Simply put (…and stop me if you've heard this one before), the fibers of a dowel are parallel to the body of the screw, and the thread of the screw is nearly perpendicular to the wood fibers. If (in the turning of the fastener) the thread doesn't actually sever the fibers, they will be severely compressed. This happens for each of the many rounds of thread the screw root has. Either way, their ability to withstand the (extractive) tension of the threads drops far short of what's involved in a customary tightening down of the fastener.
In short, the weaker of two grain orientations.
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William Ballard RPT
WBPS
Saxtons River VT
802-869-9107
"Our lives contain a thousand springs
and dies if one be gone
Strange that a harp of a thousand strings
should keep in tune so long."
...........Dr. Watts, "The Continental Harmony,1774
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Original Message:
Sent: 04-19-2022 00:37
From: Jon Page
Subject: Filling wood to redrill for lid hinges
oyou are re-writing wood working technology? End grain does not hold screws well. That has been known for a very long time. The only way for a dowel to add strength is to install it perpendicular to the screw hole, this way the screw goes thru the dowel.
I have done this for music panel screw holes. When the hole is stripped and the area compromised, I'll drill from the bottom of the panel to install a dowel. This also adds strength to the compromised area. I've even installed two dowel for the screw to bite into and to reinforce the area. Finish is not an issue on the bottom of a music panel.
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Regards,
Jon Page
mailto:jonpage@comcast.net
http://www.pianocapecod.com
Original Message:
Sent: 04-18-2022 21:32
From: David Armbrust
Subject: Filling wood to redrill for lid hinges
The grain orientations of a dowel is perfect for repairing a stripped screw. Think of the wood as tightly bundled straw fibers. The screw threads bite into the fibers and you would need to pull the entire plug out for it to fail. This will not happen because the glue is holding the dowel tightly in place. The reason this glue bond is so tight with a dowel plug is that we are glueing face grain to face grain.
Think of how an hammer head is attached to a hammer handle. The typical metal wedge used in a hammer handle end grain cause the wood to expand slightly and tightly hold the head to the handle at the same time it is holding the wedge in place even without threads on the metal wedge! The same thing happens when we drive a screw into the wood end grain. Of course as I previously stated you need to drill a proper size hole for the screw or you risk splitting the dowel plug. Again imagine a hammers metal wedge that is too large or too small.
If the preference is cosmetic instead of strength, such as when we are trying to hide a screw with a wood plug then it is better to cut a plug into face grain as Jon suggest as end grain will absorb more finish and will make it much darker and more visible than the face grain plug. The face grain plug glue bond will also be weaker because you are gluing end grain to end grain which never works well. This is because end grain soaks up the glue and does not leave much glue at the glue joint.
As another example of how weak this glue bond is when you want to remove a face grain plug that is hiding a screw that you now need to access, just drive a screw into the face grab plug. It will hit the hidden screw and it will easily break the glue bond and pop the plug right out.
David Armbrust
Sarasota Florida
Original Message:
Sent: 4/18/2022 3:25:00 PM
From: Jon Page
Subject: RE: Filling wood to redrill for lid hinges
Do not use a hammer shank or dowel. the grain orientation is wrong. You'll need to cut plugs for a proper repair unless you use leather or epoxy.
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Regards,
Jon Page
mailto:jonpage@comcast.net
http://www.pianocapecod.com
Original Message:
Sent: 04-18-2022 08:19
From: Scott Cole
Subject: Filling wood to redrill for lid hinges
Greetings,
We need to fill and redrill the enlarged screw holes for a square grand lid. What's the current thinking on how to fill in the holes? Epoxy? Wood filler? Titebond?
thanks!
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Scott Cole, RPT
rvpianotuner.com
Talent, OR
(541-601-9033
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