Skeleton Side Wall Advice

[Strop]

I am still planning away but have decided to use the Steve Fredericks build style. I am just thinking through the ply I intend to use. The sheets are all 2400mm x 1200mm.

For the skeleton piece I have a choice of 12mm, 15mm or 17mm structural ply. It is my intention to have this piece sit on the floor level with the outside. The maximum height this wall needs to be is 1155mm so I just need one join to make the length - 3100mm. To fill in the holes I plan on using SL Polystyrene Foam. I can't buy it in any of the thickness of the ply but can get it cut down. Same price for every thickness. So the question is what width. Is there any advantage in 12 over 15 over 17 mm. Weight differences not huge - no real need for a lot of cold weather insulation either. So is running the cabling inside conduit worthwhile - needs a thicker wall. Any othe things that a thicker wall size helps? A thicker pice of ply here would also allow me to route out the last 45 mm of the sheet to slip over the trailer sides. I could then use some scrap ply to pad out the bottom to cover the rest of the trailer sides. The 15 or 17mm ply I am thinking would be better for this.

Also with that white polystyrene should I get it cut down to the exact width of the wall or 1 mm thinner.

Inner wall will be 3mm so no real worries there because I won't need to join the sheets to do what I want.

Outer wall I was also planning on 3mm ply but I have the problem that the sheets are not tall enough. Trailer frame 50mm and floor 17mm and then another 34mm for roof equals total height of 1256mm. - oops 56mm over sheet size. So my thinking here was to cut the sheets to fit without any joints just butting the pieces together. Thinking that I should make a joint about 200mm from the top so the piece has some substance when glues on. Does this make sense? Also is 3mm thick enough for the outside wall. Not sure if then skinning with Aluminium or Fibreglass sheeting.

I was going to make my template out of 7mm ply with butt joints to achieve size needed.

So some advice from experienced builders would be great.

Thanks

Laurie

[KCStudly]

I have been using 5mm (3/16 inch actual) ply for all of my interior skins, top and bottom floor skins, bulkhead skins, cabinet shelves and ceiling, and I am thoroughly pleased with this choice (with the exception of some minor trouble getting the front radius to form to a 13-1/2 inch radius... I had a buckle that I ended up reinforcing with epoxy and glass weave... I would have kerfed that section some, if I had it to do over). That being said, there are plenty of people who have used 1/8 inch (3mm) skins (or even two layers of 1/8) and are happy with that choice.

It is unfortunate that you can't match a stock wall core thickness to a stock insulation thickness. I wonder if laminating two different thicknesses of ply together would get you where you need to be without costing more than custom cut foam? The other considerations for overall wall thickness are door flanges (if using a manufactured door), window flange thickness and door hardware (if making your own doors and/or installing separate windows), and edge trim. Each of these items can take a lot of detailed work to make fit correctly, seal well and look good. It would be well worth selecting and working to a wall thickness that is compatible with the hardware that you choose for these items, otherwise you may be having to do "work arounds" and getting creative with "solutions".

Plan well and good luck with your build!

[danlott]

One consideration for the plywood thickness would be what trim material will you be using. If you can only get aluminum trim in a certain width, than that may determine the thickness of the plywood you would end up using. Think about how you plan to finish your trailer. Where and how will you be using trim moldings?


Dan

[Strop]

I have almost convinced myself that you have to buy all those bits and pieces you need for your build before you buy a bit of timber - just so you plan is fixed and the variables are taken out.

I have found some windows I like but they need 27 or 29 mm walls. Without actually seeing them I am unsure of whether they can be cut down for thinner walls of whether I have to put a timber spacer in. For that reason I think 12mm is out. I previously found some windows but when I went to buy they were all gone and he i s not doing an import for 12 months.

I got a response from the polystyrene bloke last night and he said their cuts are + / - 2 mm. They come in 10/20/30 mm thick sheets. 30mm is fine for the roof. Might have to use 20mm for walls but not sure of the best way to trim them back level. Ideas? I don't want hollows as they will become visible when skins glued on.



Dan, I am thinking I am going to use fibreglass sheeting. Comes in cut to you length pieces @ 1500mm wide. Side walks ok with that width and build width of 1490mm gives me 5 mm to play with each side when affixing it. I hadn't thought about the trim size and how much width I needed in the wall to have something to fix it into. As I said earlier I need to source this stuff first so that I don't get to that stage to find there is nothing to fix it into.

