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 either I'm Superman or
the machine screws I buy from Lowe's are made out of junk steel.

I guess the upside is that at least the screwheads don't strip first
/

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.

Thanks.

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 either I'm Superman or
the machine screws I buy from Lowe's are made out of junk steel.

I guess the upside is that at least the screwheads don't strip first
/

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.

Best wishes,

Chris

Christopher Tidy 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.












Best wishes,

Chris

John Doe wrote:

snip

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.

You shouldn't be breaking even the poorest screws just threading them
into a tapped hole without tightening them. Something is seriously wrong
here. Either that or you're trolling :-).

Try McMaster-Carr. They may have sets of screws.

Best wishes,

Chris

Christopher Tidy wrote:

John Doe wrote:

snip

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.

You shouldn't be breaking even the poorest screws just threading
them into a tapped hole without tightening them. Something is
seriously wrong here. Either that or you're trolling :-).

Like by ignoring the question and for some strange reason insisting
that threading a machine screw into a properly tapped hole is the
only valid application for a machine screw. Plastic screws into
properly tapped holes. Threading screws into a hole is not the end
objective. The objective is to keep the pieces together. I can tell
that the bolts aren't strong enough, that's why I ask for better.

Try McMaster-Carr. They may have sets of screws.

If they are better than the apparent crap I get at Lowe's.















Best wishes,

Chris



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Try this site.

http://www.microfasteners.com/index.cfm

Bruce

John Doe wrote:
Christopher Tidy 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 or the you are seriously failing to provide the whole
picture. 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
..









Best wishes,

Chris

John Doe wrote:
Christopher Tidy wrote:

John Doe wrote:

snip

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.
You shouldn't be breaking even the poorest screws just threading
them into a tapped hole without tightening them. Something is
seriously wrong here. Either that or you're trolling :-).

Like by ignoring the question and for some strange reason insisting
that threading a machine screw into a properly tapped hole is the
only valid application for a machine screw. Plastic screws into
properly tapped holes. Threading screws into a hole is not the end
objective. The objective is to keep the pieces together. I can tell
that the bolts aren't strong enough, that's why I ask for better.

Try McMaster-Carr. They may have sets of screws.

If they are better than the apparent crap I get at Lowe's.















Best wishes,

Chris



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I suspect that you don't even know what you don't know.

Drill and tap the "bottom" part correctly for a machine screw of your
choice. Drill a hole in the "top" part slightly larger than the body of
said screw. Place the screw through the top part and turn it into the
threaded hole of the bottom part. The top part will now be held tight to
the bottom part by the head of the screw.

Randy

Randy Replogle spamgoeshere1 verizon.net wrote:

I suspect that you don't even know what you don't know.

Heya Bert.

Drill and tap the "bottom" part correctly for a machine screw of your
choice. Drill a hole in the "top" part slightly larger than the body of
said screw. Place the screw through the top part and turn it into the
threaded hole of the bottom part. The top part will now be held tight to
the bottom part by the head of the screw.

I know that. Unfortunately it has nothing to do with the question or
my current situation.

Maybe I should have just asked for better machine screws without any
description, but some people prefer to know what's going on.















Randy


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John Doe wrote:
Randy Replogle spamgoeshere1 verizon.net wrote:

I suspect that you don't even know what you don't know.

Heya Bert.

Drill and tap the "bottom" part correctly for a machine screw of your
choice. Drill a hole in the "top" part slightly larger than the body of
said screw. Place the screw through the top part and turn it into the
threaded hole of the bottom part. The top part will now be held tight to
the bottom part by the head of the screw.

I know that. Unfortunately it has nothing to do with the question or
my current situation.

Maybe I should have just asked for better machine screws without any
description, but some people prefer to know what's going on.

Bingo.

This is a discussion forum, not just a free information
service. Most of the members are very knowledgeable
and appreciate polite give-and-take discussion.

On Mon, 25 Feb 2008 21:20:49 GMT, John Doe
wrote:


I guess the upside is that at least the screwheads don't strip first
When I bought my lifetime guaranteed screw drivers from Lee Valley, I
asked if the guarantee still applied, even if the Phillips drivers
were only used for removal and never for installation.
Gerry :-)}
London, Canada

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.


















