Having trouble with parallel faces.

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Forum topic by AESamuel posted 02-25-2015 08:41 PM 815 views 0 times favorited 5 replies Add to Favorites Watch
View AESamuel's profile


78 posts in 1218 days

02-25-2015 08:41 PM

Hi there,

Beginner-ish woodworker here.

I’m planing some sapele (11” x 4” x 1 1/4”) and I’ve got one side flat, and the two sides at 90 degrees to the reference face, but when checking if the opposite face is square I get different readings from the sides. If I reference off of one side then the opposite face is well out of square, but if I reference off the other side then the opposite face is nearly square!

This is really confusing me because the two sides are square to my reference face, but I’m getting very different readings on the opposite face! Hopefully that makes sense.

Can someone enlighten me as to what might be going on here?


5 replies so far

View AlaskaGuy's profile


4127 posts in 2305 days

#1 posted 02-25-2015 08:47 PM

huh, what tools you using?

-- Alaskan's for Global warming!

View AESamuel's profile


78 posts in 1218 days

#2 posted 02-25-2015 08:54 PM

I’m using a stanley No.4 and a cheap-ish combination square which I have checked using the pencil trick to make sure it is accurate.

View Picken5's profile


250 posts in 2687 days

#3 posted 02-25-2015 09:48 PM

You might want to re-check your combination square. The blade/ruler on some of the lower-end combo squares won’t always square up properly when you tighten the locking nut. Or the locking nut isn’t staying tight. You may want to look into picking up an inexpensive try-square. (But check it for square in the store before you pay for it.)

Sometimes, when checking for squareness, I run into instances when something measures out of square when it shouldn’t be. When that happens, I pull out one of my precision engineer squares. I use these mostly for aligning tools and such, but they sure help me get my head on straight when this sort of thing occurs. Usually, I find the original issue was with my combo square—like a bit of sawdust crept in under the blade while I wasn’t looking.

-- Howard - "Time spent making sawdust is not deducted from one's lifetime." - old Scottish proverb

View ColonelTravis's profile


1768 posts in 1890 days

#4 posted 02-25-2015 10:48 PM

If your face is perfectly flat and if your sides are exactly 90 to that face, geometry says your square has a problem. If your square is perfect, your board has a problem.

I usually check a board in three places for flatness and squareness. Are you measuring from the same spots?

View AESamuel's profile


78 posts in 1218 days

#5 posted 02-26-2015 07:18 PM

I’ve solved it! Pure user error, I don’t know why but somewhere along the way I marked my face as flat when it clearly wasn’t!

Thanks guys.

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