Hand-starting threaded fasteners

L

longview7

#1
We supply welded sub assemblies to automotive Tier 1 and OEM manufacturers. Is it an industry-wide common practice to hand start nuts and bolts 3-5 turns before applying power tools? Because this has been my experience with all of our domestic and foriegn automotive customers for over ten years, I believe it is.

Just recently, a Tier 1 has imposed a new standard that "All fasteners must thread freely by hand to their full length." This seems like an excessive requirement. "freely by hand" varies by operator finger strength. While we are responsible to control weld spatter, it is impossible to assure to no debris will enter the threads prior to assembly. They impose 3rd party containment at each incident.

Have you ever heard of such a requirement?

Thank you,
 
S

smkeilman

#2
Short answer: sort of, but I don't work in automotive, either.

Longer answer: This sounds to me like someone may have gotten burned recently, perhaps for giving an OK for some questionable parts. Case in point: we machine oil manifolds. When we started, we could pack them in crates however we wanted. There was one part that fit two to a crate very nicely. One day, we are told that all manifolds must be shipped in separate crates. We had never had a problem with our packing; we had even been complimented on it. We think the OEM was having problems with parts hitting each other and getting damaged in shipment. So, one part, one crate, packed in foam.

Properly made screw threads will assemble by hand to full length, so it's not outrageous to demand that your parts are made correctly. Since your concern is weld splatter (and you admit to this being your problem to control), I don't really see any path forward besides plugging all of the holes, perhaps with set screws. You could have small slots cut into the set screws to try to break any splatter off when they are removed.
 
L

longview7

#3
Thank you for the reply. I suspect the new requirement is a reation to some other issue, but there was no explanation offered.

The parts we are shipping are made correctly. Weld splatter from out process will stop a bolt that is being driven by a power tool. Finger tightening fully can be stopped by a minor bit of dirt.

You have a good idea about the hole plugging, but that will be labor intensive. But we are dealing with 15,000 threaded holes per day. The concern I have is that this new requirement is well outside the norm and will be impossible to meet without a requote for the labor. Customer says "same price, no negotiation."

I have never heard of this requirement. What is the industry standard?
 
S

smkeilman

#4
I don't think you're going to find much of anything. There are some clauses that could help you, however. For example:
ISO 2768-1:1989 Annex A-A.4: "Exceeding the general tolerance should lead to a rejection of the workpiece only if the function is impaired"

The ISO and ANSI/ASME thread specs will tell you that for a threaded hole to be conforming, a GO thread gage must assemble freely by hand for the entire thread length. We have had parts rejected and returned for this issue. Even if a gage won't assemble, you may be able to say function is not impaired if a fastener assembles. However, fighting a Tier 1 or OEM over that might not be in your best interest.

If the splatter will stop a power driven bolt, then you have a legitimate process problem. You are rendering components unusable because of your process. I assume that your business arrangement stipulates that you supply conforming product, which kind of backs you into a corner. If a component does not assemble, and weld splatter is determined to be the cause, you will likely find yourselves on the hook for it.

The reason I suggested set screws is that the only way to send conforming product is to remove them, and the only way you will remove them is if you have a good hole.
 


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