Floating Tenon Problem

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I would, but this isn't the first time I have noticed this. It has happened with maple and cherry as well. I just thought I would finally post and see if I am the only one that has experienced this, AND it looks like I am not alone (see Rick above).
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Swingman wrote:

Leon,
I use a Multi-Router as well, so I don't think it's a method question.
Rick http://www.thunderworksinc.com
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"Rick" wrote

Rick,
Beautiful work! Your website is elegantly done (the photographs of your work are stunning), and your "What I Believe" statement is reflected in everything you see therein.
All in all, visiting your site and seeing your work is an inspirational experience, providing food for thought for every serious woodworker. Thanks for the sharing!
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wrote:

Howdy,
Here's my take:
I believe it is an issue of differential compression -
Suppose we have a block that measures 2"x2"x2", and try to compress it.
The block will compress less when the force is applied to the end grain.
I suspect that then you are cutting the end grain mortise, the forces of each cut (yes, they are happening fast, but they are really a series of individual cuts) compresses the stock more than when cutting into the cross grain. After each cut, and the compression it causes, the wood springs back to its original position. Because of that differential, the end grain mortise is smaller than the cross grain mortise, even though they are cut with the same setup.
These things are hard to describe. I hope that what I've written makes some sense.
All the best,
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Kenneth

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Yes, that does make sense! Thanks for posting.

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*SNIP* of interesting mechanical hypothesis
That could could have some validity, except that those using the Multi- router find that to be untrue. Same exact approach to the application except the difference in the jig. If they don't squeeze up on the Multi-router (read: tank-like jig) then I am thinking as mentioned above it could actually have to do with the cutting itself.
It isn't a hard stretch to think that (especially a mortise cut with a router) would deflect away from one side or another. And if you clean up the middle as you go, the bit might lean a thousandth or two towards the empty area, away from the solid sides. Remember, if it only leaned ONE thousandth in on each side, that would make it two thousandths in aggregate, and that would make a really snug fit.
Hmmm.....
Robert
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On Tue, 4 Mar 2008 18:56:00 -0800 (PST),

Hi Robert,
When I suggested the compression idea, I was not thinking of the pressure of the jig, but the pressure of the cutting tool itself...
All the best,
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Kenneth

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My thoughts exactly... Kenneth beat me to the punch.
I think that the longitudinal wood fibers are "compressing" slightly as the cutter makes a "shearing" cut along the same axis as the grain.
One way to test this theory would be to make both the end grain and cross grain cuts and then measure the mortises with a dial caliper. I wouldn't be surprised if the difference is more than a few thousands... and that would confirm this theory.
The remedy I favour is a swipe or two with a sharp shoulder plane. Veritas makes a nice one:
http://www.leevalley.com/wood/page.aspx?c=1&pH430&cat=1,41182,48945
Cheers.
Michael
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On Wed, 05 Mar 2008 04:20:47 GMT, "toolman946 via

Hi Michael,
I'm sorry I beat you to it... <g>
But if we are correct, another remedy would be a sequence of lighter cuts.
All the best,
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Kenneth

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wrote:

As long as you're testing this, test it with a straight cutter vs a sprial cutter (OP stated he was using a spiral cutter). I would think that the compression, if present, would be worse with the straight cutter.
my $.02, ymmv, etc....
jc
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I already do that. No remedy. You still might be on the right track though.

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No prob... great minds think alike! (lol)
Your's is probably younger, though... hence the speed.
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Hey, Kenneth.
The point I was thinking of when bringing up that particular jig is that it holds the router in a perfect position, rock solid, and creates a near perfect cut.
Since the only voice we have heard from that indicates no difference in the fit from end cuts to face cuts when using that particular jig, I suspect that the jig may have something to do with it.
In the end, I don't really know. It is too easy to run the tenon over the belt sander for a great fit.
Robert
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