So, I've got a King sliding miter saw. Not the best brand around, but not the worst. I've had it for several years now.

Have noticed recently that it's not cutting square. If I'm doing a straight cut on a 12" board, the top and bottom will be out by a full 1/4"! That's not good.

I've put a carpenters square on the deck along the fence, and dropped the blade down to one side of the square. Adjusted the adjusting screws until it appeared perfectly straight while running the slider the full length.

It's still not cutting straight, and I'm not sure what I'm doing wrong.

Anyone have ideas or different methods that are considered best practices?

It's driving me a little insane and I'm not buying a new slider because I'm not smart enough to fix the perfectly (almost) good one I've got!

 

Is there slop or flex in the saw? I have a cheap one that stays 90 degrees when you move it when it's not running but I think the blade has a bias because when cutting the saw flexes and the cut goes crooked. I've even clamped a board in it, made a cut then brought the saw back down to see the gap between the blade and wood where it pulled over during the cut.

Are your adjustment screws staying in position. If not would a jam nut or some blue loctite help?

 

Have you confirmed the carpenter's square is indeed 90 degrees?

Have you checked the fence of the saw to make sure that both sides are straight in relation to each other and not angled?

Have you checked to see if the cut is square when not sliding the saw out?

When you are making your test cuts, do you have material on both sides of the blade?

After adjustment, is the cut still out 1/4" or was there any improvement?

Did you check to see if the blade is bent or wobbles when it turns?

 

If it has a tilt function, make sure that there is not any debris that may have gotten in between the two plates that may be keeping it from closing square to everything else.

 

Thanks for the ideas folks. I'll be using it this weekend, and will pull this thread up to check for all the items you've mentioned.

I'm quite sure the screws aren't moving or loosening after I adjust.

I never even thought to check if the carpenters square wasn't square! That's pretty funny.

The fence is all one piece.

I never thought to check the blade after a cut without the saw running. Lately I've just made the cut, looked at the result and was disappointed!

As well, I don't think I've checked it when I wasn't using it as a slider. Maybe I'll bring out my other one and see about that.

Speaking of which, my other miter saw is a little Ryobi that I've had for years. It's a great little saw, but about 2 years ago when you try and turn the blade to make an angle cut there's a serious grinding noise and it gets very difficult to move it at all. I took it apart and couldn't find anything preventing it from moving (debris, etc.).

Anyhoo, thanks again.

 

Can't be one piece if the saw cuts through it. Put a straight edge across it and check it.

 

I'm probably not using the term fence correctly. I'll see if I can find a pic of the saw I've got or take one in a bit. It's cold outside and I am only on my second cup of coffee this morning.

Well that's rather telling. The only images of a saw like mine that I can find on the net are ones taken so people can sell them or otherwise get rid of! Bad pics. I'll take one myself.

Here we go:




Man it's cold out (for a Saturday morning).

 

So you dragged it out and took a picture, but didn't put a straight edge on it?

With these pics I can see the crazy design they have for truing the saw. It requires movement of the fence instead of the movement of the gauge. I think it is very possible that the fence can be knocked out easily.

 

This is trued similar to my offset motor Ridgid. You loosen the 4 hex cap screws, draw down the blade and lock it down, set a framing square on the blade and on the frame on both sides, then tighten down the hex screws, rechecking as you go.

 

Ha! Never thought of that! I'm a painter, thus why I suck at this kind of thing. I'll bring it out again and do that, along with Chandler's suggestion. I'm pretty sure that's exactly what I did last time though, so maybe the thing is swinging out of square when the blade's running.

Or something crazy like that.

Well, I went through the process of adjusting the screws again. I do believe that perhaps the fence is getting moved out of square somehow, but I'm pretty gentle with my tools so I don't know how that'd happen. It was definitely out about 1/4" at full extension of the slide.

Anyhoo, here's two pics with the square tight against the fence, blade at full length of the slide and close to the fence. It looks square now and I hope it stays that way.

 

I'm not real familiar with sliding miters but if you can cut a groove across a wide board without cutting all the way through and measure the kerf. If it's much wider than the blade thickness, you will know the head is canted heel to toe regardless of the fence/blade relationship.

 

I understand everything you just said Toolmon, up to the part where you said head is canted, etc. Not being sarcastic, I just don't know what you mean.

 

Sorry, I'll try again. I mean that the motor/blade assembly may be tilted left or right so that the blade is not parallel to the direction of travel and it's going through the work on an angle cutting a wider kerf.

 

Ah, thank you Sir. Now I get it. I'll have to check that on another day. I live on the shore of Lake Huron and it's cold and very windy out! Whoa. I'll remember your suggestion though and find a nice wide piece of scrap to test that on. Hopefully there's an adjustment screw for what you're mentioning.

 

Once the saw is trued up, you will get better results with a better blade. The one you have on there now looks suitable for cutting 2x4's to length, but that's about it. If it's dull, a dull blade is hard on a saw, as is cutting too quickly. (carbide does not mean "never gets dull" as some people might think.) 40 tooth blades are pretty aggressive and are good for rough fast cuts... but not for fine work that requires precision.

An 80 tooth carbide will produce much finer (and strighter) cuts. Some saws also work better with thinner kerf blades, which since they take out less material as you cut, aren't as hard on the saw, so they seem to cut easier.

You've probably already checked this, but I think drooplug is wanting to ensure that your fence is not bent and sitting cockeyed... the left side should be in the same plane as the right side. So raise your blade, check then entire fence with a straightedge. Basically the way you checked the blade for square in your picture is only checking "one side" of the fence. Your blade would be true with the square whether you check it on the left side or the right... whether you are just lowering the blade, or lowering it AND sliding it.

You would also check to ensure the motor and blade are not set on a bevel by placing the square vertically to ensure the saw is actually cutting the board at 90°.

Many sliding miter saws (especially the less expensive models) have some slop to them, so this may be what you are experiencing. This would be magnified by a dull blade or if the user was pulling the slider faster than the blade (and saw) could reasonably handle. I think that along with the quality of the saw to begin with are probably the most likely problems.

 

Thanks XSleeper, I'll check those issues out as well. I haven't changed that blade in a while, and will also keep my eyes open for a sale on a good one.

 

Thought I would let you guys know that I chose the coldest and windiest day of winter so far to bring my poor saw back out for a test run. Had to build some shelves for the kitchen.

Reread this thread several times, adjusted and checked everything I could. Blammo, thing worked like a charm, and was perfectly square on a full 12" cut. Not a measurable amount of difference from one side of the board to the other.

Oh, bought a new 80 tooth blade as recommended as well. Very nice smooth cutting. Kind of went nuts and bought a 200 tooth blade for my table saw as well.

If anyone reading this ever has to change a blade on their miter saw. DO NOT completely disassemble your blade guard unless you absolutely have to which is highly unlikely. Stupidly I did so and figuring out how to piece it back together took over an hour and left me swearing to the point my dogs wouldn't come near me.

Anyhooo, thanks again.