# Why won't my 45 degree corners every line up?



## wilschroter

Hey guys, I can't for the life of me figure out why when I cut 45 degree corners for doing trim (door frame, window casing, etc) that the joints never seem to line up properly. I'm using a solid DeWalt miter saw and pay extra special attention to make sure my work is pressed well against the fence. Yet - I constantly get these gaps like you see in the photos.

Is there an obvious trick to this? I've cut an awful lot of wood, but this is one thing I can't seem to figure out.


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## putty

I get that too, my thoughts are that the blade is flexing. Try taking a slow easy cut


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## wilschroter

@putty I'm already taking it pretty slow, but given that the miter is locked at 45 degrees, I'm not entirely sure how there could be much play in a 3/4" cut depth. That said, I could be totally wrong I just didn't think that short of a cut could allow for that much variance.


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## Unknowncraftsman

I think it's because the cut is not flat. 
Could be the saw could be the material moves during cutting.
Lay a ruler on the cut hold it up to the light and look with your best eye.
Good Luck


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## LeeRoyMan

Is the board your wrapping around square? That could be holding you off.
The angle of your fundangle could be off. 
Or your wood could be moving as your making the cut. (a duller blade facilitates this)
Try clamping the piece to the fence and then make the cuts.

I'm sure you have checked, but if the wood was moving while you were setting up the saw, then you won't know if the saw is right. You need to clamp the wood to make your test cuts setting up the saw.


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## wilschroter

I suppose I never thought about the wood moving during such a short cut. I assumed I could hold it in place for the 5-10 seconds (at most) it takes to make the cut. I think you guys are suggesting that during that time, the work is somehow moving slightly along the fence.


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## LeeRoyMan

> I suppose I never thought about the wood moving during such a short cut. I assumed I could hold it in place for the 5-10 seconds (at most) it takes to make the cut. I think you guys are suggesting that during that time, the work is somehow moving slightly along the fence.
> 
> - wilschroter


Don't assume, It happens. You don't have to take my word just make some cuts, with your wood clamped, and see if it makes a difference. The point is to eliminate probable causes.


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## MrRon

I don't believe any saw will cut a 45° miter ±000. No mater what saw you use, there will always be ±degree off. Just a couple of thousands off from 45° can result in a gap. The longer the cut, the more noticeable will be the gap. Woodworking doesn't rely on precision. A 1/64" (.015") tolerance is all most will hope to attain. The nature of wood doesn't allow for precision machining as it does for metal. Wood is subject to expansion/contraction/warping, cupping, twisting, bending, etc. Even a perfect 45° miter will over time open up. That is why they invented wood fillers, putties and "gap filling" glues and epoxies. The best one can do is to make the miter as close as you can and fill the gap afterwards. Don't fret it; we all have the same problem. I also do metal working and angle cuts can also be difficult, even with the machinery and precision tools at my disposal.


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## Delete

+1 Mr.Ron.

Those cuts are not that bad for a miter saw, a light mitersaw coupled with the high speed of the blade will generate some vibration even in the best balanced blade and drive, the vibration will cause some creep.Unless the work is firmly clamped and the miter perfectly set, that much of a gap is probably average results.

If you take your miter and using a mitering jig with a hand plane, a couple of passes with the plane will give you the perfect miter your looking for. If you have deep pockets and do lots of mitering, requiring perfectly trimmed miters, a miter trimmer like this is the way to go IMHO.


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## sansoo22

+1 For what MrRon said. Wood filling glues and putties help out a lot

+1 For a miter jig and hand plane to make them near perfect. Although season changes can open them up still so refer back to Mr Ron.

The only other thing I'm wondering is after you make the cut do you let the blade stop before raising it up? I've made this mistake before on cuts I wanted super accurate. Due to the high speed of a 12" miter saw and the inherent vibration I've noticed the teeth on mine can "drag" sometimes if I raise it up while its spinning down. Which results in a miter cut that looks like it has a very slight radius to it similar to your bottom pic. Hope that made sense.


