I glued up two three inch strips of baltic birch plywood intended
for special-purpose fence. After attaching a 3/4" strip of ash to
the top, the damn thing warped. Not severely but enough to annoy
me. Any ideas why this would have happened?
And, if I leave a forty pound cement block resting on it
overnight, is there any chance of "unwarping" it? Or is it a lost
I thought the baltic ply was supposed to be extraordinarily
stable but this is my first time building a jig with it.
Your insights are appreciated.
firstname.lastname@example.org (Keith Hanlan) wrote in
Did you glue the ash to the baltic birch ply glueup, perhaps?
Was the glue waterbased?
Maybe the ash has different expansion characteristics than baltic birch
ply, particularly since it still has 'grain'.
The advice to veneer both sides of a piece is so that the veneer won't
warp the substrate.
If you set it down on edge in a well ventilated corner of the shop for a
few days, it may settle back down. Then, perhaps, joint the face
lightly, to establish 'flat'. Check again in a few more days. Then
shellac everything lightly, wax the surfaces, and enjoy.
I guess that's all it takes. The ash had been well-dried but I
glued it shortly after ripping the 1.5" strip from a 5" strip.
That was probably my mistake. I should have let the strip relax
after disturbing its equilibrium and then jointed it again.
My dumb mistake but that's how I learn...
I think that that advice only really applies to wide surfaces. I
was just covering up the edge of the baltic ply.
That's not really an option for baltic birch plywood. The outer
veneers are too thin.
That's a good idea. I think I'm going to need to finish my jigs
from now on.
Thanks for your advice.
I wanted to put a 3/4 x 3/8 dado in the top for a t-slot extrusion.
I though that the ash would be a better seat for it than plywood.
I also completely forgot that I now have a dado blade set for my
table saw (I've only used it twice in the past six months) and didn't
like the idea of forcing a router bit through that much plywood glue.
That's a yes.
Were the plywood strips cut the same way and glued symetrically?
E.g. if the plywood was A-B you'd want to glue A-side to A-side
or (more likely) B-side to B-side and have parrallel grain on
both sides of the glue joint.
If that is how you did the plywood then I concur that the ash
must have crooked (crook is at right angles to bow)
If it were me, I'd trash the existing and start over.
Call it tuition if you want to fell better about the loss<G>.
This time, I'd cut some rabbits in both the ply and the ash, then glue
it up as an assembly.
Trust me, it won't warp.
That's a good idea. Having a four-inch wide beam would make it
easier to place the second fence perpendicular to it. (What I am
trying to do here is have one extra-long fence that attaches to my
current mitre fence and then have a second extra-long fence that I
can add to and remove from it at exactly 90 degrees. I want to do
this so that I can cut mating oblique compound mitres at the
"right" end of one board and the "left" end of the other *without*
adjusting either the mitre or the blade. This would be easy with a
dual-bevel compound mitre saw but I can't afford one right now.
The original reason for the ash strip, which I hadn't mentioned,
was because I wanted to put a 3/8" x 3/4" dado along the top for a
T-slot extrusion. I though that putting it into the edge of the
plywood (even doubled to 1.5" thick) wouldn't be a good idea. I
was probably wrong on this count. I also planned to put a vertical
post into each of the fences so that I could run something rigid
between the two posts to fix the two fences at 90 degrees. I think
now that I'll use a square sheet of plywood that has brackets that
hang over the top edge of each fence.
Time to sit back and think a bit harder about what I'm trying to
do here... (persuade SWMBO that $400 for a nice mitre saw might be
a good investment...)
consider a miter sled. if you need complementary miters at other than
45 degrees, you could make the head swivel. I made mine from 2
triangles of 3/4" baltic birch ply (face laminated!) on a 1/4" melamine
bed with baltic birch for the runners. 2 runners seems to work better
for me than 1. the triangle of BB has a hole drilled in it to get the
head of a bar clamp into to keep the workpiece from slipping around
during the cut.
Keith Hanlan wrote:
no,you were probably right on this count.
I run one face of the box beam long to make a lip I can clamp stuff to.
I'm not a big fan of aluminum t slot extrusions. the inclusion of a
high thermal coefficient of expansion but low humidity coefficient of
expansion material like aluminum into a low thermal coefficient of
expansion but high humidity coefficient of expansion material like wood
makes me nervous. but then I live in Arizona.
mostly, though I don't like aluminum's tendency to gall.
Keith Hanlan wrote:
that's probably a good approach.
Keith Hanlan wrote:
my table saw with a miter sled way outperforms any miter saw I have
ever used. the mass of the saw, beefier arbor, bigger motor belt drive,
etc... all add up to a much better cut. I have _seen_ miter saws that
will outperform my sled setup- but they cost more than my truck. heck
the blades alone cost more than my miter saw. my bigger miter saw has
deeper cut capacity than my table saw with a miter sled setup, but the
cut quality is less than stellar.
consider investing in a miter trimmer instead.
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