Do a google search for "304 stainless material properties" to find the yield strength.Shear calculations are done using 60% of the strength. (it's typically done with tensile strength, but I prefer a "soft" failure and extra wiggle room...so I use yield)Calculate the cross sectional area of the pin...pi*radius*radius. Multiply this area by the shear strength you calculated to get the force required to cause a yield failure.Most folks prefer to have a minimum 3x safety factor at max working pressure. ie...if you want to use it at 3000psi, the calculated failure should be at least 9000psi.Also google double shear...if your pin is in double shear, adjust accordingly.Might find something useful here; https://www.gatewaytoairguns.org/GTA/index.php?topic=97198.0Al
Al's explanation above was for the "single" shear case, where there is only one shear plane on the pin....Bob
304 SS is not the greatest choice, IMO, because of the wide spread between the tensile strength (75Ksi) and the yield strength (31Ksi)…. For example, 2024-T3 aluminum has a slightly lower tensile, but a higher yield than 304 SS.... I am not suggesting you use an aluminum shear pin, just pointing out there are much better choices than 304 SS if you want to calculate the allowable load using the yield strength.... Most steel pins would be far stronger, the material a Grade 5 bolt is made from has a tensile of 120Ksi and a yield strength of 92Ksi....A single 3/16" pin has a shear area of 0.0276 sq.in. and using 60% of 31Ksi (18,600 psi) for 304 SS, that gives a shear strength of (0.0276 x 18,600) = 513 lbf. per pin.... assuming only 1 shear plane per pin....You are correct that to determine the force on the part, you need to calculate the area of the ID of the tube, and then multiply by the pressure.... Then triple that to give the retaining force required at a 3:1 safety margin.... Bob
Look at how the Disco valve is installed.... It uses three 8-32 screws on flats milled onto the sides of the valve, and the holes in the tube are the diameter of the head.... This is because in many installations the stress on the holes in the tube, trying to distort the wall (make the hole egg-shaped) is greater than the shear stress in the screws.... There are many things to look at when installing a valve in a tube, the shear strength of the pins/screws is just one of them.... The bearing load of the screws/pins in the tube wall is another, and the possibility of the holes tearing through the end of the tube if the screw holes are too close to the end yet another (the QB79 tank block is a perfect example).... Which failure occurs first, and how that failure occurs (yielding, which is a "soft" failure.... or breaking, which is a catastrophic one)…. are all important things to consider when pinning a valve or end plug into a tube.... With the stock Disco screws, the screws shear first.... With upgraded, high-tensile screws, the pressure to failure increases by over 50%, and in addition before the screws shear, the holes in the tube start to distort.... I would far prefer the latter mode of failure to the former.... Bob
I would use a purpose designed dowel pin such as this....https://www.mcmaster.com/98381a510They list the breaking strength as 5,900 lbs. which is so high that the load bearing of the pin in the tube will definitely be the limiting factor.... If you can drill the hole straight through, you will get 2 shear planes from the one pin.... doubling the force required to break it.... Using 2 pins would double that again.... With four 3/16" holes in a 1018 steel tube with a 0.065" wall, which has a yield strength of 54Ksi, you would have a safety margin of 3.6:1 to yield at 2000 psi for a tube with a 0.745" ID.... The loaded area of each hole in the tube wall is the hole diameter x tube wall thickness....Bob
Good solid advice Mr. Bob is giving here. 303 and 304 stainless are not much more than non rusting cold rolled steel. Very poor. One of the worst materials you could possibly use. 4130 or any grade 8-18 fastener would be vastly superior. 416 is stronger than the 300 series, but still far too weak. For what ever reason, people have it in their minds that ss is stronger. Exactly the opposite is true. I was very surprised when Magnum used ss for his supposed stronger fasteners. Knife
SS is notorious for galling.... and seizing....Bob
I would be trying an MDS hammer with a brass or steel core, depending on the weight you need.... However, you can't use that with a Disco/22XX trigger, you need a drop sear trigger like the MRod or PRod designs....Bob
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