Why is my table top glue up cupping?? Please help.
Hello all – newish woodworker and member here..
Here is the breakdown for my situation:
Yesterday, I purchased (5) 10 foot long 5/4 S3S kiln dried red oak boards ranging between 6”-7.5” wide for a tabletop with breadboard ends. This will be for a trestle table I’m building. I purchased the lumber from a local lumber yard (about a 30 minute drive) from my work shop. I live in Southern California (within a desert climate) and both my workshop and the barn where the lumber is stored are very similar leading me to believe the environment is similar too (temperature and humidity).
I had each of the 5 boards cut in half for easier transport and brought them back in my truck. We’re in a bit of a heat wave with no end in sight (approximately mid 90’s with 20-30% humidity). The red oak was in full sun on that 30 minute drive home. I put it in the shop on some sawhorses and left it for a couple hours. The wood was warm to the touch from the sun.
Before purchasing the wood, I spoke to a Rockler employee, explained the similar environments between my shop and the lumber yard I was buying from and he advised that I don’t let it acclimate. He suggested I mill and glue up the same day. There is also another person who’s been working in my shop for the last 40 years and suggested the same thing. I’ve read it’s best to let the wood acclimate but since I don’t have much experience I decided to take their advice.
After letting the wood cool off a bit (waited approximately 2.5 hours), I milled the wood to its final thickness (1 1/8”) only removing 1/8” of material thickness. I jointed the boards very well so when I butt the edges together, the seam disappears. I then used a biscuit joiner for the first time (Dewalt joiner with dewalt #10 biscuits) using 6 biscuits across the width to join together the 60” long boards. Also used titebond 3. This was now in the evening and the temperature was in the mid 80’s/ humidity 29%.
This was also my first time making a hardwood edge to edge glue up panel. I’ve read and heard many different methods to do so.
This was my chosen route:
I used a mallet to seat the biscuits into one of the board edges as the biscuits fit was quite tight. I did not put glue in the slot beforehand. I then used a glue bottle with a roller head to apply the glue to the other mating piece, making sure that the one edge I applied glue to was completely covered. I then used the mallet to drive the boards together as much as I could (I left about a 1/4-1/2” gap. Once I completed this process across all 8 boards, I then used (5) parallel clamps to clamp the boards together until they were snug. I did not alternate the clamps on bottom and top. I just had them clamp from the bottom and made sure to not over tighten for fear of inducing cupping. This process took about 15-20 minutes for the glue up.
One thing I realized after clamping is that I had very little squeeze out. This was one of the mistakes I’m assuming I made. Upon this realization, I took a glue syringe, diluted some titebond 3, and did my best to squeeze some glue in the seams. It did work some – but definitely should’ve applied glue to both boards.
Afterwards, I visually inspected the flatness of the panel. For the most part, it was fairly flat except one of the end boards (on the corner and about 20” long where it was tilting up.
This morning, I went to check the glue up panel and noticed that it was cupping in the middle. There was about a 3/32” dip in the middle that was not there last night.
Later in the afternoon, the gentlemen who also works out of this shop suggested to use a belt sander to get it flat and to attach the breadboard ends as I mentioned in the beginning and is still my plan. After about 14 hours of clamping, I released the clamps. I then came back a couple hours later to look and noticed the panel is cupping even more now! About 1/8” at the worst part!
I found someone online who suggested that excessive heat and humidity will cup panels. Although it’s not humid here, it is hot. They said you can turn the panel over and sometimes the cupping will correct itself. So I did that. Upon flipping it over, I noticed the bottom somehow seems flatter than the top which doesn’t make sense to me. I will see how it looks in the morning.
My plan is to either add the breadboards tomorrow after trying to flatten the top some or cut the table top back into the 8 individual boards and start over. Can I add the breadboards via mortise and tenon first and then flatten the entire top?
Any insight here? I’ve read so many different ways to approach this and would love to salvage this glue up if possible without losing more thickness!
Thank you so much for your time reading this!
Derrick
Replies
I always let lumber acclimate to eliminate the question. No squeeze out says the joints might be starved and not as strong as they could be, but not necessarily a fatal flaw in a steady-ish environment. Not alternating the clamps was a mistake IMO. When you tried to add thinned glue to a closed joint you were just pouring water on/into one side and causing problems down the road for finishing.
I would wait a solid week (at least) to let it dry and see what it does. Put it on stickers convex side up with a little weight on top. Doing anything before it settles is a baaaaaad idea. The gaps are not huge ones, it might come back to flat.
Step away from the belt sander! How will you cut joinery for your ends if the thickness of the top varies?
Thank you so much MJ - I've read an overwhelming amount of folks saying to let the wood acclimate - I'm not sure why I didn't - I just moved to the desert and thought maybe the rules would be different here. I'll chalk it up to my inexperience..
I just checked the table top with my moisture meter (that I did not use first....) and I received a 12.5-13% rating.. To compare that number, I found some old pieces of 3/4" mahogany and maple living in the shop and their moisture level was about 12%. Would that 1% discrepancy be the culprit?