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I would try to buy bolts that are properly graded for anything
important (above golding a picture frame on the wall).

i

John Doe wrote:
Christopher Tidy wrote:


John Doe wrote:

snip

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.

You shouldn't be breaking even the poorest screws just threading
them into a tapped hole without tightening them. Something is
seriously wrong here. Either that or you're trolling :-).


Like by ignoring the question and for some strange reason insisting
that threading a machine screw into a properly tapped hole is the
only valid application for a machine screw. Plastic screws into
properly tapped holes. Threading screws into a hole is not the end
objective.

I didn't say it was. You've misread what I wrote.

Best wishes,

Chris

Randy Replogle wrote:

snip

I suspect that you don't even know what you don't know.

Drill and tap the "bottom" part correctly for a machine screw of your
choice. Drill a hole in the "top" part slightly larger than the body of
said screw. Place the screw through the top part and turn it into the
threaded hole of the bottom part. The top part will now be held tight to
the bottom part by the head of the screw.

That's another possibility, that he might be tapping the holes in both
parts. If so the starts and ends of the threads may not be aligned, so
that the two parts act like a locknut. If this is the problem, only tap
the hole in the part furthest from the head of the screw. Drill a
clearance hole in the other part.

Best wishes,

Chris

John Doe wrote:

snip

Maybe I should have just asked for better machine screws without any
description, but some people prefer to know what's going on.

Okay. It would really help if you could post a picture of the two parts
and the failed screw. Then it would be much less a case of guesswork.

If you don't have any web space, e-mail the picture to me and I'll host
it for you: cdt22 AT cantabgold. DOT net

Best wishes,

Chris

Jim Stewart jstewart jkmicro.com wrote:

John Doe wrote:
Randy Replogle spamgoeshere1 verizon.net wrote:

I suspect that you don't even know what you don't know.

Heya Bert.

Drill and tap the "bottom" part correctly for a machine screw of
your choice. Drill a hole in the "top" part slightly larger than
the body of said screw. Place the screw through the top part and
turn it into the threaded hole of the bottom part. The top part
will now be held tight to the bottom part by the head of the
screw.

I know that. Unfortunately it has nothing to do with the question
or my current situation.

Maybe I should have just asked for better machine screws without
any description, but some people prefer to know what's going on.

Bingo.

This is a discussion forum, not just a free information service.

So you want a little discussion before answering my question?

I usually prefer a concise question, from someone asking for help.

Most of the members are very knowledgeable and appreciate polite
give-and-take discussion.

Yeah, I'm ****ed at crap machine screws from Lowe's messing up my
project, and I guess it shows. It's definitely not a beautiful day
in the neighborhood here.

Whether it's understood or not, once again. I'm simply asking about
where to buy stronger machine screws than the zinc plated type I get
at Lowe's. And maybe whether stainless steel is the only way to
significantly increase strength from those type of machine screws
that break when you torque them.

Are those machine screws acceptable for anything? I'm surprised
anyone in this metalworking group would appear to be defending them.















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Christopher Tidy cdt22NOSPAM cantabgold.net wrote:

John Doe wrote:

snip

Maybe I should have just asked for better machine screws without
any description, but some people prefer to know what's going on.

Okay. It would really help if you could post a picture of the two
parts and the failed screw. Then it would be much less a case of
guesswork.

Your "guesswork" would go out of orbit.











If you don't have any web space, e-mail the picture to me and I'll host
it for you: cdt22 AT cantabgold. DOT net

Best wishes,

Chris


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On Tue, 26 Feb 2008 00:21:54 GMT, John Doe
wrote:

If you want strong, buy HoloKrome screws. I believe J&L is in the UK.

Pete Keillor

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

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Tue, 26 Feb 2008 00:44:51 GMT, John Doe
wrote:


Hey JD,

Don't buy ANYTHING that has a "slot-head".

Put a decent chamfer on the clearance bolt-holes. Some screws, in
fact most screws, have a root radius, which is why you place a washer
under the head.

