Where to buy machine screw assortment?

wrote:

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
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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
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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.
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    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.

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

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.
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John Doe wrote:

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
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I keep a basket full of recycled used paper towel portions (from non-chemical/biological uses). They can be used for cleaning bolts too. Fold the paper towel into several layers, hold it on the bolt with your fingers, and use a cordless drill to slowly spin it off of the bolt. To get rid of plastic chips on plastic screws, just move them around against the carpet.
Have fun.

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A few notes about machine screws and where to buy them:
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.
I was taught to use Grade 5 or better bolts in the automotive world.
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.
If you want strong, buy HoloKrome screws. I believe J&L is in the UK.
http://www.microfasteners.com/index.cfm
Try a company like Fastenall for good screws.
http://www.mscdirect.com
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