Moving forward I will alternate the clamps. And I agree 100% about the addition of diluted wood glue. It wasn't wise.
I took heed of your advice by adding some weight to the convex side of the cupping - I used a 3' x '3' piece of melamine and put 20 lbs. on it with my adjustable dumbell. If this is too much weight, please let me know :) I can adjust. I will monitor the top for 1 week, checking the moisture, cupping, and gaps along the way. Oddly enough, per my straight edge, it almost looks like it's cupping from both sides?? Is that even possible?
Having a better view of the underside of the table top now, I noticed I have gaps in the joints and no glue accompanying those gaps. Could the lack of glue coupled with not alternating the clamps be the main culprit?
I also agree 100% about the belt sander. If anything, I would make a router sled to flatten it.
If this doesn't flatten out after a week, I might start over with new lumber. The gaps on the underside make me think there will be problems down the road.
I really appreciate your advice MJ!
First, I totally agree with the comments offered by MJ. In my experience I'm not optimistic that the top will return to "flat". But I would certainly wait a few days before doing anything.
If my read is correct, the top is about 6o inches long and between 60 and 70 inches wide. In IMHO that is too large for 3 clamps and certainly the clamps should alternate over and under. I have learned that these large glue-ups do better when you place cauls above and below at the end of the boards and then clamp the panel flat all the while you are clamping the edges together.
Again, it is my experience to do perform the milling of lumber in two steps. I do an edge and face clean-up and stack the lumber for a couple of days or longer. Then to the final milling/sizing. All of this milling is done on both sides of faces of lumber.
Agreed on being patient! I've got 6-7 weeks to finish this table so I've got some time.
The final dimensions will be 60" x 43.5" including the breadboards. As of now, the table top panel is 60" x 45"..
I've used cauls in the past on plywood strip glue ups. I will definitely incorporate these on the next go around! This was my first time using a biscuit joiner for some reason I thought cauls wouldn't be necessary because the biscuits would keep the edges aligned. But that doesn't mean it won't cup. How hindsight really is 20/20.
If I end up starting over with new lumber, I will definitely do the "skip plane" method you mention.
Thank you for your input!
When I make a top for a big table, I glue it up in stages. My dining table consists of five 8-inch wide boards, since my jointer is an 8-incher. Counting the boards from one to five across the width, I glue up one and two, then four and five, then join the first glue up to board three (the middle board), then when that dries glue it to the four-five glue-up. Doing it in stages makes it much easier to keep things flat. I then put on the breadboards, which I do with Dominoes -- much simpler than doing the standard tenon on the ends of the long boards required for a table top.
Gluing this up in sections is my plan for the next go around. Using biscuits, I’ll dry fit to ensure the joints come together as they should. Since my top consists of (8) 6” pieces, I’m going to glue it up in halves and then once dried, join it together. Seems much more manageable than all 8 l!
I have noticed that most of the time red oak will move quite a bit as it acclimatizes (even if it is quarter or rift sawn). It takes a long time to stop moving. If worked while it still has moisture to lose, it will even crack and split. It would not be my first choice for a table top now. Weigh it when you first buy it and check it often to notice weight loss and when it stops losing weight. Moisture meters are good but weighing is something I would also do .
Great idea about weighing it ecyor! I never considered it - the red oak was not my choice, I'm building this table for someone and they like the red oak. Consider your tips noted! I personally prefer red oak for flooring..
Fully agree with letting wood acclimate to your shop and clamping from both sides. I have used cauls in the past which helped a lot. In addition, I saw a demo once where the maker cut the glue edges at very slight opposite angles. The claim was that it forced the wood to lie flat during glue up. Never tried it. Cauls & opposite clamping always worked for me.
Good to know Woodstock16! Thanks!
1/8 inch cuping over a wide glue-up is not uncommon and should easily be rectified by the breadboard ends and apron. The clamping method however will lead to a weak joint , you realy need more clamps distributed on both sides and you may have exceeded the glue working time. Search this site for glueing pressure, the May 2010 article suggests 900 psi for Red Oak, nothing most of us can achieve .
I agree with the sentiment that you can never have enough clamps.. This will be a trestle table and I'm trying to avoid any apron/top stretcher. The breadboards are definitely going on but wouldn't it too much stress be introduced to the seams by forcing the breadboards on with an 1/8" cup? I;ll look into that article now! Thanks Gulfstar
I agree with all of the above
I'll add this. Biscuits are fine and will keep the edges aligned.The width of the tabletop is your issue. You really need more support than just the ends. Supports (AKA stiffeners) accross the width at at least one, possibly two spots in the center of the top will restrain the top from cupping. Some achieve this by attaching metal channel or angle to the underside, I usually use a sliding dovetailed brace.
I love the idea of a sliding dovetail brace - I considered it but was a bit intimidated - is this a very complex process to add EdWeber?
