miter joint glue-up problem

[jim gossage]

i am building some small picture frames, about 5x15", and i am having a problem getting my miter joints to close during glue-up. the frame pieces are flat except for a 1/4" dado in the back. during a test clamp with a band clamp, all 4 miters close perfectly. then, i brush on a thin even layer of tite-bond III on each miter surface, and clamp it up. the frames come out perfectly square, but each joint is open very slightly to the naked eye (probably by a few thousandths). it seems like the glue is producing a thin but finite layer that widens the joint. any recommendations on how to solve the problem? is the problem inadequate clamp pressure with the band? please save me - christmas is looming ever closer!

[Todd Jensen]

Inadequate clamping pressure. Personally, I don't care for the band clamps as I think they leave too many variables - its simply impossible to target equal pressure to all miter joints with one clamp IMO. I like a Maestro style spring clamp for miters. If your cuts are true, your frames will still turn out square by using individual clamps for each miter. The clamps pictured are pretty big but they have small ones for delicate work.

http://i191.photobucket.com/albums/z66/grizzified/m1201_clamp-all.jpg

You can find them or something similar at your local woodworking store. The best price for them that I've found is online at coastal tool: http://www.coastaltool.com/cgi-bin/SoftCart.exe/clamps_vises/maestro/m1201_clamp-all.htm?L+coastest+xhqz7432ffb4e9b4+1198004705

[keith ouellette]

I have never done it but read an article about about this subject. It involve 4 wooden l's with perfect 45 deg angles. The l's were placed at the corners and i think the trick was to use four clamps. two one way and two perpendicular and put very light pressure on the first two then the other two in a way that all the gaps closed evenly. I think the first two clamps were only used to line everything up and then by tightening the perpendicular ones the l's wood keep the pieces from slipping. Hope that made sense. It has been a while since i read the article.

[Will Blick]

45 deg. miters seem to be the most perplexing joint to many ww's. The simplified check list is as follows.

1) Insure that cut is exact 45, or the total of the two sides = 90 deg., which is the benefit of using a miter slide, cutting each piece on the opposite side of a stationary blade.

2) Insure there is NO bevel angle on the blade (which can expose a gap, even if you have perfect 90). Again, a miter sled is self correcting in this regard.

3) Insure opposite sides are of EXACT length. Cut them together, or cut without moving the stop. Lay them atop each other to be assured they are identical lengths...

If you pass these 3 items, you are assured a PERFECT dry fit.....

With a perfect dry fit, clamping method is not as significant as you are not forcing the clamp to overcome cut errors. However, you are still confronted with an end grain to end grain glue joint, which, at best, will be a weak glue line. Assuming there is no stress on the joint, biscuits or other loose tenons are not required.


A good miter clamp is one where the clamp force is going THROUGH the middle of the miter joint. The spring clamp shown above is a good example, but sometimes they leave small dents in the wood. If this part of the wood will not be exposed, they are an excellent and fast miter clamp system. Here is another one...

http://www.miterclamp.com/302_1choice.jpg

If you can't live with the dents, then you need a more complex type clamp system to pull the joint together. Here is an example of a GS system that will direct the clamp force IN THE MITER JOINT.

http://www.mikestools.com/Carpentry-Tools/gross-stabil-miter-clamping-system-mcx.jpg


This GS side clamp miter system comes with a few different angle blocks for 45's, 22.5's, etc. The nice part of this system is, it works well with profiled wood, such as picture frame moldings, as it grabs the ends of the moldings, not the decorative face.


However, if the wood is flat on both sides, clamping becomes easier. I use this clamping system, which will work with ANY miter angle...


http://www.mikestools.com/images/Gross_Stabil_Pages/Gross%20Stabil%20Pictures/gross%20gsp%20lar1.jpg


Of course, not all miter joints require such attention...but for my critical miters, (either expensive wood, or miters that will experience future stress) I apply the proper clamp system. It does eat up a lot of time vs. the spring clamps, so pick n choose wisely. The spring clamps are excellent for door casings, where the joint never has any load on it, AND, the wood is nailed to the wall, something a frame does not have the benefit of.

