Total Composites flatbed build
- Thread starter andy_b
- Start date
The shop I bought the flatbed from: 4 Corners Trailers in Bayfield, CO.
Alloy
Well-known member
If the 2 bolts for each spring mount do not pass through at least 1/2" alum or 1/4" steel there's no way I'd put a camper on this and head off road.
Use Urethane for bump stops not UHMW.......BUT.......adding the blocks will reduce the amount of movement.
rruff
Explorer
This is more typical of how spring mounts are done: https://expeditionportal.com/forum/...site-panel-camper-build-thread.213614/page-28
The subframe rests on the frame rails over the entire length, and only comes up when there is twist. The two frames are also hard mounted to each other at the rear.
You are relying on the spring mounts and attachment bolts to take all the lateral loads, as well as some vertical loads. I think it would be better to emulate something like the above... hard mount the two frames in the rear, have the subframe rest on the frame over it's length with a UHMW strip in between, weld on some U channel near the front to capture side-side motion of the subframe, and move the rear springs forward (or maybe remove them?). Then all the springs need to do is resist vertical lifting... and you don't want too much of that resistance lest it add too much stress to your subframe and box.
A 3 point mount can also work well for this.
The subframe rests on the frame rails over the entire length, and only comes up when there is twist. The two frames are also hard mounted to each other at the rear.
You are relying on the spring mounts and attachment bolts to take all the lateral loads, as well as some vertical loads. I think it would be better to emulate something like the above... hard mount the two frames in the rear, have the subframe rest on the frame over it's length with a UHMW strip in between, weld on some U channel near the front to capture side-side motion of the subframe, and move the rear springs forward (or maybe remove them?). Then all the springs need to do is resist vertical lifting... and you don't want too much of that resistance lest it add too much stress to your subframe and box.
A 3 point mount can also work well for this.
This is more typical of how spring mounts are done: https://expeditionportal.com/forum/...site-panel-camper-build-thread.213614/page-28
The subframe rests on the frame rails over the entire length, and only comes up when there is twist. The two frames are also hard mounted to each other at the rear.
You are relying on the spring mounts and attachment bolts to take all the lateral loads, as well as some vertical loads. I think it would be better to emulate something like the above... hard mount the two frames in the rear, have the subframe rest on the frame over it's length with a UHMW strip in between, weld on some U channel near the front to capture side-side motion of the subframe, and move the rear springs forward (or maybe remove them?). Then all the springs need to do is resist vertical lifting... and you don't want too much of that resistance lest it add too much stress to your subframe and box.
A 3 point mount can also work well for this.
Because I have a regular truck rather than a cab-chassis, the framerails not flat. I suppose I could take up the space with UMHW or similar. These spring mounts are designed to manage lateral load and fore-aft, which is why they nest inside one another rather than the example above. The manufacturer of the mounts said that 4 mounts should be able to manage a 2500 gallon water tank. Who knows how true that is.
A hard mount was considered and the spring mounts can be easily replaced as such. I think if I were to put in a hard mount, those closest to the cab might be a more appropriate location.
Part of the issue I've had is finding someone local to me that would be willing to talk about a project like this. The builder above seems to do great work but is located pretty far and never returned emails or DMs. In addition, most of the builders I could get in touch with to build a subframe were only able to do so in steel. Weight is a consideration on the 350/3500 trucks. This was a known limitation at the start of the project. Only ITB in Canada was willing and able to make an aluminum subframe, but that would prevent me from having the camper body be removable as well as add cost.
The design limitations I've imposed on myself for an inexpensive, flatbed mounted and removable camper body does cause some problems, but I don't think that they're insurmountable. I'm hoping this works and that other people who might be interested in this route can learn from my mistakes lol.
rruff
Explorer
You could try loading something on your flatbed that is an appropriate weight (and CG would be nice too) and put it through what you consider to be normal use... see what happens?
My mounting will be "non standard" and designed and built by myself, too. If it fails at least I'll know who to blame...
Alloy
Well-known member
You could try loading something on your flatbed that is an appropriate weight (and CG would be nice too) and put it through what you consider to be normal use... see what happens?
My mounting will be "non standard" and designed and built by myself, too. If it fails at least I'll know who to blame...
There's also the people around you that may suffer if it fails.
Edit: ...when it fails
GoinBoardin
Observer
A three point was mentioned so I thought I'd speak up. I wouldn't do one again. I'd go four point in a diamond pattern. The three point, even with shocks to damp movement, sways a lot, and pitches to the downhill side during off camber situations. Mine is hard mount in the rear, single pivot up front, with a popup flatbed camper. If I did go three point again, the pivot would be under the lightest end of the camper (mine is front heavy, so I'd go rear pivot this time). This would mitigate the pitching effect to some degree, I think.