Here's a link to a video with the process as part of the build. The sliding dovetail starts at about 8:50 but the entire video is worth watching.
https://www.youtube.com/watch?v=EksxQN7_Les
These can be as big or as little as you want. They can also be part of the leg assembly. There are many ways to utilize this method.
This is the exact video I was thinking of!! Ishitani is one of my favorites!
Consider letting this one go if you will be eternally unhappy living with it or delivering it to a client. Start over with fresh boards and incorporate all the very good advice given so far.
Then use this first one as scrap to dial in the cutting of your beadboard ends. Eventually you'll find a way to incorporate it into a project. A small matching side table maybe?
I agree - I’m too much of a perfectionist to live with something sub par to my standards. I like the idea of using it as my guinea pig for the next one should that be the case. Either way I’ve made peace with my situation. This is the only way I tend to learn - success through failure.
Thank you Elmaduro.
The one time biscuits truly suck is when you cut something apart and realize you have to lose 1/2-3/4" to get back to clean lumber! You'll be able to get the breadboards out of it at least.
Good point MJ - if I can salvage this wood for the breadboards and trestles themselves, I’ll be happy. My plan is to glue up some stock to create these pieces..
An 3/32 or 1/8 inch cup in a solid wood glue up almost four feet wide is not that out of the ordinary. You call it trestle table, so you don't have an apron in the equation, but a cup of that size will likely pull out when you fasten the top to the trestle crossmembers, even allowing for the fact that you won't want to over tighten the screws at the outer edges lest you present it from expanding and contracting. Getting a truly flat top at that width is hardly easy, and you say you're a beginner so I wouldn't beat yourself up too much.
While all the theories here have merit, I bet most/all the issue stems from your clamping technique and glue-up approach, maybe with an assist from imperfect edge joining, and only a little from any moisture change. It is very easy to introduce twist and cup when gluing up edge joined boards if the clamping pressure is not centered and balanced, which takes some experience and care to achieve and is made all the harder if you put all the clamps on one side. And depending on how the forces are in play, what seems reasonably flat in the clamps can bow as soon as released.
As I read your post, you glued the whole thing up in one go--what appears to be eight boards at once. If that is what you did and you managed to only get 1/8 in cup, my hat is off to you. That is way too many boards to try to glue up at once and be reliably successful, at least in a hobby setting, or at least by me. I would do it in three sub-sections.
Also, yes, you should put glue on both edges and, no, you should not use biscuits that are so tight you must whack them in with a mallet. That wastes time and will make it harder to close up the joint with the clamps, which are both antithetical to success. You should test fit the biscuits during a dry run and set aside any that won't go in with just a nudge (loose is OK, too, for this situation).
A belt sander is not going to help remove the cup. A belt sander is a good tool for removing the inevitable slight mismatches between adjoining boards and making the top feel/look "flat" in that sense. But be careful and resist the temptation to only sand the joints--you need to go over the whole surface with the tool even if that seems counterintuitive.
Finally, and most importantly, what you don't want to do is leave a wide glue up like that just hanging around for days or weeks unrestrained by being attached to something that will hold it flat. To do so invites really severe cupping. I make the top last for this reason, but if you haven't made the base you could devise some temporary arrangement.
Thank you so much for your input DS_NECT - despite the outcome I appreciate the compliment.
I agree with your prognosis of improper clamping technique, glue application, and taking on all 8 boards at once. Your point on the tight fitting biscuits makes a lot of sense. I'm not sure why so many of them were so tight. Perhaps I need to make two plunges with the biscuit joiner per each slot.
Also, your comment about the table top looking flat in the clamps until releasing it and presenting a bow/cup was true. The cupping was accentuated upon releasing the table top from the clamps.
Last night, I turned the table top upside down (convex side up) and just a few hours ago, I applied 25lbs. on top. So far, the cupping has been minimized but the lack of glue, visible gaps, and potential stress to the joints from the added weight makes me consider that this top should be rebuilt? Any thoughts to this? I've attached some pics of the gaps if you didn't catch them above..
IF I do, I will glue in sections, alternate clamps, dry fit the biscuits and apply glue to both sides. If I have to buy new lumber I will do this after letting the lumber acclimate for a week or two.
Thank you again!
My first advice is to set this top aside for a little while, a few days anyway, then come back fresh to deciding the answer to the question of what, if anything, to do different. During the interim, either attach the top to the trestle base, if built, or put it between battens, as someone else suggested.
Looking at your pictures, image #1 looks like a decent, tight joint. #2 and #3 appear to show significant gaps; something you might be able to get the point of a utility knife blade into, if I'm interpreting the images correctly. That's definitely not what you want, appearance-wise or structurally. But at the same time, it doesn't mean the glue-up is going to fail catastrophically, either. It's just a table top, not an aircraft wing. Tonight, I ate dinner on a white oak table I made around 20 years ago that lives outside on our screen porch and endures a regimen of rain and sun which has caused some of the joints to open up similarly, yet it's still going strong.
