5 Cut Method Math

Cut 5

Two observations/questions...

I thought the accumulated error warning was in terms of angular measures, not distance measures. For example, being off by a degree on cutting a miter would yield a 2 degree gap.

Secondly, I'd think you would see a different distance result if you kept the side length 4" in your example instead of starting with a 4" square and making cuts. If you measure the lengths of your final sides in the graphic they aren't 4". For example, make the first cut, mark off 4" and make a second cut, mark off 4" and make a third cut, etc. Can you easily mock that up? I'd be curious to see the difference.

John

Ah, you're right. (slap forehead)

How does one calculate the accuracy level in degrees that the method will get you? Obviously it depends on the length of the sides and the delta distance you accept in your fifth cut from front to back.

How close to 90 degrees will I get if I use a 18" square board and accept a delta of 0.004" on the fifth cut?

(snip)

snipped-for-privacy@garagewoodworks.com wrote in news:31710c09-a7cf-4135-a57c-9b3eb5b08cf3 @s7g2000yqm.googlegroups.com:

cf3

Hey cool. I'd appreciate it if you could show the equation(s) you used. (degrees only) Thanks.

Seems close enough to 90 to not worry about it... ;~)

snipped-for-privacy@garagewoodworks.com wrote in news: snipped-for-privacy@j8g2000yqm.googlegroups.c om:

Sure thing, Brian, here you go:

Accumulated error of 0.004" in five cuts = 0.004 / 5 = error of 0.0008" per cut.

Error of 0.0008" at a distance of 18" gives the tangent of the angle at 0.0008 / 18 = 0.000044444444....

Inverse tangent of 0.0000444... (that is, the angle whose tangent is 0.0000444...) = 0.002546 degrees.

snipped-for-privacy@j8g2000yqm.googlegroups.c

Thanks Doug. That's actually what I had originally, but I started to second guess myself. I appreciate your help.

We do something like that I guess when we tune our sliding table saws. We = take about a 48" square and spin it 4 times and then measure the thickness = of a thin ripping at the front and the back and see if they're the same. I= f they are, we've got a nice square cut. If not, we scientifically calcula= te the difference and use a calibrated striking mallet to bump it into squa= re. ish. Works great! JP

I absolutely need one of those calibrated striking mallets!!! It must be a home-built as I can't find one at the hardware store.

Ralph