DirtWhiskey
Western Dirt Rat
I think you're being a little brutal here.
rruff
Explorer
Curious what your setup is like. Do you have a description somewhere?
On my truck the frame is only flexy in the rear, which is where the "pivot" will be. Not really a pivot, but 4 poly cab mounts spaced close to the center. As you noticed, if you hard mount the rear, the camper will follow the tilt at the rear of the frame. If you hard mount the front, the camper will stay even with the cab (or close anyway).
DirtWhiskey
Western Dirt Rat
Following this thread very closely. Almost exactly what I want to do except I will be investing in a Pro tech or Alum-line setup and paying a bit of a premium for the deck. Pro Tech because they build their decks with huck bolts/rivets and no welds, which is the most durable way to build with Aluminum. You see that with most military gear (see: Schott industries etc). Alum-line is in consideration because they will build you anything your heart desires at a reasonable cost out of aluminum and they lay beautiful stacked dimes in said aluminum. I will probably overpay for the bed but I will handle the mounting myself and hopefully save a few dimes there.
This mounting system concept looks sound to me. Only thing I'd do is lay down some wood strips to span the gaps in front and behind the frame humps/hips to spread the load across the frame rails. Otherwise you are putting a lot of load on the spring mounts. The spring capture brackets should only catch load in tension (pulling) and prevent forward, side and aft movement and the rails should bear the downward load IMHO. I would also probably weld (or have somebody weld) some half inch plate to the back of the aluminum where the spring bolts go through so the holes don't elongate.
IMHO his spring style is probably the most efficient and easy as it negates the need for additional side limiting ears. I see no real compelling reason for solid rear mounting, but I am probably going to do it because it seems like most people do it that way?? I'm not an engineer but this type of mount has been used on thousands of water trucks. I buy and sell some big rigs and I've seen this style or some variant of this style of mount many times. In fact a big rig upfitter that does water and tank trucks might be the best path on rigs like this as I've had the same experience as you: nobody knows what I'm talking about when I talk to typical flatbed and trailer companies. All of these fancy three/four point systems show up in threads on expedition forums but are they really the way? Seems you could make some really expensive mistakes without a solid understanding of the engineering and modeling side of things, point loads, cracked frames, stresses, load swinging etc.
To me, this way of mounting a flatbed camper is the way to go if you ever plan on using your truck with the camper off, which I do. The flatbed is the "subframe". Smart.
This mounting system concept looks sound to me. Only thing I'd do is lay down some wood strips to span the gaps in front and behind the frame humps/hips to spread the load across the frame rails. Otherwise you are putting a lot of load on the spring mounts. The spring capture brackets should only catch load in tension (pulling) and prevent forward, side and aft movement and the rails should bear the downward load IMHO. I would also probably weld (or have somebody weld) some half inch plate to the back of the aluminum where the spring bolts go through so the holes don't elongate.
IMHO his spring style is probably the most efficient and easy as it negates the need for additional side limiting ears. I see no real compelling reason for solid rear mounting, but I am probably going to do it because it seems like most people do it that way?? I'm not an engineer but this type of mount has been used on thousands of water trucks. I buy and sell some big rigs and I've seen this style or some variant of this style of mount many times. In fact a big rig upfitter that does water and tank trucks might be the best path on rigs like this as I've had the same experience as you: nobody knows what I'm talking about when I talk to typical flatbed and trailer companies. All of these fancy three/four point systems show up in threads on expedition forums but are they really the way? Seems you could make some really expensive mistakes without a solid understanding of the engineering and modeling side of things, point loads, cracked frames, stresses, load swinging etc.
To me, this way of mounting a flatbed camper is the way to go if you ever plan on using your truck with the camper off, which I do. The flatbed is the "subframe". Smart.
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DirtWhiskey
Western Dirt Rat
Come think of it, those springs, if they are rated for 2500 gallon water trucks, might be a tad too beefy? On the link you sent (THANK YOU FOR THAT BTW, that saved me some fab time) they describe it as a 3000 psi spring. I guess you could do some testing and if it really too stout, and you get too much flex transfer to the flatbed, then use some smaller springs. I've heard of a few builders who use engine valve springs but I can' remember what kind or the rating. There is a thread on here that went deep into the recesses of spring theory. I'll try to dig it up.
Good conversation. My $.0002 below:
I thought about that, but I'm having trouble finding something that approximates it either size-wise, weight, or both. Obviously, there will be a lot of road testing on non-public roads before I unleash myself on the streets.
What your solution is to this problem?