Try a proper supplier, like Fastenal or somebody's "Nut & Bolt"
Company locally, or any mill supply house. Ask for "Grade 8" in
whatever style you need. Be prepared to spend more money than at
Lowes, but depending on what and where and how many you buy, the best
Holo-chrome's might not be a lot more bucks. Personally, I find that
Allen-head bolts are less likely to break than cap screws. Not sure
you can buy "machine screws" in Grade 8, but purchased from a good
supplier they will be at least Grade 5.

Twice (at least) in previous replies you mentioned using stainless
bolts rather than the zinc-plated machine screws used at present. You
should note they S/S are NOT stronger that good steel bolts. In
fact, may be quite a bit softer if they are not also Grade 8 or
better. "Stainless" is a quality of the material, and not directly
related to strength or holding/breaking capacity.

Take care. Good luck.

Brian Lawson,
Bothwell, Ontario.

On Feb 25, 1:20 pm, 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 either I'm Superman or
the machine screws I buy from Lowe's are made out of junk steel.

I guess the upside is that at least the screwheads don't strip first
/

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.

Thanks.

I have done many time what you are describing, only using self-
drilling sheet metal screws and an electric drill to drive them. You
and I were both over torquing the screws. Somewhere there is a table
of allowable torque on the screw you are using. If you can find a
toque indicating screwdriver and limit your indicated torque to the
amount allowed for that screw, you will be home free.

The Lowe's screws are undoubtably made in China qand are usually junk.
Try a company like Fastenall for good screws.

Good luck,
Paul

The Lowe's screws are undoubtably made in
China qand are usually junk.
Try a company like Fastenall for good screws.


Even buying from Fastenal is no guarantee of
quality. Lots of their stuff is from
interesting sources. I especially see it in
small (#6) setscrews. They spin the socket out
very easily. For that application I buy
HoloChrome from MSC. #6, #8 and #10? Fastenal
stuff is OK. If you are trying to screw them
into an unthreaded hole in aluminum, it isn't
going to matter if they are hand made by elves
from unobtainium barstock and lubed
with yak butter---the little buggers are going
to break.

On 2008-02-25, 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 either I'm Superman or
the machine screws I buy from Lowe's are made out of junk steel.

The latter is more likely.

But -- by "halfway through" to you mean with the screw half-way
into the aluminum? You are asking about machine screws, not self-taping
screw, based on the subject line of your posting, so I have to ask: "Are
you tapping the holes prior to trying to install the screws?" Machine
screws are *not* designed to make their on threads.

If by "halfway through" you mean "when you have about half of
the screws the project requires installed and tightened" then there is
something else seriously wrong, and junk metal is quite likely.

I guess the upside is that at least the screwheads don't strip first
/

:-)

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.

What I would suggest is black oxide finished screws, unless you
need to have light colored screws.

Go to someplace like MSC:

http://www.mscdirect.com

and register there (you have to register before making your first
purchase) and then they will send you a massive catalog ("the Big Book")
which you can use to look up tools and supplies more easily than I find
their web based presence to allow. Then you can phone in a purchase
(remembering the account number you got when you registered) and
typically they will deliver by the next day. (Hopefully you are not in
Canada, because they insist on using UPS for delivery, and UPS insists
on charging a customs brokerage fee on packages to Canada.)

Note that you will find the prices for a box of 100 screws
better than the prices for 10 screws of the same size in Home Depot. I
don't have a convenient Lowes to compare to for prices, but I would
expect them to be similar to Home Depot.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Hey Tim. Are you spewing ignorance just so you can spam your website
in your e-mail address and in your excessively long signature on
USENET? Does spewing nonsense while claiming to be logical help get
you into discussions about logic that (you think) helps promote your
website?










Tim Wescott wrote:

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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

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Brian Lawson wrote:

On Tue, 26 Feb 2008 00:44:51 GMT, John Doe
wrote:


Hey JD,

Don't buy ANYTHING that has a "slot-head".

Put a decent chamfer on the clearance bolt-holes. Some screws, in
fact most screws, have a root radius, which is why you place a
washer under the head.