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## WoodenDreams

I'd check the blade angle to the fence, then adjust the angle marking to the blade angle lock down. Any time I change the angle of the miter saw I recheck angle for accuracy.


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## EarlS

Actually, that isn't too bad, IMO. A dollup of glue, maybe a biscuit and some clamps will close the gap. I'd rather have the gap on the inside of the corner than the outside. You could spend a lot of time and effort making a lot of scrap trying to get it perfect.


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## bigJohninvegas

I too struggle to get a perfect miter cut on a miter saw. And I get better accuracy on my table saw. 
I also do not trust either saw to lock at 45. Even the miter saw that has the preset miter locations. I will use a trusted square, or digital protractor to set the miter at 45. 
And then everything else mentioned here I feel applies as well. Good sharp blade, slow and steady cut,


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## bilyo

I'm not an expert in the operation of miter saws. But, I think that if you set your cut angle to 90 deg then make a jig to hold your work pieces at 45 deg left and right and cut the pieces in those relative positions, they will match up better even if the actual angle is not a perfect 45 deg.


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## SMP

Yeah i have the $700 dewalt saw and get the same thing with the blade flex. On my to do list is build a shooting board like Carlos mentioned, thats the most cost effective. Paul Sellers has a great video on making one, just so many other projects going on.


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## wilschroter

@CarlosintheSticks - a miter trimmer - EXACTLY. That's what I was missing!

Once again the community here has been a life saver. Couldn't be happier with all the responses and support. I'm planning on re-trimming my entire house but was starting with a few areas and frustrated early. I knew there had to be a trick to this and the miter trimmer is definitely what's missing.

All great feedback on the saw lock downs too. No reason to avoid that in the future.


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## crippledcarpenter

it is blade flex. A lot of saws have thin kerf blades and if not perfectly sharp, It creates friction and you can cut a slightly rounded line. similar to a dull band saw blade. if you use contact cement and some emery cloth on the fence, it will give you a better gripping surface and help reduce board walk when you are making these and other cuts.


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## Delete

Thanks SMP, "Shooting Board" thats the term that escaped me in previous post. Here are plans for two relatively easy shooting boards for trimming 90 and 45 degree ends with your hand plane. Click jpg to expand for best view.

https://2.bp.blogspot.com/-O8UtkTVapoY/XLDEv4RnQMI/AAAAAAAAIW8/mHbPwXv25903eWehm96TOVg_cULAUhyQACLcBGAs/s1600/Shooting%2BBoard.jpg


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## splintergroup

I'm in the blade flex or workpiece moving camp. Is your saw a sliding CMS? If so, are these cuts being made on the saw by cutting from the inside of your frame to the outside? The cut angle looks quite good, but the gap at the inside appears to be a bit of wiggle in the blade as it enters the wood. If your saw is a basic "chop" type saw, I'd lean more towards the workpiece moving ever so slightly as the blade makes contact. Try clamping the (test) pieces if you can and see if anything changes.

There are great blades available that are stiffer than stock units which may lessen the flexing effect.


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## Bonka

I made a 45° shooting board and use a low angle jack plane. Take the same number of passes off of each end and it has been on every time.
I should add this is to be done after using a table or miter saw.


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## Lazyman

I wonder if the spring miter clamps you are using are making it look worse because all of the clamping pressure is right at the corner. Any visible saw marks could be just enough to cause it to pivot slightly at those points with all of the pressure at the corner. A shooting board should fix that but after you get the spring clamps on, try putting some bar clamps inline with the inside corner and see if that will close up the gap a little.

I just made a frame clamping jig like this to make a bunch of painters panels for my sister in law and as long as the angles are truly at 45, it makes quick work of clamping up frames. Definitely worth the time to make if you clamp up a bunch of frames.


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## kelvancra

A friend owned a framing shop in Centrailia, Washington, and when I told her I was getting near perfect cuts, she called bull. However, all she'd ever used was a compound miter saw.

I was using a, now, ancient Delta, which would only make single angle cuts (0-45). Too, it was easier to pull in to alignment, and I ran full kerf blades.

