I asked this question before and got lots of good answers but here is the dilemma. I have a 12 inch Rigid compound miter saw. I have adjusted and squared it many times and have an interesting problem. When I cut say a 6 inch wide board, 90 degree crosscut, it is square from the side against the fence but not from the other. I can flip it over and cut again with the same result. I have tried this with factory edge board and with boards I have ripped on my table saw. It still comes out the same. Am I just losing my mind or just an idiot? How is this possible? Be kind please, lol.
If I am understanding your description, your saw is not quite square.
Any misalignment should show itself from both edges if you are using a long enough square.
I know you already understand the need to ensure your board edges need to be parallel as well but I will through this comment in here for new woodworkers can benefit from this topic.
Any deviance from 90 degrees on a sliding saw will increase as the board width increases. I would take a wide piece of plywood say... 10 " wide and about 24" long which you have verified has a straight edge against the fence and the opposite edge is parallel so your starting point is established. The board must be placed so it it spans and is in contact with both fence edges. The 24 " should be enough to let you make several cuts and get your saw aligned. Make a full width cut and check for square from both edges. Any difference from square is how much you have to adjust your saw and bring it into a good alignment. Make the adjustment and repeat this process until it is perfect. You should have no trouble with alignment after this and locked your saw down to keep it.
I don't know what you have as a square but check it to eliminate it being the cause. Other than that the only other reason I can think of is excess play in the saw itself as it travels across the cut but that should be OK. Just be aware of that.
I hope this is of some help to you. The sliding saws can be very fussy to align.
You're saying that if it doesn't touch the fence on the opposite side then that could cause the problem? What if you just need to trim a 1/4 inch off? I have checked with several different types of squares.
Nope, all I am trying to help you with is getting your saw squared up. The reason for the board touching both fences is to ensure the blade is completely square to the entire fence area of the saw. This is the best approach to take and it allows you to cut from both sides of the blade with absolute confidence. This process is hard to nail down in a few sentences and not being able to see everything involved so bare with me on this one. I just want you to succeed and get your mind off the nagging concern of every cut you make not being square. It's much more enjoyable to concentrate on what we are building.
In regards to the bearing of the saw being a potential culprit, you still must square the saw up as best as you can before looking at the bearing I think. Again I don't know how old your saw is etc.
This is the best advice I can try to convey to you and I hope you can get this sorted. If I can help in any way at all just fire it up here. I check on messages several times a day whenever I can and minimize the time delay.
I just had a look at another person's mitre saw problem on the weekend, a different brand, but also problems with alignment. Turns out the fence is split and one side of the fence was set accurately, the other was off by a degree or so which meant depending on where you were cutting some cuts would be ok, others were not. Very frustrating for him but and easy fix.