Try a proper supplier, like Fastenal or somebody's "Nut & Bolt"
Company locally, or any mill supply house. Ask for "Grade 8" in
whatever style you need. Be prepared to spend more money than at
Lowes, but depending on what and where and how many you buy, the
best Holo-chrome's might not be a lot more bucks. Personally, I
find that Allen-head bolts are less likely to break than cap
screws. Not sure you can buy "machine screws" in Grade 8, but
purchased from a good supplier they will be at least Grade 5.

Twice (at least) in previous replies you mentioned using stainless
bolts rather than the zinc-plated machine screws used at present.
You should note they S/S are NOT stronger that good steel bolts.
In fact, may be quite a bit softer if they are not also Grade 8 or
better. "Stainless" is a quality of the material, and not
directly related to strength or holding/breaking capacity.

Right, strength. It doesn't have to be noncorrosive, so yeah I was
asking about stainless steel's relative strength. Thanks.













Take care. Good luck.

Brian Lawson,
Bothwell, Ontario.

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.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Mon, 25 Feb 2008 23:18:25 GMT, John Doe
wrote:

Christopher Tidy wrote:

John Doe wrote:

snip

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.

You shouldn't be breaking even the poorest screws just threading
them into a tapped hole without tightening them. Something is
seriously wrong here. Either that or you're trolling :-).

Like by ignoring the question and for some strange reason insisting
that threading a machine screw into a properly tapped hole is the
only valid application for a machine screw. Plastic screws into
properly tapped holes. Threading screws into a hole is not the end
objective. The objective is to keep the pieces together. I can tell
that the bolts aren't strong enough, that's why I ask for better.

Any steel screw will have greater strength than the aluminum they are
threaded into. If you are twisting the head off I'd agree with
previous posters that there's a problem with the threads in the
aluminum or that you are over toqueing the screw.

Jim Levie wrote:

Any steel screw will have greater strength than the aluminum they
are threaded into. If you are twisting the head off I'd agree with
previous posters that there's a problem with the threads in the
aluminum or that you are over toqueing the screw.

Would you agree that a harder/stronger higher grade bolt takes more
torque to break?

"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.

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.

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?

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.

Now to read the rest of this, and *try* to resist commenting
again.

Good luck.














Good Luck,
DoN.

--
Email: dnichols d-and-d.com | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---


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From: "DoN. Nichols" dnichols d-and-d.com
Newsgroups: rec.crafts.metalworking
Subject: Where to buy machine screw assortment?
Date: 26 Feb 2008 05:39:31 GMT
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Trying to thread a machine screw into some aluminum.

You could be getting galling on the threads, where the aluminum gets
"gummy" under pressure and stops being a good sliding surface for the
steel. You might try lubricating the threads before assembly, using
antiseize, or even going to a thread insert (like Helicoil or
Keensert) in the aluminum.
--Glenn Lyford

On Tue, 26 Feb 2008 05:32:50 GMT, with neither quill nor qualm, John
Doe quickly quoth:

Brian Lawson wrote:

On Tue, 26 Feb 2008 00:44:51 GMT, John Doe
wrote:


Hey JD,

Don't buy ANYTHING that has a "slot-head".

Put a decent chamfer on the clearance bolt-holes. Some screws, in
fact most screws, have a root radius, which is why you place a
washer under the head.

Try a proper supplier, like Fastenal or somebody's "Nut & Bolt"
Company locally, or any mill supply house. Ask for "Grade 8" in
whatever style you need. Be prepared to spend more money than at
Lowes, but depending on what and where and how many you buy, the
best Holo-chrome's might not be a lot more bucks. Personally, I
find that Allen-head bolts are less likely to break than cap
screws. Not sure you can buy "machine screws" in Grade 8, but
purchased from a good supplier they will be at least Grade 5.

I was taught to use Grade 5 or better bolts in the automotive world.
Good stuff.