I showed her a few of my frames and she seemed annoyed that a simple miter could do what she could with her shears, and more.



> I don t believe any saw will cut a 45° miter ±000. No mater what saw you use, there will always be ±degree off. - MrRon


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## Jared_S

Get a better blade, and make sure the entire leg or head casing is supported.

Perfect miters are obtainable and repeatable, good trim carpenters do it every day.


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## MrRon

> @CarlosintheSticks - a miter trimmer - EXACTLY. That s what I was missing!
> 
> Once again the community here has been a life saver. Couldn t be happier with all the responses and support. I m planning on re-trimming my entire house but was starting with a few areas and frustrated early. I knew there had to be a trick to this and the miter trimmer is definitely what s missing.
> 
> All great feedback on the saw lock downs too. No reason to avoid that in the future.
> 
> - wilschroter


Don't forget house trimming is different from making a picture frame with 45° corners. There are no 90° corners in a house. You will find any number of different angles that can be as much as ±5° from 90 and each has to be tailor made. House trimming is a trial and error affair. You trim until it fits. Always start at the corner and work away from the corner. If you have to meet somewhere in between corners, you want to be able to butt up the moldings with a straight cut. Doing it at the mitered end is a lot my difficult.


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## MrRon

> Get a better blade, and make sure the entire leg or head casing is supported.
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> Perfect miters are obtainable and repeatable, good trim carpenters do it every day.
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> - Jared_S


Don't compare trim carpentry with picture frame making. There are no 90° corners in a house. Trim carpenters will use putty to fill gaps. Getting a gap free joint with your first cut is a matter of luck


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## Jared_S

> Get a better blade, and make sure the entire leg or head casing is supported.
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> Don t compare trim carpentry with picture frame making. There are no 90° corners in a house. Trim carpenters will use putty to fill gaps. Getting a gap free joint with your first cut is a matter of luck
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> - MrRon


I dont know, my casing legs are cut and pre assembled to 90 degrees.

Ill agree base and crown are whatever, but putty is never used on a proper job


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## ruger

Jared,,, those are very nice miters.


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## anthm27

Your stock could be cupped, EDIT: (it may ever so slightly cup after being cut)
Or, try cutting your pieces a quarter of a blade width too long at each end, then the final cut is just trimming that quarter of a blade thickness off your mitre. I would never use an initial mitre saw cut as my joint. Even on straight butt type joints the final cut is just a 1/16 th type of trim cut for accuracy. 
That way no blade flex.
Regards
Anthony


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## MrRon

> Ill agree base and crown are whatever, but putty is never used on a proper job
> 
> - Jared_S


Yes I was referring to base and crown moldings. doing moldings around doors and windows is similar to making a picture frame. A corner can be more or less than 90°, but because it's only 3 sides, the gaps are easier to close up; a picture frame must be exact.


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## kelvancra

I always treated trim carpentry like picture framing. Only the angles changed. If a corner were 91 degrees, I cut at 45-1/2 degrees.



> Don t compare trim carpentry with picture frame making. There are no 90° corners in a house. Trim carpenters will use putty to fill gaps. Getting a gap free joint with your first cut is a matter of luck
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> - MrRon


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## kelvancra

Just curious, are you pulling all four corners to the center at the same time, or one [or two] at a time? Just moving one side of a frame up or down 1/64th can monkey wrench the works enough to annoy you.


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## LeeRoyMan

> The best one can do is to make the miter as close as you can and fill the gap afterwards.
> 
> - MrRon


Sorry, I disagree,
I would hope one has more pride in their craftsmanship than to settle for that statement.


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## mdhills

Any irregularity can cause this-flatness of table/fence, slight misalignment of saw, pieces creeping during the cut.

Can you cut a square end that lines up perfectly?

