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<DIV><FONT face=Arial size=2><EM>> Bob Hull wrote: <BR>> I've
had a couple of problems with making and<BR>> drilling composite
blocks. Just one to bring up<BR>> with this post.
<BR>> <BR>> On the three composite blocks I have made thus
far,<BR>> (5/16 cap of delignit on multi-lam) I am getting
a<BR>> warping after we expoxy the two together. The plate<BR>> web
screws are able to straighten this out but, this<BR>> isn't what I
want. <BR></EM></FONT></DIV>
<DIV><FONT face=Arial size=2><FONT size=3>Warping <EM>after</EM> laminating the
cap on? Is that to suggest that both the Multilam base and the Delignit cap were
flat prior to bonding? Or do you mean the base was warped after resawing and
planing, and remained warped after capping?</FONT></DIV>
<DIV><BR><EM>> Does this have something to do with how we're resawing<BR>>
or planing the block down to thickness? We're not<BR>> paying any
special attention to how many laminations<BR>> are remaining. I have
heard that this isn't important<BR>> and also the contrary. </EM></DIV>
<DIV><EM></EM> </DIV>
<DIV><FONT size=3>I can only assume (until I hear differently) you planed
down the Multilam (but prior to capping) and found that it developed a good
curve to it. I have had that happen also. I just capped a Mulitlam pinblock with
8 mm Delignit and had the most bowing occur I ever have seen. After
resawing and then planing the Multilam from 37 mm to about 24 mm thick it
developed about a 15 M radius curve (or bow or warp). </FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>I figured I needed to bend the Multilam backwards
and bond my cap to it - and then maybe it will end up straight - because I know
there will be significant springback from applying only one thin lamination.
Well, I bent it back to something smaller than a 15 M radius (curve was
reversed), glued the cap on and ended up with a permanent reverse curve - less
than 15 M maybe, but still too much for me to accept. So clearly, this was
bending the base into too small a reverse radius curve (or arc
actually).</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>So I resawed the cap off, planed it down to 4 mm, resawed
another thin cap and planed it down to 4 mm also and planed my Multilam base
back down to 24 mm. BTW, after cutting and planing the base down to 24 mm, I was
right back to the 15 M radius curve in it.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Boy, am I glad I upgraded from my two-blade 12"
Dewalt hobbyist planer to my new 20" Grizzly planer. That little guy
woulda' been toast running all these pinblock hunks through it!</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>So I bent the Multilam base backwards again - but only a
little bit past flat this time (a 15 M radius over the length of a 60-inch
cord has a height of about 20 mm - the reverse curve I put on the Multilam base
this time had a height in the middle of 3.5 mm). Then I bonded the two 4 mm
Delignit cap pieces to it while in that shallow reverse curve. I used a two-part
urea-formaldehyde resin adhesive that sets up to hard-rubber hardness in three
hours. I unclamped the block after three hours and clamped it to a flat table
overnight. I just checked it today and it came out perfectly
flat.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>So this effort ended up a success, but it sure was a
round-about way of getting there.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>I can only guess that the proper reverse curve to put in the
base with a single 8 mm thick cap would be maybe double my 3.5 mm reverse curve
- or about 7 mm or so (three laminations will have less springback than two).
But that's just a guess. So if I were to try and state some kind of rule to use
when this happens, with the very little bit of data I have - or have estimated,
it might be to bond the cap to a reversed curve on the base that is 1/3 the
height of the unstressed warp/bow/curve. That's probably what I'll try next time
I make another capped block.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Oh, and, of course, cross my fingers! ;-)</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Hope this helps.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Terry Farrell</FONT></DIV>
<DIV><FONT size=3>Farrell Piano</FONT></FONT></DIV></BODY></HTML>