Where to buy machine screw assortment?

John Doe wrote:


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
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John Doe wrote:

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 .

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David Billington <djb djbillington.freeserve.co.uk> wrote:

Is there something wrong with asking for better machine screws in the UK?

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.

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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wrote:
If you want strong, buy HoloKrome screws. I believe J&L is in the UK.
Pete Keillor
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John Doe wrote:

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
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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?

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    [ ... ]

    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.

    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.

    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.

    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.

    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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"DoN. Nichols" <dnichols d-and-d.com> wrote:

And I'm trying to tell "we" that it really doesn't matter.

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.

And you're planning to tell your imaginary kill file friend on me.

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?

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.

Good luck.

cantabgold.net> <T3Hwj.2792$fX7.296 nlpi061.nbdc.sbc.com> <47c350b0$0$2452$fa0fcedb news.zen.co.uk> <CYIwj.7001$Mw.6323 nlpi068.nbdc.sbc.com>

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    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.

    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.

    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.

    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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DoN. Nichols wrote:
<snip>

This is what I've been trying to establish. It only requires a yes or no answer, but he's unwilling to give one. I don't think we can help him any further unless he provides a proper, unambiguous answer.
Best wishes,
Chris
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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
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"Roger Shoaf" <shoaf nospamsyix.com> wrote:

I'm satisfied with the other answers.

That's not really what I wanted to know.

Can't do that.

Maybe.

Go fuck yourself.

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John Doe wrote:
<snip?

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

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John Doe wrote:

That's not the answer to the question I asked above. Please read it again. If you answer the question I asked, it will make it much easier for everyone to help you, and will make the answers we give more relevant to your problem.
We're not here to criticise you unfairly; we're just trying to understand the problem better.
Best wishes,
Chris
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Time to get a life, Christopher.

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John Doe wrote:

Hope you find it before it's too late. PLONK
--
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John Doe wrote:

Well, it was you who lowered the tone of the discussion. I asked a reasonable question, which you refused to answer.
I'm inclined to think that you are putting screws into untapped holes, but for some reason refuse to admit it. It's a strange attitude if you actually need a solution to your problem.
Best wishes,
Chris
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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
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Try this site.
http://www.microfasteners.com/index.cfm
Bruce
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