But keep in mind, all miters are subjected to the stress of the wood expanding across its width. This is the greatest cause of miters opening up in the future. It doesn't matter if the wood expands or contracts, the joint will open as it changes the angle of the cut, i.e., you no longer have a perfect 90. The greater the wood width, the greater the risk of the joint opening from exp./contraction. Anything 4" or wider, I invest the clamp set up time to insure a closed miter for many years. I also may add a spline or biscuit.

Of course, you should pay attention to the moisture content of the wood also, no different than making furniture. And like furniture, you must consider your finish as another line of defense. This is the reason, in the picture frame industry, both MDF and polystyrene moldings (with decorative faces applied) are so popular as they eliminate the "future opening" variable. If the joint has no gaps when complete, it should be good for life, assuming no mechanical loads loosen it.

Hope this helps...

[Dan Barr]

These aforementioned clamping systems are all very nice.

If you have the money, get one of those. the system im going to tell you about can be frustrating. until you practice it a few times you might not understand how to square up the frame.

here is what i do for some of my miters.

The blocks with the tall dadoes can be bought or made. cheaper to make them. i just cut a 1/4" dado about 2" deep in a 3" x 3" x 3" block. space the dadoes 7/8" or 3/4" from the outside in order to leave sufficient room for the clamps. Then i made the little corner blocks as well. just three small square scraps, PERFECTLY SQUARE AND PERFECTLY FLAT. Screw them together. if you screw up the corner blocks teh system wont work. if your piece isnt flat and the corners dont come out to 90 degrees, then you will push your miter apart by the same amount of error. (clamping will push your miter at 89 or 91 degrees, miter will split on top or bottom, the two contacting corners will shear past one another and the joint slides apart.)

Pressure applied to the clamps must be deliberate and slow. you can alternate from one diagonal of the frame to the other or from one side of the frame to the other. (AS LONG AS YOU DO IT SLOWLY) slow is the only way to keep the assembly square. check for square as you apply pressure too.

in the configuration shown, you could apply pressure to the bottom right two clamps at the same time, then the other two clamps at the same time (top right and bottom left). or you could go with the bottom two clamps then the right two clamps.

i usually give a half twist per then switch to the other set. Once you get the hang of this system you will think that you can really get tons of pressure on the miters. DONT DO IT! once you get too much pressure on any one corner the joints will start to equalize. this will slowly push the frame slightly out of square and leave you with gaps. once you have the corners snugged and square, only give the clamps a couple more half twists each.

Wax the insides of the corner blocks to prevent glue from gripping and sticking your frame to the blocks.

v/r

dan

[Greg Cole]

KP blocks are sold for bessey clamps. Identical to what Dan posted but made from plastic & not made from "free scrap" in the shop.
I bought a set of KP blocks for my collection and now have a wooden set so I can clamp 2 rail n stile doors at a time for example.
I won't comment on the other clamping "systems" as I have no hands on, I find ways to use the clamps arsenal I already have as storing special use stuff or things rarely used is a PITA.

Cheers.
Greg

[Mike Golka]

It may be as simple as doing a rub joint with the clamp you are presently using. This is a technique that segmented turners use to join the segments of the rings. All you do is after applying glue push the joint together and move the pieces back and forth against each other to sqeeze the excess glue out. Work in such a maner as to end up with 2 halves for the final 2 joints.

[Will Blick]

Greg, I will 2nd the notion of "storing stuff".

There is always a better tool to do a job. But, you have to find it, pay for it, learn it, then, the inevitable question, where to store it, then wonder, how often will I use it? Shop space is at a premium...

