Purpose of a lip on try squares

[misha]

Does anyone know the purpose of the lip on a try square? On ones with markings, it's a lot easier to use a thinner piece to find the right mark. However, on machinist or wood try squares, it seems that if the stock and blade were flush, it could be used as a saddle square as well.

 

[Mini Me]

I will take a guess and surmise it is all about rigidity and hence accuracy over a lifetime of use. You can buy squares that have the option of removing the lip
https://www.amazon.com.au/Machinist-Hardened-Precision-Engineer-Square-75x50mm/dp/B07QQNTZJT?th=1

 

[Crazyraceguy]

I would guess (and it's purely a guess) that it depends on the way you use it. If you are primarily checking for square on the inside, either would work fine. However, if you are using it on the outside, the entire unit has to be perfectly square to the workpiece too. The ones where the blade sticks out, that is not a problem. Something like squaring a jointer fence would be easier with less contact, similar to why companies like Woodpeckers bevel the edges of aluminum squares.

 

[Packard]

Our QC manager used those types of squares, but never like we use a square for woodworking.

We had a granite flat plats.  It was about 6” thick and about 3’ x 4’, and resting on a heavy duty welded steel frame. It was ground to precise levels of flatness. 

When our QC manager wanted to check if something was square, he would rest it on the granite plate.  He would then take the machinists’ square and rest the wide section on the granite plate and slide it over to the part he was checking. 

If he needed precise numbers, he would use a dial indicator on a stand and take measurements at various heights on the part. 

Just about everything he measured, first had to rest on the granite flat plate. 

I’m not sure what you mean by “lip” however. 

I would note that there are also cast iron flat plates that are Blanchard ground to flat.  The advantage being that it is magnetic. 

The granite plates come in various thicknesses.  The thicker plates are more stable. 

 

[woodbutcherbower]

Try squares have lips because their mouths and teeth would look really weird without them. Just my opinion.

 

[Packard]

I’m guessing the lip is the bit of blade extending past the base.

I will hazard a guess.

These are generally used on a granite surface plate with it balancing on the thicker base.  The part being checked for square is then slid up against the outside of the L, not the interior.

My guess is that the base is recessed to avoid an erroneous reading made by picking up the base and not the intended blade.

I understand that the base is recessed, and the blade is not extended as a lip.  A different way of thinking on this.

Unfortunately, my ex co-worker/friend died a couple of months ago and I have no one in QC to ask.

 

[rmwarren]

That type of square is a machinist square. Having the blade extend past the base prevents any misalignment when standing upright on a surface plate or the bed of a milling machine.

More info than you probably want:https://uk.rs-online.com/web/content/discovery/ideas-and-advice/engineers-squares-guide

RMW