Gluing Doors up Flat?

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Forum topic by John Bauer posted 11-14-2009 05:06 AM 5817 views 2 times favorited 15 replies Add to Favorites Watch
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John Bauer

18 posts in 3117 days

11-14-2009 05:06 AM

I am building a bunch of cabinet doors for my parents and I have always struggled with keeping the doors flat. Square hasn’t been an issue. I have the parallel jaw clamps and everything I have read seems to indicate that is all I need. I have a flat bench too but I still get a corkscrew in about 1 in every 4 doors I try. I have been thinking about building some simple jigs out of MDF (which is flat by my standards) and some toggles or bolts – to emulate some of the commercial panel clamping jigs I have seen.

I am of two minds about this. The first is that what I am doing is good enough but wood moves … get over it and move on. The second is that I either need better tools (i.e. clamping jigs) or better technique. I am focusing on the tools because I think I am doing ok on the milling flat, etc. and because it is easier on my ego.

Any ideas or suggestions?

15 replies so far

View Julian's profile


880 posts in 3526 days

#1 posted 11-14-2009 05:16 AM

You need to make sure your stock is stable and flat. If you don’t give the wood time to acclimate to the environment it can move enough to twist a door. You also need to make sure you joint and plane your stock. Once all is flat and stable you shouldn’t have a problem with the glue up using your parallel clamps.

-- Julian, Park Forest, IL

View GFYS's profile


711 posts in 3472 days

#2 posted 11-14-2009 05:31 AM

Check to see if all the twisted doors are twisting in the same direction. There are many reasons twisting can occur. Diagnosing the problem can be complicated. The fewer variables you eliminate the easier it will be to diagnose.

View tooldad's profile


660 posts in 3716 days

#3 posted 11-14-2009 05:46 AM

When my students have that problem is because of a few possible situations. 1- didnt start with a flat board, meaning they didn’t face jointer then go to the planer, but more often #2 is the way the student handled the piece on the router, didnt keep it tight or flat when routing.

You can put a 1×2 scrap of oak vertical across the top and bottom across the stiles and rails to act as kawls (sp?) and then use a couple of c-clamps to keep them flat. I do that on some of my panels when gluing them.

View WhittleMeThis's profile


125 posts in 3374 days

#4 posted 11-14-2009 06:10 AM

I have seen a lot of problems due to wood stability, so you planed it flat cut it to dimension and all of a sudden its bowed, well it may have a lot to do with the wood itself. Well dried and accumulated wood has far fewer problems.

View gizmodyne's profile


1779 posts in 4091 days

#5 posted 11-14-2009 06:10 AM

Take a picture the next time you do a door glue up. You should be able to get them close to flat.

Do you have a good set of parallel clamps?

-- -John "Do I have to keep typing a smiley? Just assume it's a joke."

View mcase's profile


446 posts in 3130 days

#6 posted 11-14-2009 06:52 AM

Setting up some cauls with clamps can keep the stiles from drooping out of plane from the rails. But even so it doesn’t take much to skew a door. 1/2 degree out of plane can be a big warp over three feet. I confess that despite my best efforts in any series of doors I’ll get at least one warped. Part of the problem is in the milling. Its hard if you are using off-the-shelf dimensioned lumber. Currently I buy 13/16” planed three sides lumber. I do this for two reasons: one, its way cheaper than dimensioned stock, and two, by planing it to 3/4” and jointing it myself I get true edges and actual even thickness throughout. However, while starting with 13/16” allows me to get true thickness it does not allow for face jointing out any real warp. I have bee leaning more and more toward starting with full 1” rough-sawn when it comes to doors and face jointing and planing it true myself. I do not mind the extra work (I’m half way there already), but it does mean I’ll want a bigger jointer if I’m going to do any appreciable amount. Preferably a 12” but at least an 8”. I don’t know how your equipped, but if you have the capacity, starting with rough full 1” and face jointing out the warp and then dimensioning the stock yourself may improve your success rate.

View GFYS's profile


711 posts in 3472 days

#7 posted 11-14-2009 08:24 AM

whittlemethis is correct…if you have a warped board just because you plane it flat doesnt mean it will always stay that way. Timber bound wood can warp again.

View Catspaw's profile


236 posts in 3816 days

#8 posted 11-14-2009 01:52 PM

Cauls will force the work flat. If you have to force it flat….it’s not going to be flat when you release it from the clamps.

Unstable wood is no.1. IMO, if you mill up a blank out of warped wood, it will warp again. You will release tensions on it by milling it. If it wanted to warp in the first place it will continue to do so.

Reserve your naturally flattest stock for panels. Square edges from the jointer will ensure the two pieces will want to be in plane with each other. And I have a theory about clamping pressure. Too much compresses the joints and when released, the edges expand and could add to the problem.

