On 2008-02-26, John Doe wrote:
David Billington djb djbillington.freeserve.co.uk wrote:
John Doe wrote:
Christopher Tidy cdt22NOSPAM cantabgold.net wrote:
John Doe wrote:
I'm doing an important project. Trying to thread a machine
screw into some aluminum. Halfway through, the machine screw
twists apart just below the head. The heads breaking off is not
uncommon here. I don't put all that much pressure on them, so
[apparently] the machine screws I buy from Lowe's are made out
of junk steel.
[ ... ]
I need more strength than just enough to thread the machine screw
through a correctly tapped and cleaned hole. If the screw is
going to break so easily, it probably won't hold the pieces
together either. That's my problem.
I agree with Christopher here in that something is very wrong with
what you are doing
Is there something wrong with asking for better machine screws in
the UK?
or the you are seriously failing to provide the whole picture.
Considering how badly the picture is being distorted, more is clearly
not better for a troll.
I need better/stronger machine screws. I'm seriously not
understanding why anyone would suggest that machine screw quality
makes no difference, and that all that matters is threading the
screw into a correctly tapped hole. How to use machine screws sounds
like a completely different subject.
This sentence from your initial post:
"Halfway through, the machine screw twists apart just
below the head."
leaves us uncertain whether you are saying that each screw breaks before
the head bottoms (in which case there is some problem other than simple
quality of the fastener) or that you start getting broken screws before
you have half of the screws installed and tightened.
We are trying to figure out exactly what the conditions are
under which the screws are breaking, and a lot of the initial answers
were addressing the implied condition that the screws were breaking
before they were fully into the workpiece -- that is, before the head
was even clamping down the other part.
We make suggestions, and you attack. ISTR that you came in with
a similar behavior a couple of months ago or so.
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 took two interpretations and answered both of them with my
initial response before reading more than your original post.
I would suggest though that you may want to look at thread forming
fasteners which are often used for ductile materials such as
Aluminium, drill the hole fit the fastener, but you need to work
out it is suitable for your job which sounds like a problem at the
moment .
And that is something stronger. Besides a stronger machine screw (at
least stronger than junk steel), maybe something different will work
too. I might go with stainless steel. The fitting must be extremely
tight. A correctly tapped hole will not work.
Huh? A correctly tapped hole is the starting point for using a
machine screw -- either in the workpiece, or in a matching nut.
BTW -- it does *not* take Superman to wring off 6-32 screws.
They are the weakest for their size of any common screw. The threads
are too deep relative to the size.
I will look into
thread forming fasteners, but I've heard that a machine screw into
aluminum can do that.
A machine screw should *not* be asked to do that into aluminum,
or any other material. There are screws specifically made for the task,
but the standard zinc-plated screws are not.
So -- does this mean that you are not drilling and tapping the
holes? Just drilling them? Do you assume that the term "tapping" means
to mark the location with a center punch? I've seen people make that
assumption.
Unfortunately, as I keep trying to get the
message across, the cheap machine screws I have give way under too
little pressure.
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.
Of course you can get better screws. I posted MSC as a possible
source. Others have pointed to a couple of other sources. I even
suggested the black oxide finished screws instead of the zinc plated
ones. They tend to be much harder screws.
I know they aren't going to be strong enough for my
application.
None are if you are trying to form the threads with the screws,
unless you purchase specific thread forming screws.
Now to read the rest of this, and *try* to resist commenting
again.
Good Luck,
DoN.
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