Twice (at least) in previous replies you mentioned using stainless
bolts rather than the zinc-plated machine screws used at present.
You should note they S/S are NOT stronger that good steel bolts.
In fact, may be quite a bit softer if they are not also Grade 8 or
better. "Stainless" is a quality of the material, and not
directly related to strength or holding/breaking capacity.

Right, strength. It doesn't have to be noncorrosive, so yeah I was
asking about stainless steel's relative strength. Thanks.

Since I'm using more and more ACQ treated lumber, the need for
non-corroding hardware has led me to stainless research. McMaster has
half a dozen stainless alloys and their differences astounded me.
From their comparison chart + delving into the individuals:

17-4 PH Stainless Steel, 140,000 psi
Combines the high-strength of alloy with corrosion resistance of
stainless steel.
18-8 Stainless Steel, 70,000 psi
Offers excellent corrosion resistance; it may be mildly magnetic.
Alloy 20 Stainless Steel, 80,000 psi
Also known as Carpenter 20, it's nonmagnetic and especially
resistant to stress corrosion.
300 Stainless Steel, 80,000 psi
Meet more stringent specifications such as military
specifications. All are passivated (a nitric acid treatment that
creates a passive film to protect the stainless steel from oxidation
and corrosion).
316 Stainless Steel, 80,000 psi
Offers even better corrosion than 18-8 stainless steel. It
contains molybdenum, which increases resistance to chlorides and
sulfates. It may be mildly magnetic.
450 Stainless Steel, 170,000 psi
Offers more corrosion resistance than alloy steel.

Unrated hardware, Class 2A, has a 60,000 psi strength.
Grade 5 with a zinc plating is double the strength at 120,000 psi.

--
Such is the irresistible nature of truth that all it asks, and all it wants,
is the liberty of appearing. -- Thomas Paine

"John Doe" wrote in message
...

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.



The answer to your question is no. Screws are not made to work in
incorrectly tapped holes so you can get them very tight.

Weld the pieces together. Use locktite, go troll the cat news groups.

--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.

On Tue, 26 Feb 2008 06:02:23 GMT, John Doe
wrote:

Jim Levie wrote:

Any steel screw will have greater strength than the aluminum they
are threaded into. If you are twisting the head off I'd agree with
previous posters that there's a problem with the threads in the
aluminum or that you are over toqueing the screw.

Would you agree that a harder/stronger higher grade bolt takes more
torque to break?

Absolutely the higher grade screws will be stronger than the
ungraded "mystery metal" screws at the local hardware store - but on
small #6 and #8 screws you can easily surpass the breaking strength of
even the highest grades with a hand screwdriver and a "Don't know my
own strength!" wrist. Been there, Done that, Have the T-Shirt.

Too much torque is still too much torque. If you get too good of
screws that will take being over-torqued without failure, you'll just
start pulling the threads out of the aluminum fitment they are screwed
into.

They do make torque screwdrivers that click when you reach the
proper setting. If you can't feel when it's tight, you might want to
invest in one.

And there are design limits for screws - if the assembly isn't
strong enough a "super screw" isn't going to buy you much. You need
to increase the screw size, use multiple screws, or redesign so that a
bracket or tab takes the load, and it's not all on a screw in tension.

-- Bruce --

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 either I'm Superman or
the machine screws I buy from Lowe's are made out of junk steel.

I guess the upside is that at least the screwheads don't strip first
/

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 don't know if you can find any commodity-grade stuff that is
much better. You can get certified aircraft-grade fasteners
from an approved source, but they will cost a lot more. Still
have to watch out for counterfeit stuff there, too.

I buy stuff like this in 100-piece boxes. For electronic-style
stuff (ie binding head phillips machine screws), I buy it from
Digi-Key. Lately I have had to go to stainless for ROHS
reasons, the zinc-plated stuff is non-compliant for some reason.

For other stuff like socket head cap screws and button head
(Allen) screws I get them from MSC. I have had some with no
threads, way off-size allen sockets, etc. But, I have had no
problem with screws breaking off - from either source.

