Starting a home build FG and looking for lots of advice.

[SkiFreak]

Happy to here that you found my website useful.
I had not realized that your subframe was made from aluminium (or aluminum, for those of you in the other half of the world); I thought it was zinc plated steel. Knowing this now, might I suggest some strengthening plates on the inside of the sections (near the chassis step) that only have circumferential butt welds (areas with red circles).

It is not easy to see from the images, but how much clearance do you have between the bottom of your front subframe rail and the top of the air cleaner box?
On my truck I have allowed for 35mm of lift between the chassis rail and the subframe. This equates to about 50mm of movement at the air cleaner. My front rail is behind the nub at the top of the air cleaner, but your rail is directly above it (red arrow). Do you have enough clearance here when your subframe articulates?

 

[1aquaholic]

Aaaa well I'm welding on a 1/8th inch plate the entire top surface of the subframe so hopefully that will do it, also more 2x2 tube welded above for the bed frame and below for the compartments which will strengthen that area.

I don't think I have 50mil of clearance over the air filter, I'll measure later today, thanks a lot for that number. Another spot I may have to modify.

j

 

[1aquaholic]

Really....no response, I must be really messing up and no one wants to touch it?

j

 

[SkiFreak]

I had not responded, given that you have obviously looked over my website and seen how I approached this subject; but to summarize my design...

I use an eight point spring mounting system with no fixed mounts.
The design of the mounts is such that six of the mounts provide the fore/aft/lateral support of the subframe. This is accomplished by "nesting" the lower mount into the upper mount. The front mounts are of a different design, allowing for unencumbered lateral movement. The reason for doing this is the step in the FG chassis. The six rear mounts are along the same horizontal plane, but the front mount isn't, which will result in different movement in that area when the chassis twists. The front spring mounts simply assist in allowing/restricting vertical movement of the subframe. The bolts are all grade 8, 3/4" UNF and have centering washers to locate the springs and Niloc nuts are used to secure the bolts. The bolts are never placed in shear, as the mounts secure the subframe positioning (as previously explained). The sole purpose of the bolts is to hold the springs, which in turn holds the subframe and chassis together.
I have utilized 50mm x 25mm polyurethane bar as the buffering material between the subframe and chassis. My logic for doing this was that this material is pretty much maintenance free. There is a 240mm polyurethane section at the front and a 3030mm section at the rear, giving me nearly 100% contact between the chassis and subframe on all but the step section of the chassis. This allows for good distribution of weight across the entire chassis, reducing the possibility of having point loads.

Is this the best way to mount a subframe to a FG chassis? Who the hell knows? All I can say is that it is the way that I have chosen to do it and that I am happy with my design.
Would my design work for you? Well, that's for you to decide.

What I will say is that any design that incorporates a kinematic type mounting system needs to take into account clearances at the subframe articulation limit.
I have already pointed out the area around the air cleaner, but this also includes the distance between the bottom of the subframe and the top of the tyres (as highlighted by dlh62c). If mounting boxes off the subframe, you also need to allow sufficient room between the inside of the box and the chassis.
With a 35mm gap between the chassis and subframe of my truck I have about a 150mm differential in height between each side of the subframe.

 

[dlh62c]

Really....no response, I must be really messing up and no one wants to touch it?

I wouldn't say your messing up!

I'm just not sure what your body build up plans are?

The sub-frame for a camper build is kinda like the foundation of a house, everything is based and built upon it.

 

[1aquaholic]

Thanks to both of you for all the great info!

j

 

[GR8ADV]

I will chime in here for no other reason that it is an open forum. I took only one philosophy class in college, and learned maybe one thing from it. "one need not add entities" In other words, keep it simple. A structural member is very predictable. Every connection that is welded or bolted to that member is a potential for a problem. Kind of like a water pipe, one solid piece of 200 feet of plastic pipe is predicable. If you welded or bolted 10-20 foot pieces together to make up that 200 feet, every joint is a possible place for it to leak. Not that you have a problem, but you have one heck of a lot of welded joints in this frame. Is there an advantage to this type of lattice?

 

[Maninga]

It's an interesting looking frame design. For the small rise, I'm not sure why you wouldn't have gone flat the full length, rather than flat, 2 inch rise, then what looks like an angled section. Makes it easier to generate a flow internally. My floor is anything but flat, but I'd built my interior to work with the rise (about 7 inches).