If, after sleeping on it a bit, you do decide to rebuild the top, you will want to rip the boards apart at the glue lines, using a table saw, a band saw or a circular saw guided by a straight edge. Start by splitting the glue-up in half as nearly as possible, so that you are then working with relatively manageable pieces. Once you have everything separated, redo on the jointer and glue ups in segments (which may themselves need to be jointed). Do the best you can but recognize that 100% perfection may not be achievable at this stage, but neither is it necessary. ...Whatever you do, it will be all right. I have been doing this 35 years and remain amazed both by what I made early on with little skill and tools and how much I manage to still mess up now.
Finally, don't plunge the biscuit jointer twice. It's normal that the fit of biscuits varies from somewhat sloppy to extremely tight, especially if the container has been open a while. Just set aside the outlier biscuits, particularly, in this application, the tight ones.
I really appreciate this DS_NECT! I splurged on a track saw (should be arriving in one week). Perhaps some battens will hold it steady until it arrives or I’ll just use a circular saw with a straight edge to bisect and finish ripping on the table saw. I made the top first and don’t have the base… next time I build a top (perhaps if I rebuild this) I’ll make the base first. I think you’re right about those gaps being big enough to fit a utility knife tip in. The good news is that the gaps appear to only be on the bottom side but I’d rather there be no gaps.
I will take some time to consider this - thank you.
And thanks for the biscuit tips! I’ll be sure to buy more than needed so I can have plenty to choose.
Being my first hardwood panel glue up, I’ve already learned so much from this answers on this post. I appreciate it!
Ditto! 1/8” over that distance? A child could push down on it to flatten it! All good comments, but a little overkill in some recommendations.
Thanks eddo234 - I'm happy to be in the ballpark of flat!
Never say "oops" always say "there" . We've all done it, I just did it. Sometimes I will make detailed plans all the way even to full size drawings and sometimes I just wing it. Scratch a sketch add some numbers and let the thing evolve. I'm making a small table,turned oak legs with walnut feet. My mistake was proportional and not structural. I began carving the feet and a couple of seconds into it I realized that what I saw in my head and what I had just committed to were not the same thing. So do you start over or do you change up? No one will know that I made a mistake, I'll know and it will bother me were I to see it again. I changed up. If I were in your situation I would change up. The materials are precious. You acquired them for the project. I would cut the top apart replane if necessary and rejoin them. So what if your table top is 44" and not 45". I would leave the dowels and work around them. They're not seen and trying to cut them out would cause you to lose too much material on each board. They won't hurt anything staying in there. You may have to modify your design, that can be a good thing.
I have timberland in West Virginia. I will harvest some trees get them to a mill , sawn into lumber ,wax the ends ,stack them stickered on an open truck and then driven to California. A few days at 60 miles an hour, add in a little Mohave desert and you have instant dry kilned. I suspect you may have had a little bit of that effect on on the lumber you transported. Oak is tough, it reacts. When the humidity is up I've found myself heating the shop to nearly 100 degrees to get the humidity down working with oak. I have never heard from anyone, " Don't let the wood acclimate. "
ahh the ol' surgical vernacular.. I like it Pantalones868. Thanks for this reply. I can definitely see the value in changing it up. The table is for a specific breakfast nook and ideally the table top will end up being the 43.5 x 60" I've set out to create. I do have an extra piece of red oak that could be added were I to resaw and plane... I also have never heard that either - funny enough though one of my favorite fine woodworkers on YouTube (Ishitani) builds a trestle table and appears to do so from a board that is outside his workshop. Maybe it was just set there temporarily but regardless I can see the value of letting it sit as does everyone else on here it appears.
Except me, I never believed in acclimating and never heard about it, and we processed one million bd.ft of hard maple a year into fine solid wood furniture that still holds straight today.
The pictures are telling, personally I would rip the panel in the joints and laminate a new one adding a strip for the lost wood, no biscuit.
"Except me, I never believed in acclimating"
Agreed, it doesn't matter. Make that everyone else but two...
Three. For production projects. For personal projects I usually let the lumber sit for weeks, only because that’s how long it takes to get around to personal projects. :-)
That's so interesting Gulfstar - did you mill to final dimensions all at once or in stages? I love woodworking but it's so challenging as there seems to be different opinions across the board (pun intended)...
Most of the wood came from our kilns and some dried lumber came in trucks. The rough lumber Is cut to length and then ripped, glued into panels and rough planed to about 7/8’’ for 4/4 . It then goes through a 36 grit timesaver for close to final thickness then to the machining department. Follows final sanding . This was the factory, skip the first 6 minutes and you will see pics of the kilns and plant, a 3 storey hardwood building now taken down for condos.
The people you see I worked with them, I was 24 then and just started my working life.
https://tvcw.org/visionner/CHEM/2042/A20060102-lusine-meubles-roxton
So Gulfstream. Are you recommending not acclimating or do you mean you dont? Your million board feet was it checked for moisture when you purchased it?
