Whats the secret to miter joints?

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Forum topic by flysniper posted 05-19-2009 10:28 PM 16373 views 5 times favorited 29 replies Add to Favorites Watch
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3 posts in 3498 days

05-19-2009 10:28 PM

Topic tags/keywords: question oak miter saw joining

OK, whats the secret to miter joints?

I can’t seem to get them just right.

I’m using a 10” compound miter saw. verified it’s 90 degree square on the horizontal and vertical plane. but for what ever reason the joints never seem to ‘match up’ cleanly.
Trying to build a shadow box out of 1×6 red oak.

My joints STINK!
I’ve been trying on and off on little projects to get it right, I’m not eve close, not even in the same neighborhood.


29 replies so far

View SCOTSMAN's profile


5849 posts in 3789 days

#1 posted 05-19-2009 10:39 PM

your saw may not have been set properly at the factory.In fact it sounds as though it hasen’t so set it up yourself it should have minute setting abilities within the hand book check this and try again.I wonder if it’s had a fall at anytime or been knocked badly to set it off but it sounds like a facotry problem easy fix check the manual good luck Alistair

-- excuse my typing as I have a form of parkinsons disease

View PurpLev's profile


8547 posts in 3852 days

#2 posted 05-19-2009 10:40 PM

have you tried cutting oversize and planing down?

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View marcb's profile


768 posts in 3877 days

#3 posted 05-19-2009 10:42 PM

You need a near perfectly tuned saw, and use stop blocks so that, as skeezics said, you have exactly the same length. Anything else will fail you.

I’ve not done any in a while, but one tip I’ve seen is to cut the first couple long so you can verify the saw settings, then if you have 2 corners on 1 side that are open you cut that piece a hair shorter. Lots of trial and error to get a perfect one.

Also a miter trimmer will help you are going to do lots of them like frames.

View CharlieM1958's profile


16281 posts in 4422 days

#4 posted 05-19-2009 10:44 PM

Skeezics is right…. the opposing sides being identical in length is critical. Also make sure your pieces are flush against the fence when cutting.

Another thing is that it can take a lot of experimentation to get the whole thing clamped just right so that the corners are drawn together well.

-- Charlie M. "Woodworking - patience = firewood"

View a1Jim's profile


117340 posts in 3781 days

#5 posted 05-19-2009 10:55 PM

Hey Mike
when making miter joints you angle has to be dead on an all the pieces need to be exactly the same size.
Your miter saw is not accurate enough to give you good miters. Here’s a fool proof way to make miters. You first make a sled for your table saw that has a runner that fits in your miter slot on your table saw.
It can be made of hard wood, metal, or plastic, but it must fit your groove with out any play in it. then you attach the runners (TWO) to the bottom of a piece of 3/4” plywood so that its perfectly square to the runners. Some times its easier to put one runner on place it in the slot and mark were you second runner will go and the apply the second runner. after this is done the sled should run parallel to your fence assuming your fence is square. Next glue and screw some strips to the front and back of your sled at least 2 1/2 ” high so that you have a tray type sled . when attaching the 2 1/2” strips watch were you put the screws because your saw blade will be cutting part of the way through your sled. after making the sled you will tilt your table saw blade to 45 degrees and run the sled across the sled so that it cuts all they way through the plywood (ONLY) Now to making the miters you lay the wood flat on the sled and cut a 45 degree cut then you measure over on your sled to the length you want you box and clamp a piece of wood there as a stop.
Then you turn your wood over and cut the other end of the wood and you repeat until all four of your sides are done. The main thing to do is mark the end of each miter after you cut it right or left depending what side of the blade the cut was made THIS IS IMPORTANT because when you go to glue it up you put one of each on each corner One left and One right this makes sure you get good corners in that it will make up for your table saw not being dead on 45 degrees.
It may seem I’ve repeated what others have said but when I first started typing this there were not any other post.

-- wood crafting & woodworking classes

View flysniper's profile


3 posts in 3498 days

#6 posted 05-20-2009 12:10 AM

Any way you could provide a picture of said ‘sled’.
I tried to follow, but I’m a bit of a visual kind of guy!
I had not thought about using both sides of the blade. Using the miter saw, I would make one 45 cut using the right side of the blade, rotate the board around, and make the second 45 using the right side of the blade. I now see why it would be benefical to make one cut on the right and one on the left for each side.

I”m begining to believe that the Mter saw, is not the right tool for the job.
A table saw would be easier, but I guess that would depend on the length of wood. Might be kind of difficult to slide a 12 foot board with a 2 foot sled.


