Correct material for pins.
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Re: Correct material for pins.
Re: Correct material for pins. -- Donn	Post Reply	Top of thread	Forum

Posted by: Cragyon ® 09/30/2003, 06:42:32 Author Profile Mail author Edit

I used to design for fatique machine in the helicopter industry. We used a material that was loosly reffered to as as "Stress Proof" round. I think this material was 4130 or 4430 stress relieved steel.

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Re: back hole pins
Re: Correct material for pins. -- Donn	Post Reply	Top of thread	Forum

Posted by: RKimball ® 09/29/2003, 23:44:08 Author Profile Mail author Edit

I have machined several in my youth. You are almost right. 4140 or 4130 HT. You purchase the bar in the HT condition. If the pin is straight and has no head you need only saw it and drill the pin holes. If it has a head it must be put into a lathe and turned to the shape required. While in the lathe it is wise to apply a small taper on the small end to assist in "banging" it into place. In the HT condition the steel has the right values of shear strength over wear. You want them tough! You don't want them so hard as to break. These knee pins are somewhat of a wear part. And they do take quite a tough life. If the wear of the bushings is so bad as to have worn a "moon" into the knuckles you would be wise to have new 4130 rings made and replace the old ones at a weld shop. If new bushings are placed into the ruined knuckles they will simply quickly extrude to the bad shape and loose the less slack condition you are wishing to regain. You'd be back in the shop too soon, again loosing production and profitability. My quess is the pins you need to replace are the ones near the pivot point and at the first knee from the base, am I right? Yes I know, this IS a much less expensive way, and you can have spares made at the same time providing additional cost reductions, than purchasing the pins from the OEM. Good luck! -randy- ** The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, don't fail to listen to suggestions. -randy-

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RE: stress proof
Re: Re: back hole pins -- RKimball	Post Reply	Top of thread	Forum

Posted by: RKimball ® 10/02/2003, 23:27:31 Author Profile Mail author Edit

Hi, Actually, if my memory serves, 'stress proof' is a material that machines a lot like cast iron. It is favored for its ability to stay straight when machined and for being quite ridged. Being of a powdered & granular structure it tends to be stressless or at least very low in internal stresses (a great and welcomed trait). Machinists love it. However, it is soft in wear quality in a rubbing situation. It is best suited for shafts that have tight parts locked to its diameters where ridged straight properties serve us well. It is wonderful in helicopter transmission shafts where rotational speeds are high and a straight balanced shaft is a must. 4130 HT is the stuff most used in gun parts and other places where an ability to wear well and handle stresses of shear or those similar to explosions are encountered. ... as my memory serves.. correct me if I'm wrong. -randy- ** The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, don't fail to listen to suggestions. -randy-

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Re: RE: stress proof
Re: RE: stress proof -- RKimball	Post Reply	Top of thread	Forum

Posted by: Donn ® 10/03/2003, 08:16:44 Author Profile Mail author Edit

Hi. Thank you for the prompt response. Your information and experience is very much apprieciated. I believe 4140 purchased in the HT condition is the way to go.

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Re: RE: stress proof
Re: Re: RE: stress proof -- Donn	Post Reply	Top of thread	Forum

Posted by: fake_plastic ® 11/01/2003, 08:39:44 Author Profile Mail author Edit

Hi, My company makes excavator attachments. WE use induction hardened mild steel pins You can normally get away with EN8, but if you're planning on using a breaker then induction hardened pins are the way to go

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