[48Rob]

I have almost convinced myself that you have to buy all those bits and pieces you need for your build before you buy a bit of timber - just so you plan is fixed and the variables are taken out.

There is a good bit of design and thought that goes into creating a nice trailer.
On the surface, it would seem pretty easy to "build a box" but as you suggest, the list of variables can be quite long, and every change mid stream can create fitment issues on other parts or sections.

Part of the challenge (and fun) of designing and building your own trailer is to overcome the hurdles and learn to think on the fly, redesigning as you build.

Rob

[KCStudly]

I'm guessing that the tolerance in the foam cuts is due to variances in how a hot wire cutter works. Depending on the heat and speed of cut the wire can take a wider swath.

It would be a bit of work, and is messy, but the foam does sand fairly easy. A big long board and some coarse strips; glue the foam into the skeleton and use the frame as a guide to sand to. I used this technique in a few spots where my foam was slightly thicker than nominal. 3mm is a lot to take down by hand, though, over such a big area.

Talk to the guy and ask if he can do the hot wire work after you install the foam?

[tony.latham]

I'm on build #3 using Steve's Shop Manual. #1 and #3 are 5 x 10's using a 3/4" (19mm) skelton and 1/4" interior/exterior skins. #2 was a 4 x 8' using 1/2" (12mm) skeleton and 1/4" (6mm) exterior skin and 1/8" interior skin. The all work fine. With the 12mm skeleton, I was a bit leary of using a crown stapler to tack down the ceiling onto the wall lip (splitting the ply?) and used #6 FH wood screws. It worked fine and didn't slow me down much. I'm a bit more comfortable with the thicker walls on the longer 'drops. I think Grant Whipp uses the 1/2" (12mm) core for his builds and has built more teardrops than I'll ever see.

It all works.

Tony

[Strop]

I have a number of options to work with the frame skeleton and the foam. I did find some 13mm foam last night. The problem with all the foam suppliers I have found is that they are a 6 hr drive away. I am going there over Christmas so that may will be a delay in starting. Also just getting a garage built onto my house where the building will take place so I have time. I am still trying to find some local providers though.

I like the idea of the big file made out of timber and sandpaper. It only cost $5 per sheet to get them cut so if I just get them trimmed to 18mm then hopefully I will only have to sand down 1mm - worst case scenario or add a bit more glue to bring the 16mm pieces up.

I still need to have a wall width of 27mm as I said earlier unless I can cut the windows down. Wonder if the wife will buy me two windows as an early christmas present.

Tony (or anyone else) is 3-4mm ply too thin for the outer-skin?

I have had a bit of a play with the skeleton design.

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I have not rounded the corners of the skeleton plan as I will. Get the old soup can out of the cupboard and draw them in.

The thicknesses of the supports are 50mm. Not sure if that is too small - strength wise. The window weighs 5kg from memory and I could increase the size of the support under it which will take all the weight, if needed. My calculations show that the wall with an inner and outer skin should weight around 28 Kg (62 lbs) Skelton should weight 16 Kg (35 lbs). Walls are approx 3 m/sq so 3mm ply weighs about 6kg so going to 6mm ply would increase the total weight by 6kg a side - 34kg (75lb). Would also give me almost the 27mm width I need.

You can also see on the diagram where I plan to join the two sheets. Again the join will only be 50mm. Is that enough?

Anyway comments on the skeleton appreciated.

Laurie

[Strop]

I have left out somewhere for the guards to mount to. Back to work.

[Strop]

Added 2Kg (4.5lbs) to skeleton weight. Will just have to look a bit more at the tyre axle setup.

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[Strop]

Funny how you read things and they bring you back to basics. I think I had the door too far towards the front so as to negatively impact upon getting in & out. I have moved it back, but any advice as to it's location appreciated. Also I looked at the windows again and found that a bigger window was actually cheaper than the one I had planned for so, I have gone for the bigger window. Not sure if this is a good idea or not.

Widnow site http://camec.com/windows-shades-spares/odyssey-plus-688/odyssey-plus-4-radius-corner-window-565mm-x-610mm-white-frame-27mm-clamp.html

What concerns me is where the window is positioned in the door. I don't have one that I can go an sit in and see so some help needed. I have marked in the cutout under the window space where a 20cm mattress would come to. The bottom of the bottom cutout in the door, would be 11cm up from the floor, so a 10 cm mattress would also work.

