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Are two 3/4' boards glued together stronger than an 1 1/2' board?

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Forum topic by steveinaz posted 09-03-2015 12:30 AM 1279 views 0 times favorited 8 replies Add to Favorites Watch
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steveinaz

17 posts in 636 days


09-03-2015 12:30 AM

I’m building my first chair. I was able to purchase used 3/4” red oak stock for next to nothing. I thought if I glued the stock up I could end up with enough 1 1/2”stock to build the chair. The glue cost would be insignificant because the wood cost was so low. I’d get practice flattening boards with my jointer. If the project blows up my out of pocket would be relatively small. And I thought the stock would actually be stronger. I will likely have finishing issues, but that doesn’t concern me. Do I have this right? All help is appreciated.

-- Steve in AZ


8 replies so far

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WDHLT15

1572 posts in 1937 days


#1 posted 09-03-2015 12:53 AM

Should work fine if you match the grain and sand well to get rid of any surface glue.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln. hamsleyhardwood.com

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crank49

3980 posts in 2432 days


#2 posted 09-03-2015 12:58 AM

May be about the same strength, but the big difference is in warp resistance. You can arrange boards glued together to cancel out each others propensity to warp, twist or bow.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View MrUnix's profile

MrUnix

4209 posts in 1660 days


#3 posted 09-03-2015 01:09 AM

Laminated wood beams are stronger than solid ones, so I don’t see why it wouldn’t be as good. Although,as mentioned, finishing it so it’s not noticeable will take a bit more effort.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

View pintodeluxe's profile

pintodeluxe

4853 posts in 2274 days


#4 posted 09-03-2015 01:12 AM

I haven’t had any warping issues with chairs, because it is an indoor application. Laminations are important for projects exposed to the elements, like front doors.
Your idea will certainly work, and I debated on doing that myself. In the end I went with solid 6/4 stock because the joint lines can be hard to hide (on the back legs / backrest for example). If you look for rift sawn grain pieces to make your glueup it might work out okay.

Good luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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Matt Rogers

69 posts in 1431 days


#5 posted 09-03-2015 01:24 AM

Laminated wood can be stronger than solid, but that is not always the case with only two boards. Saying that all laminated wood is stronger would mean that I could take two boards with bad grain runout, huge knots or checks and glue them together and it will be stronger than a solid piece of wood with perfect straight grain and no knots. The glue line add nothing to strength, and must be a perfect glue-up or it will actually weaken the piece.

A perfect straight grain piece of red oak without knots and from a tree with good growth will be as strong or stronger than two pieces of red oak glued together. It may be less stable, but that is also up for debate as solid wood can be quarter sawn and oriented for stability where as a laminated piece may have a flat grain board glued to a quarter sawn board, resulting in different expansion and contraction on each side.

Laminating the wood reduces the chances that flaws continue very far through the wood. It is the same idea that fiberglass uses. The glass fibers are so small that they cannot contain the microscopic flaws that cause glass to crack and break, so the material reaches much closer to its theoretical strength than a large piece of glass. So taking wood and cutting it into several small pieces and mixing them up distributes the flaws in the wood and places a flaw next to a stronger piece of wood reducing the effective flaw length and impact. Plywood is a different story because half of the wood runs in a different direction, so it is not as stiff or strong as it could be, but sometimes the strength gains from the lamination can still make good plywood very stiff.

-- Matt Rogers, http://www.cleanairwoodworks.com and http://www.cleanairyurts.com

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RobS888

1984 posts in 1306 days


#6 posted 09-03-2015 02:07 AM

I’ve had good results with titebond transparent.

http://www.amazon.com/Franklin-International-6123-Titebond-8-Ounce/dp/B006R9JGQC/ref=sr_1_8?s=hardware&srs=3028778011&ie=UTF8&qid=1441246000&sr=1-8

EDIT:

Here is a shot of a leg I made using the transparent glue. The white oak was from the same board and I tried to match the grain well. You can see on the far right there are 2 boards, but not so much in the rest of the piece. I was so impressed I sent a picture to my wife.

-- I always suspected many gun nuts were afraid of something, just never thought popcorn was on the list.

View steveinaz's profile

steveinaz

17 posts in 636 days


#7 posted 09-03-2015 02:59 AM

Thanks so much for all the great replies. I can’t say enough good things about this site and the people on it.
Steve in Scottsdale, AZ

-- Steve in AZ

View Kazooman's profile

Kazooman

624 posts in 1414 days


#8 posted 09-03-2015 11:57 AM

One thing to consider. You mentioned that this is used stock. What sort of finish does it have on it? If it is something that penetrated deep into the wood then the glue joint may not have as much strength as one made with new stock. You will have to joint and plane the material to try to get a fresh surface. The 3/4” stock may end up as 1/2” .

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