[Charles Wiggins]

i am building some small picture frames, about 5x15", and i am having a problem getting my miter joints to close during glue-up. the frame pieces are flat except for a 1/4" dado in the back. during a test clamp with a band clamp, all 4 miters close perfectly. then, i brush on a thin even layer of tite-bond III on each miter surface, and clamp it up. the frames come out perfectly square, but each joint is open very slightly to the naked eye (probably by a few thousandths). it seems like the glue is producing a thin but finite layer that widens the joint. any recommendations on how to solve the problem? is the problem inadequate clamp pressure with the band? please save me - christmas is looming ever closer!

Check out this solution: http://www.newcastletriton.asn.au/Hints%20&%20Tips.htm#Mitre_Joint_Gluing_Jig

Or this one:
77428

Or maybe something like this combined with the band clamp. If you make the notches slightly tighter than 90 degrees, that should put the force toward the center of the miter joint.
77432

[Dan Barr]

Charles,

im going to have to oppose you on the engineer cornered blocks. i made a set of those (at exactly 90 degrees) and they were quite the mess. they have no bottom support to hold the faces flush. so, you have to go around feeling the faces and checking fror flush on top of checking for square. there is really not enough time in my opinion. (especially if your using Titebond or any other PVA glue)

Another thing that those blocks do. they lead you to believe that you could just clamp the opposite corners. it does not work. you will inevitably force the frame out of square. also, the clamps tend to fall over because you have nothing to hold them in a particular position.

the pictures i posted show the corner blocks which are similar to your engineer cornered blocks except my corner blocks havethe bottom support, are square, and are used in tandem with the clamp holding blocks.

Those blocks could be made to work but you'd end up making the same thing i have posted.

v/r

dan

[Todd Jensen]

For me, I use the clamps I mentioned above almost daily so they work out. The reason I like that type as opposed to some of the other systems mentioned is that there is no clamp weight involved, which can sometimes tweak a joint. Also, these other systems require a bit more fussing with than the simple spring clamp, and the small indentations left are really very minor if you use an appropriate clamp size for your project. JMO, you probably should just experiment and see what works best for you. I think all of the options mentioned are viable solutions, and while I recognize storage is a premium, I don't think you can have too many clamping jigs and/or jigs in general. I work out of a 20x20 garage that also houses my ATV and still have plenty of room for jigs. (Of course, my friends call me the 'fabricator' or the 'jigmaster', so I realize I'm a little jig eccentric)...:D

[Lee Schierer]

There are lots of different clamping systems available. My personal favorite type is 90 degree corner pieces with threaded rod running from one to the next. Here is one type: http://woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=71712&LARGEVIEW=ON

However, the clamping system doesn't answer your question. Where did the gaps come from. If your joints were in fact tight when dry, most likely you overclamped the pieces when you applied the glue and clamps, bowing the individual side pieces slightly causing the joints to appear as if they had opened. With long or thin frame pieces it is fairly easy to bow the sides and throw off the corners. It doesn't take tons of pressure to glue miters. In fact the cheapest clamp you can use is simply tape. You can lay the pieces flat on tape (masking or strapping) and place the next corner tight to the first, then fold the whole thing up to make a square, taping the last corner. Check the fit, open up one corner so you can lay the pieces out in a line flat, apply the glue and fold them up again. Cheap, easy and it works. :D

[Will Blick]

Charles, that newcastle glue joint jig was brilliant. WW's sure are resourceful. I would think that jig is will provide max. pressure, with minimal fiddle time. Only drawback is, you can only do one joint at a time.

For speed, I like the picture frame 4 corner clamp with the threaded rods. All 4 corners can be joined simultaneously. Pressure should be sufficient for most miters. I may have to try one .... but, then, another jig, another thing to store :-)

[Charles Wiggins]

Charles,

im going to have to oppose you on the engineer cornered blocks. i made a set of those (at exactly 90 degrees) and they were quite the mess. they have no bottom support to hold the faces flush. so, you have to go around feeling the faces and checking fror flush on top of checking for square. there is really not enough time in my opinion. (especially if your using Titebond or any other PVA glue)

Another thing that those blocks do. they lead you to believe that you could just clamp the opposite corners. it does not work. you will inevitably force the frame out of square. also, the clamps tend to fall over because you have nothing to hold them in a particular position.

the pictures i posted show the corner blocks which are similar to your engineer cornered blocks except my corner blocks havethe bottom support, are square, and are used in tandem with the clamp holding blocks.

