Machinist square

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Forum topic by willhime posted 10-04-2015 10:10 PM 2300 views 0 times favorited 15 replies Add to Favorites Watch
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128 posts in 1781 days

10-04-2015 10:10 PM

Topic tags/keywords: tip question resource measuring tool

I’m in the market for a machinist square. From what I’ve researched, down to the 1,000’s of an inch, which is supposed to what you’re shootin for. I ended up on incra’s 7” right angle. On sawmill’s forum, there was a discussion on them, and one guy said he just buys the plastic architect’s triangle at office depot, or the like, which runs in the 1-2 dollar range. I was sold on that for a minute, but figured after awhile, they’d break, chip, or get lost. The SE brand looks decent, as far as cost, along with Enkay. Thoughts on bitin the bullet for the incra ?

-- Burn your fire for no witness

15 replies so far

View jonah's profile


1976 posts in 3540 days

#1 posted 10-04-2015 10:36 PM

I can’t speak for the plastic architect’s triangles, but the $3 plastic speed squares at the big box stores are perfectly square.

View Ghidrah's profile


667 posts in 1464 days

#2 posted 10-04-2015 11:42 PM

I Have 3 machinist squares, 2, 6 and 12” all are at or below .002. In early 09 when I set my rear fence on my panel sled I used 2 12” right angle drafting squares from Staples. 4 yrs later I heard about some new fence squaring process from a Mr. Ng. I tested my sled and got a reading of .0017? I was happier than a pig in you know what.

My machinist squares cost a crap load more than the plastic squares if I do drop a plastic square oh well, drop a machinist square and I’d probably stab myself in the neck to punish me.

-- I meant to do that!

View TheFridge's profile


10818 posts in 1728 days

#3 posted 10-04-2015 11:50 PM

I wouldn’t trust cheap plastic for equipment setup. Just me.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Lumberpunk's profile


334 posts in 2579 days

#4 posted 10-05-2015 02:01 AM

6” Engineer’s squares at Lee Valley for around $20 CAD… served me well for many years. They say .001/inch deviation over the length of the blade (British Standard 939 Grade B)

-- If someone tells you you have enough tools and don't need any more, stop talking to them, you don't need that kind of negativity in your life.

View jonah's profile


1976 posts in 3540 days

#5 posted 10-05-2015 02:05 AM

I wouldn t trust cheap plastic for equipment setup. Just me.

- TheFridge

I have three of those plastic speed squares – two yellow and one orange. Each one is as square as my eyesight and testing methods can measure. Certainly square enough for my purposes. Read my review for the methods I used to test the things.

View Dark_Lightning's profile


3367 posts in 3351 days

#6 posted 10-05-2015 02:12 AM

FWIW, my wife uses those plastic triangles from Jo-Ann’s. They are dead on. If you are cutting little isosceles right triangles with about a 4” hypotenuse, your basic quilt building block better be pretty good, before you sew them into a quilt for a king-sized bed. They come out amazingly square.

-- Random Orbital Nailer

View DW833's profile


220 posts in 2124 days

#7 posted 10-05-2015 02:12 AM

I purchased two of the engineer squares. A 4” and 6” from Lee Valley. I don’t use them much anymore.
Now I use a 6” combo square for everything. Is it as accurate as the engineer squares, plus I can use for
everything from general WW to machine setup. If I had to do it all again, I wouldn’t buy the engineer
squares. You may want to consider a good quality 6” combo square.

View AlaskaGuy's profile


5005 posts in 2551 days

#8 posted 10-05-2015 07:59 AM

I have several drafting triangles of different sizes. They are right on the money.

-- Alaskan's for Global warming!

View Gentile's profile


321 posts in 2060 days

#9 posted 10-05-2015 10:14 AM

I use a set of engineer squares I bought at Harbor Fright years ago, they work great. I also use drafting triangles.
Accuracy, is not a big concern, I ain’t putting a man on Mars, just building a bird house…

-- "I cut it twice and it's still too short"

View Tennessee's profile


2893 posts in 2756 days

#10 posted 10-05-2015 12:04 PM

The “cheap” plastic squares are as likely to be more accurate than you might think. If you walk into a Hobby Lobby or other good hobby stores, they dominate the shelves. They are used for layout by a whole bunch of different people from all kinds of hobbies and livings.

I take them over the multi piece metal ones any day.

Why? Because the molds used were injection molds that were most likely made in a mold shop populated by CNC machines and craftspeople who work in terms of .0001 as a lifestyle. And every piece molded has to be true, or the whole load comes back. Those of you who worked in plastics know what I mean.

Metal two piece units are subject to some kind of attachment, which involves lots of variation from pressure when clamping, dimension issues in joints, etc. I trust my plastic triangles and squares, and have some that are from the 70’s.
Single piece metal ones can be dropped and bent just a hair, throwing them off.

-- Tsunami Guitars and Custom Woodworking, Cleveland, TN

View Planeman40's profile


1334 posts in 3003 days

#11 posted 10-05-2015 08:47 PM

Square is square is square!

Simply place the square on a known straight edge, scribe a fine vertical line, flip the square over, align it to the same known straight edge, and bring it up to the scribed line. If there is a perfect match, the square is square! About a year ago I had a retired Lockheed engineer friend making something in my shop. A stickler for accuracy, he checked an old Stanley square using the above method before he used it. I had been using this square for a while and never noticed anything wrong, but he proved to me this file old square wasn’t really square. I picked up one of my cheap Harbor Freight squares and we tested it. It was dead on! So you really can’t be sure until you have tested one. Price doesn’t make it perfect. Cheap squares can be perfect too. Check them ALL before using!


-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View nicksmurf111's profile


369 posts in 1692 days

#12 posted 10-05-2015 08:59 PM

Nothing is wrong with “cheap” plastic. I just end up stepping on them though. A square is a square. Some are even adjustable.

I do have to say that I like Starrett combination squares though.

-- Nicholas

View Ocelot's profile


2127 posts in 2880 days

#13 posted 10-05-2015 09:53 PM

[edited to remove quote and unneeded verbiage. I hope I didn’t offend by disagreeing with anybody.]

I have the Incra 7” “perfect square”. It’s fine, but I wouldn’t buy it today – because of the price. (I also have the 45 which I may have used once. I certainly wouldn’t buy the 45 today, although you can actually use the 45 as a “square” because of the way it is made.)

I also have a “6 PEC double-square which costs half as much and as far as I can tell, even with the moving parts, it’s just as square, and you can also measure with it. I like it a lot.

You can buy a Grizzly set of 4 engineers squares for $25 on Amazon with free shipping. I would probably go with that.

I think it’s a good idea to have more than one square in the shop, so you can check them against each other whenever you are in doubt.


View daddywoofdawg's profile


1028 posts in 1817 days

#14 posted 10-05-2015 10:13 PM

I saw then started doing this,as I needed a small square to check my band saw table to the blade.I tok off the ruler on my combo square and use the metal “square”.It’s free and good enough.

View fivecodys's profile


1276 posts in 1878 days

#15 posted 10-05-2015 10:20 PM

I use a plastic artists square, a speed square, a traditional square, and a machinist square.
As far as I can tell they are all “square”.

-- I always knew I would grow old, But I expected it to take longer!

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