Flattening a Table top with 2 leaves after glue up (would love some suggestions)

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Forum topic by zippymorocco posted 02-28-2016 10:33 PM 1415 views 0 times favorited 14 replies Add to Favorites Watch
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39 posts in 1464 days

02-28-2016 10:33 PM

I am making a 44” by 78” table top with two additional 18” leaves. I have the glue up finished and have begun to flatten the pieces individually. I stopped before getting too far into it realizing that I don’t have a good plan on how to make everything level and line up. Does anyone have a good system to assure that all of the table top and leaves line up regardless of what configuration it is put together in. This seems like it could end in disaster if I don’t come up with a good process to assure that everything is flush, in line and the same thickness.

Thank you,


14 replies so far

View OSU55's profile


1927 posts in 2165 days

#1 posted 02-28-2016 11:58 PM

Depends. How do you normally flatten a tabletop? Hand planes, drum sander, planer, and sanding, you get the idea? What are your available options to flatten this one? I would be using hand planes. I would get the backside relatively flat and then attach it to the table support system and hand plane in place. If it is fairly rough just after glue up I would do some of the rough flattening on a bench.

Another option with hand planes would be to build a make shift support system on sawhorses or something that was large enough for that top with all of the leaves in place.

View zippymorocco's profile


39 posts in 1464 days

#2 posted 02-29-2016 12:57 AM

Thank you for the response.

My process for flattening tops is as follow. Take as much care before glue-up to get each board flat on the jointer and planer. Glue-up carefully using cauls to keep things flat. Then a mixture of hand planes, belt sander and random orbital. This has worked well with tops so far but this is my first project with multiple parts.

The top came out of glue up in really good shape. Nothing is too far out but it still needs work.

View bearkatwood's profile


1659 posts in 1187 days

#3 posted 02-29-2016 01:01 AM

The absolute easiest way is to find a local cabinet shop and take it over there, they usually have big belt sanders that can do it in minutes and depending on the person could be around $20-$40 or so.

-- Brian Noel

View hotbyte's profile


991 posts in 3151 days

#4 posted 02-29-2016 01:13 AM

Even if you plane all piece to same level, they must line back up when removed/inserted. Leafs I’ve see all have little short alignment dowels, either wooden or metal, that go into a matching hole.

View zippymorocco's profile


39 posts in 1464 days

#5 posted 02-29-2016 01:20 AM

I do have some Brass alignment dowels. Also I have taken projects to a cabinet shop in the past so if I had to I could go that route. I am a little worried that it might come back too thin. I on’t have a lot of extra thickness to work with.

View JBrow's profile


1366 posts in 1096 days

#6 posted 02-29-2016 04:49 AM


The requirement that the two 18” extension leafs work in any position is a difficult requirement. For these requirements to be met, the top and bottom surfaces of the top and extensions must be flat and parallel and the same thickness. Even if the top and bottom surfaces are parallel, the alignment pins must be very precisely located. Otherwise, the table top would align in one position but not in another.

I believe that OSU55’s suggestion to flatten the bottom of the top and the extensions, then fasten it to the table base and flatten the top side could lock you into a single configuration. If this were the only configuration of the extensions, it would work well. However, I suspect that, no matter how much care is taken, there will be variation in the top and the extensions in other configurations and thus the extended top would be out of alignment.

The only alternative I can think of to that of sending the top and extensions out to a cabinet shop is to use precisely located splines and a mating flushing jig with a replaceable jointing surface. The flushing jig with a replaceable jointing surface represents the finished top and the thickness of the flushing jig with the replaceable jointing surface (installed on the flushing jig) represents the finished thickness of the top. When the top and extensions are flush with the flushing jig, the top and extensions should be flush with one another no matter where or how the extensions are installed.

The jointing surface could be ¼” hardboard fastened with countersunk screws to the flushing jig. It must lie flat across the entire surface of the flushing jig. The flushing jig could be MDF or plywood. The jig would be about 6” – 8” wide and a few inches longer than the table is wide.

