Why is my miter saw not cutting straight at a 45-degree angle, even though the wood is flush against the back and not warped?
Asked by Nanna Jensen 
6 months ago
Last Updated: May 9, 2024
Hey, can anyone lend a hand in figuring out what’s up? Haha, I’m starting to think my miter saw might need some adjusting. Whenever I try cutting at a 45-degree angle, it never comes out straight. The bottom always seems off. The wood is snug against the back and there’s no warping, but this keeps happening with all my cuts.
Make sure to pull the piece away from the blade after cutting through, before lifting it up. It seems like you’re doing that part right with the upswing of the saw.
It looks like the board is likely to be cupped.
The back of the trim stock features a lower and upper “foot” separated by a slight valley. Do both the upper and lower feet touch the fence when aligning your cuts?
That’s correct, there is a top and bottom foot. I can’t be entirely certain, so I will make sure to verify next time. It does seem that way, right?
I also have a budget mitre saw and I always double-check my 45-degree angles with a square.
You might want to try cutting it with the face of the board against the fence and see if that makes a difference. It might be a bit trickier and you could need to do some touch-ups later. Another option is to raise the fence by using a taller or thinner piece of wood.
Seems like the blade is bending
Hey , I agree with your thoughts as well. Let’s figure this out together!
Hey, . Do you think the board is getting loose because of incorrect pressure while cutting? Also, just a heads up, the board might have a top and bottom piece on the back causing it to cup – could that be the issue you’re facing?
Hey, here. Just a quick tip on the compound miter saw – if you’re experiencing some flex in the thin kerf blade, make sure you’re pulling straight down towards the table parallel with the 45-degree angle of the blade!
It seems like the issue could be a combination of the board not being flat and potential errors in pulling due to the compound saw. You might want to consider switching to a thicker saw blade just to be safe. Unsure about the current blade on there.
Diablo offers good quality blades at a decent price point. Make sure to check the packaging to confirm it’s compatible with your miter saw, including the tooth angle grinds, kerf thickness, and number of teeth for a smoother cut.
If you take a look at the end of the board, you’ll notice that it curves along the width and has a slight cupping.
I also enjoy using Diablos. They offer a faster cut with less flex. Experiment with cutting slower to improve precision. I have a fiber blade on my miter saw designed for cutting metal, and sometimes I need to remind myself to take it slow.
When using a 12″ blade, it may tend to deflect and cause an irregular cut. To prevent this, try using a very sharp standard thickness blade (non thin kerf) and cut slowly. If the issue persists with a 12″ blade, consider mounting a 10″ blade instead in the saw.
CMT produces top-notch blades. I prefer using Diablo on the construction site, but opt for CMT for my personal blades at home.
Agrees with all you say, especially the importance of keeping the blade sharp.
Before anything else, make sure to securely clamp the material to the base. When working with lightweight materials like trim, even a slight lift can result in these curves. If it’s still happening even after clamping, consider changing the blade or ensuring that the fence is tightly secured. Another possibility could be a broken or misaligned bevel gauge.
As mentioned earlier, the trim is cupped. Unfortunately, I often come across 5 1/4 bases that are cupped as well. Additionally, I suspect you are cutting with the piece standing upright against the fence. If that’s the case, I have found that it works better to cut it while laying flat with a bevel cut.
I actually found that interesting because I observed it more when it was flat on the surface. Maybe I didn’t have it properly secured on the saw when I cut it.
The surface might have a noticeable curve to it.
If it’s uneven, just flip it over to easily spot the higher edges.
When you slice through, you’ll notice that there’s significant pressure, causing the cut piece to shift slightly.
The saw can also move the board when pulling or pushing it, especially if too much pressure is applied. It had me puzzled once, but I believe you’re correct. I’ve seen cupped boards do the same thing, but it didn’t click until I read your comment.
Are you slicing it horizontally or vertically?
Hey ButchKendra, I was also curious about that. It really depends on what you’re looking to trim.
It really varies depending on how hungover I am, .
In the saw blade?
Are you cutting it vertically or horizontally?
I feel like I notice it more when it’s flat on the ground, I’ve tested both because it was really bothering me. I’ll need to experiment.
So, when you’re choosing a miter saw, make sure it’s square by holding up a square to the blade when it’s down.
Looks like the trim definitely has a cup in it. Try using a different piece of wood and clamp it securely to the back guide.
Have you tried using another piece of wood instead of the standard clamps that come with miter saws? It might provide better results.
Instead of cutting flat and tilting the saw, try cutting it vertically at a 45-degree angle.
The board may be cupped.
Possible reasons for this include cupped material, a dull blade, movement of the material during saw operation, or pulling to the side while pushing down on the saw. This is a common issue when using a sliding miter saw at a 45-degree bevel.
When cutting while standing, ensure that the extension supporting the trim is at the correct height. Even a slight angle in the trim can cause issues.
When using the saw, secure the wood by clamping it to the fence or create a notch in a 2×4 block to hold the clamp against the fence. Typically, mitre saws include a clamp for this purpose.
There’s a crown on the trim that gives it a rounded end, just like you see here. Pros usually cut it straight and cope it to make a 90 angle with this trim.
That doesn’t apply to an outside 90! That rule is for inside corners.
You’re correct, I didn’t examine it closely enough.
Do you really need to take a closer look to realize you’ll probably have both inside and outside corners? That’s not a good way of thinking, my friend.
