# Help Needed: flattening a table top and keeping it flat



## Mortalis (Jan 10, 2016)

I am currently working on a sofa table style table for a friend of mine. I was provided table legs (Mahogany) and am making a table top to match. 
The lumber came finished one side but cupped a bit while allowing it to acclimate so I jointed the finished side to flatten and then jointed the edges to be perpendicular. I then planed the other side to be parallel with the first side. I alternated the end grain to minimize any further cupping and used biscuits to join 4 pcs 1" x 4" x 48" rectangle. 
This is where my agita begins.
I tried to use my Stanley block plane and Porter CAble power plane to flatten the resulting glue up. First thing that happened was that when I tried to hand plane across the grain all I did was tear up the faces. I use the scary sharp process to sharpen my plane blade with some relief at each corner. I ended up going out and purchasing a Wood River Block plane withe the same end results. I ended up using my power planer and belt sander to get the two table top faces flat. While I was letting the top rest from weekend to weekend the top cupped rather drastically. I spent another weekend with the belt sander getting both faces flat again. Again, a week later the top cupped.
I have decided I need to somehow structurally hold this top flat. I thought about sliding dovetail across the width of the top and then using mating dovetailed edge grain boards. I have also thought about using stretchers attached with screws to draw the 'bottom' flat.

I need to advice on what I need to do to flatten the top and keep it flat.

TIA


----------



## conifur (Apr 1, 2015)

Maybe some cleats on the bottom.


----------



## Mortalis (Jan 10, 2016)

Cleats…..that's what I meant to say when I poster 'stretchers'.

I was concerned the table top was not thick enough to engage enough screw thread to be able to accomplish a flattening effect. Do you have any how to vids or examples to explain the proper method for using cleats?


----------



## conifur (Apr 1, 2015)

First I maybe wrong but a 'stretchers'. run with the grain, a cleat is perpendicular to the grain. An yes you use a screw that goes into the top about 3/4ths of its thickness.


----------



## gfadvm (Jan 13, 2011)

If that wood is that determined to cup/misbehave, I'm afraid that it will crack when you flatten it with cleats. Sorry, but I've been there. Maybe inlay some bowties after it is through cracking?


----------



## bandit571 (Jan 20, 2011)

One other option? Breadboard the ends. 









Simple enough to do. Just add glue at the center only. Add pins/dowels/nails from the underside for the outer ends.


----------



## tturner (Nov 5, 2012)

Experience-
1-Is the material completely dry? 
2-Is it very cold or hot In the shop? Extreme temperature changes can and will cause wood to cup-especially Oak.
3-Is the shop area also dry? High humidity levels can cause wood to 'walk'


----------



## Mortalis (Jan 10, 2016)

I know I didnt mention the shape of the table top so I appreciate the breadboard suggestion but the table top is oval.

As far as the atmosphere in the shop, it is variable with the weather. I live in Massachusetts near the water and it is most of the time humid in the summer and dry in the winter. The shop is my two car garage. I allowed the lumber to acclimate with spacers in between the layers for two weeks before starting the project. In the winter I use a propane heater.

I have a mock up of the table in my projects section.


----------



## conifur (Apr 1, 2015)

Cleats…..that's what I meant to say when I poster 'stretchers'.
Well as I told the X, I flunked mind reading 101 in College. How would the heck I know what is in your mind, and vocabulary that is miss directed??


----------



## a1Jim (Aug 9, 2008)

Welcome to Ljs 
Along the lines of tturner's comment,I'm thinking it's a moisture problem ,one side has more exposure to heat or air blowing on it.you can plan it until the cows come and you won't get it flat. introduce some moisture to the concave part with say a damp sponge and see if that helps flatten it out ,it may take more than one application to get it closer.Be careful about using cleats you have to allow for wood movement.
The possibility also brought up by tturner is that wood was not dry to build with,you want it to be around 8% before you build with it.
another issue could be the way the wood was milled ,some wood will move all over because of the type of wood it os or it was milled from a tree that had internal stress.
here are a couple links that might help in the future.

http://www.wood-database.com/wood-articles/wood-and-moisture/

http://toddpartridgedesign.com/sr_pages/documents/UnderstandingWoodMovement.pdf


----------



## bandit571 (Jan 20, 2011)

Oval top….use a spline. Cut a dovetail slot across the width, one near each end. Make up a dovetailed shaped spline to slide across, in the slot. Usually were made of a hardwood. One screw in the center of the spline to hold it in place. No glue.

