Adjustable Squares shootout..Starrett VS B&S, Mitutoyo and Chineseum

[EricU]

Instead use another blade or straight edge, align it to the square and clamp it to the bench so it won’t move.

Now flip the square and use feeler gauges to check between the blade and the clamped straight edge.

So you are relying on the straight edge to be parallel from side to side?  A good straight edge is one-sided.  Even the $100 ones.  If it's cheaper than that, it's not really a straight edge.  

There are a lot of uses for a combo square in a machine shop.  Obviously it's not a precision reference.  Sorta like the difference between the Starrett precision levels and their machinist levels.

I watch tubelcain videos occasionally, but the truth is he often just makes things up. Never does things "wrong" wrong, just in ways that would probably get you laughed out of a machine shop. He has one video where he squares up a lathe tailpiece. Spends the first half of the video making a silly wood holder for his indicator when you can just use a magnetic indicator stand on the chuck. I've often wondered how many of those wood holders are out there. The part where he actually squares the tailpiece was good.

[Phil Thien]

Eric, my straight edges are all Starrett and they’re straight with parallel edges.

Combination square blades also have parallel edges otherwise they wouldn’t “work.”

But for this test you could also use a piece of wood jointed straight.

[bandit571]

All well, and good....until the humidity changes in your shop....and the precise wood changes on you.....some tools work better for metalworking, but are waste of time, and cash doing wood working.   One day the humidity is 10%,,,,next day it might be 100%.....

[Timberwolf]

That sure is true, they'd beat you with it if they saw you using one.

One thing that caused me grief when I got serious about woodworking, was the compounding nature of inaccuracy/errors.

Parts slightly off from 90-degrees could snowball into assemblies that wouldn't assemble or looked terrible/gappy.

And I struggled with the "draw a line and reverse."  Parallax would engage and I was never sure how close I was.

But the clamped straight edge (I actually use a spare blade) works wonders.

.........................
And I struggled with the "draw a line and reverse." Parallax would engage and I was never sure how close I was


and you could take it to the bank that you were not "that" close....

[AHill]

Every square he tested is good enough for woodworking. It really doesn't take much of a gap for light to pass through. The wavelength of light he's probably using is around 450 nanometers, which is 18 micro inches or 0.018 thousandths of an inch. So, you can view light in a gap greater than 0.018 thou inches.

[EricU]

I first found him because of metal working, and I think that's his main focus. A lot of my metalworking doesn't require much precision either.  1mm tolerance at best.

[Phil Thien]

Every square he tested is good enough for woodworking.  It really doesn't take much of a gap for light to pass through.  The wavelength of light he's probably using is around 450 nanometers, which is 18 micro inches or 0.018 thousandths of an inch.  So, you can view light in a gap greater than 0.018 thou inches.

That is a good point, I was struggling with larger problems with my original combination square, than he is demonstrating.

[pprobus]

I first found him because of metal working, and I think that's his main focus. A lot of my metalworking doesn't require much precision either.  1mm tolerance at best.

Agreed.  And then there's the "rough carpentry" of metalworking and the "fine cabinet building" of metalworking and with both, combo squares can have their uses.  You don't need anything better than a combo square if you're cutting something or even lining something up for many welding jobs, as a matter of fact, since you can use the weld material to fill in gaps, you can be even sloppier than a lot of WW'ing that we do.  Filler material is usually stronger than the weldable base material that many hobby metalworkers use, so filling in those gaps with weld (and with some joints you actually need to introduce gaps for full weld penetration) will result in a joint that is stronger than the base material. Whereas if you're building a model steam engine, then a combo square might be OK for the initial cutting of the material down to size, but will not be good enough for checking things when you perform the precision machining needed to get a smooth working engine.

[Scoony]

I noticed that on the Starrett, the blade was not all the way into the square. The bottom of the groove is machined so that it has raised rib down the middle. It is there so adjustments can be made as needed. I will have to take one of mine apart to look, but does that rib go the full length of the groove?

As he stands it up on the granite surface, there is a gap under the end of the rule. Does the blade need to be completely in the groove to be square?

[bandit571]

Hmmm...decided to check out the square I have been using lately...

   
Just an old Stanley 8".....those two lines are from the test..where you mark a line one way..

   
Then flip it over, and mark a second line right beside the first...
 

   
And see IF the 2 lines are parallel...like these...guess I can keep using this one....