.. How long do you have it stored before you use it?
Milled to dimensions, milled to parts? Climate controlled work area? Where I've been involved in production runs from rough stock to out the door the materials have been around a little while, so you might say acclimated by default. Good dry lumber doesn't take long to equalize to an environment.
Wood came from the kiln on rails straight to the crosscut, came dry from trucks also with no delay to the cross cut. In Canada, in an old poorly insulated wood factory it gets 25% Rh in the winter and 60+ Rh in the summer, wood outdoor would be at 50% Rh. None of that mattered, if dried properly at 6 to 8 % well built furniture will whitstand seasonal changes . And yes, I bought the wood, and checked moisture on the dry wood with a pin meter.
My experience; I build at least 2 tabletops a month (on commission) edge-gluing various species. My all-time favorite was a Gabon ebony top. Hey, it was the client's $900+ for the wood alone.
Regardless, to the point. Acclimating or not, I'm a big fan of cross-clamping width-wise with a minimum of 2 cauls per for every 1-1/2' of length. Cauls or "stickers," depending on your teacher, will hold the boards flat. I like C-clamps for the job 'cause I can tighten the life outta them. Never had a top fail when they're cross-clamped.
Oh, you'll acclimate or not. Depends on how the vote for/against comes out.
Mikaol
That's really interesting Mikaol in regards to the cauls going down the length every 1.5'! I've only used cauls at the ends and it was for plywood. Think I'll incorporate this for Round 2 - Thanks!
Industrial QC in a massive facility drying its own lumber and using it straight from the kiln is apples and orangutans to this man with his truck trip and 5 clamps. Some levels of experience don't really scale to the basement shop where a chair build might takes weeks, not minutes.
It IS pretty cool to hear about though...will check out the video tomorrow.
As an engineer with a growing interest , another idea comes from old timber drafting board tables. A set of evenly spaced shallow longitudinal cuts on the underside , creates stress and cupping relievers, and can make the breadboard ends and any underside brace and cross board stiffener more effective.
“[Deleted]”
Thank you all so much for your input! I did not expect so many responses and I'm grateful for your time and words. I'll be updating you all throughout the process.
I would add, there might be some confusion over when to glue up.
I agree the boards could have acclimated more, It I doubt that was the problem. When to immediately glue up is after jointing.
The combination of the trestle and BB will easily draw out 1/8”.
Future reference, I always keep any size top in battens up until I’m ready to finish and install. That may be a life lessen specific to me and my environment —high/fluctuating humidity & no climate control. NOTE: be very careful where you store the top. The battens can create shadow lines impossible to remove. Keep it covered with a blanket. A lesson I’ve learned in an excruciating way!
Also, I’ve ripped a top apart simply b/c I changed my mind about the grain pattern. The biscuits won’t have an effect. The biscuits should be glued in.
When I have a wideglue-up, I build the rest of the project first. Then I mill, glue-up, and install in about 24 hours. Leaving a wide panel sitting around is just asking for trouble, even if it's just a ding.
The amount of cup the OP had for a really wide top is pretty minimal. Proper fastening to the table base is really all that's needed.
Thanks John_C2! From what I've read, the sooner I can glue after milling, the better. Also makes sense about saving the table top for last - I'll make this adjustment moving forward. Since your approach is to alsoi install within the 24 hours, do you sand the bottom of the table before attaching the base?
You may, depending on your particular environment and the Moisture Content [MC] of the stock you're working with, wish to mill the stock oversize first. Even to the point of jointing one face [usually the best] and then one edge first and then let it sit [Evenly supported, of course] for a few days before cutting them to just a bit oversize, checking them for dimensional stability, doing any necessary adjusting and then cutting the pieces to final size that are needed for each stage of construction. Yes, there is a world of difference between a professional manufactory replete with dozens of assembly line workers and a solo wood worker at his [or her] task in a shop built and set up for one.
Thank you for this! Yes - in retrospect I do agree with this process. I don’t see how taking extra time to mill in stages could hurt - however rushing the milling process just might?
Thank you RobertEJr - the moisture content is only about 1% off from the wood that's been in my shop for years - I'm still checking the MC over the next week to see how much it changes. It's dropped .5% since yesterday.
A couple days ago I flipped the table top over (convex side up) and now, what once was the convex side, is concave (only about 1/16-3/32").
I'm familiar with battens as in"board and batten" for siding, but what are battens for woodworking?
They are the same idea; cross pieces cut longitudinally [with the grain] that are attached cross grain to panels like doors, table tops, etc. For doors and panels, the best way is to have either the fastener at one end [or the center one] solid and the rest of them using a slightly elongated hole to allow for controlled seasonal expansion across the width.
For glue ups they are clamped to both sides [top and bottom] of the panel about every 1½'/2' to keep the panel as flat as possible. The panel is also clamped in an alternating sequence [bottom then top, usually, but not always, in an odd number] to pull the boards together, usually starting at the center first and then alternating towards the ends from there.