View Scott Bryan's profile

Scott Bryan

27250 posts in 4026 days

#7 posted 05-20-2009 12:57 AM

Mike, Here and Here are a couple of videos that John Nixon posted on building a sled with mitering capabilities. This will probably be the next project on my list.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View juniorjock's profile


1930 posts in 3969 days

#8 posted 05-20-2009 01:20 AM

Doesn’t matter if I use the miter saw or the table saw, if I don’t have stops set up so that the pieces will be exactly the same, the joints won’t work.

View Tim_456's profile


172 posts in 3799 days

#9 posted 05-20-2009 01:41 AM

I’ve had success with a jig that attaches to my miter saw that sort of ensures I’ll get a “perfect” miter. One thing i’ve found is that it’s difficult to make to 45deg cuts but it’s not difficult to make complimentary cuts. Basically if one cut is 46deg the other can be 44deg to still add to 90 ;) To do that I have a jig that’s 90degrees where the vertex of the angle is sheared by the blade. It’s basically a V with the point aiming at the blade. I put one stick on one side and the mating stick on the other side. If the set up or saw is off, the slop is taken up by the complimentary angles. I also use this on my table saw and RAS. it’s not perfect and you still have to get all four sticks the same length, but it does help to minimize the slop in the saw or any inaccuracies. I’ll post a picture when I get back home and hopefully that’ll make more sense;)

View Marc5's profile


304 posts in 3546 days

#10 posted 05-20-2009 02:41 AM

I had the same problem and one of my friends introduced me to shooting boards. Cut the piece about a heavy 1/32 big and plane it down a few thousands @ a time with the shooting board until the board is the right size. It works for me.

-- Marc

View scrappy's profile


3507 posts in 3634 days

#11 posted 05-20-2009 09:17 AM

Found out the hard way my pre set stops for the miter saw are NOT at 45deg. Did my adjustments and all is fine now.

Also one of the biggest problems with miter cuts is the material wants to move just slitly as the blade pulls to the angle. Put a piece of sandpaper on your back fence with pressure adhesive and it will keep your stock from creeping. This will ensure that the start and finnish of the cut is in the same place. ( it only needs to move a few thou and your joint will not match)

Good luck.


-- Scrap Wood's the best...the projects are smaller, and so is the mess!

View dustbunny's profile


1149 posts in 3499 days

#12 posted 05-20-2009 11:52 AM


a1Jim has the answer. I was also having trouble cutting angles for 45deg, did some research and found a table saw sled is the way to go. I caved in to my dislike for building jigs and built one, the results you will get will be amazing. I use mine all the time instead of the miter saw or miter attachment. Invest your time into building one, you won’t be sorry.


-- Imagination rules the world. ~ Napoleon Bonaparte ~

View Steelmum's profile


355 posts in 4166 days

#13 posted 05-20-2009 12:51 PM

Do not miss the creeping described by Scrappy. Creep is the enemy!

-- Berta in NC

View NY_Rocking_Chairs's profile


521 posts in 3801 days

#14 posted 05-20-2009 02:14 PM

When it comes time to glue up. Use masking tape to tape the pieces on the outside of the miter. You can still lay the two pieces flat on the table, apply glue and then “hinge” them together. When I built the knife block, the main block is all mitered corners. I taped the 4 pieces together, laid them flat on the work surface, applied the glue, rolled the box together and then applied my strap clamps. The tape kept the joints from shifting around on you while you are getting the clamps tight.

For ensuring each side is the same you could start with a board twice as wide, cut the miters on the table saw and then rip the board in half, you will have 2 identical sides that are guaranteed to be the same size.

-- Rich, anybody want a peanut?

View Francisco Luna's profile

Francisco Luna

943 posts in 3597 days

#15 posted 05-20-2009 03:30 PM

Mike, I have never tried a box, but as a Finish Carpenter a can give you some keys:
-Make sure your blade is sharp and its intended for finish, 60-90 tooth (CMT, Freud Industrial, Matsushita). Allow the machine to reach full speed before making the cut. I have seen people plunging the arm when the blade is barely spinning.
-With an accurate square, preferably a machinist combination aquare, check your blade in reference with your fence and base, at right angle.
-Visually inspect the machine, look for imperfections, bent parts, loosen bolts.
-wood in NOT something “mathematically right”....... it moves! So, my best friend when doing casings joints or installing crownmolding is a SHARP adjustable mouth – Low Angle Block Plane. when I find an small gap, acouple of shaves will take care of that. believe me,you can have the $1400 Festool Kapex in your shop and still have the same problem…it’s not the machine, it’s the wood!

-- Nature is my manifestation of God. I go to nature every day for inspiration in the day's work. I follow in building the principles which nature has used in its domain" Frank Lloyd Wright

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