Reply by Lazyman

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Posted on Box joint blade set no longer cuts 1/4" kerf???

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4078 posts in 1921 days

#1 posted 02-10-2019 03:16 AM

I guess I am a little like you, I want to know why…
Did you make the jig or did you buy one? Here are the things that occurred to me to look at. I assume that it is the gaps and not the fingers that are too thin? Is the finger to finger spacing exactly 1/2”? Measure it across an entire board and make sure that there is no cumulative error.
To get measurements in thousandths of an inch, I assume you are using a caliper. Is it possible that your jig is not perfectly perpendicular to the blade? I can imagine a way of cutting a 1/4” slot at a slight angle and then when you measure with your caliper, if you insert the blades perpendicular to the face of the board, it would measure slightly narrower and the finger joints won’t mesh properly. Shimming your blade may not fix that problem. You might get sloppy joints. Note that is a different problem than if your blade is not parallel to the miter slots. This is where the backer board of your jig is not perpendicular to the blade.

Finally, I can’t image that it would make that much difference and I don’t know what the thermal linear expansion of carbide is like but what is the current temperature of your shop? Even if it isn’t cold enough to measurably affect the width of the blade, I wonder if a really cold temperature could affect the length of the threaded rod that is being used to control your jig? Just thinking about variables that could theoretically affect your finger joint jig.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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