Troubleshooting Miter Saw Inaccuracy

When a sliding compound miter saw starts cutting miters a half a degree out of whack, a trim installer starts tearing his hair out. Here's some advice on what could be wrong with the tool. May 22, 2007

I'm having a really bad time with one of my 12" Dewalt sliders. In the midst of trimming a 4000 sq. ft. house I noticed that the saw was cutting one of the 45's at 44 1/2 degrees. I loosened and reset the indexing protractor. I got the saw cutting Starrett square and the left side 45 is perfect. The right side 45 is still off 1/2 a degree.

By now this thing is really getting to me (the 6000 l/ft of moulding starts to stare me down). The fences are perfectly straight in the same line. The blade is cutting perfectly - no dragging. The only thing I can think of is the protractor is bent or something. Dewalt accurately cuts these stainless protractors so they slide and there is no lateral movement. So what the heck is going on here?

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor F:
Have you checked the fence for vertical square? I had that problem with a cabinet saw once. It made me screaming crazy until I got a tip from a Delta tech to check the table position.

From contributor V:
I wouldn't get too hung up on it. Since you know it is off on that side, you can override the stop one half degree until you figure out how to adjust the detent. I rarely get to cut any actual 45 degree cuts when I am trimming houses anyway. Its mainly about testing corners for the angle that fits and then cutting the parts.

From contributor F:
I have had the same problem with the same saw. Its unusual too because the indexing protractor is one piece. It worked perfectly for a long time without adjustment and then went out. I've played with it until it's close, but can't seem to get it perfect.

From the original questioner:
Just for your info this is my install saw - my shop chopsaw has now been in constant use for 6 years. It is used for perfect miters as well as rough cutting 8/4 mahogany planks. It is always square, only had to adjust it once in 6 years (took about 5 minutes). I have used every chopsaw made and I still think the 12" Dewalt slider is one of the best.

From contributor M:
In the spirit of constructive ideas, why not get a little more basic with the troubleshooting process. What is the status of your blade? Is it old and possibly getting dull, or is it brand new? Dull blades can track strangely as compared to new or newly sharpened blades.

Also, does it spin true? The centripetal forces can induce more wobble in the 12" blade as compared to the smaller blades. Both problems can manifest themselves into the issues with the 1/2 angle offset that you're describing.

Again, just some simple empirical observation things that came to mind. I've got the DW 712 8-1/2" SCMS and love it - and all of the problems I've ever had with it (which were few) were blade-related.

From contributor J:
Since this is a constant error I would look for something bent or maybe as simple as built-up hardened dirt underneath. Another thing may be that when the blade gets to that side it may be going out of square vertically to the bed. Also half of a degree really isnt a lot. If you are doing base, crown, etc. coping is more accurate and easier.