Been used under the lids of many an old Hope Chest…


----------



## DrTebi (Jun 16, 2009)

Did you put finish on the top after planing it? If so, remember that you should put finish, or at least a sealer like shellac, on both sides of the table top. I have had even MDF cup severely after putting finish only on one side…


----------



## AlaskaGuy (Jan 29, 2012)

Give us more history about the wood. If it cupped while acclimating in you shop that means there was a moisture change in the wood.

What were/are the dimension of the wood?

I assume it was some kind of Mahogany, which species?

Where did this wood come from and why was it finished on one side? I assume finished means like a film finish and not finished planed on one side.

What was the moisture content when you got it and what is it know?

After jointing the finished side did you keep the wood in a manor that allowed air circulation around all side. Hopefully you didn't lay it flat on a table with no air to one side. How long between milling and glue up?

Wood moves with change in moisture content. No so much with the temperature. Temperature can have an effect on the moisture in the air but hot or cold by its self won't make it warp?

What part of the country are you in?

When you glued it up did the mating pieces fit together good so you didn't have to force the joint together with clamp pressure?

Are you sure it was flat when you took it out of the clamps? It it was, when (how long) before the top cupped?

I can't help but think this is a moisture problem, the wood appears to still be losing or gain moister (the later being most likely) and doing so unevenly.

I reserve the right to ask more questions later.

I


----------



## rwe2156 (May 7, 2014)

As you've already learned, you used the wrong tools to flatten the top. My advice is to have someone hide that electric plane out in the wood shed somewhere and swear them to secrecy ;-D

How close to finish dimension is the top? This will determine what you can/can't do.

You've got two problems: 
1. Cupping: a moisture issue. When you planed the board you opened up new grain and differential in moisture content on each side causes the cupping. I would try a1Jim's rec first, but I've had poor luck with that.

Mechanical solution to cupping many times doomed to failure down the road. One remedy is to rip the top into narrower strips and re-glue. Another is to simply start over.

In the future, never leave the wood in an unconditioned environment like a garage, especially certain times of the year. Bring wood inside the house to acclimate, or put in plastic bags. On a wide top I will usually clamp or strap it between two flat boards with stickers and leave for up to a week. Sometimes a particular piece of wood is just rascally and has internal tensions do to grain you can't do anything about it.

2. Grain tear out can be a very difficult fix. A scraper is your best bet here. Perhaps turn board over?

Welcome and good luck!


----------



## Mortalis (Jan 10, 2016)

I really appreciate all the comments.

I want to first say to Conifur, my comment after your explanation of trying Cleats was in no way meant as a slight or to be snide. I appreciate your correction as I sometimes get mixed up in my terminology.

Now, back to the topic at hand.

When the lumber was delivered I unwrapped the boards and put them to one side in my garage/workshop using sticks I cut from some scrap plywood that spanned the width of each board placed every 12" or so along their length. The lumber was stored horizontally one on top of each other. The wood was purchased a dried finished all sides cut to 48" lengths of Santos Mahogany. Sorry to have misled…the lumber arrived as finished all sides. I paid for finished 2 sides if I recall correctly. Purchased from AdvantageLumber
I ran the lengths on my Jointer to flatten and then my Planer to parallel.
I biscuit joined 4 boards with the end grain alternating. 
I used the power planer (which actually did a good job) whereas the hand plane tore the crap out of the grain, then belt sander to flatten both the top and bottom and then left for a week to come back the next weekend.
I had the top sitting on my workbench when I first noticed the cupping. I did some online research and was informed that the cupping is due to moisture. More on one side than the other. When I went to check, lo and behold, the sided that was faced down was very moist. 
I placed the wood strips I used during storage under the top with the moist side up. The cupping seemed to minimize after a week of sitting and then the next weekend I saw that there was slight cupping and started in the flattening process again. After sitting again for a week till the next weekend the cupping was back.

I dont own a moisture meter so I cant tell you what the moisture level is in the boards but this winter here in Mew England has been rather wet. I have not applied any finish or sealer.

Long story but that's the history.


