Over engineered or under-thought?

[AGM_AU]

Hi all. I’m hoping this post works as it’s my first (for the last 3 years it’s just been Lurking-and Learning).

The short story. I’ve spent a bit of time trying to come up with a Tiny Trailer to tow behind a Holden (Chevy) Cruze, which fits in the Garage, takes a queen size mattress (and doesn’t feel claustrophobic), will be “reasonably” aerodynamic at 100 Km/h (62 MPH) and has enough Galley & storage space. So far I’ve got it down to possible 290 Kg (640 lbs) with a hefty trailer frame that is still under thought and development. LOL, I may be reaching here considering the tow vehicle specs, but design & research time costs little (I can dream).

My question relates to a vertical support on the V nose radius that is 19 x 42 x 1176 lg (roughly 1 x 2 timber from what I can understand from US timber sizing). I’d like to use (and rely on) Polyurethane adhesives to avoid possible water damage issues from using nails/ screws etc. Gluing the end grain of the timber doesn’t seem wise due to the 1.2 square Inch profile. But adding the mounting blocks increases that to about 5.5 square inches for the connection on the vertical member, and 7.8 square inches for the mounting block connection to the ½ inch plywood floor on that section.
LOL…..am I over engineering (and over thinking) things, or does this seem reasonable to all of you who have actually built one of these little escape machines?

Cheers!

Tony

[KCStudly]

Welcome!

How thick is the plywood over and under the posts? I wonder if you could substitute Kregg pocket screws for the corner blocks.

Regardless, I think you should consider adding base and cap rails to (or spacers between) the posts similar to the non-curved wall frames of the vee. That way your skins have support around their full perimeter, otherwise you could pop the skin away at the base of the wall pretty easily when stowing cargo, etc.

You don't want to screw or nail the outer skin into the edge of the floor and ceiling ply anyway, so the extra blocking or base/cap rails will be needed. And since you will have to fasten the skin, at least temporarily while the glue dries, there are going to be plenty of holes to seal anyway, so a few more screw heads from the outside won't make that big of difference, IMO.

[citylights]

I agree with KCSTUDLEY, install blocking between the nose ribs top and bottom. That gives extra area for glue to lock in the ribs and gives an all around surface to attach the inside and outside skin. Your V nose front construction (yours is horizontal) should be very similar to a standard tear front curve (standard would be vertical).

With the blocking glued and screwed between ribs, I would just put one screw through the floor and roof into each nose rib and glue. In fact, that is how I did my standard tear ribs. Plenty strong.

Also, you must consider that the curved sandwich construction shape will add tremendous strength too.

Also thought I would mention that your tire and axel appears dead center in the trailer. As tears have a heavier galley, the Alexa should be 1/3 of the way in from the back as a rough guess. There is a guide and calculator on this site to find the ideal axel location, but after you go through the effort, it will end up... ...about 1/3 up from the back.

[MtnDon]

I am not sold on polyurethane glues for gluing wood to wood. Not convinced that it makes a stronger joint than Titebond II, or III if worried about water. Finewoodworking did some tests a few years back with the yellow glues, epoxies, old fashioned hide glue and polyurethanes. The poly's came in dead last, with yellow glue being best. I have found the polyurethanes do glue foam to foam better than most other glues. However in my more normal house to furniture building (non mobile) I have little use for the poly's. I will admit that maybe the poly's might be good for gluing end grain to side grain better than yellow glue as that is a difficult joint to glue well.

[AGM_AU]

KCStudly & Citylights, thanks for your assistance and the welcome. LOL…if only I got that sort of response time from my bank!

The floor in the nose section is intended to be 12mm marine ply, as is the skeletonised top frame. If I laminate two 12mm ply profiles together to form the cap rails, that’ll give me just under an inch and a half overall mating surface for the ¼ inch ply skin and glue. Sound about right?

I’ll have to check out a supplier for the Kreg gear in Aus.

City…..yup, the axle is almost centre to the cab at the moment. LOL….an unfortunate (sort of) circumstance of the V form nose. I ran the centre of gravity with 40 L of water, plus a portable fridge/freezer and an extra 25 Kg of sundries in the galley. Allowed for another 40 Kg of various items (battery plus sundries) in the nose storage, and that’s where it put me (roughly). The trailer frame is one of the next things I have to tweak for its configuration and layout, after I have the cab nutted out. Before it hits the shop floor I’ll adjust it for a suitable hitch weight.

[AGM_AU]

Don, thanks for weighing in on the Polyurethane glue.

How is TB 3 to work with on a vertical surface? Most of the modules in my attempt are torsion box arrangements (e.g floor in the main cabin, walls) that I can work with on the horizontal. So for most of it, I can work with for a glue that’s tends to run. Titebond isn’t that readily available via the larger chain stores in Aus, but I see the company has a local web presence, so I should be able to find it somewhere.

[KCStudly]

I wouldn't worry about the brand of glue so much. TB2 is water resistant PVA wood glue and TB3 is waterproof PVA; both yellow glues. I think the reason the brand is so popular here is because that is what is stocked at our big chain stores. If you can get it and it is reasonably priced, I would say go to the trouble of using it because it is a good product, but if it is costly there, and you have other brands that work well, feel free to use them.

The TB2 is fairly thick and should not run much on a vertical surface if applied thinly with a roller. When face gluing large wood panels to large foam panels I have found that a thin even coat with no puddles is preferred as it gives the wood a chance to take the moisture from the glue before it becomes trapped. If you use too much glue or have blobs and puddles the glue will kick on the wood before the moisture is gone and you will be left with wet glue trapped by the foam for a very long time.

