First myog backpack test (thanks to David Chenault)

[Ivo Vanmontfort]

I would like to thank David for his insights.
I used his experience to make my own prototype
of a backpack.

Cheap material is used for this first test.

For the frame, I used laminated oak.

Strong and not as heavy as aluminum.
His last myog backpack article was the basis for my design.
Supplemented with the article "Contoured side panels for improved load carry in frameless packs"

Some thoughts in dutch on my blog

[Nathan Meyerson]

Looks great! And for your first, it looks very well made.

Cheers!

p.S. What kind of sewing machine do you use?

[Ivo Vanmontfort]

I work with a singer samba 4 machine

[Nathan Meyerson]

No way! That's the first sewing machine I ever called my own. I pulled mine out of a dumpster my freshman year of College.

Treated me well for years. Struggled sewing through more than a couple layers of heavy fabric and working with Foam was a pain, but there are ways around those issues.

Exciting to see that same machine Again. Mine was given to a friend a couple years subsequent when I picked up a Pfaff 130.

Nowadays I can't imagine using anything non-industrial short of a sail rite.

But I still remember the good old days…

[David Thomas]

Great job! I've always like the laminated wood stays when people go that route.

Making the thin layers of oak is quick enough on a table saw (although you make more sawdust than veneers). But here are a few other ideas:

Other, lighter density woods will give you the same stiffness in only a little more thickness and, overall, save weight. No one uses oak in an airplane, right? For highest strength to weight, they use spruce (specifically Sitka Spruce).

A layer of fiberglass on each side of the wooden stay really leverages the strengths of each materials – wood and FG.

An easy source of wood veneers without sawing your own is 1/8" plywood. I keep a sheet or two of it around at all times for various projects, but another, potentially free source of veneers are any interior doors or closet doors – they are all hollow-core with thin veneers glued to some cardboard blocking on the inside. I dumpster-dive for those, made easier because our trash transfer station lets you put useable stuff to the side for others to salvage. I've made foam-core ladders (every light weight) and BIG fishing nets (we're allowed to catch salmon in a 5-foot-diameter net) by laminating strips of that very thin plywood. Usually, it is 3-ply and 2mm, 3mm or 1/8" in thickness.

[Ed T]

Really nice looking work!
Ditto on the selection of wood.
Best strength/weight ratio is found in softwoods.
Western Red Cedar could be a good choice for resisting rot.
It's generally not as strong as spruce though.
With the softwoods the selection of the piece itself and how it is sawed is critical.
You want quartersawn with tight grain for highest strength.

[David Chenault]

Briljant!

[Ivo Vanmontfort]

I

Thanks for the comments

I like how kifaru makes his stays (wood+carbon)

I was thinking about using plywood
but I had my doubts about it.
In plywood, the veneer is crosswise bonded and not in the same direction.
What is the impact on the strength?
I soak the wood a short time in water to give it shape.
Sometimes the glue they use for plywood is not very water-resistant
But maybe I should giving it a try.

[Ken Thompson]

Fjallraven uses laminated birch stays. Lighter and better carbon footprint than aluminum they say.

[[ Drew ]]

Whoa, those Kifaru stays look fantastic. Available for purchase?

[Ivo Vanmontfort]

I do not know.
but when myog, then it's adjusted to my back.
You can not curve a Kifaru stay.

[David Thomas]

>"In plywood, the veneer is crosswise bonded and not in the same direction.
What is the impact on the strength?"

The thin plywood is usually 3-ply, so the outer layers are going lengthwise, while the inner layer is going crosswise. That does help reduce the chance of it splitting (if you haven't bonded it to FG or CF). It would reduce the longitudinal strength a bit compared to all grain going lengthwise, but the inner layer's effect as a spacer – getting your outer layers further apart – is a huge help in strength and stiffness.

>"I soak the wood a short time in water to give it shape.
Sometimes the glue they use for plywood is not very water-resistant"

The really nice stuff is knot-free, BS-1088 Marine Okoume as is sold for constructing boats (I've made four).

But I've had no problems with "door skins" during the assembly process nor in extended outdoor use (some bits have been out in the sun and rain for 5 years now), if I coat it thoroughly with a decent quality finish. Stepping up to a "spar varnish" and those pieces and boats look fine now, 15-20 years later.

But my best answer is: experiment. Slap together a stay from solid wood and another one from glued-up plywood strips. Quick & dirty. Weigh them and then test them to destruction on a bathroom scale. PM me with dimensions if you want some plywood strips mailed to you.

[Ivo Vanmontfort]

Recent new attempt
Thanks David, 3x 3mm Plywood strips were the way to go.
They are not much lighter than oak (240gr/for two 650x10x25 mm stay’s)
took the easy way: no carbon fiber inside
Some pictures and a link to some (dutch) thoughts

[Author]

Posts