All Replies on Expansion and Contraction..Am I thinking correctly

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Expansion and Contraction..Am I thinking correctly

by CharlesNeil
posted 02-09-2017 06:30 PM

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63 replies

63 replies so far

View diverlloyd's profile


3759 posts in 2464 days

#51 posted 02-10-2017 10:52 PM

I have to answer that meme every time. Even being a meme that is very useful to have answered. It’s just so useful. Not to mention the meme if funny.

Charles will you update us on the finished project

View canadianchips's profile


2632 posts in 3604 days

#52 posted 02-11-2017 01:08 AM

Food for thought.
Everyone has calculated for 25 inch board solid board.
He is using 3 boards…..each one might be 8.3”
Assuming each board moves & expands equally, the above math might be close (we are all guessing)
The Length of that joint is 33.36”
The length of individual boards is 11.31”
I will confident to say the boards are going to check and crack elsewhere before that joint moves !
“Just my thoughts”

-- "My mission in life - make everyone smile !"

View TopamaxSurvivor's profile


18784 posts in 4283 days

#53 posted 02-11-2017 04:10 AM

I just had a quick flashback to Trigonometry. If the width of the boards shrinks by 1/4” (1%) from 25” to 24 3/4”, the miter angles will change by about 0.3 deg each. The gap formed would be almost 3/8”.

This agrees with JayT s result above using Sketchup.

- ChuckV

We have to deduct points because you didn t show your work :)

- RichTaylor

I would have told them I used my slide rule ;-)

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Rich's profile


5142 posts in 1196 days

#54 posted 02-11-2017 04:42 AM

I would have told them I used my slide rule ;-)

- TopamaxSurvivor

Wow. Slide rule. I have to share this. During my time in engineering school at the University of Wisconsin many years ago, I had a recurring nightmare that I forgot my calculator for a test. It came true for an exam in my fields class. If you have studied electrical field theory, you know you kinda need a calculator. This was back in the mid ‘70s, and my professor was a cool guy who said I reminded him of Johnny Fever on WKRP.

The exam was in a lecture pit, and I searched frantically through my backpack. The calculator just had to be there. It wasn’t. I went down to the professor, and asked if there was anything he could do to cut me some slack, like let me take it later. He pulled open his drawer and said you can use one of these. Two Picketts. Well, I’m a Post man myself, but I figured I could make it work.

You see, I found a slide rule laying around when I was in 4th grade. Without instructions, and no one to teach me, it took me several months of picking it up, being clueless, picking it up again, until one day I put the index on the C scale on 2 and saw 6 on the D scale opposite 3 on the C scale. It was a magical moment. I asked for a Post Versalog for Christmas my freshman year. I even refused to use a HP calculator when they got affordable at $500 because “you don’t need all of those decimals.”

This fields exam was a little scarier, with some very complex math, but I completed the exam and when I handed in my blue book, he was blown away. He said he was just pulling my leg and figured I had no clue how to use a slide rule. I got a 97.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Aj2's profile


2650 posts in 2405 days

#55 posted 02-11-2017 05:46 AM

I agree with jay and Chuck.. so its as i described above, it will float .. did a quick test run with the dogbones and a few pocket screws and dominoes, joint looks good,

Thanks guys, guess I wasnt thinking correctly… old dogs and new tricks.. thanks again

- CharlesNeil

That’s a very cleaver solution it just might work.
Wood can be both mysterious and amazing.
Good luck


-- Aj

View ArtMann's profile


1462 posts in 1423 days

#56 posted 02-12-2017 02:30 AM

I have seen many, many maple counter tops built up like a work bench top. Of course some have mitered corners. I don’t recall ever seeing one where the miter opened up due to expansion and contraction. I don’t see how that would be worse than 3 glued up walnut boards. I would definitely use mechanical fasteners on the under side like those used to hold mitered Formica counter tops. I might even be tempted to use long pocket screws. I would put silicone rather than glue in the crack. It will stop moisture from working its way to the under side and is still flexible enough to absorb a little movement without coming apart. That is how it is done with laminated counter tops.

View 000's profile


2859 posts in 1506 days

#57 posted 04-25-2017 04:14 AM

Just curious how progress is going. Any results yet?

View Joe Lyddon's profile

Joe Lyddon

10867 posts in 4659 days

#58 posted 04-25-2017 06:47 AM

Artman... Sounds like you’re Right ON.. to me… All makes sense…

-- Have Fun! Joe Lyddon - Alta Loma, CA USA - Home: ... My Small Gallery:

View jerryminer's profile


960 posts in 2048 days

#59 posted 04-25-2017 09:44 AM

I have seen many, many maple counter tops ….. I don t see how that would be worse than 3 glued up walnut boards.- ArtMann

The maple counter tops I’ve seen (and built) have typically been “edge grain”, aka quarter-sawn.

These walnut boards will be flat-sawn.

The FS walnut is likely to expand/contract at about twice the rate of the QS maple

-- Jerry, making sawdust professionally since 1976

View benchbuilder's profile


285 posts in 3057 days

#60 posted 04-25-2017 10:35 AM

You coild use a quarter sawen pice about 2” wide at the miter ( between the two mitered pices) with a slot in it on both sides for the wood to movr in and it wont look as if its coming a part.. With the two miters fitted into the center 2” pice each pice can move without messing up the joint.

View CharlesNeil's profile


2501 posts in 4477 days

#61 posted 04-25-2017 12:09 PM

They have been in for several months now and no issue , did the dominoes in slotted mortises , just used them loose for levelers , then did the dog bones , to pull it together, all is good thus far, of course i finished every thing, ends underside .. sealed it well.. time will tell

View pontic's profile


722 posts in 1215 days

#62 posted 04-25-2017 01:13 PM

yes, they re going to move since they are solid wood.. no doubt.. I think it all depends on the moisture content of the boards and if some are as dry as the others.. if it were me, I woukd miter them, route for a spline to go the width of the miter, but stopping anot inch or so from the edge.. and use those “T” bolts to draw the joint tight and use no glue.. the spline and T bolts should keep the seam tight and with no glue, allow for movement..

- RBWoodworker

What he said.

-- Illigitimii non carburundum sum

View jerryminer's profile


960 posts in 2048 days

#63 posted 04-25-2017 09:48 PM

Charles—Thanks for the update. I think we all want to learn from your experience with this. I would love to have you report back in a year or so (after a full cycle of seasonal changes).

The dog bones should hold the miter together. I’m curious about how far the end of the countertop “swings” over time.

Again, thanks for sharing

-- Jerry, making sawdust professionally since 1976

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