6-32 is the weakest standard screw thread, due to the ratio of
minor diameter to major dia., so if that is the size you are
using, it's an added complication. You might also want to check
the quality of your taps, the way you use the taps, the size of
the pilot hole, etc. The screws should go in effortlessly. If
there is significant binding, then the thread is off in some
manner, or the hole isn't clean. I use spiral-flute taps (not
spiral POINT) as much as possible, they can be run in in one
continuous motion, producing a chip similar to a long, curly
drill chip. This makes it much easier to clean the hole after
tapping. I rip a little piece of a paper towel off and twist it
into a thin cone and poke it into the hole and twirl it to get
the chips out.
(Professional shops use compressed air, but my family would
object to this late at night.)

Jon

John Doe wrote:
Like by ignoring the question and for some strange reason insisting
that threading a machine screw into a properly tapped hole is the
only valid application for a machine screw. Plastic screws into
properly tapped holes. Threading screws into a hole is not the end
objective. The objective is to keep the pieces together. I can tell
that the bolts aren't strong enough, that's why I ask for better.
The point here is that if the screw is binding in the thread,
and requires more than a twist of the finger to put it in with
NO load, it will bind a LOT WORSE under axial load. This is
probably the MOST common failure mode of a screw or bolt. The
thread binds up to the point that the shank fails in torsion,
not from axial tension.

Without knowing more about what size bolt/screw, what kind of
tension you are trying to achieve, what alloy and how much
thread engagement there is, it is REAL hard to advise further.
If you need 1000 Lbs of axial force out of a 6-32 screw, you
need to go up a couple sizes. If a 1/2-13 is breaking off at
only 1000 Lbs axial load, you have to be doing something wrong,
or the bolts are made out of recycled beer cans.

Jon

"Roger Shoaf" shoaf nospamsyix.com wrote:

"John Doe" jdoe usenetlove.invalid wrote in message
news:CYIwj.7001$Mw.6323 nlpi068.nbdc.sbc.com...

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.



The answer to your question is no.

I'm satisfied with the other answers.

Screws are not made to work in incorrectly tapped holes so you can
get them very tight.

That's not really what I wanted to know.

Weld the pieces together.

Can't do that.

Use locktite,

Maybe.

go troll the cat news groups.

Go **** yourself.









--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.




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From: "Roger Shoaf" shoaf nospamsyix.com
Newsgroups: rec.crafts.metalworking
Subject: Where to buy machine screw assortment?
Date: Tue, 26 Feb 2008 07:37:48 -0800
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" wrote:

Trying to thread a machine screw into some aluminum.

You could be getting galling on the threads, where the aluminum
gets "gummy" under pressure and stops being a good sliding surface
for the steel.

Yeah, I think so, and apparently others have hinted at that when
talking about lubricant. Thanks.

You might try lubricating the threads before assembly, using
antiseize, or even going to a thread insert (like Helicoil or
Keensert) in the aluminum.
--Glenn Lyford

Much to my pleasant surprise, the primary fastener looks like it
might do the job without any extra strength, so the hole can be wide
enough for just pushing a strong bolt through and securing it on the
other side with a nut. And that will hopefully function as a
momentary/temporary hold in case things start to fall apart.

John Doe wrote:

snip?

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.

So you are attempting to drive a machine screw into an untapped hole?
Please don't see this question as being confrontational; I'm just trying
to figure out exactly what's going on.

There could be a number of reasons why you need a close fitting thread.
If it's for location, try to rethink the design. Use dowel pins or a
milled slot for location, and screws in clearance holes to hold the
joint together. But if you must have precise, close fitting threads you
can buy special taps for the purpose. Screw threads are assigned various
classes of fit, which range from a close fit to a loose fit. You will
need to buy special taps for a close fit. They're used in instrument
manufacture. They'll cost more, but they are available.

If you want a close fit to prevent the screws from coming undone due to
vibration, use spring washers or loctite instead.

Either way, driving machine screws into unthreaded holes will break
them. Even if they're really good screws.

Best wishes,

Chris

Christopher Tidy wrote:

So you are attempting to drive a machine screw into an untapped
hole?

I was asking for specific locations to buy stronger/better screws,
but the information about grades and stuff is probably at least as
useful.














Best wishes,

Chris