I am just getting into clamping up boards for table tops, etc..
Aren't you supposed to make the jointed edges straight, so the you don't
NEED much clamping pressure?
I have a limited variety of bar and pipe clamps. Some are more rigid than
others. Sometimes I have to use cauls to keep things flat because some of
my clamps do bow somewhat. I assumed that I just have to work harder to get
everything straight and to do the gluing and clamping immediately after
final jointer work so things don't have a change to deform overnight.
Am I just putting too much effort into making straight boards in the first
place?
Am I wasting too much wood trying to get things straight? (I only have a
jointer with a 4 foot bed.)
If I spend the money on heavy duty clamps, then can I get away with wavy
boards, or is there a downside to using huge clamping pressures later on?
Pete Stanaitis
---------------
Just my opinion on a few of your thoughts....
I don't think a woodworker worth his salt is buying heavy clamps with
the purpose of joining wavy edged boards. Most do their very best to
produce a straight board in the first place. The straighter the boards,
less clamping pressure you need, obviously. I stopped using the jointer
for edge panels once I got a decent table saw (& fence) and glue-line
blade. A saw with enough power, properly set up to be perfectly square
and parallel, with a good, sharp, rip blade will give results that will
allow you to skip the jointer.
Don't looks at cauls as a "have to" tool. Instead, look at them as a
"get to." Like any other jig or tool, they make the job easier and
improve the results.
I also have a limited supply of clamps. Last time I glued up some wide
panels, I did something that made it easier with fewer clamps. I only
glued panels wide enough to fit through my planer. I then ran the
narrower glued panels through the planer and glued them together to
their final, or near final width. I used a card scraper on the
remaining glue joint to feather the edge perfect where it wasn't. I
found this to be a very efficient and less stressful way to manage the
process of making wide panels without dozens of large, heavy cabinet
clamps. Also, I found it easier to cut the panels to final dimensions
after gluing them up a little larger. Under some circumstances, this
also makes things less stressful and more efficient.
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
...
Test data indicates that glued joint strength increases w/ higher
clamping pressures up to very high values (US Forest Products Lab and
others; DAGS if you're really into the details. I've posted these links
in the past in this newsgroup so the google archives are another place
to look; again only if you really care; in general I'd say it's not of
significance to worry about).
The thing about the clamping force is that the actual pressure applied
along the length of the board between clamps drops off w/ distance so to
get a significant force along the entire length requires some way to
either distribute that force more uniformly, increase the applied force
and/or use more clamps.
And, of course, the quality of a joint is definitely dependent on the
preparation--a pair of boards that aren't well fitting may be brought
together by force and the glue will hold them together when dry and the
clamps removed but that residual strain will still be there and be a
source of movement and/or even joint failure w/ time.
So, the answer is that yes, you should try to make joints fit and yes,
best results are still obtained when clamping pressures are fairly high.
But, you generally don't need to bend a stout clamp, either... :)
--
I've seen and read these reports, but what we really have to ask
ourselves is, "is it really applicable to the project?"
For your typical woodworker's panel project, a table or a cabinet door,
how strong does the joint really need to be? We already know that most
panels will split in the middle of a board instead of the glue joint.
We already know that most edged glue joints aren't being used for any
kind of real load bearing.... so again, why bother with the ridiculously
high clamping pressures?
It's akin to the arguments we get into about accuracy. Do we need
accuracy in woodworking that gets down to the width of an atom? No, we
need accuracy somewhere around the amount the measured distance will
increase or decrease to to expansion and contraction of the wood. We're
not building o-rings for the space shuttle. :-)
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
...
...
Well, if I didn't put enough caveats in for you the last sentence above
should have done.
But, my take is if you're bothering to do a glueup for anything that's
not just throw-away craftwork, why not make it be "the best it can be"
or why bother? I'm convinced from the difference between my early and
later work's longevity (and I'm enough of an ol' phar... by now that
early stuff is past 40 which is starting to get enough to see what
did/didn't work) that glue joints last longer w/ higher pressures and
better fitting than without as well.
When I first began, all I had was some pretty light Big Lots-type bar
clamps and while the old Craftsman jointer was set up well, some of
those panels have developed problems w/ age whereas later don't show
signs as of yet...
So, my general advice to OP is my stand on the subject...I'll agree that
the extremely high pressures studied under some of the conditions by US
FPL for commercial manufacturers are beyond the need of individuals, the
general trends shown there are worthy of noting.
--
The subject comes up again and again and for a beginner reading this
thread, it's worth presenting both sides, again.
Because you reach a point (I would argue, quite soon) of diminishing
returns. Using your argument, we should all be using a micrometer for
all our measurements. We should be be sanding down to 1500grit on
everything. Why not? It's smoother.
I'm not saying glue joints don't last longer with higher pressures. I'm
saying, you reach a point where it doesn't matter at a much lower
pressure than you'd think.
Maybe it's not the gluing pressure you used. Maybe it's all the other
factors that come into being when you're less experienced.
My only point.
... and only noting. :-)
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
First of all, your boards should not be straight to join them.
They should bow in a little toward the center. So that the ends touch
first. The reason is that during seasonal changes shrinkage happens at
the ends first, and if perfectly jointed the boards will split at the ends.
After jointing on the joiner, I hand joint the bow in..
You always need to apply proper pressure to glue up boards. Not light
pressure. Heavy pressure. I use light pressure to align... Then heavy
to clamp.
On 6/16/2012 12:03 PM, Pete S wrote:
I would guess that depends on where you live.
If you live in Nevada not an issue (arid).
If you live in the North East... ISSUE.
The humidity here in the summer and the cold dry air in the winter makes
it a bigger deal.
If you live somewhere that its always humid no big deal either.
On 6/17/2012 12:41 PM, -MIKE- wrote:
"tiredofspam" wrote in message
I would guess that depends on where you live.
If you live in Nevada not an issue (arid).
If you live in the North East... ISSUE.
The humidity here in the summer and the cold dry air in the winter makes
it a bigger deal.
If you live somewhere that its always humid no big deal either.
==========================================================================See my post on the subject.
On 6/17/2012 12:41 PM, -MIKE- wrote:
That's the the issue I'm talking about.
No one argues RH changes cause wood to expand and contract.
What is not universally excepted in woodworking is the practice of
joining bowed instead of straight boards to keep them from cracking at
the ends.
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
"-MIKE-" wrote in message
On 6/17/12 11:03 AM, tiredofspam wrote:
Acceptance or practice of that theory is hardly ubiquitous in the
woodworking community.
======================================================T
Quite true. I have seen some people do it that way but the vast majority get
them strait as possible before glue up. My sister has a table that my father
built when I was 1 year old in Germany. We had it with us in Ethiopia,
Turkey and Japan. It has also been from coast to coast in the U.S. It now
resides in Texas. Beside the dings it has picked up over the years, it is in
perfect shape. Nothing loose and no splits or cracks. I have a coffee table
and end table that he built in Japan in the mid 70s. They went from there
(humid) to eastern Washington state (very dry) to western Washington
(humid). They too are perfectly sound. My father believed in strait and
tight fitting joints. So do I.
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
That's what's beautiful about this hobby and country.
You can believe or do what you want.
To each his own.. I'll still prepare mine as I do. It works for me, and
has never split. I have refinished things that have split (none that I made)
A student's desk.
A cutting board. (really gets wet then dry quickly)
A table.
I chose to believe that my repairs by cutting down the split, then
jointing and springing helped. They have not failed since.
Sorry if I misspelled or are unclear, I have one eye patched right now..
I think I cut my cornea again... damn..
On 6/17/2012 4:05 PM, CW wrote:
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