On 2008-02-26, John Doe wrote:
"DoN. Nichols" dnichols d-and-d.com wrote:
We are trying to figure out exactly what the conditions are
under which the screws are breaking,
And I'm trying to tell "we" that it really doesn't matter.
and a lot of the initial answers
were addressing the implied condition that the screws were
breaking before they were fully into the workpiece
Better to go with the stated condition, that the screws were
breaking with too little torque. Since you don't know how much
torque I apply, you'll just have to take my word for it.
If the breaking torque is being reached before the head comes
into contact, *I*, at least, have to assume that you are trying to form
threads by screwing the screw into an unthreaded hole, which is not what
it was made for, and it *will* break.
I've never seen you *deny* that you were doing this. Clearly
deny that, and we will consider other things.
And 6-32 are *very* weak screws, and if made of the typical
zinc-plated butter steel which is used for the blister-pack stuff sold
by most home user hardware stores, they certainly will not survive being
used to *form* threads.
If you want to form threads -- either get the screws made for
the purpose (you're not likely to find them in Lowes), or get a
thread-forming tap. Note that when you are *forming* threads, you need
a larger tap hole than when you are using a normal thread cutting tap to
make the threads. If you try to use the tap drill for a thread cutting
tap, you will even break a thread forming tap as it clogs up with too
much metal.
We make suggestions, and you attack. ISTR that you came in
with
a similar behavior a couple of months ago or so.
And you're planning to tell your imaginary kill file friend on me.
I think that I did wind up tossing you into the killfile at the
time, but I changed newsreaders and am starting over. You are getting
very close to going into it again.
We're *trying* to help, and to do that, we need to understand
the precise conditions under which the screws are breaking. You
seem to have later suggested that the holes are properly drilled
and tapped, but it is not totally clear that was what you said.
I've said this several times already. I'm asking about bolt
strength, not about methods. Talking about methods is misconstruing
my original post. I mentioned the method because it happened to be
how I determined that the bolts on using are crap. Doesn't matter if
I am holding the small end of the bolt in a vice, the bolt breaks
too easily. How else am I supposed to determine bolt strength? Why
isn't that method okay? What other method would you suggest for me
to get an idea of bolt strength? Screw it into a correctly tapped
hole?
Yes -- and then measure the torque needed to break it off. Or
screw it in to normal torque and pull up on the plate held down with the
screw and measure the breaking point. Screwing it into an untapped hole
is putting stress on it in the wrong places, and it is of course going
to fail.
Little pressure -- or before you even get the screw in far
enough for the head to contact? This is the kind of detail which
can make a difference in you getting useful answers.
I've gotten plenty of useful answers about screw strength, IMO,
probably at least enough already. Some people aren't inclined to
give useful answers. Some people just don't know (for example, folks
living in the UK when asked about "USA chain stores"). Some people
just want to talk about fastening stuff, and that's okay with me.
Well ... my first answer to you told you where *I* would go to
buy the good screws -- before it became apparent that you will probably
similarly break good screws by similarly mis-using them.
When you have this many people asking you to clarify your
question, it must mean something other than that you are communicating
clearly.
DoN.
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