----------



## JBrow (Nov 18, 2015)

Mortalis,

I will share my thoughts, although I am not sure how much help I will be. I believe as you and others stated, the problem appears to be a moisture problem. I eliminated internal stresses being the cause of the cupping because I assume the edges were fairly straight during the glue-up and the cup is fairly uniform. Additionally you mentioned one side of the glue-up was noticeably damp. You also stated you heat the shop with a propane heater.

First I wonder whether you are inadvertently introducing a lot of moisture into the shop. A propane heater (or kerosene heater) not vented to the outdoors generates more or less a gallon of water for every gallon of propane burned. This could perhaps be the source of your moisture. If your propane heater is not vented outdoors, then opening the garage door for a few minutes when you are done for the day (and a few minutes throughout a long day of shop time) may help reduce the moisture level in the shop.

If moisture is the culprit, the glue-up cupped because the wood fibers on one face were relatively moist while the wood fibers on the opposite face were relatively dry. The greater the difference in moisture content of one face compared to the other face, the greater the cup. The cup appears because the moist wood fibers swell and thus increase the width across the face, while the relatively dry side width remains mostly compressed across the width. The result, if my reasoning is correct, is that the crown of the cup is on the moist side of the wood.

If this analysis of cupping is correct, then it suggests what I would try to return the glue-up relatively flat. Unfortunately, it will take mostly time. This effort is intended to squeeze the moisture ladened fibers together to force moisture out of the fibers. I would position sets of straight cauls across the width at each end and at least one, maybe two, in the center evenly spaced along the length of the glue-up and on each side of the glue-up. In other words, cauls would be on each face of the glue-up with the glue-up between the cauls. Then I would draw each set of cauls together with clamps (squeezing the glue-up toward flat), being careful to avoid overtightening the clamps. I would worry that overtightening the cauls would crack the glue-up. With the cauls clamped in place, stand the panel up on edge (not on end) and place the panel where it can receive good air circulation around the entire panel. Placing a piece of plastic on the floor will reduce humidity from the concrete floor. About daily, check the glue-up, and tighten the clamps if they become loose. The loosened clamps indicate the panel is returning to flat. Continue the process, tightening clamps as needed until the panel is as flat as it will go, which suggests moisture content has stabilized. Introducing a fan and/or de-humidifier in the shop environment to circulate and dry the air would speed the process, but I would not blow air directly on the panel, just mix up the air in the shop. Since winter has finally come to Massachusetts, you may find the process to go fairly quickly unless somehow moisture is being introduced to the shop.

If this process gives you a flat enough glue-up, applying a coat of finish along the end grain edges may help reduce further moisture uptake, but also can impede moisture trying the escape the panel. Immediately before applying final project varnish, mill the edges to remove the applied "stabilizing varnish", sand the edges and get the first coat of finish on the table top as quickly as possible. Having said this, I would resist doing this step, preferring to avoid the problem of later dealing with removing the "stabilizing varnish".

If this prescription fails to work, rwe2156 suggestion of ripping the glue-up and starting over with the milling process after the mahogany has acclimated would be my next step. If you go this way, now may be the time to add a moisture meter to the workshop. You could then check moisture content of the faces to ensure the lumber is balanced before milling. A moisture meter is probably cheaper than the final fix. I believe the final answer is probably as rwe2156 suggested, start over. I am sure the mahogany was not cheap, so this is the answer of last resort.

Regarding any form of mechanical fasteners or joinery to get and maintain a flat panel when the root cause was not addressed, is, again as rwe2156 opined, likely doomed for failure. The forces of wood movement are simply too great to restrain.

Good luck, and let us know how you solved the problem. After all, I may encounter the same problem on my next project.


----------



## Mortalis (Jan 10, 2016)

Stupid question time.

What would a moisture meter do for me other than tell me that both sides are not the same?

Not trying to be flip, just honestly asking? These things arent cheap and I dont know what value it would add to my woodowrking. If someone could elaborate I would be much appreciative.


----------



## a1Jim (Aug 9, 2008)

Mortalis
It would tell you if you want to use wood or not depending on how dry it is.


