sheet metal.


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Re: attaching deck to trailer, bolts or screw?

Postby QueticoBill » Fri Apr 21, 2017 11:55 am

I agree that carriage bolts will in all likelihood last longer than the self taps. Frankly, either will easily outlast me or probably anyone living today so I am not concerned. Classic strong as possible versus strong enough debate.
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Re: attaching deck to trailer, bolts or screw?

Postby aggie79 » Sat Apr 22, 2017 11:02 am

As part of an air conditioning upgrade, I had to remove my tongue box. The deck screws, after 7 years of installation, were still so tight that I needed to use an impact driver to free them.

Many old canned ham trailers used deck screws to hold the cabin to the frame. Ultimately, some did fail after 30-40 years but that's plenty enough time for me.


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Re: attaching deck to trailer, bolts or screw?

Postby earl84 » Sun Apr 23, 2017 12:59 pm

My teardrop frame came from a large old pop up camper, I think a 1988 model. Took it all apart, kept the frame. The deconstruction revealed the it was held on with nothing but deck screw, spaced probably 24 inches apart, a total of around 60 screws. Maybe 1/4" shank on them. Not a single one had failed, come loose, or any indication that they were going to fail or come loose. That's what I needed up using, along with four 5/16 bolts per side to hold a 2 x 4 on each side of the trailer exterior frame to give me a little bit of extra width. Super easy to install, and they will all be hidden under the mattress or galley cabinets.
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Re: attaching deck to trailer, bolts or screw?

Postby working on it » Sun Apr 23, 2017 10:20 pm

  • Why not use both carriage bolts and Tek screws to attach the flooring? I did, and it was a well-considered choice. The eight 3/8" carriage bolts thru the original c-channel crossmembers will probably exert less hold-down force than the 3 or 4 dozen Teks I used along the floor perimeter, since they penetrate into the stronger rectangular tubing.
  • carriage and teks.png
    carriage and teks.png (337.88 KiB) Viewed 716 times
    Teks around the perimeter, adding the most holding power
  • The floor decking was installed in two parts, 1/2" birch plywood bolted down as the base, for strength, and 1/4" luan glued and screwed over it, for its' smoothness and coloration. The carriage bolts were partially sunk into the burch, leaving the heads slightly above the surface plane; the luan sheet added on top was intended to thicken/strengthen the floor, while also covering the partially exposed carriage bolt heads.
  • The carriage bolts, being slightly sunk into the ply, weaken the ply, and would be subject to pull-thru, under high duress situations, and, they were mounted into c-channel, possibly the weakest frame structure. Whereas, the Tek screws are adding more clamping force, holding the decking to the frame, without any weak points in comparison. I've used Teks in race car building, and have never seen any vibrate loose, and the vibrations and stress the Teks have survived is probably greater than a TD or TTT will ever likely encounter. Plus, the Teks are installed into the more rigid perimeter tubing, and are so many in number, that even the improbable loosening of a few Teks, will not jeopardize the deck-to-frame mating.
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  • featuring: 3500 lb Dexter axle w/brakes & HD leaf spring system > riding on General Grabber 27x8.5-14LT tires, LED lighting inside, A/C & heat, AGM battery 12vdc, 110vac from extended run generator onboard or park power, Coleman dual-fuel stove & Northstar lantern
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Re: attaching deck to trailer, bolts or screw?

Postby QueticoBill » Fri Jun 02, 2017 12:23 pm

What I'm finding is that number 12 and smaller are available self drilling and self tapping; and that larger are just self tapping so you need to drill a hole first. Does this seem to agree with those that have used these?

If I'm drilling for 1/4 or 5/16 sell taps, I'm wondering if it's worth it over flat head or carriage bolts. On the other hand, a box of 2 dozen #12 self drilling and tapping screws is pretty simple, inexpensive, and quick. Considering the leaf spring hangers are attached with 8 bolts around 3/8", and two dozen no. 12's are near the same cross sectional area, seems simple.

And I recall a number of occasions where I've left something sitting on the roof of my car and it's been there many miles later.
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Re: attaching deck to trailer, bolts or screw?

Postby KCStudly » Fri Jun 02, 2017 2:09 pm

Just a little engineering spitball here, comparing the cross sectional areas is okay for a back of the napkin kind of approach, but another way to look at it is friction in the "bearing face" of the joint. It isn't always the shear strength of the fastener that makes a joint; sometimes it is the tensile strength. If the clamping force is great enough, then the friction between the two surfaces insures that there will not be relative motion; w/o relative motion the fastener will never see shearing forces. So with more smaller fasteners you get a more uniform clamp, and therefore more uniform friction. (TLAR analysis in effect.)

Another argument in favor of several smaller fasteners is that we are dealing with wood. Wood can move around and change with humidity and temperature (hopefully less so when we do a good job of waterproofing!), so by my way of thinking a few extra small fasteners hedges the bet if one or two should happen to become compromised.

Now this has come up many times before, some may argue that you could get away with no fasteners and your cabin might never slide or fall off of your trailer, that since your trailer hitch pin is just 5/8 diameter that you might get away with just a couple of healthy bolts. I say nerts to that. I believe that the cabin should stiffen the trailer frame to prevent relative motion when the chassis would otherwise flex. By eliminating relative motion you eliminate the potential for chaffing between the surfaces and the wear that might otherwise occur to damage that precious waterproofing. So it makes sense to me to spread more smaller fasteners over the length of your trailer, than to just use a few in, say, just the corners. This is also another good argument for using some sort of caulk or bedding compound when mating the cabin floor to the trailer.

Over engineered? Maybe. That's right, I'm still not camping yet :? :lol: , but I always say if it doesn't take anymore effort to do something with a little logical thinking behind it than it does to toss a dart and see what you get, then why not put a little thought into the process.

Truth is that however you get there, most methods will work one way or the other. There are no rules, except to have fun doing it!
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Re: attaching deck to trailer, bolts or screw?

Postby QueticoBill » Fri Jun 02, 2017 3:25 pm

Thanks and yup. I suspect that since I do not expect to off road, that just putting divots in the bottom of the deck for the hex headed bolts on the trailer would have decent odds of being sufficient. And I know that more smaller fasteners is usually preferred - at least for permanent fastening. Leads m to reopening the idea of the cabin be removable, and having a second "deck" for utility or other use. Always more opportunities....
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