I would not use plywood for the blocking because that still leaves you screwing into edge grain. I would use your equivalent to 1x nominal boards (3/4 inch actual thickness, or approx. 19 mm).

1/2 inch ply is about the low end limit for pocket screws, IMO.

[grantstew8]

Interesting thread, thanks. TB3 is a d3 or d4 ova flu. (Auto correct???) pva glue... Most external pva glues are d3..it means it has a chemical reaction and does not turn back to mush if it gets wet. I've used evostick external (blue bottle not green) for my build. The data sheets should tell you what kind of glue it is.
If in doubt use Tb3; the last thing you want is it coming apart...

[aggie79]

I respect and admire the authors of the above posts and their builds, but I may offer a slightly contrarian viewpoint for consideration.

My first comment is with regard to adhesives. Unless you are making very tight joinery, as in furniture or cabinetry, I wouldn't use any of the furniture type PVA or polyurethane glues for the structure of your teardrop. I would recommend a construction-type (framing) polyurethane glue such as Loctite PL Premium construction adhesive. These types of products have "gap filling" properties that can accomodate greater tolerances than furniture type adhesive and a long open time that allows you time to position and fasten your framing (especially important if your are building by yourself as I did.)



Regarding the blocking, whether or not additional blocking is needed also depends upon how tight your blocking to skin butt joint is. That said, you will have a much easier time if you provide additional thickness along the 12mm ply. I would use a second thickness of 12mm ply for the additional blocking. As long as you use a suitable adhesive between the blocking and plywood skin - again I would recommend PL Premium - you don't have to worry about the strength of screws or nails into the end grain of plywood. I did use fasteners to attach my wall skins and roof skins to my plywood framing but their use was temporary until the PL Premium had set.

The pictures below show my hatch construction. The parallel "ribs" or spars are plywood. The transverse framing is poplar. (I used Kreg pocket screws to fasten the poplar to the plywood ribs and then later added corner blocking to help hold the framing square while it was being skinned.) I used PL Premium construction adhesive to glue the 3mm plywood skin to the hatch framing. Screws (fastened through the end-grain plywood ribs) were used to hold hold the plywood skin in place until the adhesive set and then they were removed.









Regarding the Kreg or pocket screws, I have a Kreg tool and used it frequently in my build, but I think an easier and stronger method of fastening your vertical framing in the front is to fasten the framing top and bottom through the deck and roof plywood.

[KCStudly]

Aggie79 is the voice of experience and makes a very valid point about the construction adhesive. I sometimes forget about the PL glues because, for the type of construction I have used in my build, I have used very little of it.

[AGM_AU]

Cheers both Grant and Aggie.

Aggie, I had considered construction adhesives, but wasn’t quite sure if they were the best choice. I’d read so much in the forums regarding both polyurethanes and TB 3 that they seemed like a logical choice based on popular and tested use. I’ve used construction adhesives in the past and have been amazed in the strength of the bonds in dis-similar materials (e.g. ply to steel). LOL…PVA (or cabinetry type glues) are also a bit of a “cultural bias” on my part. Dad was a carpenter/cabinet maker who apprenticed in the 50’s. PVA pretty much flowed in his veins (probably along with a host of other chemicals that nobody really thought about until Occupational Health and Safety became a “thing”).

The skinning method you demonstrate in the pictures would work well on the V nose of what I have planned. Thanks for the insight.

It never ceases to amaze me just how much knowledge the participants of this forum have, and how freely and readily they share it. Thankyou all.

[PKCSPT]

"It never ceases to amaze me just how much knowledge the participants of this forum have, and how freely and readily they share it"

They are better than google

[BlackCatRacing]

Strongest glue I have ever found in my 25 years of being a carpenter slash do it yourself-er is 3M 5200. Sticks to about anything, is waterproof (actually cures with water) and stays flexable. There is one disadvantage though and it is that it takes up to a week to cure... If you have the time, or are using screws also I highly recommend it. Best of luck and I like the teardrop design.

[rowerwet]

my tear is entirely built with PLPremium (which may not be sold or sold under the same name in other countries), no screws staples or nails. each joint was screwed together with drywall screws to dry, then the screws were removed and the holes filled. I used the "internal chine log" method. anywhere you want two panels to join you put in a block of wood, 1" wide on the glued face, with one glued face on each panel and every joint oozing PLp to make sure it was full for waterproofing.
While I like it and it is waterproof, I don't know if it saved me much money over marine epoxy and fiberglass tape joints, and it is heavier than epoxy and glass. If I ever build another plywood tear it will be with epoxy and glass joints, that way no joint needs extra wood to reinforce it, and my spars could be made of 1/4" plywood. Super light like a modern stitch and glue boat, or airplane structure design.

[AGM_AU]

Strongest glue I have ever found in my 25 years of being a carpenter slash do it yourself-er is 3M 5200. Sticks to about anything, is waterproof (actually cures with water) and stays flexable. There is one disadvantage though and it is that it takes up to a week to cure... If you have the time, or are using screws also I highly recommend it. Best of luck and I like the teardrop design.

Thanks BlackCat The 3M gear is usually pretty hard to go past in general. I've used a bit of the products that Selleys produce, and always found them to be very effective.
http://www.selleys.com.au/adhesives/construction/

Sika is also pretty amazing. I've seen more than one bond made with these products that was a more than a little hard to break (think running repair on a pick-up tailgate hinge where the bolts rattled loose and were lost, tailgate hinge to skin on auto paint, lasted years and was still tight the day we scrapped the truck at work!).
http://aus.sika.com/en/solutions_products/02/02a012.html

Cheers for the input. LOL, my design may not be as svelte and aestheticly pleasing as some, it's got some of my personality in it. Short, squat and built to a set of parameters to fulfil the task at hand in an efficient manner.