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Will a tongue-and-groove correct for slightly bent boards?

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Forum topic by Ryan Sandler posted 07-19-2019 01:14 AM 764 views 0 times favorited 15 replies Add to Favorites Watch
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Ryan Sandler

29 posts in 902 days


07-19-2019 01:14 AM

Topic tags/keywords: pine joining tongue and groove question

I’m working on a desk top that I’m constructing out of reclaimed pine heartwood floorboards. The thickness of the boards is a little on the thin side, so I’m trying to minimize planing as much as possible while still ending up with a flat surface. The trouble is that some of the boards have bowed a bit over their length.

Now, I was planning on joining the boards by cutting a short (say, 1/8 inch) tongue-and-groove, primarily to help with alignment (again, in hopes of minimizing planing of the glued-up panel). The bowed boards are flexible enough that I’m pretty sure I could bend them by hand enough to get the tongue-and-groove to seat. Would this work, long-term? Or will this just cause problems, such as warped panels, broken joints, cracking due to wood movement, etc.


15 replies so far

View BuckeyeDennis's profile

BuckeyeDennis

34 posts in 146 days


#1 posted 07-19-2019 02:28 AM

I had basically the same problem with a batch of 3/4” solid cherry that I was milling into T&G paneling. I bought the lumber rough, and decided to pay a sawmill to mill them flat and straight-line them, as I didn’t have a large enough jointer to face-joint them. That was a mistake – I should have bought an 8” jointer and flattened them myself. The sawmill just ran them through a thickness planer, which left in some pretty good bows.

To salvage the lumber, I invested in a set of Jessem Clear-Cut router guides for my router fence. They can generate enough down force to squash the bows flat to the router table while you’re milling the tongue and the groove (and they also keep the boards tight against the fence). That’s the real trick — with the T&G milled on center, it wasn’t hard to mate up the bowed boards nice and flush.

In my case, the cherry T&G is nailed to the wall flooring-style, with small gaps for expansion. But I test-fit some panels flush, and I wouldn’t be afraid of doing a glued-up panel with it. The internal stresses from bending out the bows didn’t seem that large.

-- Dennis 'We are all faced with a series of great opportunities, brilliantly disguised as impossible situations.' Charles Swindoll

View nickbatz's profile

nickbatz

259 posts in 528 days


#2 posted 07-19-2019 04:15 AM

I would do that with dowels – mainly because I have a dowel jig, not necessarily because it’s slam-dunk the best way to do it. :)

But the jig I have – Milescraft Jointpro – clamps down both boards you’re edge-joining, so the dowel can only go in the same distance from the faces. In other words, it would be harder to misalign them than it is to get them aligned perfectly.

As an aside, that jig is also very useful for drilling straight holes in things you can’t reach with a drill press even if you’re not using dowels.

View bilyo's profile

bilyo

774 posts in 1550 days


#3 posted 07-19-2019 02:52 PM

It would help to know how thick the boards are and how big the desk top will be. I’m assuming that the “flooring” is at least 1/2”. I am guessing that if the boards only have a slight bow that can be flexed straight by hand then you probably don’t need the T&G. Cut your boards to rough length. Then edge joint them. If you have a place to do it, clamp them or weight them to hold them flat and edge glue them to make your top panel. Again, if you are dealing with only slight bows, this should be enough to make a flat panel. When your panel is complete, you will likely still need to do some surface planing/sanding/scraping to get a smooth surface.
If you decide to do the T&G, I suggest you use a hand held router with an T&G bit set. This will better follow the curve of the boards and keep the T&G centered.
Once the top is completed, you will fasten it down with screws or clips allowing for expansion and contraction. If done properly, you should not have any issues with warping or cracking with either joining method.

View Ryan Sandler's profile

Ryan Sandler

29 posts in 902 days


#4 posted 07-19-2019 03:18 PM

@bilyo Thanks for the input, that’s really helpful. I will probably still try for the tongue and groove, just to help with alignment—I’ve never had a ton of luck keeping boards well aligned for a simple edge joint even when they all start out flat.

For the additional info: the boards are currently a little fatter than 3/4 inch (.8-.85” depending on the piece), and I’d like the finished panel to be not too much thinner than 3/4 inch. The top will be 60” x 22”.

View Lazyman's profile

Lazyman

3661 posts in 1835 days


#5 posted 07-19-2019 03:42 PM

With a bowed board, it may be challenging getting the tongues and grooves perfectly centered or at least consistent along the entire length. Be prepared to do some planing after glue up where there is a (hopefully) minor alignment issues at the least.

One thought though. Desktops are usually relatively thick so if the boards are already less than 3/4, that might not be thick enough for a nice solid desktop. With the bowing issues and potential thickness issues, not sure that this is the best choice for a desktop, especially if it is going to be fairly large.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View LesB's profile

LesB

2151 posts in 3890 days


#6 posted 07-19-2019 05:24 PM

Use a router with a slot cutting bit ($10 to $50) or a biscuit slot cutter ($70 to $200) and biscuits is the easiest way I can think of for aligning the boards during glue up. Biscuits do not appreciably strengthen the glue joint but they are great for keeping the boards aligned.