BUT.... IS THE WINDOW IN THE BEST PLACE? Should it be higher / lower?

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[KCStudly]

My thinking on the window placement is that since the door should be where your hips are, its not like you will be looking out the window when you are laying down. So the window should be higher up (like you have it) so you can have a nice field of view when sitting or kneeling.

On my doors, what it really came down to was the fact that I am using a pair of lift off hinges. Between the two lift off hinges, positioned as high and low as practical (given the rounded corners of the door) and the door latch on the other side, I wanted these points to form as close to an equilateral triangle as possible. My thinking was that the loading on the door seal would be more even that way and the seal would compress more evenly. So, while keeping aesthetics in mind and not crowding anything too close together, or too close to an edge, I let that be my guide. Not having to worry about aluminum trim (I'm building canvas covered Foamie) eliminated some of those conflicts, as well.

[tony.latham]

"Tony (or anyone else) is 3-4mm ply too thin for the outer-skin?"

I wouldn't have a problem with it depending on what you're finishing the build with and how you joined your skeleton wall. Are you going to fiberglass or cover with aluminum? I think Steve recommends two layers of 1/8" (3mm) for the roof with fiberglass and no aluminum. I'm comfortable with one layer of 1/8" (3mm) covered by .040" aluminum (backed by hard foam).

On the 5x10 I have going right now, I joined the 3/4" (18mm) skeleton plywood by using a spline joint. In my opinion, it's a weak method of joining plywood until it's strengthened by the interior/exterior sheathing acting as a glued on gusset. (a scarf joint would be better) I've got the spline joint just forward of the door. After sheathing with the two layers of 1/4" it's fine.

The interior/exterior sheathing is butt-joined over a 4" strip of the skeleton piece at the rear of the wall and It's plenty strong.

Make sense?

Tony

[tony.latham]

Strop:

Shouldn't that "sheet join line" be solid all the way from top to bottom? I'm assuming that's in reference to where you're joining your skeleton piece to make your wall 10'?

Here's what my current build's skeleton wall looks like:


Thus my spline joint is covered by two sheets of 1/4" ply –and they butt together back there at that "sheathing joint" line. (and covered by a piece of 1/2" ply for Fredrick's method of sealing the hatch).

Tony

[Strop]

KCStudly, thanks. Yes i had originally positioned the window to look out really. Now it is a compromise between my needs and my wives needs to ease getting in and out. I have filed away in the head about the hinge/handle orientation.

Tony I am doing a half lap join on the skeleton. I was hoping that 2" overlap would be enough as long as I was ready to put the outer skin on as the next part of the process and not handling the skeleton too roughly. It would not be hard to add an extra inch and run it full length but I was thinking light with the strength coming from the skins.

I am planning on putting a fibreglass skin on the outside. It comes in 1500mm widths cut to your desired length. Also it is 1.6mm thick. Thinking it is the same stuff as you see on modern white smooth skinned vans. I am sure it will be significantly lighter than aluminium.

Now to the outer skin. 3mm (1/8) sheets are very hard to join I imagine (never tried it before). I have an issue with sheet size here and I know I will have to do 3 pieces per side, the height and length exceed sheet sizes I can get. I was thinking of again having a join separating the front and the back at the same location as the join in the skeleton. I would then need to have a sheet doing the bottom 3/4 of the front and another sheet doing the top part of the front. I was planning on just butting these sheets up against each other (I will have to extend the location of the skeleton join all the way through). The join on the two front sheets would be at the top of the door height, to maximise what it can glue onto.

I can see on your skeleton that you have left the areas for the bulkheads to go into. I was thinking of doing it slightly different.

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In the (quick mock up) you can see the outer wall (dark brown), part of the skeleton (blue), the inner wall (Ply colour) and the proposed cupboard outlines. I was going to shape it to the exact shape of the shelves and then glue it into place so the shelving unit slips into the 3-4mm slots. Perhaps the 3-4mm each side is not enough for cutting errors but I hope I can cut the bulkheads pretty accurately.

With Steve's building method I am still trying to figure out why you need to put any inner skin in place if you are putting shelf units / kitchen cupboards in which will cover the skeleton. I will have to go back and reread though.