----------



## JBrow (Nov 18, 2015)

Mortalis,

I think your question is a serious one and not at all flip. For me, spending a $100 on a moisture meter or on a tool is a meaningful question and an easy choice. I would rather buy the tool. In fact I only recently acquired a moisture meter, and it was a Christmas present. I never saw the need for one, but then I never encountered the problem you are describing. Now that I have one, I will use it.

If in fact you have a moisture in the lumber problem (and I think you do) and your shop environment did not add moisture to the mahogany (which is not certain), then the lumber used in the glue-up had too much moisture and was not ready to work. Perhaps your lumber supplier provided wood with high moisture content.

In the future you could use the moisture meter to check the lumber before beginning the milling process. I think 12% to 8% is the generally acceptable moisture content when you begin a project, but I am not sure. In any event, wood that is not dry will eventually move in unpredictable ways as it dries, and, once milled, becomes a big problem.

Your experience is a frustrating one, especially after all the work you have done to remedy the problem. I doubt you want to repeat this experience. A moisture meter used to measure moisture content beforehand could possibly save this aggravation in the future.


----------



## tturner (Nov 5, 2012)

> Stupid question time.
> 
> What would a moisture meter do for me other than tell me that both sides are not the same?
> 
> ...


No stupid questions here. Thats why we're here and we're all friends in wood. I think we've agreed your trouble here is probably moisture, or wet wood.
Ive not used a moisture meter and if you don't want to invest in one, then you have to know the history of the wood you're using. Ask the person you're buying from how was it dried? For air-drying, we usually want 1 year of drying per inch of thickness, rough sawn. If 4/4 material is kiln dried, it should be dried for about 6 weeks. This is after the log has set for 6-12 months, depending on the diameter. Good luck with your project and be sure to post pictures of the completion. 
Much like painting-where the paint JOB is no better than the surface its put on, your wood project is no good without quality materials. If the wood aint good…


----------



## Mortalis (Jan 10, 2016)

I took some pictures of the top with a yard stick across the width. The amount out of flat seems to be about the same as when I started posting.


----------



## a1Jim (Aug 9, 2008)

I know there are lot's of rules of thumb regarding figuring out how dry your wood is or how long it takes for wood to dry. Just keep in mind, Rules of Thumbs =s guessing. the rules of thumbs in one location will differ according to the humidity of where and how wood is stored and what kind of wood it is. If you are making a project you want to last a long time and you've invested in good wood you should know what's moisture content is. Many times the folks selling the wood will have a moisture meter and will let you use it on the wood you're buying. People who think that moisture content is not important are making very rough furniture or just don't have enough experience to realize is that it is a very important issue.


----------



## JBrow (Nov 18, 2015)

Mortalis,

When you say the table top is now like it was when you started, do you mean after you initial glue-up and flattening process and before the weekend to weekend rest or after the rest and cupping? It is hard to tell from the photos just how flat it is. The top photo suggests a center crown, while the second photo suggests a center belly. Did you flip the table over to take the second photo? But then I may just be seeing photographic distortion and shadows. It is difficult to tell.

By the way, it looks like a great job cutting the shape in some beautiful lumber! It looks like a true ellipse. I cannot imagine cutting the shape out of that heavy slab on the bandsaw.

I did not mention it before, and perhaps you have this accessory; in the past I outfitted my belt sander with a sanding shoe before sanding glue-ups to flat. The sanding shoe is flat and surrounds the sanding belt. The sanding shoe thus limits the depth to which the belt sander can remove material. As a result the deep trenches that can otherwise arise when using a belt sander are avoided.


----------



## Mortalis (Jan 10, 2016)

Ooops sorry.
Yes, the top photo is the 'top' of the tabletop and the bottom photo is the tabletop flipped to show the 'bottom' of the tabletop. My comment about the cupping is that since I started posting (Jan 10th) the amount of cupping has remained basically the same. The thickness of the slab is just under 1" and I want to try to keep it as thick as I can because the legs are beefy.


















Since I bought these lengths online from a NJ outfit and I live in New England it will be a long ride to borrow a moisture meter. I may order one off Amazon. They have a wide assortment and I saw one for around $50. Only thing is the accuracy of the unit is ±5% or something like that.