-- Les B, Oregon

View nickbatz's profile

nickbatz

259 posts in 528 days


#7 posted 07-19-2019 06:49 PM



Use a router with a slot cutting bit ($10 to $50) or a biscuit slot cutter ($70 to $200) and biscuits is the easiest way I can think of for aligning the boards during glue up. Biscuits do not appreciably strengthen the glue joint but they are great for keeping the boards aligned.

- LesB

And that’s a variation of my thinking – biscuits, dowels, same idea.

Intuitively, it seems a whole lot easier to align a few individual points along the length (i.e. biscuits or dowels) than to cut a groove along the entire length. And if you miss on one of the holes/dowel slots, you just go on to the next one and leave it empty.

But I don’t think you’d miss.

View tywalt's profile

tywalt

61 posts in 611 days


#8 posted 07-19-2019 09:14 PM

All the above solutions would work… but I’m questioning using stock thin enough to only allow a 1/8” T&G and that is flexible enough be bent by hand for a desk top. If you’re determined to use this stock, can you reinforce it with a stable sheet good (mdf, BB ply, etc) and “veneer” your reclaimed wood to the top and edge band the sides? A way overbuilt apron would help keep the whole table rigid if not.

-- Tyler - Central TX

View Ryan Sandler's profile

Ryan Sandler

29 posts in 902 days


#9 posted 07-19-2019 09:39 PM



All the above solutions would work… but I m questioning using stock thin enough to only allow a 1/8” T&G and that is flexible enough be bent by hand for a desk top. If you re determined to use this stock, can you reinforce it with a stable sheet good (mdf, BB ply, etc) and “veneer” your reclaimed wood to the top and edge band the sides? A way overbuilt apron would help keep the whole table rigid if not.

- tywalt

This made me realize I wasn’t very clear about my plans for the tongue and groove. I meant short tongues/shallow grooves (say 1/8”). Tongue thickness would be 1/4” or so, since the boards are around 3/4”.

View bilyo's profile

bilyo

774 posts in 1550 days


#10 posted 07-19-2019 09:42 PM



All the above solutions would work… but I m questioning using stock thin enough to only allow a 1/8” T&G and that is flexible enough be bent by hand for a desk top. If you re determined to use this stock, can you reinforce it with a stable sheet good (mdf, BB ply, etc) and “veneer” your reclaimed wood to the top and edge band the sides? A way overbuilt apron would help keep the whole table rigid if not.

- tywalt


That may work if you don’t glue the “veneer” to the sheet goods. If you do that, you will have wood movement problems. Something will either buckle or split. You would need to screw them together using elongated holes to allow for movement.
However, note the OP’s comment above saying that his material is more than 3/4”. Should be enough.

View nickbatz's profile

nickbatz

259 posts in 528 days


#11 posted 07-19-2019 09:56 PM

Absolutely 3/4” is enough for a desktop, even if it’s plywood.

Proof: I’ve been sitting at this 3/4” desk for something like 13 years, have sold and shipped about 20 of the same model all around the world, and have made four myself. :)

View therealSteveN's profile

therealSteveN

3353 posts in 1021 days


#12 posted 07-19-2019 10:03 PM


One thought though. Desktops are usually relatively thick so if the boards are already less than 3/4, that might not be thick enough for a nice solid desktop. With the bowing issues and potential thickness issues, not sure that this is the best choice for a desktop, especially if it is going to be fairly large.

- Lazyman

+1

For a desktop I would start with 6/4 stock, so any such issues could be dealt with correctly. Forcing wood to go to a shape it doesn’t want to be in can be done, with enough heat applied to the correct woods. As a general suggestion, the wood usually wins in the end.

-- Think safe, be safe

View DrDirt's profile

DrDirt

4588 posts in 4189 days


#13 posted 07-19-2019 10:06 PM

It will certainly help, if there is slight bow of each board, see if you still get good grain match by flipping boards so that the curves cancel each other… but also if the desktop is going to be on a base with either drawer box or an apron, that will also hold/pull the top flat with the casework.

-- “The two most important days in your life are the day you are born and the day you find out why.” Mark Twain

View jdh122's profile

jdh122

1087 posts in 3265 days


#14 posted 07-19-2019 10:09 PM

Personally I’d just edge glue them using lots of clamps and cauls. Second choice (since you’ve mentioned you have no luck with edge glue-ups without mechanical indexing) would be biscuits. I wouldn’t be that keen on pushing the boards through a tablesaw or router table exerting the kind of pressure needed to make sure the tongues and grooves are centered in the boards despite the warp.

-- Jeremy, in the Acadian forests

View nickbatz's profile

nickbatz

259 posts in 528 days


#15 posted 07-19-2019 11:39 PM


Personally I d just edge glue them using lots of clamps and cauls. Second choice (since you ve mentioned you have no luck with edge glue-ups without mechanical indexing) would be biscuits.

If you have lots of clamps and cauls, sure, you don’t need biscuits (or in my case dowels, which I’m guessing are better than biscuits but take more work). However, Ryan did say that the boards can be straightened if he bends them, so it doesn’t sound like they’re that bad.

I like Izzy Swan’s idea a lot. One of these days I’m going to make some of those – only not totally out of plywood.

By the way, he just announced that he’s wheelchair-bound due to slipped discs (spondylolisthesis), and I feel really bad for him. I hope he gets good care and that he hasn’t had bad care in the past, i.e. that his condition wasn’t neglected enough for him to have developed irreversible nerve damage.

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