Questions regarding experiences with loctite & using 680 or 630 series retaining compounds as thread-lockers

Hi everyone,
Is there anyone in the forum that has used any of the 600 series loctite "retaining compounds" as thread-lockers ?
I have tested some loctite # 262 & #2760 thead-locker on a #10-24 screw with a small pattern hex nut having a height of 7/64". I tried black oxide finished & stainless screws with stainless and brass nuts. After 24 hours, the strength was not satisfactory. Loctite said that the #2760 is some of the strongest thread-locker they make & does not need primer and even works in the presence of a small amount of oil. I did not use primer as loctite said that the primer is already in the #2760 and advised against it's use. The screws were brand new out of the box and appeared clean and dry.
Someone suggested using #680 retaining compound as a threadlocker and said that it should be stronger than threadlockers. I see no reason a retaining compound would not work as a threadlocker unless the gap in the screw threads is too large for the retaining compound to dry properly.
Loctite lists the # 638 retaining compound as "maximum strength" but the # 680 has a shear strength of 4,000.00 PSI
Loctite's technical data sheets don't list the strength of each product in the same way and it makes it very difficult to compare products. They should just list the torque necessary to break the nut loose in each case and provide data for large and small nuts.
This thing never gets hot and is always used at room temperature. I just want to use a threadlocker or retaining compound to permanently lock the nut to the screw with the greatest amount of strength possible. It's no problem to wait 24 hours for the assembly to dry.
Loctite only recommnended using threadlockers, but someone out in the field said they had used the 680 loc-tite as a threadlocker with success.
What loc-tite product will produce the strongest bond and/or the greatest resistance to the nut breaking loose and/or backing off ?
I am going to test some of the 680 and perhaps 638 retaining compound, I just wanted to see if anyone had any experiences they could relate to me that might help me choose the best product for the job. Perhaps a two part epoxy would be stronger, but then I have to mix it and I would rather use a single part product already mixed.
Thanks for your help. John
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Remember that Loctite is not a replacement for adequate torque. Envision it as a lubricant and not a "screw glue" and you will be much better off.
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John2005 wrote:

John-
I've been futzing with loctits for YEARS even used 680 retaining compund for drill busihings, didn't have great luck with 680...wouldn't cure
I finally gave up on all the various types & settled on two (well actually three)'
242 for screws I wanted to remove 272 for PERMANENT installs (must heat to 450F+ to remove)
also I use 243 for sloppy MIL connector threads...243 is a gap filler
When I want the stuff to work 100%...I solvent clean (acetone) & use primer....let dry much longer than min suggested time
If I read your post correctly...you want permanent, high strength
I'd suggest......... clean with acetone (both items) , use primer (little glas bottle w/ pump spray) LOCTITE Primer N 7649 & 272
http://bosunsupplies.com/products2.cfm?product=L9509 http://shop.resellerratings.com/sf-1/pid-33591780/MD-0
in a few hours (at the most) it'll be hard
Do a 1/2" threaded connection as a test coupon....I know these connections cannot be removed without heating.......
272 info says 3/8 to 1" but I've used it down to 1/4" so give 10-24 a shot
cheers Bob
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Hi everyone,
Thanks for the tip on the #272 loctite and primer bobK207, I will give it a try. I will also try cleaning before I use the primer.
BCK, I really need a "screw glue", or something that can really lock this thing down. Can you recommend anything other than loctite ? I perfer a one part already mixed product over a two part epoxy, but any recommendations for something that will produce the strongest bond would be appreciated.
Thanks again, John
BobK207 wrote:

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John,
Loctite can serve that purpose if you use it in combination with adequate torque. Can you apply adequate torque or do you need guidance with this?
BCK

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Hi BCK,
Thanks for your reply. How many in-lb of torque would be adequate for a 10-24 screw in order to make the loctite work properly ?
Due to the way the screw and nut work in my application, I cannot tighten the nut very much, all I can do is just snug it down to take up axial play. I doubt I could torque it down to any type of spec that loctite would specify.
I would say that I could torque the nut down to 5 to 10 in-lb.
Thanks again, John
BCK wrote:

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Dear John2005:

Better not use loctite. This compound does not "harden" until the air (actually oxygen) is squeezed out. How about a nylock nut?
David A. Smith
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Hi David Smith,
Thanks for your reply.
I don't really have the space for a locknut. I tried some of the "top lock" nuts from mcmaster carr, but they did not work well in the application. I need to permanently lock the nut to the screw.
If I can get to it, maybe a spot or tack weld will do the job. I only have about .044" of room on top the nut for the weld though, and that's using a small pattern 5/16" hex nut that is only 7/64" high. I am also using a delrin washer under the nut so the heat might hurt the washer. A stainless washer may work, but the delrin is nice because it allows for less friction and noise when rotating the screw (the nut "rotates with" the screw as the screw is turned to adjust another part up or down).
Thanks again, John
N:dlzc D:aol T:com (dlzc) wrote:

