Bevel cut angle on wood different than measured on blade

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Forum topic by 1dea posted 09-26-2017 02:18 AM 1269 views 0 times favorited 3 replies Add to Favorites Watch
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3 posts in 846 days

09-26-2017 02:18 AM

Topic tags/keywords: bevel

I have a new miter saw (DWS780) and was doing the calibrations for tweaking up the miter and bevel angles.

For the bevel, I measured the angles by using the blade with a digital angle ruler. One span of the ruler on the base and the other span lined up against the blade. The 0, 22.5, & 45 degree left bevels were a bit off so I made the adjustments. I made sure that the ruler was totally flush against the blade and not on the side of a saw tooth.

Then when I did some practice cuts on real wood (2×4’s and MDF pieces), the angles were slightly off but extremely consistent. The 0 degree cut was off by 0.3 degrees, and the 22.5 and 45 by about the same. Noting the direction by which the bevel cut was either too shallow or deep, I tweaked the adjustments so that he actual cuts on wood gave 0, 22.5, and 45 degrees.

I made sure the ruler was zeroed out and calibrated throughout and made these measurements all a few times to make sure and check if they were consistent, and they were. I also used a 7” square to confirm the 0 degree cut on the wood – the cut was flush with the later empirical adjustment for the actual wood cut, whereas it was slightly off with the angle ruler 0 degree set on the blade.

Now when I measure the blade with the digital angle ruler, it is off by the amounts that the cuts were off before, which is what you would expect if things are consistent.

Question is: Why is there a difference between what is measured with the ruler calibration on the blade, vs. how it actually cuts? Does the high RPM on the blade change the blade aspect or something? Does the force between the blade and the wood change the blade aspect?

I see lots of videos on the internet about doing the adjustments with an angle ruler, but haven’t found anyone talking about how the calibration with the angle ruler might be different than what happens in practice.

3 replies so far

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3 posts in 846 days

#1 posted 09-26-2017 02:32 AM

Note that using the 7” square against the base & blade also shows off by a small amount against the blade when I get perfect 90 degree cuts on the wood. If the 7” square is flush on the blade for 90 degrees, then the wood is cut off by 0.3 degrees. Just as with the digital angle ruler measurements.

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1408 posts in 2556 days

#2 posted 09-26-2017 09:22 PM

Is the surface of the blade that you are referencing to perfectly flat and perpendicular to the axis of the shaft in the arbor? I have had a few cheap blades where the area between the arbor and the teeth was not flat. The area nearer the arbor was a bit thicker than most of the face of the blade. If the edge of your ruler is hitting a high area near the arbor it would throw the measurement off. Have you tried mounting another blade?

I think you have solved your “problem” by adjusting your saw so that the final cuts give accurate angles at the desired settings. Time to just make some sawdust.

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3 posts in 846 days

#3 posted 09-26-2017 09:41 PM

Yah I better go check the blade. I did change it to a Freud 100T which are great blades, but I should put back on the original factory Dewalt blade and see if there is a difference, or if there was some problem with the install, etc. Seems so weird.

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