"Saw Cut" vs "Shear Cut": What is the difference?

[westsail42]

Not really for metal boat building, but I figure the people here would know.

I am building a rudder and am having the interior frame parts CNC waterjet cut. The outfit doing the cutting prefers "saw cut" stainless. One of my sources of SS sheet can provide "shear cut".

Now, I am a neophite in this area.

What is the difference?

I presume the saw cut stainless was cut with a saw blade, and shear cut stainless was cut with?

Are there differences in tolerances?

Thanks all

[charmc]

A plate shear is a large hydraulic press that cuts metal by pressing down against a sharp-edged die to cut the plate. Oversimplified, it's breaking off a section of the plate with a huge force. A saw cut will be better able to follow any curves in the pattern. With stainless steel, which is more brittle than carbon steel, he might be concerned about possible stress from the process, which could lead to stress cracking or some other premature failure over time.

[Rusty Bucket]

Are the people doing the sawing or shearing the metal supplier and the people doing the cnc water cutting using this raw material to make your parts? If so I'm guessing that the supplier is set up to easily shear sheet goods, a shear is a big blade that easily and quickly cuts sheet goods. I;m having a hard time figuring this one out, I would think that your cnc operator would prefer the sheared material over the sawed stuff. Why don't you ask these guys and share with us their answer meanwhile I'm going to call a friend who has a cnc waterjet and ask him. regards rusty

[lazeyjack]

another thing is shears often leave a bent part, unless the shearing is done by guillatine Still a hammer fixes most things eh

[dick stave]

What grade of stainless are you using? More than likely you are using 304 or 316 ( the latter being more corrosive resistant ). It shouldn't make a difference to your waterjet profiler, as most plate is sheared ,and angles, bars, and round solids etc.are generally cut in a saw.When they profile your parts they will nest them on a flat sheet or plate,and how the edges have been cut are not a consideration. They will effectively become waste .Austenitic stainless steels are not more brittle than carbon steels, they are actually more ductile. No grain consideration is made when forming as a result.

[charmc]

Originally Posted by dick stave

What grade of stainless are you using? More than likely you are using 304 or 316 ( the latter being more corrosive resistant ). ... Austenitic stainless steels are not more brittle than carbon steels, they are actually more ductile. No grain consideration is made when forming as a result.

You're right, Dick, austenitics are not more brittle, unless cold worked. That's what I was thinking of, but a shear cut would not be enough to induce any problems there.

Stress cracking in a marine environment is more likely as a result of chloride (salt) corrosion. 316 will resist chloride corrosion better than 304. Best is a duplex stainless grade, like 904L, but that can get pretty pricey. If the boat will be in tropical waters, then duplex stainless will more than pay for itself by resisting chloride corrosion 3-4 times longer than 316 (water temperatures around 90 deg F and above increases the rate of chloride corrosion). If the boat will be mainly in temperate or colder waters, then 316 SS will be fine, and is easier to weld.