Thanks for the clarification! I’ve got lots of extra off cuts perfect for cauls
The cup "in the middle" is probably across the whole top, the 20" on one corner tilting up sounds more like twist. Might be just one board to fix.
Thanks again for your input _MJ_
That's correct in regards to the cupping and the corner board.. Perhaps I can just replace the outside board. But I might have an issue...
What I've deemed to be the underside of the table (which was on the underside upon glue up) has tiny gaps along the joints which I've attached pictures to above. In some of these gaps, you can't see any glue (I applied glue to only one board which was a mistake, although I covered that one board completely with glue. There very well may be glue in those areas where the gaps are, but my question is: Would this be a deal breaker for this tabletop? Can I not get any extra glue in there? Or would the breadboards provide enough support to prevent those gaps from getting worse? I know that depends on how well I make the breadboards and the environment the table lives in..
I agree with the comment below that the culprit may not be wood movement; it may actually be your preparation (working primarily off of your statement that you are new to this approach)
I highly recommend that you watch Bob Van Dyke's 'spring joint' video on edge joining two long boards. It is excellent, removes the need for multiple clamps (although cauls on the ends are still a good idea for wide glue ups), and creates a true and flat board.
Thanks! I'll check this video out today. I'm also expecting the book "Understanding Wood" which will be arriving today, and I've seen in other threads on FWW as highly recommended. Looking forward to it!
Gulfstar, I don't speak French, but the video felt a bit like a memorial... have they shut down completely for condos?
It gives me perspective on your affinity for big 'ol iron. That is/was a helluvah an operation!
Yes it shut down and the building leveled for building condos on the lake shore just behind. There was no way we could compete with offshore made furniture and the style became out of fashion and the owner did not adapt to the new market like Ethan Allan did in the US.
Well, dcodco101, sure looks like you've stirred up the almost never dormant "Help" gene in a lot of woodworkers. Good luck on your journey and just remember this: as much as I appreciated the late, great Jim Varney's sense of humor ["Know what I mean - Vern?"] his John L. Sullivan dealership commercials in Sacramento, CA.: "You know Vern, sorta like your first wife - 'Quick, Cheap and Easy'" doesn't always apply to the curve [a.k.a "Bumps in the road"] of learning.
I say that quote too often - I’m just so grateful so many people are willing to share their experiences. I look forward to passing the torch.
UPDATE:
I’ve been monitoring the moisture content and it’s been consistent with other wood pieces that have been living in my shop now for a long time.
I have decided to take many of the suggestions you all have generously shared, cut apart this table top, and start over with your aforementioned advice. I’m picking up where I left off on Friday and will post my progress until completion!
Thank you all again - looking forward to a well built table at the end of this.
Derrick
If it cups again, just tell people that it was intentional and designed for aerodynamic stability.
Ha!
Just completed the full re gluing of the table top last night!
I applied many lots of the advice given on here and overall it was a success -
*I left the old glue up as it was to further acclimate as was mentioned by many. After flipping the top over, the cupping did minimize some but it was still there. I monitored the moisture content and it was consistent with the other lumber in my shop. To be fair, the moisture content was already consistent with the existing lumber I've had already so I'm not sure that acclimating was absolutely necessary for this particular instance. However, leaving the glue up as it was (in cupped form) and unsupported was a mistake on my end as I went through the process of refilling/assembling as the boards had a slight bow from being left as they were. Even after sending them through the planer again only removing a small amount of wood from the faces 9mainly to clean up any glue residue from the prior glue up).
*_MJ_ recommended that I have to lose 1/2-3/4 of width to cut out the existing biscuits form the first glue up, someone else on here mentioned that I can just leave them in because they'd do no harm. I followed the advice of the latter because it seemed to make sense to me and I didn't want to lose more width from the table top. In my experience, this was not a good choice and threw off the new glue up for me. Here's why: when I'd re joint the edges, I'd get a crisp edge, but due to the nature of the biscuit after cutting, what was left of the biscuit would swell out beyond the freshly cut joint which prevented the edges from making a tight joint. I had to keep jointing the edges until I achieved an acceptable seam and proceed.
*Speaking of biscuits, I ditched my DeWalt #10 and went with Lamello's #10 after reading a few reviews about these biscuits being more consistent in size. However, they still fit far too tight after cutting new slots in the boards. I then tried re plunging slots in the existing biscuit remnants in the edges, against DS_NECT's advice, which helped some, but not enough. The problem was still present. I switched to cutting a #20 slot, thinking the extra lateral space would help but the issue lied with the thickness. I decided last minute to abandon the biscuits until I can figure out what the problem is. The lamella biscuits I ordered arrived in a cardboard box so I'm sure they've absorbed some moisture along the way. I had the thought in retrospect, what if I put them in the freezer? Any thoughts on this as a mean to contract them??
*I did the glue up in two installments: first, I glued up the table top in halves and then the next day (last night) I glued both halves together. This proved to be much more manageable!