Thanks JBrow. 
I used the three nail method to create a MDF template (you can see it off the back right leaning against the cabinets) then traced the template and rough cut the slab with my jig saw (the slab was too heavy to try to wield around at the bandsaw). I then applied two sided tape to the template and used my router with a template bit. 
One thing I didnt account for is that the biscuits all show along the edge at the slimmer point about a 1/3 of the way down from the smaller radius end at all four spots. That's another challenge I have to deal with once I get the flatness taken care of.

I'm pretty good with the hand belt sander and I havent dug in yet and I've used it mainly to do the flattening. By the way, that streak you see running the length just right of center of the 'bottom' (hence why it is the bottom) is from a set screw loosening up that holds one of the blades on my power planer.


----------



## Mortalis (Jan 10, 2016)

Here is the mock-up I sent for the customer's approval.


----------



## sawdustdad (Dec 23, 2015)

just like the fable about the scorpion and the frog. Warping is in the nature of solid wood. How much depends on the wood and it's treatment. Sometimes the wood you get is reaction wood, cut from a leaning tree or a large limb. No cleat or assembly technique will prevent warping/checking. You gotta know when to hold 'em and know when to fold 'em, to use another axiom.

The only sure solution is a veneered plywood top. Take your wood and resaw into 1/8 inch veneer and apply to a plywood substrate. Treat the edge with veneer as well.


----------



## JBrow (Nov 18, 2015)

Mortalis,

A moisture meter with a precision (how well a variety of readings reflect the actual measurement) of ±5% should work ok. I would prefer a pen style moisture meter but others may differ. I suspect the accuracy from inserting pens into the wood will give more reliable readings.

±5%, and I am digging deep to remember, means that for a given measurement, 95% of the time the readings from meter will be within 5% of the true reading. Therefore, taking multiple readings and averaging the results will get you closer to the true reading. But for what you are trying to measure, ±5% with a couple readings is probably ok. Others may differ and bear in mind that until recently I had no moisture meter.

The other piece of gear to consider is a shop humidity meter. The humidity meter will let you know the moisture content of the shop air. a1Jim points out that the humidity of the air where the lumber is located affects the moisture content of the lumber- and I agree. Therefore, since you are heating with propane and may be working in a relatively humid environment when the heater is in use, you can determine to what extent humidity, if any, may impact your work. Luckily, a humidity meter is not very expensive. A search turned up a few for around $15.

https://www.google.com/search?q=humidistat&ie=utf-8&oe=utf-8#q=humidity+meter

Have you decided how to deal with cup? One option for dealing with cup which has not been mentioned is let the top set. I have heard it said, "When you are having woodworking problems, just walk away for a while." In this case, perhaps giving the top some time to stabilize may allow you to re-flatten it with greater confidence. You don't suppose the top returned to original flat and the cup you now see is from the second flattening?

This top sounds like a nightmare. I did not realize you had an exposed biscuit problem. Have you decided how to deal with this problem? I double re-cutting it to a slightly smaller size is anything you would consider. After all, unless you know where the biscuits reside, you may remove the ones showing while exposing others. You could consider edge banding, but getting a good looking joint would be difficult, making the tight end bends would be a challenge, and getting the glue to bond on the end grain could lead to eventual glue failure. Therefore, I suppose you plan to use a slot cutter on the router, router out the biscuit and fill the voids with mahogany splines. Matching the grain to make the splines disappear will be a challenge; unless you kept the scrap from when you cut out the top with the jigsaw.

Nice - great looking legs! In the last few years I too have introduced curves into my projects. It really makes the finished product look good.


----------



## mrg (Mar 10, 2010)

You said you heat the garage with propane. When the propane heater is running it causes condensation. This causes the wood to absorb the moisture from the air. You said the wood was wet on the bottom on the bench this is caused by the temperature swing.


----------



## Mortalis (Jan 10, 2016)

Haven't heated the garage in a week. Went out today and checked the top. Still cupped the same as shown in the pictures.
I've rediscovered my #80 scraper. Watched some vids on how to sharpen the iron. Been scraping away at the dome of the cup on the 'top' of the table top. Witlin' away at it.


