Slide-outs - any reason to not use a DIY dovetail slide

[SPF40plus]

Hi everyone,
I'm looking for feedback relating to DIY slide-outs and if anyone has used a dovetail slide mechanism? Or, if you have something else that is low profile and capable of supporting heavy loads. This is for a heavy truck application, but I know that a lot of trailer builders use slide-outs so I'm asking in this thread. If there is a better place for this question, please let me know.

I've been considering telescoping SHS (square tube) and wall mounted slides, but neither are giving me what I need. The two most important features are minimising the overall floor thickness, and keeping most of the structure in the floor. The truck bed is 1.35m (4.5') off the ground already so we are looking for every saving on height possible, and trying to keep the centre of mass as low as possible.

The camper is going to be 5m (17') long and 2.4m (8') wide. The slide out is going to be the entire length of the driver's side, and extend out 0.75m (2.5'). And the camper can be taken off the truck by use of jacking legs. What I'd really like to do is have two of the jacking legs in the slide out and the other two on the main box.

I have enough room in the floor to have between 0.6m (2') and 0.9m (3') of overlap between the main box and the slideout, and I can either make the dovetail the entire length of the overlap, or have a shorter carriage at either end.

Ideally, I'd make the mechanism out of mild steel, but could also make it out of 4140 or 5160 if necessary. I'll likely use a brass or bronze gib so I can adjust the engagement as needed. I won't use the gib to lock the mechanism.

Any feedback is appreciated.

 

[NatersXJ6]

I’ve never tried that, but what you describe sounds to me like torsional rigidity could cause issues if your floor structures aren’t stiff enough. How will you power the slide in and out? I can see it getting stuck and binding if slightly misaligned going back in.

Sounds like fun though! I say if you have the time and the cash to experiment… go for it!

 

[Victorian]

Hi everyone,
I'm looking for feedback relating to DIY slide-outs and if anyone has used a dovetail slide mechanism? Or, if you have something else that is low profile and capable of supporting heavy loads. This is for a heavy truck application, but I know that a lot of trailer builders use slide-outs so I'm asking in this thread. If there is a better place for this question, please let me know.

I've been considering telescoping SHS (square tube) and wall mounted slides, but neither are giving me what I need. The two most important features are minimising the overall floor thickness, and keeping most of the structure in the floor. The truck bed is 1.35m (4.5') off the ground already so we are looking for every saving on height possible, and trying to keep the centre of mass as low as possible.

The camper is going to be 5m (17') long and 2.4m (8') wide. The slide out is going to be the entire length of the driver's side, and extend out 0.75m (2.5'). And the camper can be taken off the truck by use of jacking legs. What I'd really like to do is have two of the jacking legs in the slide out and the other two on the main box.

I have enough room in the floor to have between 0.6m (2') and 0.9m (3') of overlap between the main box and the slideout, and I can either make the dovetail the entire length of the overlap, or have a shorter carriage at either end.

Ideally, I'd make the mechanism out of mild steel, but could also make it out of 4140 or 5160 if necessary. I'll likely use a brass or bronze gib so I can adjust the engagement as needed. I won't use the gib to lock the mechanism.

Any feedback is appreciated.

you are taking a lot of structural strength out of the camper by making the whole side slide. This can of course be compensated with a proper engineered structure ….. what’s your plan?

 

[SPF40plus]

I’ve never tried that, but what you describe sounds to me like torsional rigidity could cause issues if your floor structures aren’t stiff enough. How will you power the slide in and out? I can see it getting stuck and binding if slightly misaligned going back in.

Sounds like fun though! I say if you have the time and the cash to experiment… go for it!

That is a good point.

The truck bed the body is sitting on is supported by a three point pivoting frame with a gimbal at the front. I can have the front tyre 0.5m (18") off the ground and there is less than 6mm (1/4") twist in the truck bed. I think I'll make a single slide and twist it to see if its a problem. Thanks.

