How good are cheap Machinist's Squares?

Guys,

does anyone own a cheap Machinist's Square set from Harbor Freight? Price is great I just want to make sure it's not a piece of junk.

Thanks

Reply to
Alex
Loading thread data ...

Harbor Freight stuff is kind of a crap shoot. If you do buy them, compare hem to a known good square.t

Reply to
Kahlo

If you do compare them to a known right angle and find them a little off, a traditional "strongarm" method for improving them is to peen the blade leg near where it joins the thick leg. Peen it at a spot off the centerline of the blade on the side where "swelling" the metal makes the blade warp in the correct direction.

You may have to check and take a little off the edge of the blade if the peening makes it bulge out a little.

HTH,

Jeff

Reply to
Jeff Wisnia

Reply to
Tim Killian

I have a three piece set from Harbor Freight that are made in India. If you set them on a flat surface (mill table) and check them against each other, you can not see any error. Checking all against each other ensures the angle is actually 90 degrees.

Dan

Reply to
dcaster

Not sure what Dan means here. If they were all. say, 89.5 deg. and you nested them all together, they would be in agreement - but they would not be

90 deg.
Reply to
Robert Swinney

You place them "back to back" on a (good) surface plate. If there were only two, and they were both off the same amount in opposite directions, say at 89 and 91 degrees, they'd mate ok and you wouldn't know, but if there's 3 or more and they "black out" in all permutations, then they all must be damn close to 90 degrees.

Same principle as scraping and checking three surface plates against each other.

Jeff

Reply to
Jeff Wisnia

There is no need to compare squares.

The simple method is to draw a line across a smooth clean piece of stock, metal or timber, then turn the square over and draw another line across the stock on top of the first. If the square is any good the lines will be as one but any error will show them diverging at twice the error.

Reply to
John G

Flipping squares on a white sheet of paper his is not nearly accurate enougth for precision metalworking tolorances... the thickness of hte pencil/pen/marking device/ line is not fine enough to see minute angle differences... particularly as most of hte HF squares are in the 4-6' range... 8-12 if the OP buys the larger ones. Not nearly long enough to see an angle difference .... unless the square is horribly out of square.

The accepted way to measure is to place the reference square (assumed to be a perfect 90 degrees) and the test square on a flat surface plate (plate glass will do) with a soft light placed behind the two squares. Gently push the two squares together... if they are perfect 90's, you will see a thin sliver of light getting smaller and smaller until it literally blacks out.

The eye is extrodinarily sensitive to light and you can see differences literally to ten thousands of an inch -- if not finer. Minute differences are simply lapped until perfect.

This is how most manufacturers test precision squares.... but they use a darkened room as well. And as one poster mentioned, 3 squares are required to truly test 3 unknown squares.... if you do have a reference square, then the above method works fast and easy.

Steve

John G wrote:

Reply to
Steve Koschmann

I got a 3" import square from my supplier that seems excellent. Heavy.... If HF is similar, no problem. May want to check w/ your local supplier, might be competitive.

I got 6" carpenter's squares from my local 99c store for... 99c. About 87 degrees....

Reply to
Proctologically Violated©®

Thats good enough for woodworking but not hardly for machinists. ...lew...

Reply to
Lew Hartswick

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.