Those blocks could be made to work but you'd end up making the same thing i have posted.

v/r

dan

Dan,

Sorry you don't like that idea. I was just playing off of the fact that Jim was using a band clamp. Notice I said to make the notches SLIGHTLY TIGHTER than 90 degrees (89 1/2 or so). If you were careful and sized the block so that the tips of each side of the notch came halfway down the miter the effect of this would be to pinch the two sides toward each other with the pressure in the center of the miter, not toward the inside or outside ends of the miter. Basically a shop-made version of this: http://www.woodpeck.com/besseyvariangleclamp.html

I certainly wouldn't try that type of jig with bar clamps - that would be a PAIN in the asterisk. As far as face alignment goes - what about having a bottom on your corner blocks prevents one side of the miter from rising? With my system, once the band clamp was set you could put a single F-style clamp across both sides of the miter face to even it up, as long as the face and back were relatively flat. Otherwise I'd dowel the joint.

If your system works for you, GREAT! Maybe it'll work for Jim too. Just trying to give him options.

[John Gornall]

Get a picture framer's vise. These were originally made by Stanley about 100 years ago. There are usually lots on ebay or you can buy a new imported clone such as the Professional Miter Vise at Woodcraft.

They are a great way to join frame corners. A little glue and clamp one corner at a time. You can tweak the joint into perfect alignment as you tighten the vise. The vise allows access to the outside of the corner so you can drill and put in a brad or 2. Use a nail set to put the brad below the surface and fill with a wax filler.

This is the way most framers joined frames in the 20th century and many still do.

If you want to go a little further and have lots of frames to do get 4 of these vises and put them on a flat level table so you can do 4 corners at once.

[jim gossage]

So many jigs....so little time! thanks all of you for your ideas. its amazing how many different ways it can be done. i need to spend a little time figuring out which way will work - and get the frames done by christmas. i'll update you with my progress after xmas. thanks again

[Charles Wiggins]

Dan,

Sorry you don't like that idea. I was just playing off of the fact that Jim was using a band clamp. Notice I said to make the notches SLIGHTLY TIGHTER than 90 degrees (89 1/2 or so). If you were careful and sized the block so that the tips of each side of the notch came halfway down the miter the effect of this would be to pinch the two sides toward each other with the pressure in the center of the miter, not toward the inside or outside ends of the miter. Basically a shop-made version of this: http://www.woodpeck.com/besseyvariangleclamp.html

I certainly wouldn't try that type of jig with bar clamps - that would be a PAIN in the asterisk. As far as face alignment goes - what about having a bottom on your corner blocks prevents one side of the miter from rising? With my system, once the band clamp was set you could put a single F-style clamp across both sides of the miter face to even it up, as long as the face and back were relatively flat. Otherwise I'd dowel the joint.

If your system works for you, GREAT! Maybe it'll work for Jim too. Just trying to give him options.

At least the editors of Woodsmith and ShopNotes like my idea. (http://www.woodworkingtips.com/etips/2007/12/21/sn/print/)

[Jim Dalton]

Will Blick's check list is essential. I use an Incra 1000 SE and one of those digital angle gauges with the rare earth magnets to insure that I have a perfectly fitting frame when it is dry fitted.

I then turn the frame components upside down on my bench, that is, with the inside of the frames down, and put a long strip of fiberglass reinforced tape along what will be the outside of the frame. If the frame is to be rectangular, I start with a long side.

Where the miter joints meet, I allow about 1/32" overlap of the sharp ends of the miters. Once all four frame pieces are taped, but with no tape excess on the ends, I flip the entire assembly over and apply glue into the open miter joints. I like the Henkel single component polyurethane liquid in a bottle which I buy at my local Lowe's home center. It seems to give a better bond on end grains than Titebond, which I used before. But, as Will said, if the joints are not stressed, most any good glue will work.

