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Questions regarding maximumYield stress for standard hardened steel dowel pins

Hello everyone,

I would like to ask if anyone could please help me with the following situation.

I am using a standard hardened steel "pull out" dowel pin from

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as a bearing shaft. I need to know the maximum load the dowel / shaft can support without taking a permanent set and/or becoming permanently deformed or bent. I need the shaft to always spring back to its original position after the load is removed.

I emailed Mcmaster, but they were not able to give the maximum Yield strength of the dowels.

Does hardening increase the maximum Yield stress? If so, is there a way to calculate or estimate how hardening affects the yield stress ? If I know the yield stress, then I can compare the maximum yield to the bending stress given by my beam design program, and I think this will tell me if the dowel can support the load without taking a set.

Here is what Mcmaster said about the dowels and material...

"Hardened Steel- Made from hardened steel such as C1541, or 4037 and

4140 alloy steel. Core Rockwell hardness is C47-C58 (surface hardness is RC 60). Shear strength is the amount of force that the side of a pin can withstand before breaking. Single shear strength is the amount of force applied against a fastener in one place causing the fastener to break into two pieces. Single shear strength is 130,000 psi. An internally threaded tapped hole in one end of these pins lets you pull them out with a removal screw or a threaded puller such as 92330A (see page 3083 ) and reuse them. All meet ASME B18.8.2. Length tolerance is =B1.010"."

I would appreciate any advice or suggestions on how I can get a close estimate on this, and what would be a reasonable safety factor to apply. Nobody could get hurt if the device fails, but I just need it to be reliable. I have to consider several factors when choosing a shaft size, and everything fits in a tight space.

There are tradeoffs and space constraints when going to a bigger shaft, so I need to know how to estimate this in order to make the best compromise. It's desirable to use the smallest shaft diameter possible, that will support the load with a reasonable safety factor & not take a set.

Thanks for your help. John

Reply to
John2005
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Call the manufacturer and speak to an applications engineer.

With luck they still speak English.

GWE

Reply to
Grant Erwin

Hi Grant,

Mcmaster would not give me the manufacturer contact details, nor would they contact them on my behalf.

Thanks John

Reply to
John2005

Ouch. Try thomasnet.com to search for manufacturers directly, or look in the MSC catalog for an equivalent part (msc-industrial.com) but listed with the manufacturer's name. I'm guessing a smart guy can be talking to an AE in an hour.

GWE

Reply to
Grant Erwin

4140 at Rc 47 will have a yield of approx 190,000 psi. Hardness correlates pretty well with *tensile* strength for most common carbon and non-austenitic alloy steels. Correlation with yield is not as reliable. I pulled the yield from the data on 4140 in "Modern Steels and Their Properties", Bethlehem Steel.

Be careful of fatigue if your pin is subject to cyclical loads at high stress.

Ned Simmons

Reply to
Ned Simmons

"It's desirable to use the smallest shaft diameter possible, that will support the load with a reasonable safety factor & not take a set."

That diameter may not be large enough to act as an adequate bearing surface under the given load.

Tom

Reply to
Tom

Hi everyone,

Thanks for your replies Ned and Tom,

Having adequate bearing surface is no problem with the smallest 3/8" OD shaft I wanted to use . With a 3/8" OD cantilevered mounted dowel / shaft, my beam design software calculated a bending stress of 67.8 KSI and a deflection at the end of the dowel of .00649". The dowel is only

1.48" long, so I was a little concerned with the amount of deflection and bending stress. I was worried the dowel might take a permanent set.

They make dowels out of different steels, but I am guessing they are close in yield strength (at least I hope). If someone sells the same part number in several different materials, and I never know which material I'm getting, this could cause a problem if I get a material that will not handle the load.

I guess the question is, will standard dowels handle this amount of stress without taking a permanent set, and can I count on the different materials having reasonably close maximum yields ? I did not see anything in ASME B18.8.2 on this matter.

If I can count on all of them having a maximum yield of at least 80,000 or 90,000 PSI, I think I will be OK. I wish I could find a chart that shows how hardening affects yield for different steels, but I have not found one yet.

Thanks again, John

Reply to
John2005

Machinery's Handbook has tables of "mechanical properties of selected carbon & alloy steels" quenched and tempered, that gives specs at different hardness. 4037 & 4140 are listed.

Tom

Tom

Reply to
Tom

Greetings John, On several occasions I've needed to get more information about a product than the folks at MSC could give me. Each time they called the manufacturer while I was on the phone. And each time the technical information I needed was given. I have also just called MSC and asked for a manufacturer's number so I could call them at a later date. Msc has always given me the phone number and other contact information. Grant's rec. to try MSC is a good one. Eric

Reply to
Eric R Snow

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