I'm often asked about using plywood for making a bandsaw frame I always advise it against it
because half the grain is in the wrong direction so it won't be a strong or as stiff but how much
weaker is it so I'll use my joint strength tester to test a whole bunch of pieces of
plywood particle board OSB MDF and solid wood in comparison each of my samples is
five centimeters wide and the supports here are 15 centimeters apart or 2 inches and six
inches first test 15.2 millimeter piece of plywood along the long grain pretty good
[Music]
sailing here 265 kilograms next up a slightly thinner piece of solid Pine
but I had programmed the machine to only go to 300 kilograms and then back off just to
protect it physically so I bumped that limit up to 350. oh and the gear is coming off the motor
okay that's good and broke this didn't actually break across all the way because I'm only applying
force in one spot here so I need to put this thing on top of my Pusher to spread it out a bit more
300
okay that exceeded the maximum Force
so this piece is half the width because my tester isn't strong enough
foreign
this was marginally thinner and half the width of the plywood but almost the same failure strength
now that plywood has three thick layers along the length of it let's test it in the other direction
158 versus 265 not a bad showing for cross green let's try some solid wood cross grain [Music]
foreign thicker than this and half the width its braking force was less than
a fifth so cross grain this is less than a tenths the strength of this stuff long grain
next test some Baltic birch plywood
that max out 350 kilograms that my thing applies that's close to 800 pounds so I bumped up the
maximum allowable Force again this time to 380 kilograms that's over 800 pounds
needs a bit of help the motor's starting to skip at those forces okay we broke it even though this
Baltic Birch is a fair bit thinner than this stuff it failed at a much higher force it should have
failed that half of this Force if it was by thickness and such the same strength as this
I like to use this stuff because it's got thin Plies and it looks a bit like Baltic Birch but
not the same quality overlapping pliers here for example and also probably popular instead of birch
foreign about the same strength as these pieces of plywood even
though it's actually about two millimeters thicker
I took all my fill numbers and thicknesses for the sample so far and worked out how
strong those would have been if they had been half an inch thick and that's based on the
assumption that the same piece of wood twice as thick would be four times as strong which
is also why it would oriented this way if you push down is much stronger than flat like this
so this is the five play relatively thick stuff this is some Thin plate plywood same relative
strength then this is Baltic Birch and this is solid Pine so you can see the Baltic Birch in
a solid Pine are about the same Baltic Birch being a bit stronger whereas these ones are
half the strength of solid wood and then these two are cross grain tests and you can see that
contributes hardly anything so as expected plywood is half as strong because half the grain is in
the wrong direction the Baltic Birch is strong because the Birch itself is just a stronger wood
and I said the Birch is a stronger wood well let's test some Birch
got three samples of birch here of different dimensions and adjusting for the dimensions
they all came out very consistently and putting those on my graph this is
the solid Birch which is stronger than the Baltic Birch but not twice as strong but my
understanding is that Baltic Birch is actually a particularly good sort of birch which is why
it comes from the baltics but now let's try the particle board OSB and MDF foreign [Music]
I plugged in the numbers for a particle board MDF and OSB and this is what it looks like on
my chart adjusted for size the particle board is maybe a third to a quarter of a strength
on average of the plywoods so quite weak as expected the MDF did better half as strong
as my weakest plywood samples and then the OSB actually has an orientation so across the grain
the tests were quite weak along the grain this is actually quite comparable with the plywoods
although one of my long grain OSB pieces failed relatively weakly so in summary particular Bard
is just crap for strength it's maybe a third to a quarter strength of plywood MDF is better possibly
half the strength of plywood OSB as long as it's along the grain is quite comparable to plywood
most of the time but it's inconsistent but across the grain it's only half as strong as plywood