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.
Is stainless steel necessary, or is there an assortment of zinc
plated (or whatever similar type) machine screws/nuts made out
of decent steel someplace on the Internet or at a USA
chainstore? I need sizes like 6, 8, & 10.
I assume that you're tapping the holes first, right? If not,
that's your problem.
Screws should thread into tapped holes very easily. If your tap
is extremely worn, that might be the problem. Or you could be
using the wrong size of tap. Or you might not be cleaning out
the swarf from the hole after tapping.
But I doubt you could break even the cheapest screws by simply
threading them into correctly tapped and cleaned holes.
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.
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. I will look into
thread forming fasteners, but I've heard that a machine screw into
aluminum can do that. Unfortunately, as I keep trying to get the
message across, the cheap machine screws I have give way under too
little pressure. I know they aren't going to be strong enough for my
application.
OK, _I'll_ give it a try. I'll give you some facts and some comments:
Fact: Taking perfectly good machine screws and forcing them into
untapped, undersized holes in aluminum will break them, regardless of
grade or quality.
Comment: So, logically, if a machine screw breaks when you force it
into an untapped, undersized hole in aluminum, it doesn't mean that it's
a bad screw, it means that you aren't applying it correctly.
Fact: Jamming a fastener into a hole where it doesn't belong doesn't
make a 'nice tight joint'. It makes a poorly made, undependable joint.
It's kind of like tying a quadruple granny knot: it's hard to take
apart when you want it apart, but when you _don't_ want it apart it'll fail.
Comment: So, logically, you shouldn't do that.
Fact: The strength of a bolted joint doesn't correlate well with the
fastener torque unless you're using clean, properly dimensioned threads.
Comment: Uh -- you can figure this one out.
Fact: Loctite is your friend.
Comment: So, logically, if you want a properly made, permanently
fastened screw joint, you should get decent screws and put them in with
Loctite red or something stronger. If Loctite red isn't strong enough
for you, see if there's anyone on this group that you haven't alienated
and ask (nicely) for advise on the right stuff to use.
I have never had problems with the fasteners that I get from Home Depot.
I treat them like grade 2 bolts, and everyone is happy. If I need
something stronger I get it from McMaster or Small Parts, and everyone
is happy.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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