7075 aluminum issues

I think you should send the parts out to be thread rolled. Or see if you can get a die to roll the threads on your machine. Rolled threads are stronger. Jim

What grade fasteners are you buying?

Gunner

"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist

What is the radius of the shoulder?

Richard

sunsh> I'm making small parts with M4 (close to 8-32) threaded male ends. The

Geeze. Everyone is just asking you questions instead of answering yours.

Are these parts subjected to much vibration? If so, is all due attention being paid to avoiding stress risers -- at least as much as is possible in a threaded part?

Your two questions....

Gunner

"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist

Yes, there's a LOT of vibration, they're part of a turnbuckle assembly on RC cars/trucks (nitro/gas powered).

They're threaded > Geeze. Everyone is just asking you questions instead of answering yours. >

Sunshine:

I had a similar situation a few years ago. I bought SS screws with the desired threads, removed the heads and mounted them in the body of the knurled head screw. My volume was not many but the solution was great.

Bob AZ

You certainly answered my first question, and if you don't know the answer to the second -- well, I think you answered it, too.

I don't know how 7075 is for fatigue resistance, but aluminum is generally always worse than steel, and you're in an environment where I wouldn't be surprised seeing steel fail in fatigue.

Do some web searches on "fatigue" and "stress risers". You should find some food for thought. There was an interesting thread on this group recently about a model boat gearbox shaft that a guy was having problems with, with a good response detailing the design of fatigue-resistant threads.

Basically you want to avoid sharp edges, particularly ones that go into the material. With time and vibration such edges will crack, and once they start the crack will propagate pretty quickly.

Is the material Aluminum, or steel? If aluminum..they are going to fail. Period. End program. Full stop. This application calls for something other than aluminim. Something steel and properly heat treated.

As Ive read the follow up comments about this being for RC car front ends...you are using the wrong material or the wrong heat treat if steel. You may have somewhat better luck if they were made of titanium than aluminum, assuming the proper grade and heat treat. And rolled threads.

Sometimes..there simply is no free lunch

Gunner

"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist

"sunshine-x" wrote in news:1154392558.018780.145040 @b28g2000cwb.googlegroups.com:

The shoulder should be a radius or taper to reduce stress risers. 6061 may be a better material than 7075 for your application as it is slightly more ductile. Rolling the threads would be better than a cut die. How far from the pivot is the tube supported? This sounds like the bounce of an unsupported tube is breaking the link at the weakest point (end of the threads.) If you support the tube with a slotted plastic support just inboard of the tube/threaded piece interface, you would probably see substantial life increases of the threaded ends.

Aluminum has a fatigue life rather than fatigue resistance. Most likely you will have to change to steel fasteners. If you use plated high strength/alloy be careful of hydrogen embitterment. These need to be baked immediatly after plating.

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You have already described the problem as 'breakage'. Since most people running screw machines seem to know their stuff, please don't be offended by the simplistic questions/remarks.

Have you examined the thread using an optical comparitor to see if the proper thread form is indeed being generated?

Have you specifically looked at the ending of the threaded portion to see if there is any abrupt ending which would create an abnormal stress point? From my limited experience with 7075, it tends to come off in chunks.

Perhaps a simple change in type of lubricant, or method of application could make a significant difference.

Are the chips loading up in the threading die?

Is there a 'neck' at the end of the thread to minimize stress?

Another possibility is the application itself, and the parts are not installed 'square' and the resulting stress in use is causing the breakage.

Maybe I did not understand. I take it the threaded part is the same overall diameter as the unthreaded part. I think that I assumed that the threaded part was noticeably smaller in diameter than the main body.

If the threads are the same diameter, then there is no shoulder, and my question/comment did not apply.

Richard

sunsh> This part is about 0.2" at the shoulder, is round, and inserted and

I agree - but in a F.A. mode - are the threads full - or does the die slam into the head and then reverse out - stressing / stretching the head ....

Might be an adjustment needed.

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member

Jim Sehr wrote:

That's a great question - I'll have to ask our machinist. From looking at the part, I'd think it's not, however I'll ask the expert tomorrow and update the thread.

Mart> I agree -

They're currently made from 7075 Aluminum T6 rod, and are machined using a screw machine with a die for the threads.

I'm not certain what I should be doing post-machining for heat treating. I've tried re-ageing some and will be testing them shortly to see if there's a difference between them. My procedure was very simple, 250 - 270 deg. F in the toaster oven for 24 hours.

I'm th> Is the material Aluminum, or steel? If aluminum..they are going to fail.