 

[SPF40plus]

you are taking a lot of structural strength out of the camper by making the whole side slide. This can of course be compensated with a proper engineered structure ….. what’s your plan?

Yes I am.
We have a fold out deck at the rear (roof and floor) that needs to be supported, and the slide out. I'd like to try and build the structure so that the main box has a rigid wall on the other side to the slide-out, and then the slide-out has a rigid outer wall, and then make the connection between the two share the bending moment, and torsional stress. Also, as mentioned I'd like the structure to be mainly in the floor to keep the CoG as low as possible. I know that I'll likely need a connection point on the walls but I'd like this to be to stop wobbling rather than taking any great proportion of the load.

Part of the reason for doing this way is so that you don't need a separate structure for the floor of the slide out - it stays fixed to the structure underneath. You do need a folding section of floor to allow the slide-out to move though.

I haven't decided whether we make a custom composite panel for the walls or if we use one of the local composite panel suppliers. I think this decision will come down to how much flex there is in the structure, and if the composite panel is likely to explode when the structure is stressed. If we make a custom panel it will be aluminium outer, extruded polystyrene thermal panel, and then 4mm (5/32") hardwood ply internal. This will be fitted to a 50x25mm (2"x1") 1.6mm thick (1/16") steel RHS frame. Our custom panel is about 25% heavier than the commercially available product, but it much stronger in shear, and at critical points the aluminium can be formed around corners.

Cheers.

 

[SPF40plus]

I don't have any images yet, but will post them up in the next few days.

 

[NatersXJ6]

That is a good point.

The truck bed the body is sitting on is supported by a three point pivoting frame with a gimbal at the front. I can have the front tyre 0.5m (18") off the ground and there is less than 6mm (1/4") twist in the truck bed. I think I'll make a single slide and twist it to see if its a problem. Thanks.

Maybe just to clarify a bit: When you say dovetail slide, I’m thinking of something like the guide ways on a metalworking lathe or mill, just tight tolerance metal on metal contact spreading the load over a long distance with barely enough tolerance to allow a lubricant between them. Is that what you are thinking?

When I talk about twisting, I’m not thinking so much of a twist in one slide, but a twist in the floor that makes 2 slides mis-align and bind. If they are not perfectly parallel and in plane with one another, I would think there is potential to have them stick. Being out in the woods with a slide that can’t close doesn’t seem pleasant to me.

 

[SPF40plus]

Maybe just to clarify a bit: When you say dovetail slide, I’m thinking of something like the guide ways on a metalworking lathe or mill, just tight tolerance metal on metal contact spreading the load over a long distance with barely enough tolerance to allow a lubricant between them. Is that what you are thinking?

When I talk about twisting, I’m not thinking so much of a twist in one slide, but a twist in the floor that makes 2 slides mis-align and bind. If they are not perfectly parallel and in plane with one another, I would think there is potential to have them stick. Being out in the woods with a slide that can’t close doesn’t seem pleasant to me.

What you are thinking is correct. I had a look last night and did an analysis on how much twist would potentially stop the slide from working and it seems 2 degrees would do it unless the joint was sloppy, and then you don't get the benefit of the mechanism anyway. If the slide is fully engaged the problem would not come up, but like you say if the slide is out, and it slumps then it is possible that it could bind up and I would have to use serious force to retract it, which would most likely cause damage.

Thanks for the reality check, back to the drawing board...

 

[billiebob]

What I'd really like to do is have two of the jacking legs in the slide out and the other two on the main box.

hopefully plus 2 on the other side of the main box ?? 6 in total ??

I wonder what kind of overlanding you do. Big slides on Class As that never leave the highway and camp in National or Private Campgrounds with PAVED drive thru sites are one thing. Expecting to do the Rubicon with moving body parts is another. Sounds like you are in between those realities but knowing how, where you overland might help focus the answers. Also knowing what vehicle this is mounted on will help.