In order to align the flushing jig with the top and extensions, flatten one face of the top and the extensions, doing no flattening work on the other face. Route a groove with a slot cutting bit using the flattened face as the reference surface on which the router rides. The slot can be a through slot emerging from the edges or a stopped slot, leaving a couple of inches from the edges un-slotted. Cut snug fitting splines. Route a mating slot in the flushing jig, using the side of the jig that is NOT fitted with the jointing surface as the reference (opposite face from the jointing surface). This should make the flushing jig even with flattened surfaces of the top and extensions. This is important so care is required when routing the slots and preparing the snug fitting splines.

Put the top (or extension) and the flushing jig together using the spline for alignment and clamp in place – enough to keep the parts from separating. Then flatten the previously un-flattened face. Once the piece is flat and flush to the flushing jig, replace the jointing surface of the flushing jig, since this operation will likely remove some material from the flushing jig jointing surface. Repeat until all mating edges are flushed up. Check the fit and fine tune as may be required. A very slight chamfer on the mating edges could be used to celebrate the joint and conceal any slight unevenness.

When the project is finished, splines would be used for alignment and a locking mechanism used to keep the extensions in place.

View pintodeluxe's profile


5784 posts in 2989 days

#7 posted 02-29-2016 05:14 AM

I think you could make a case for hiring a shop with a wide drum sander. I take my wide panels to a local woodworking shop, and in under an hour they are all cleaned up and uniform in thickness. The shop I use has a 50” wide helical head planer combined with dual drum sanders. Tearout is absolutely non-existent.

In fact I’m heading over there next weekend to finish a bunch of tops and panels for an entertainment center.
It makes a fun fieldtrip.

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

View OSU55's profile


1927 posts in 2165 days

#8 posted 02-29-2016 12:37 PM

Yes the requirement to have the leaves fit any configuration pretty much forces you into finding a drum sander/planer wide enough to accommodate the top. Any way you choose to do it has the possibility of getting it too thin – it’s a function of the shape of the glue up and stock thickness. The drum sander/planer would be the best option to leave the most thickness – less chance of correcting misalignments with moving the leaves around.

View zippymorocco's profile


39 posts in 1464 days

#9 posted 02-29-2016 02:47 PM

Thank you all. Sounds like a drum sander is the way to go. I am glad I hadn’t put too much effort into it yet. I am going to give the shop a call and see if their machine can handle it. Will let you know how it goes. I like this option. I can now concentrate on the base which has all the fun joinery.

View Cooler's profile


299 posts in 1019 days

#10 posted 02-29-2016 03:17 PM

I think I would arrange the pins so that it will assemble one way only.

I buy adhesive backed sandpaper in rolls, and I have mounted this on long pieces of flat melamine lamintated particle board to “joint” two pieces of stock. I would think a large piece of this stock so laminated would flatten the table (with lots and lots of elbow grease).

-- This post is a hand-crafted natural product. Slight variations in spelling and grammar should not be viewed as flaws or defects, but rather as an integral characteristic of the creative process.

View rwe2156's profile


3134 posts in 1656 days

#11 posted 02-29-2016 03:30 PM

First, I cringe a little when I hear “belt sander” but if you’re adept with it fine.

Second, unless its free or very cheap, you don’t need a shop with a wide belt sander.

You can get the main part of the top flat the way you normally do it.
After you’ve got the two leaves the same thickness and flattened, installed the hinges, test fit then hand plane down to flush with the main top paying particular attention to the seams.

If you’re hand planing you’re not seeking perfection, just acceptable flatness. .

-- Everything is a prototype thats why its one of a kind!!

View zippymorocco's profile


39 posts in 1464 days

#12 posted 04-12-2016 02:33 AM

I think the top worked out well. I ended up sending it to the cabinet shop. I just put the table together after being finished today. It looks great. Thank you all for the suggestions.

View Aj2's profile


1801 posts in 1974 days

#13 posted 04-12-2016 02:52 AM

Wow that’s a long or should I say wide table? I can see why you were concerned about the pieces aligning.From the pic it looks like a 12ft er.
Nice work.

-- Aj

View zippymorocco's profile


39 posts in 1464 days

#14 posted 04-12-2016 03:53 AM

Thank you. It is big but not quite 12’. The table closed is 44”X78” With the leaves 114”

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