*Glue: it was a sloppy job on my end but I made sure to apply more than enough glue to both edges. Even though the biscuits didn't fit super well in the first go, they sure made the panels come together flatter than this go, but I'm going to make a router sled today and flatten this top tomorrow when my 1 1/2" straight bit comes in. Fingers crossed the top doesn't cup until then.
*Alternating clamps: I think the success of a much flatter panel lied in this. I also used F style clamps to help keep the seams along the joining edges together and flat (although this didn't apply much to keeping the table top from cupping). I made sure to apply even pressure along the clamps as well as to tighten down a bit more than I did before.
*Cauls - I mistakenly didn't prepare the cauls for the glue up of the two halves but I utilized these for gluing them both together last night and I found them very helpful. I need to better prepare for the future with having everything laid out.
*After the glue ups, I verified the flatness with a straight edge. On one of the halves, I noticed the corner of one half of the glue up was twisting up. I loosened the clamp, and that raised corner managed to settle back down to a flatter position, and then I re tightened the clamp. I think the parallel clamp I was using was maybe not positioned to "parallel" and was clamping unevenly.
Speaking of parallel clamps I bought some Irwin 60" parallel clamps for this project (5) and noticed that these clamps actually bow! Maybe it's my user error that caused this but I was also told about this occurring with these clamps. I splurge for Bessey next time.
I'll keep you all up to date with the next steps!
- Derrick
Glad to hear things are progressing. ...I take it that you ended up skipping the biscuits this time, with the result that there was greater mismatch between some of the adjacent boards, in terms of their faces not being coplanar, even though the overall glue-up came out flatter. Even with biscuits, or some other alignment aid, but especially without, it's normal that a glue-up will need to be flushed up to address this condition, since even slight mismatches are very noticeable to the eye and touch. The relevant tools/techniques available to most of us hobbyists are belt sander (my go-to), aggressive random orbit sander, or cabinet scraper or hand plane, or some combination.
The problem with using a router sled is that you'll be revisiting the overall flatness of the glue-up, rather than simply flushing up adjacent boards (and notice that the latter does not require the former). That may sound like a desirable thing, but in practice it could introduce new issues, like your table top becomes noticeably thinner along one edge than another, not to mention all the extra work. (Router sleds are slooooow and usually leave a surface that needs a lot more clean-up than a planer, as I recall from the days when I used one for lack of having a jointer or planer.) But it could work, at least well enough, and if you've already done it this way, let us know how it turned out.
...BTW, I have never used Irwin's version, but it is definitely possible to bow clamps like that, especially when you get into lengths like five feet.
Thank you for another input!
You understood correct about the result of the second glue up.
And you’re right on the money in terms of the router sled. I just completed one side of flattening and it was a slow process. Yes - the finished result has left some very minor ridges but it’s nothing my random orbit sander can’t handle. And I definitely did remove more than a desirable amount of material. When I cut the first panel glue up apart, I cleaned up the faces with my planer for fear of any bowing from the panel sitting unsupported for so long. I should’ve confirmed every piece before doing so. After finishing the one side with the router sled, I’ve come to realize that the table top is now 15/16”! Much less than I had hoped for.
As I’ve mentioned, I’m still a newbie. This is my first hardwood project and my first table build. I’ve been researching so much and reading advice from others that varies so much. The guy who also works in my workshop suggested the belt sander to flatten the top.
The first reply on my forum entry warned to stay away from the belt sander. I’ve always known belt sanders to be very aggressive, to remove lots of material, and to not be a tool for accuracy.
When using a belt sander, how do you maintain a flat top without removing uneven amounts of material? Since I’ve removed more than I’d like, I’m hoping I can salvage this top by using a belt sander on the underside that I’ve yet to flatten. My plan is to add breadboards still.. would a 15/16” top be too thin for breadboards? Or would abandoning the BBs and gluing some extra wood to the bottom perimeter for a thicker appearance be better?
I’ll post some pictures soon of my progress.
PS - after flattening one side of the table top, and running out of time, I’ve clamped some jointed cauls to the end to help keep the panel flat until I finish.
Thanks again!
Why do you want the underside to be flat? Totally unnecessary.
I found the moisture meter readings of 12% to be high for a desert environment. It should equilibrate to 6-8% over time. Make sure to apply a specific gravity (species) correction for a capacitance-type meter and temperature and species corrections for a pin-type meter. The meters often come calibrated for Douglas-fir and oak will read 3-4% high (capacitance meter).
There is an argument for not equilibrating after machining. Wood looses or gains moisture faster at the end grain (end of the board). The ends of the boards will change width more if you cut parallel edges and let the wood sit a day and a moisture change occurs. When you lay up, the sides are no longer parallel and the glue bond is not as good. A similar thing can happen if the wood has recently changed humidity and the ends are at a higher MC than the center. It glues ok but if the ends are at a higher MC, they shrink more after gluing and stresses the glue line. Commercial shops may have issues when wood is machined on a Friday and glued on a Monday. In the home shop, I would saw a little oversized, equilibrate to let the moisture and internal stress change, then joint and make the other edge parallel.