Then just fold each miter joint up, letting the tape create sort of a band clamp. For the last joint, I add a second piece of tape to hold the final joint together.

This works well for me, I make several hundred frames a year as shadow boxes for displaying art tiles made by LOML.

[jim gossage]

i ended up using charles wiggins' suggestion for corner blocks along with my band clamp. it was the easiest thing to do on short notice and seemed to do the trick w/o much fuss. thanks again for all your help.

[Charles Wiggins]

i ended up using charles wiggins' suggestion for corner blocks along with my band clamp. it was the easiest thing to do on short notice and seemed to do the trick w/o much fuss. thanks again for all your help.

Jim,

Let me know how it worked.

[frank shic]

i get AIRTIGHT miter joints with the aforementioned clam clamps sold my jim chestnut.

[Will Blick]

Jim, just a quick FYI regarding stress on the glue joints.....

Putting aside stresses of the items put in the box, (which is usually not significant), the largest stress load on a miter joint on a frame, is usually expansion / contraction.

so... to be clear....

When making mitered boxes (called shadow boxes in the picture frame field), the end-grain to end-grain joint lies in the "least effected" plane for future expansion / contraction. The reason is, if using the same wood on all four sides, with same grain direction (something you should pay attention to), all future expansion and contraction of the wood, at the joints, occurs uniformly on both sides of the joint, as the wood expands / contracts over its width. So when the shadow box gains height from expansion, it does so evenly, not putting stress on the glue joint. Consider this joint a freebie, as it handles very little stress over its life from expansion contraction. Very few joints in ww are this fortunate :-)


But, the opposite is occurs with a flat miter (picture frame style). Here, the expansion and contraction of the width alters the angles of the miters, forcing the miter joint open. The wider the boards, the harder it is to keep the joint closed over time, as the forces become greater, wanting to open a larger gap. I once read on high-end door casing, where it will experience different humidity levels over time, they won't miter boards over 3". No gluing / clamping technique will hold them together, the stress is too great over a long of a period of time. Hence why I use biscuits or half lap when I try to miter 4" picture frames. This is also why you see a lot of picture frames with open miters.

It would be nice if a good finish insured no expansion / contraction over time, but this is not the case. Finish only slows down the absorption / evaporation of moisture in the wood.

[jim gossage]

will,
very interesting, thanks

[J.R. Rutter]

One issue that no one has mentioned yet is the reason that a perfectly cut and dry fit miter is open upon glue up. Any water based glue will soak into the end grain and cause local swelling. As the wood gets wider, it opens up the joint on the outside. Tight clamps help to overcome this until the glue dries and the wood shrinks back to the original dimension.

I've done cabinet doors with 3-1/2" frames and seen this happen in spades. For wide joints like this, I cut the miters so that they are slightly open on the inside. After the glue dries for a week or so, the joints look good.

[jim gossage]

One issue that no one has mentioned yet is the reason that a perfectly cut and dry fit miter is open upon glue up. For wide joints like this, I cut the miters so that they are slightly open on the inside. After the glue dries for a week or so, the joints look good.

how open would you cut them, 90.5 degrees? more? less? thanks

[Nissim Avrahami]

Hi Jim

I'm only an amateur and did not make so many mitered frames (maybe 10 in total) but I never had problems with gaps.

There are a few conditions for a mitered frame to come up square and tight:

1. The frame members (2 and 2) must be exactly at the same length

2. The miters must be at exactly 45°

3. The miter must be cut at 90° (vertically)

In theory or CAD there is no problem but, in real life, it's a little bit different....the frame members might not be exactly the same length.....the miter can deviate a little bit from 45°.....and maybe the blade is not "dead on" 90°...

For those reasons, I developed my own cutting method that you can see on the link (wow, it was my first post in SMC), and never had problems....you can also see my shop made clamping method....
http://www.sawmillcreek.org/showthread.php?t=36590

Regards
niki