For the mounting, here's how mine's been done. Link. 2 fixed, 2 spring mounts. I had initially thought the builders were going to do 1 fixed and 3 spring mounts, but assured me this would work just as well in my case.

If you're planning on putting a spring mount at the front, I'd be a little bit concerned of the subframe cracking at the front. I might be wrong, but it looks like the solid pieces are going across the body with welds connect via short pieces along length of the body. Wouldn't that introduce weakness?

 

[1aquaholic]

I totally agree GR8ADV, I wanted to go aluminum for a couple of different reasons, so added a few more cross members for strength, the transvers mostly are one piece sections and I did my best to have as few welds as possible. I will add a 1/8th inch plate of alu welded to the top which will reinforce all those welds and add structure. Simple is better, and I'll be the first to admit that I can drift off track with tunnel vision sometimes though so if anyone sees something I'm missing please let me know.

j

 

[gait]

Really....no response, I must be really messing up and no one wants to touch it?
j

Hi J,

Not a case of messing up.

Its just easier for me to discuss these sorts of issues during design when changes are relatively simple. Part way through the build, when some of the cement has set so to speak is very difficult, if only because its difficult to change. Its also easier for me if the end point is clear.

I'm set in my ways of design the whole then build which makes it difficult for me to engage with what appear to be other approaches.

 

[1aquaholic]

Maninga interior height has been a battle for me in my design, between wheel well space, counter height, and cabinets when the roof is in the down position it needs to be at cab height so every inch counts. The floor is flat all the way from the back to where the bed starts up front, the bed will rise 30 inches and all those small rises in the floor will be in a pass through compartment under the bed with doors on the outside. This will be for specific storage of sports equipment and I don't mind the uneven floor there, as a matter of fact the compartment will have wet gear there and this will help facilitate the drainage of compartment. Hope this makes sense.

j

 

[DzlToy]

Or you could use what millions of box trucks and flat beds around the world use and rigid mount the box to the frame with a piece of timber and u-bolts and be done with it.

 

[1aquaholic]

Thanks Gait, I was kinda kidding but alway looking for someone with more brains than me to check my work. Definitely easier to give advice if you have the whole picture though, I'll try to throw up some of my drawings on here soon.

j

 

[Maninga]

Maninga interior height has been a battle for me in my design, between wheel well space, counter height, and cabinets when the roof is in the down position it needs to be at cab height so every inch counts.

I absolutely, completely, utterly understand what you're talking about here. Just ask my wife. I'm probably going to end up around 2-3 inches above the cab roof-line, will still be able to containerize it without having to do any work (outside letting air out of the tyres). I've gone over the internal layouts, bed heights, cabinet heights, fridge position (was thinking last night, might build my own fridge, just to make it fit better), window positions, under bed storage, seat heights and widths, garbage bin positions, cleaning supplies cabinet, dirty laundry spot, me and wifes torso height and eyeline, actuator positions, bathroom dimensions all these multiple times (at least once a night) for the last 2 months. I'm still trying to figure out whether I want a skylight installed or not.
The builders making the shell have spent a stupid amount of time on the design too. I'm sure they're not going to make any money on this build. I think they've spent 2 weeks in CAD sofar and haven't finished, there was 2 days on the door latch and hinge arrangement for the entry door alone. Get my first draft of drawings from them either today or tomorrow.

Internal heights are a little rough at the moment, waiting for confirmation on them. Initial plans though are 4'8" at the front, 5'4" in the main body section when the roof's closed. Open, will be 6'8" at the front, 7'4" in the main body with a 2' rise. Storage cabinet under the bed will be 6'8"x5'x2'6" (LWH) plus clothes storage of 8" on top. Overall height I expect will be 8'8" with the roof closed, 10'8" with the roof opened.

 

[1aquaholic]

Boy do I hear ya Maninga I've been running those same circles for months now also. So imagine your overall height needs to be 7'6” with the top down. I live on an island and the ferry price goes up in a big way at 7'6”. I'm modifying suspension so I can lower the entire truck 4” to go through the ticket booth at a slow roll then bring it back up to drive. Will save me 5 thousand US a year. Funny looking at your interior design we have come to a similar ideas.

j