If biscuits are a little tight, put them in the oven and dry them. I also had very tight biscuits and then change the cutter. The new cutter mad a huge difference. Mine is porter cable.
Glad to see you laid it up again and it's working.
Thanks for the reply!
I’ve had my meter set to the proper setting for red oak. I’ve checked the moisture throughout the entire length of the boards and they’re more or less consistent (.5% discrepancies).
As a control, I also checked wood that has been in my shop for at least a year. The numbers match which leads me to believe that this is as dry as it’s going to get.
I also purchased this from a nearby lumber yard which keeps the lumber in a similar environment as my shop.
Great tip about the oven!
I just happened to read your initial post today and saw that you’d already redone the top.
A few things…
I think you (and everyone else) is right that the primary cause for the problem was the one-sided clamping.
Some of the folks who think that acclimation is unnecessary have a lot more experience than do I. However, I’ll note that if one is resawing a board, acclimation is essential. I’ve experienced several situations where just resawing a flat, kiln-dried board yielded two halves with a bow or a twist. The faces inside the board that are exposed to air for the first time need to reach equilibrium before one continues. Similarly, many woodworkers will not take boards to final dimensions in a single session. Instead, they’ll get close, sticker the pieces, then take the last couple of passes on the planer on a different weekend. And finally, it’s a good idea to attempt equalize the amount of material planed off of each side of a board
I completely agree with those who are noting that biscuits should not be tight. I suspect - but do not know for certain - that Ishitani employs them for alignment (and don’t get me wrong, it’s really nice to get the extra pair of biscuit ‘hands’); strength-wise, they’re not necessary. You can experiment with edge gluing a board and attempting to break it at the glue line (good luck). Aside: Ishitani’s clearly a master; his method for creating the taper on the sliding dovetail is extremely clever.
When you’re going to build something like a tabletop, it’s a good practice to joint alternating boards on alternating sides. A simple way to do this is to fold boards that will be edge glued to each other and joint them together (just a light pass). The reason is that even if the jointer is not at a perfect 90 degrees, any error introduced will be corrected when the boards are unfolded.
When looking at your photographs, it appears that your table has the boards running from side to side, as opposed to lengthwise. In any event, if you’re going to put breadboard ends on the top, they need to be on the sides with the end grain. The value of tenons is that they allow you to restrict the movement of the wood mechanically and keep the top flat (the purpose of the sliding dovetail is the same) – without glue. It’s very important that only the center of the breadboard end is glued (maybe 8 inches in the center at most). All the glue is doing is keeping the top centered in the breadboard ends – the movement is directed from the center outward. Wood is highly hydroscopic, and the forces created are quite powerful. The consequence of gluing along the entire edge will be cracking in the top.
There are many strategies to allow movement while keeping the breadboard ends tight to the top – e.g., slotted holes for screws driven from the edges, slotted holes in the tenons that capture dowels. Fine Woodworking has many projects that discuss this; here are some YouTubes with good descriptions.
https://www.youtube.com/watch?v=EnghqwOrsbw
https://www.youtube.com/watch?v=TFn7JZmyFqk
Thank you so much for this thorough and insightful reply! I really appreciate it.
Yes - I do believe the one sided clamping was the biggest issue - lesson learned!
I’ve just started implementing all skip planing and stick wrong steps 1-2 days before final milling. Much better results and is worth the time. I started implementing removing material from both sides - I think I’ll start alternating sides in the planer next time.
The biscuit debacle hasn’t been tended to yet - still finishing up the table construction. I certainly used them for alignment as there was less deviation between the boards. The Dewalt biscuit joiner claims it’s also structural but I’ve heard both sides. I prefer them as a means for better alignment. Just need to figure out why they’re so tight. Think I might try the oven trick - or a vacuum chamber :)
Yes - I saw a video on YouTube about alternating jointed edges and it’s proven to be a game changer. I did so with the first attempt at the table top - came out very tight but the glue up is where the gaps came in..
The boards are actually running lengthwise / the table is almost as wide as the length!
The new glue up came out so much better! I’ll attach a pic below - the edge joints are very tight. I decided last minute to ditch the breadboards. My plan is to use figure 8 washers to keep the table top down. I’m also adding to thin supports which I’ll half lap in the trestle top to aid at keeping the entire table down and flat while letting it move independently.
Looks great!
Thank you so much _MJ_! Thank you for offering your advice to me. I’m still amazed by how all of the contributions. I hope this post helps others in need as others’ posts sure have helped me!
It does certainly look great. But I must applaud you for "staying the course". And, yes I was an earlier commenter, look at the sheer number of posts that required much thought and time; given a chance people are more than willing to help.
Thank you! I couldn’t agree with you more on how generous you all have been. I am so happy I decided to start over after my first attempt. I’ll share some pictures when the table is complete!
- Derrick
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