Obviously, you are the smartest commenter thus far
In all seriousness, you get what I am going for. Perhaps I wasn't doing a great job being clear enough in my thoughts at the outset.
Using a flatbed for the subframe seems efficient and finding someone who could engineer something like this for me was surprisingly difficult. I am fine spending money, but some shops wanted $30k to build just the subframe, could only make it out of steel, were over a year out before they could start on my project, or were unwilling to spring mount a flatbed (ie - they only wanted to make a subframe). Also, no one was even remotely nearby, so traveling and or shipping would be an additional hassle.
As above, I will look into reinforcing the mounting points of the bracket to flatbed interface. I'll also try and work out an easy way to fill in the gaps.
And to your point about the engineering - agreed. ITB was the only shop I spoke with that had a real engineering department that did modeling based upon my truck and the load it was going to have. They provided me with a lot of useful information because their engineers are part of the process from the beginning. I can't recommend them enough. They honestly were probably about the same price as DIY, nearly as fast, and much higher quality. The only reason I'm going DIY is because I wanted to be able to remove the camper and they wouldn't accommodate that.
In the absence of real engineering, replicating water tank mounting seemed like the most direct path to the solution I wanted - a mounting system that would spare camper box the stress of travel while constraining its movement in the directions I dictate.
This dude is an ME and even he thought he didn't quite get it right the first time he built his:
Yeah, I did not realize how beefy they were until I saw them and I had the same thoughts. Getting new springs made shouldn't be too difficult...
One point about Alum-Line: they were nice, but they had no interest in talking about customization of the project or alternate methods of mounting the tray to the body. I spoke with their main shop in Cresco, IA because I was considering a Bundutec. Regarding custom work they were pretty clear that, "This is how we do it" and weren't interested in much else. I hope your experience is different.
Another shop that looks like they make a nice product is Highway Products in OR. They were more open to custom stuff (apart from creative mounting solutions).
You could try loading something on your flatbed that is an appropriate weight (and CG would be nice too) and put it through what you consider to be normal use... see what happens?
My mounting will be "non standard" and designed and built by myself, too. If it fails at least I'll know who to blame...
I thought about that, but I'm having trouble finding something that approximates it either size-wise, weight, or both. Obviously, there will be a lot of road testing on non-public roads before I unleash myself on the streets.
What your solution is to this problem?
Obviously, you are the smartest commenter thus far
In all seriousness, you get what I am going for. Perhaps I wasn't doing a great job being clear enough in my thoughts at the outset.
Using a flatbed for the subframe seems efficient and finding someone who could engineer something like this for me was surprisingly difficult. I am fine spending money, but some shops wanted $30k to build just the subframe, could only make it out of steel, were over a year out before they could start on my project, or were unwilling to spring mount a flatbed (ie - they only wanted to make a subframe). Also, no one was even remotely nearby, so traveling and or shipping would be an additional hassle.
As above, I will look into reinforcing the mounting points of the bracket to flatbed interface. I'll also try and work out an easy way to fill in the gaps.
And to your point about the engineering - agreed. ITB was the only shop I spoke with that had a real engineering department that did modeling based upon my truck and the load it was going to have. They provided me with a lot of useful information because their engineers are part of the process from the beginning. I can't recommend them enough. They honestly were probably about the same price as DIY, nearly as fast, and much higher quality.
The only reason I'm going DIY is because I wanted to be able to remove the camper and they wouldn't accommodate that.In the absence of real engineering, replicating water tank mounting seemed like the most direct path to the solution I wanted - a mounting system that would spare camper box the stress of travel while constraining its movement in the directions I dictate.
This dude is an ME and even he thought he didn't quite get it right the first time he built his:
Yeah, I did not realize how beefy they were until I saw them and I had the same thoughts. Getting new springs made shouldn't be too difficult...
One point about Alum-Line: they were nice, but they had no interest in talking about customization of the project or alternate methods of mounting the tray to the body. I spoke with their main shop in Cresco, IA because I was considering a Bundutec. Regarding custom work they were pretty clear that, "This is how we do it" and weren't interested in much else. I hope your experience is different.
Another shop that looks like they make a nice product is Highway Products in OR. They were more open to custom stuff (apart from creative mounting solutions).
DirtWhiskey
Western Dirt Rat
Noted on Alum-line. My hope is they will build what I want and ship it to me for mounting. I'll check out Highway Products for sure. I keep holding out hope to find a good used unit here in Utah. I already have an Aussie style "ute" shell made by that I would keep on the flatbed when not in camper mode. Those ARE shells are sort of fragile and my hope is the flex mount will keep it together. I really think flatbeds should all be mounted this way and I'm shocked it's been this hard to find somebody who can do it.