We skip plane, then glue up, then mill to size (assuming you can handle the size thru your equipment.) It’s easier to glue up that way (less fretting about getting edges dead flat with each other.) Even with smaller equipment, you could do narrower glue-ups, mill, then assemble the wider panel with more care at the edge alignment. It also gives you some opportuniy to flatten the panel should it warp before you get to your final size.

-- arborial reconfiguration specialist

View John Bauer's profile

John Bauer

18 posts in 3117 days

#9 posted 11-14-2009 04:40 PM

Thanks for all the suggestions. I am getting ready to try that big batch of doors. From all the comments my Bessey clamps will be fine as long as my stock is flat. That is what I thought but I wasn’t sure. It is always tempting to think that we can invent a jig to get us out of any problem. Thanks all.

View gerrym526's profile


274 posts in 3809 days

#10 posted 11-15-2009 05:01 PM

I agree with all the comments already made about milling stock flat and allowing for wood movement. However, you don’t mention the type of joinery you’re using to put together the rails and stiles.
Another source of twist is the way the joint is cut. You may want to recheck the how the machines you use are affecting the way the joints pull together when they’re clamped.

-- Gerry

View Mark's profile


1807 posts in 3275 days

#11 posted 11-15-2009 06:38 PM

after clamping the frame together and square i also clamp it solid down to my flat workbench to make sure it doesn’t warp

-- M.K.

View Scott Johnson's profile

Scott Johnson

25 posts in 2664 days

#12 posted 03-03-2014 07:20 PM

I too have struggled with door glue ups but I finally have a method that works very well for me and it is easy.
Most importantly your stock must be dead flat and square. The rails must be coped square to the rails so I always make a few extras as it seems once in a while one slips in the coping sled or you just got it wrong somewhere. I also make my stiles over length and trim the door after glue up to square it. I also soften the edge of the raised panel a bit on both side with a block plane so it starts easily into the frame. My raised panels are sized to move with a little effort in the frame.
I made a simple fixture of MDF base with right angle pieces as seen in photo one.
Here is the glue up procedure, first I choose my stiles and rails to best match the raised panels grain pattern and add space balls to the frame. I then take a piece of 1/4 plywood cut slightly smaller than the raised panel and put the frame with the panel in the fixture and make sure that my stiles and rails fit together perfectly, if not I use a a spare and move on. (photo 2) After i Know the frame will work I put glue on the bottom rail and right stile and fit the raised panel into the fixture with as much hand pressure as needed to bed it into the frame against the stile and rail and keep it square, I then take a cabinet clamp and pull the raised panel into the stile just a little more than it should be.(photo 3) Next I put my glue on the other stile and rail, remove the clamp and fit the stile and rails onto the raised panel. Using one clamp in the middle of the stiles and another on the bottom of the fixture I put just enough pressure on the clamps to keep everything square against the fixture.(photo 4). Next I take one clamp and pull the top rail down to final length against the fixture, if you have the pressure right in the above step the rail will just slide down the stile nice and square. (photo 5) I then double check everything as to this point very little clamping pressure has been used. If all looks good I move the clamp from the middle of the stiles to the top of the rails and apply enough pressure on both top and bottom stile clamps to ensure nothing moves. I then add another clamp on the left side of the rails and move the clamp from the middle of rails to the right side. Very little pressure is on the rails It is just to keep the frame square. I then tighten up the stile clamps, top and bottom and use a damp rag to clean up the squeeze out. (Photo 6). Lastly, I clamp the frame down to the fixture to insure it drys flat. Here is the stack I just completed. Out of eighteen three had a very slight gap on one corner of the frame, (photo 7) Hope this helps


Somehow my photo’s were cut off on the right side when I went to post, I don’t know how to fix so just bear in mind that the fixture has MDF strips on the bottom and right hand side keeping all square.

-- Burning wood for heat is great-- such a fitting end for all of my mistakes.

View Greg In Maryland's profile

Greg In Maryland

553 posts in 2999 days

#13 posted 03-04-2014 12:22 AM


That was a great writeup. Thanks for pulling it together and sharing your approach with us.

My only thought is that I am wondering what else you have up your hat that you can share with us.



View Scott Johnson's profile

Scott Johnson

25 posts in 2664 days

#14 posted 03-04-2014 01:00 AM

Thanks, as I said before I’m just getting back into woodworking after a thirty year hiatus to feed the family. These doors are for my shop that is over my garage. It is the last big project for my shop and I will post pic’s of the shop after I fit the doors. I haven’t been doing any big projects other than the shop and a few small things to work on my skills and learn.

-- Burning wood for heat is great-- such a fitting end for all of my mistakes.

View Scott Johnson's profile

Scott Johnson

25 posts in 2664 days

#15 posted 03-26-2014 03:31 PM

Here are the doors after they were stained and installed.

-- Burning wood for heat is great-- such a fitting end for all of my mistakes.

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