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Dear John2005:

Consider either: * two thin nuts which you use as jam nuts (might not be possible on 10-24) * a steel pop rivet with a washer where the nut would have been.
David A. Smith
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Other things I have seen done: * skive the threads into the nut with a pin punch * McMaster "toplock" or "centerlock" locknuts
David A. Smith
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Using a Delrin washer under the nut is BAD. Delrin creeps, and soon after you torque the nut down the joint will be loose again.
If you are using a 5/16 threaded section, then the minimum nut thickness should be at least 1 diameter or you will have little load bearing capability/torque holding capability. I.e. the nut should be at least .312 nominal In some cases you can use a thinner nut if it's self-locking, but a 7/64 nut on a 5/16 thread is really a jam nut and will not hold structurally.
The smallest pattern self-locking nut I would ever consider using structurally is MS21083 also called NASM21083
--
Harry Andreas
Engineering raconteur
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Hi Harry,
The nut is not for a structural load bearing application. The delrin washers seem to work fine, the nut is not really torqued down, it's just snugged down to take up axial play. The screw just moves a small slider on some dowel pins and does not require that much force to turn.
I chose delrin becasue it's supposed to wear well against steel, it's quiet, reduces friction (the nut turns with the srcrew as the screw is rotated), and is supposed to be more dimensionally stable than nylon.
The only other non-metallic washer material I considered was Nylatron GS. I considered stainless washers, but the loctite may seal the nut, washer, and mounting baseplate together. The non-metallic washers are also more quiet.
Thanks again, John
Harry Andreas wrote:

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Hi everyone,
I tested some 270, 271, 262, 2760, 638, & 680 loctite as a threadlocker on some 10-24 and 10-32 screws & nuts. Whether the thread was course or fine seemed to make no significant difference as far as strength.
I tested with and without primer using black oxide finished screws and zinc, brass, and stainless nuts. The stainless nuts had the weakest bonding, and the brass nuts seemed to have the strongest bonding although the zinc seemed close. I let the loctite dry for exactly 24 hours.
The best bond seemed to be the 680 using a brass nut, black oxide finished steel screw, and 7471 primer. I think it will be plenty strong for my application, but it did not destroy the threads when taking the nut off the screw, as a couple people told me it would. The 271 was also good, but I think the 680 was a little better, and it seemed to dry faster than the 271 using the brass nut.
The 2760 does not seem very strong at all on small screws.
I just thought I would report my findings to you in case anyone was interested.
John
John2005 wrote:

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John2005 wrote:

<snip>
John, Are you sure that you want to use a threaded fastener in this application? You might be better served by using grooved shaft and a retaining ring.
If clearance is a problem, you might consider an E-style retaining ring. You can also get bowed E-style retaining ring that acts like a spring to take up axial play
See: http://www.mcmaster.com/library/20061114/98408AAC.pdf http://www.mcmaster.com/library/9/970653/98398aac.PDF http://www.mcmaster.com/library/20060307/98555AAC.pdf
Just a suggestion.
--

Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
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And the Lord said, "Let there be lockwire."
That, or you can fake an aerospace-style self locking nut by crushing a normal nut radially in a vice until it takes on a tiny permanent deformation (the hole goes from round to oval). That will give you a degree of self-locking without changing your stackup.
Tom.
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Hi everyone,
Thanks for the additional feedback guys.
Tom Sanderson, thanks for your suggestions.
Regarding lockwire, I have not used this before, does mcmaster or some industrial supply shop sell this ? Could you please give me a little more information on how it's used ? Several ideas come to mind just from the suggestion of "lockwire" but I am not exactly sure what you have in mind.
I will also test the slightly deformed nut method you suggested.
Thanks again, John
Tom Sanderson wrote:

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Sorry, I forget that, outside aerospace, lockwire is not that common.
You can buy it from most industrial supply shops. It may be called "safety wire" too. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber92 http://www.malinco.com/aerospace/index.html
The basic technique is to drill small holes (slighly larger than the diameter of the lock wire) through the bolt and put slots or a hole through your nut. Then run lockwire through the holes & slots. As long as you right it the right direction, the nut can't back off because that would pull the wire tighter. Mechanically, it's like a cotter pin, but much easier to work with on very small installations.
Nuts with slots in them are sold as "castle nuts" or "castleated nuts" (search for "castle nuts" on McMaster-Carr).
Tom.
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If you could reach the end of the screw, a good 135 degree punch with the appropriate sized hammer in the end of the screw should deform the end enough that the nut will not come off.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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wrote:

Which reminds me: it was a surprise to find that early Rolls, had chassis bolts that were peened over their nuts, rivet style. Mr Royce tried always for the highest engineering standards too!
Brian Whatcott Altus OK
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