----------



## Mortalis (Jan 10, 2016)

Well, been out of commission for a few weeks. Got back at it this weekend. I did not have any luck with my #80 scraper.
I built a sled and rails for my router like the one the Woodwhisperer used to flatten his workbench. I attached the rails to the sides of my bench and then made then parallel with the top of the bench. I used a 1-3/4" two flute router bit in my Craftsman 15 amp router and went about router planing the top. I started with the convex side up and flattened it so that it would sit flat when turned over and then flattened the concave side so that it was about 90% flat. I then went back to the convex side and worked it a bit more. It worked really well. Only thing is, my 1" thick top is now just about 5/8" thick and I still havent gotten all the cupping out from one edge. I figure when all is said and done the top will end being just shy of 1/2" thick.

Quite a shame really that I had to waste all that expensive wood. Live and learn I guess. I just dont know what I've learned that I can use to keep this from happening again.


----------



## JBrow (Nov 18, 2015)

Mortalis,

Unfortunately I am a day late and dollar short, by I thought you would be interested in my experience yesterday and today.

I glued up red oak panels for drawer boxes and yesterday, I flushed up the joints at the drum sander with 80 grit paper. I simply stacked the four panels atop one another and quite for the day. This morning all was well except for the top panel. It had a crown that developed overnight. The remaining 3 panels were fine. The exposed freshly sanded surface of the top panel absorbed enough moisture overnight to create the cup.

I clamped one edge of the panel to the workbench, crown side down. The opposite edge was about ½" raised off the bench. The put cauls at each end of the panel and clamped the cauls to the workbench causing the panel to go back to flat. I then used a damp rag to wet the concave surface that was facing up on the workbench. I then laid the damp cloth over the panel to keep it from drying out. After about 3 hours, I removed the cauls and the damp cloth. The moisture in the panel had equalized and the panel returned to flat. During the 3 hours, I checked progress, wanting to avoid introducing a crown in the opposite direction.


----------



## rwe2156 (May 7, 2014)

Jbrow and Mortalis,

Bottom line you can't leave wood lying out at night unless you have a conditioned shop.

It took me a while to learn a basic fact acclimation means just that: the wood will seek the same moisture content as the environment. Therefore, to keep wood from moving you need to start with stable wood and maintain a stable atmosphere. You can do it all properly but if you're leaving your project in the garage or an unconditioned shop, you'll eventually get bitten like this.

BTW I've had wood warp just sitting under a fan. I have a conditioned room I can store my projects in, but when Miller time hits, I don't always remember and get bit in the A.

Try storing your wood inside your house or put in plastic bags overnight. I think you'll find it makes a diff. If I sticker wood I usually cover the top board because it will have one side exposed. I also add a little weight.

*Mortalis:*

All is not lost. One option immediately comes to mind is to laminate the whole top onto a piece of thick plywood or even MDF with an edge treatment. This will both salvage your top and give you a thicker, perhaps more attractive one. Perhaps a few weeks in the house before doing that.


----------



## Mortalis (Jan 10, 2016)

Been back at the table.
Got the top flat using a router, side guides on my bench, a slide fixture and 2" router bit. The top has gone from starting at 1" thick to now approx 1/2" thick but it seems pretty stable now and hasnt cupped or bowed for over 8 months.
Since I had to make the longer skirts I also re-made the shorter aprons so they all matched.
The edges have all been cleand up but I dont have a picture showing that. Maybe next update.









Now I am working on the inlay. I've chosen a compass rose since the customer and her husband are both sailors









I am using a combination of Curly Maple, Ebony and Zebra Wood.
Below is the mock up I created to see how it will all stack up
















anyone have any ideas how to make a jig that I can build to cut these pieces so they are all the same? I know I will need to make them without the hole for the center pieces and then cut the hole with a forstner bit to keep them round.

Just thought you all would appreciate an update even if it 18 months later.


----------



## Mortalis (Jan 10, 2016)

Pieces are all cut. They just need a bit of fit and finish then glue them all together to make one solid piece. Then inlay the piece into the tabletop.


----------



## Mortalis (Jan 10, 2016)

The table is complete. Due to my client and his wife downsizing in a year or two we have agreed that I can keep the table in exchange for a couple bottles of good Zinfandel. Although I have invested a lot of time and effort it is going to all work out in the end as upon seeing the finished table, my wife fell in love with it and wants to keep it.
Because the weather outside is nasty and my workshop is in dire need of sorting, straightening and cleaning please excuse the backdrop. I think the inlay turned out great considering it is my first attempt at inlaying.


----------

