Cylinder Square Markings, Cylinder Square vs. Granite Square

As the title indicates, two questions.

1. I saw a B&S cylinder square for sale with arcs of dots..... Never mind, I found this thread: http://www.practicalmachinist.com/vb/metrology/brown-sharpe-558-cylindrical-square-241840/

A picture of one for those who have never seen one. Pretty clever.



(It is upside down in the picture)

2. I do not have a good squareness reference in my shop. At first look, a cylinder square and a granite right angle seem to me to be rather interchangeable, but I am sure that there are advantages and disadvantages for each. What are the merits of a cylinder square versus a granite right angle? If you could only have one, which one would it be?

A cylinder square is easy to make and more or less self prooving. Depending on what you do, you may need both.

A cylinder square is good for use on a surface plate to set a squareness gauge. They are also good for checking tram, especially on something like a VTL.

A granite square is handy for checking squareness of a lathe cross slide or mill knee.

A cylindrical square provides a true vertical surface (within specs) when placed on one end, which is very handy. It provides an accurately calibrated tilted surface when placed on the other end, which also is very handy since it allows you to quantitatively determine how far tilted from vertical a test surface is.

A granite square tells you if one surface is perpendicular to another. But, if the surfaces aren't perpendicular the granite square doesn't directly indicate how far off they are.

For me, a cyl. square is best. It is somehow self-proving but there are non-obvious sources of error once you want to push it's accuracy to the limit. You can use it to "certify" an adjustable square and then you can use that one for close to anything else. Granite squares are convenient but their heft can become a nuisance and in some situation falsify the measurement. I wouldn't consider buying either unless properly tested by a competent lab under my eyes- that's the voice of experience. (The eBay stuff is rubbish.) One can make something perfectly round ( within some 0.1 microns ) or perfectly straight provided is not too long, within the same 0.1um. Squareness is many times more painful.

Thanks to all that replied. Opscimc, your statement implies to me that (some? most? all?) cylinder squares have the tilt feature that the dots on B&S 558 quantify. Or am I misunderstanding what you are saying?

A cylinder square is good to quantify the squareness of a part face to the bottom face when the part shares the same reference plane as the cylinder square. Thats it. Its a one-trick pony.

A granite square can often be used to hold smaller parts in a certain orientation as well as a reference surface for squareness. Due to the width of the square surface, the granite square is faster for setting squareness gages, but not as fast for directly checking squareness.

As for which if I could have only one? I have made that choice and have neither. I have a couple of granite angle plates, a large and a small.

Wheels, I believe B & S are the only manufacturer to have the tilt built into one end of their cylinder square. The opposite end is made square.

Ah, the joy of machining! When I think it is either A or B, suddenly C shows up. There is always something new to learn.

wheels17 said:

Ah, the joy of machining! When I think it is either A or B, suddenly C shows up. There is always something new to learn.

Click to expand...

End of year, beginning of next I'll be making a "super-precision" cylindrical square for a client of mine. It'll take a while ( and cost a bundle ) - I'll start a thread and follow the making with pics and explanations. By the end you'll appreciate why taking an ordinary square and having it measured on a good CMM is such a good solution...