Easy Cure for Miter Joint "Gaposis"





Introduction: Easy Cure for Miter Joint "Gaposis"

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

This miter joint is close to fitting, but it has a slight gap on the inside of the corner. Few things diminish a good wood project like miters with visible gaps. It is a great feeling to make a picture frame or install molding and have tight, clean miters.

Step 1: A Quick and Easy Solution to Miter Joint Gaps

Firmly clamp the members of the joint at the angle needed, in this case a 90 degree corner. Gently run a fine tooth saw down the joint between the two pieces. A back saw or a dovetail saw works perfectly. When finished, slide the members of the joint together and fasten in place with glue or nails.

Step 2: The Final Fit

This is the same joint after running a dovetail saw through it by hand. The fit is tight. The look is perfect and very professional.

If your gap is large, bring the two members of the joint together and run the saw between them again. In most cases, you will not create a fit problem for the other joints by removing a tiny bit more material at this corner.

If you are working at installing molding in a house, be aware that the corners on many walls will often be a bit greater or lesser than a perfect 90 degrees. Take a couple of pieces of 1 x 2 two or three feet long that are very straight. Fasten them together at one of their ends with a bolt and wing nut. Use this as an angle finder to check the actual angles of your corners. Measure the opening in the angle finder with a protractor. Adjust your miter saw accordingly. If there are still inaccuracies in your cuts, you will have less material to remove with a dovetail saw in order to get rid of any gapping.

This idea originally came from a high school woodworking textbook published in 1910. I believe it was called "Woodworking for Secondary Schools."



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    32 Discussions


    2 years ago

    This is incredible, and what with the timing your advice has to be a God-Send. I have alot of... erm...wonky joints to correct.

    1 reply

    I will soon be putting baseboard into a three bedroom house. I saw a Stanley Angle Divider someplace and recently did an Instructsble on how to make one. Still, some care needs to be exercised when transferring angles to a bevel finder and then to the saw. That Instructsble may be helpful to you, too.

    thanks for the info , just used your suggestions and they made a world of difference

    1 reply

    Thanks. I wish it had been my original idea. I am glad it helped you.

    Great tip! I've often ran into problems installing base boards because of the irregular corners that were over filled with drywall mud, or the factory taper used to bed the tape. I would just cut the miter less than a 45 degree so that the outside edge of the cut is "tight" and the inside edge only needs a little caulk at the top corner.

    Another problem is that the drywall board doesn't go all the way to the floor, and the base board sometimes "rocks" into the gap at the bottom, making your miter really hard to stay tight. If you find the bottom of the miter "opening" up, drive a drywall screw into the bottom plate, just under the drywall, to give your base board a backing in witch to rest.

    1 reply

    I am sorry I missed your comment. You have good solutions to common problems. Unfortunately, not every corner in a house is exactly 90 degrees. I had a little adjustable miter box and our neighbor needed trim in a couple of rooms for a social occasion. I think not one of the room and doorway corners was exactly 90 degrees. I used a bevel finder with a locking nut to check the corners and adjust the miter box. It took a little extra effort, but the results were good.

    Holly mackerel !…

    Why didn't I think of it ???…

    The simplest ideas are always the more brilliant !…

    3 replies

    I sure wish it were an original idea with me. I shamelessly stole it from a book. Since I have run into other people who learned it other places.

    I need a perfect miter joint for my custom screens. I plan to get a table disk/belt sander with a nice big disk. This tool has a miter guide for the disk. Once set up perfectly at 45 degrees, it will make a perfect miter joint, dead square to the lumber. My miter saw gets close, but when I'm cutting two inch thick lumber for corner braces, they can get crooked. This will make them perfectly square and flat.

    If all of your angles add up to 360 then all of your miters will be tight, even if none of them are exactly 45 degrees. It is kind of a case of 4 wrongs sort of make a right? So there is a trick to cutting them in pairs that is a little hard to explain but when you do it they always work out.

    I think I got it out of a woodworking magazine. You set the miter gauge for your 45ish cut, make two corners, put them together, then trim your ends without moving the miter gauge adjustment. Getting all of your angles correct involves flipping pieces over somewhere in the process. This is the big drawback of this technique if you are cutting moldings that aren't flat on both faces.

    Another trick is to err on the side of the outside being the gap, then run a metal rod on the outside closing up the gap. Wood is somewhat flexible in this regard :)

    I bought a gadget at a yard sale that sort of relies on your method Phil. I got it so cheap I just bought it for the saw it came with:


    1 reply

    The magic miter link is interesting. The nearest thing I have seen is a Craftsman electric miter saw with a device to push into the corner so the angle can be set on it. Then it is transferred to the two movable fences so they can be locked down. I think i understand the concept of flipping over complimentary pieces so the amount of error is reversed to make a 90 degree corner, still. (In the picture of the Craftsman miter saw the angle measuring device is stored on top of the electric saw.) Thanks.

    The clamp shown is adjustable. I bought it many years ago at a local hardware store. If you do not need the adjustable feature, you can get a fixed clamp for a 90 degree corner inexpensively here.

    This is a fantastic, simple tip that I never would have thought of myself. Thanks for sharing!

    From this day forth, all of my mitre joints shall be nanometre-perfect.

    1 reply

    I went a long time before I learned about this way of making good miters. After I learned about it I discovered most carpenters know and use it, as well as many others who work with wood. I wish I had been the one who first came to this idea and I could say it is mine, but it comes from someone else, as I mentioned. Post some photos of your projects sometime, if you have not already.

    what about the other 3 corners?,BEHOLD THE MAGIC EVERSHRINKING PICTURE FRAME,dont mind me i just stretch canvas over mine after sticking em together with a nail gun then wolloping with hamer to straghten up,a good quality miter chop saw would fix but im sticking with the £40 special with +/-5degree every way , a warped platter,rusty coarse blade and a really loud gearbox.