Matt


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## Unknowncraftsman

I have found miters to be very tricky. I was fooled into thinking my Bosch glide was extra special because I was producing perfectly happy free miters in soft pine and Alder.
Then the day came where I tried my setup on Hardmaple then Hickory. After getting the bugs worked I found that too much glue can spoil a good fit. 
Softer wood will absorb glue differently plus good clamping pressure can smoosh the fibers and close some small gaps.
Many other tricks that cannot be discussed to many variables.
Good Luck to everyone


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## SABi

Miter saws have this tiny error, notably in angle cuts due to their moving arms.
For a perfect cut like you want, a table saw and a jig are required. There will be no moving arm between the wood and the blade.
goodluck


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## Bonka

I cut 45° on my Delta then using a low angle Jack get them on the money on my shooting board.


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## kelvancra

A friend owned a picture framing shop and was annoyed that I claimed my miter joints were as good as hers, which were very good. Then I showed her. She was still annoyed, but had to admit they were. The reason they were so good was, I was using an old Delta miter saw, which ONLY did angles, so no accuracy was lost to the sliding or articulating aspects of the saw.


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## MrRon

> The best one can do is to make the miter as close as you can and fill the gap afterwards.
> 
> - MrRon
> 
> Sorry, I disagree,
> I would hope one has more pride in their craftsmanship than to settle for that statement.
> 
> - LeeRoyMan


I agree that a "perfect " miter can be made, but what if the angle measures 89°-17' which you can't measure with woodworking tools. To make the miter fit, you have to make trial cuts until the joint closes; a time consuming task that will cut into the profit on the job. I do precision metal working using very expensive measuring tools and machines. It is attainable in metal, but can't be transferred to wood. There are too many variables when working with wood. I use my precision tools when working wood, but it is still not easy to get gap free joints. I agree the blade used is a factor to consider.
I would also add, there is a difference between trim work on a million dollar house and a tract home. The trim has to be perfect on the million dollar house as that is what you are paying big bucks for.


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## GR8HUNTER

> The best one can do is to make the miter as close as you can and fill the gap afterwards.
> 
> - MrRon
> 
> Sorry, I disagree,
> I would hope one has more pride in their craftsmanship than to settle for that statement.
> 
> - LeeRoyMan
> 
> I agree that a "perfect " miter can be made, but what if the angle measures 89°-17 which you can t measure with woodworking tools. To make the miter fit, you have to make trial cuts until the joint closes; a time consuming task that will cut into the profit on the job. I do precision metal working using very expensive measuring tools and machines. It is attainable in metal, but can t be transferred to wood. There are too many variables when working with wood. I use my precision tools when working wood, but it is still not easy to get gap free joints. I agree the blade used is a factor to consider.
> I would also add, there is a difference between trim work on a million dollar house and a tract home. The trim has to be perfect on the million dollar house as that is what you are paying big bucks for.
> 
> - MrRon


IF YOUR NOT DOING QUALITY WORK WELL THEN YOU SHOULD LOSE PROFIT :<))


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## pottz

> The best one can do is to make the miter as close as you can and fill the gap afterwards.
> 
> - MrRon
> 
> Sorry, I disagree,
> I would hope one has more pride in their craftsmanship than to settle for that statement.
> 
> - LeeRoyMan


+1 i agree thats nonsense.never settle for second best especially if your want to call it fine woodworking.


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## northwoodsman

I have come to the conclusion that I'll never be able to dial in my Dewalt Sliding Compound Miter saw to cut perfect angles no matter what the angle is. I get them set as close as possible on scrap wood then use a feeler gauge or a piece of paper as a shim behind the wood that I am cutting to get that last fraction of a degree of accuracy. If that doesn't work I resort to a sanding block.


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## pottz

> I have come to the conclusion that I ll never be able to dial in my Dewalt Sliding Compound Miter saw to cut perfect angles no matter what the angle is. I get them set as close as possible on scrap wood then use a feeler gauge or a piece of paper as a shim behind the wood that I am cutting to get that last fraction of a degree of accuracy. If that doesn t work I resort to a sanding block.
> 
> - northwoodsman


if you want picture frame perfect miters get a guillotine miter trimmer thats what i use for perfect clean cuts.


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