 

[SPF40plus]

hopefully plus 2 on the other side of the main box ?? 6 in total ??

I wonder what kind of overlanding you do. Big slides on Class As that never leave the highway and camp in National or Private Campgrounds with PAVED drive thru sites are one thing. Expecting to do the Rubicon with moving body parts is another. Sounds like you are in between those realities but knowing how, where you overland might help focus the answers. Also knowing what vehicle this is mounted on will help.

Thanks for your question.

I am trying to have only four legs - 100mm (4" SHS) with 75mm (3") or 89mm (3.5") telescoping out. However, this is going to depend on whether the floor is stiff enough.

You are right, we will be on highway 70% of the time (that is Australian highways, so includes dirt roads), 20% on the beach and the remainder in the mud etc. The truck is the Isuzu FTS700 4x4 12.5 ton (like Wicked Turtle on this forum). The box will sit on the existing steel/aluminium tray, but will be connected to hitches directly above the two mounting points above the axle, and then one above the gimbal pin (that prevents the tray from twisting) at the front. We want to be able to remove the camper, so we don't need to take it on the more challenging tracks - we will find a camp ground reasonably close and leave it there.

We made the decision early to make the box removable because even if the truck was capable of driving through the terrain, generally we want to go to places that are remote and the height of the camper will be a problem because none of the government service vehicles are that tall. If you have a look at some of the Unimog camper footage in remote coastal areas in Australia, they spend most of their time cutting branches, or scraping through at a couple of km/h. The cab is just under 3m (10') high, and with the box on the back the truck is 3.5m (just shy of 12') tall. That includes the rub rails to protect the solar panels.

 

[NatersXJ6]

Understanding that you have a concern for overall height, and having very little experience with RVs and associated slide mechanisms, I would ask:

Does the floor height of the slide have to match the camper floor? If the slide is for kitchen cabinets and a dinette for instance, those could be accessed while standing on the main floor and the mechanism height might be consumed in the slide instead of the main floor.

Another thought, the mechanism could be overhead and the slide could “hang” from it. It might be more acceptable to duck under something than step over it?

Or, if you build the full width slide, the mechanisms could be right at the back and right at the cab, not really consuming floor space.

 

[SPF40plus]

Does the floor height of the slide have to match the camper floor? If the slide is for kitchen cabinets and a dinette for instance, those could be accessed while standing on the main floor and the mechanism height might be consumed in the slide instead of the main floor.

That is a good point. The only item that is a problem is the bathroom, which will be in the slide out.

Another thought, the mechanism could be overhead and the slide could “hang” from it. It might be more acceptable to duck under something than step over it?

Yes, I prefer this as an option. We live near the beach and our sliding doors are all supported at the top, so the track doesn't fill up with sand and salt. If this conversation means that we need to break up the slide out into parts then I think this could be an option. The reason I'm not considering this for the full length slide out is to keep the CoG down, and to minimise the number of latches and mechanisms to secure the slide outs.

Or, if you build the full width slide, the mechanisms could be right at the back and right at the cab, not really consuming floor space.

I think this is the same as the item above, but It also consumes a lot of the internal area if there are multiple slide outs. For the full length slide-out both boxes need to be independently stiff enough when travelling, and in situ. When I looked at this the weight of this option (frame) was about 30% more than my current option.

Do you have a view on which types of slide outs are easiest to seal, and lock in the closed position? This is another consideration that I have not been able to get a clear answer.

 

[SPF40plus]

Thanks for all the comments and questions. I'll post up some images of where I get to in the next few days.

 

[NatersXJ6]

Yeah, I’m pretty much out of ideas. Everything I think of is either really heavy or becomes a challenge to package into a floor effectively.

 

[billiebob]

We want to be able to remove the camper, so we don't need to take it on the more challenging tracks

So any empty deck ?? Basically making it a front wheel drive since empty with zero weight on the rear axle the rear axle will have almost zero traction.