I think meant that the base is the issue, and the saw is putting too much pressure on it.
Inspect the miter saw to ensure it’s square. If it is, you may need to replace the blade to fix the issue.
Are you using a fence that’s too short to cut it vertically?
Hey , I need to run a test. The fence might be too short, but I believe there is a bigger problem when it’s laid flat.
Is it some type of saw? It might need readjusting.
I have a Dewalt saw, fairly new. I got it from someone else, so I can’t be sure they checked everything was set up correctly.
How many are you looking to do? If it’s only a few, consider using a skill saw. Attach a speed square to the base and use it as your guide.
Hey, starting with this room but planning to do the whole house eventually. It looks like the problem might be not securing the wood properly, so I’ll give that a shot first.
You can still cut while laying flat, just pay attention to what’s going on. I often do this with hard wood too. By moving forward and back while cutting small depths at a time, you can cut thicker parts and thin parts separately. This technique eliminates the pressure and ensures a straight cut, it just takes a few extra seconds with hard wood.
There could be a couple of reasons. Is the trim cupped and not sitting flat? That might result in a round cut. Try clamping it flat. Are you cutting vertically against the fence? Sometimes the fence on certain saws isn’t perfectly square to the table, which can cause the miter to be crooked. If that’s the case, try cutting on the flat with the saw at a bevel. I’ve also come across new saws that won’t cut square when cutting flat with a bevel. They might need a 1/2 degree adjustment due to poor factory machining. Square a pencil mark on the board and experiment with different methods. It can be quite frustrating, I understand your frustration. I’ve been a custom home builder for 30 years.
The blade could use a sharper edge. When cutting, be sure to angle it correctly to avoid pushing the trim or causing the blade to curve.
This problem can be caused by thin kerf blades flexing during end cuts.
When it cuts through, try placing a board underneath and turning off the power. Make sure to not keep it running as you bring it up.
For a compound miter saw, place the board flat on the table and adjust the angle of the saw rather than using the slide to set the angle.
You nailed it
I totally agree with ‘s thoughts
Hey , totally agree 💯
What type of saw are you using? There are several factors that could be causing this issue such as blade deflection, a dull blade, not properly clamping the piece down, or the saw being out of alignment.
I was reading some comments and it seems like the problem might be that the wood isn’t being clamped down properly.
12 inch blade? By the way, larger blades tend to wobble more and can result in this issue.
Board that is cupped or blade that is dull
Curved
The blade is deflecting. I prefer using a 10” blade instead of a 12. And don’t forget to let the rpm’s increase and cut at a slower pace. It has really made a difference for me.
If you raise the blade while the saw is still running, it will gradually take off a small amount each time. That’s my trick for removing a tiny piece.
Mentioned that he just started waiting until it’s cut, so maybe that will help too.
Suggests letting the piece rest until the blade stops, then sliding the wood away and raising the blade.
When trimming, simply place the lower blade against the butt piece, start the saw, and then raise the blade.
Personally, I like to use the term ‘snatch whisker’ as a more refined unit of measurement.
Also known as C-hair 🤣
If you’re using a compound miter saw, it’s a bit easier….the angle may vary slightly due to the different thickness of the wood, so you’ll need to adjust the angle to cut off a little more from the thicker part of the board.
After
It seems like a bad blade is just one possibility.
Do you think the saw is large enough to cut all the way through?
There are two potential reasons for the issue: cutting too quickly or using a blade that has dulled.
If you lift the blade while the wood is still on it, you’ll end up cutting off more. Or if the blade is bad or dull.
Do you mind sharing which miter saw you are using?
The boards are cupped
Stop blaming the newbies on your saw 😂😂
Haha I had a modest sandwich with some modest fries on this one
You can still cut a straight edge whether you cup your hands or not.
Cutting it while standing up, instead of laying it flat, is the best way to achieve a straight cut on a cupped board.
Yep, ! Try tipping the stock to follow a drawn line when working with old, cupped barn boards.
It’s a cupped board, but you can still cut it at 45.5 degrees. Then use a bastard file to shape the joint. Once glued and nailed, it might be slightly long, but easy to fix with a quick buff using a file. Results in a perfectly tight miter.
Hey Casey, what’s up with all the harsh name calling towards the file?
It seems like was really bothered by it.
The stock is not aligned properly with the fence or deck. Make sure to tune up your saw.
As you’re cutting along the longer side, you’ll notice that it moves. There’s quite a bit of pressure on it as you’re cutting through, which may cause what you’re cutting to shift slightly.
When you’re cutting, do you prefer standing up or laying it flat on the base?
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Consider using MDF instead of pine, as pine tends to cup.
It appears that you may need to make some adjustments to the back guards on the saw. seems to know what to do.
The piece might be cupped
Usually the back isn’t flat so it sits nicely against the wall. Just make sure your tall fence is in place. I think it’s cupped though.
Is the blade inexpensive?
It seems like either the piece is warped, your saw is not calibrated correctly, or you’re not laying it flat.
Is the surface flat? It appears like you’ve beveled a cupped piece
If the wood is flat, the saw is well-adjusted, and the slider is secure… It’s possible that the arbor bearings are worn out. Also, consider if the blade is clean or sharp. How many teeth does the blade have? Are you cutting too quickly? Remember, a blade with more teeth has a smaller gullet, so you need to cut more slowly to avoid deflection.