Loctite 680 and its use in a press fit application?

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holmes_ca

........Edmund...Alberta
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Loctite is a plastic that fills gaps anywhere from .002-.015 and up, its application is that it expands as it dries, can someone explain why hobbyists and professionals alike use it on press-fitting two parts together under tonnage, surely that defeats the object, it's said it fills up all the faint irregularities in the fit, but surely the press-fit alone does that? for an exaggerated example, the pressing on Locomotive wheels onto axles, Loctite 680 is supposed to work with up to 0 .010 thou gap,

Edmund...........Alberta
 
I've put in a few thousand bushing using 620 that also is gap filling with a press fit, it just works really well
 
I had a chain saw flywheel come loose and wallow out the tapered bore. I used regular grade Locktite and the repair lasted around 10 years until the saw was scrapped.
 
The press fit does not crush out all the small surface asperities. There a still lots of very thin air gaps in a press fit. Loctite fills them and increases holding strength. Don't believe, make parts and test with and without.
 
Hi All, Coming from a mass production factory where Loctite, 3M, Bostic, and many others supply assembly materials and chemicals, I have lived and worked with the "abuse" of language an consequential mis-understandings that can arise for decades. Hence my jaundiced views below:
To pick-up on advantages of assembly with a fluid chemical bonding agent: There is also the situation where the Loctite liquid in an application acts as a lubricant during assembly, which may help some applications assemble "better", and if chemically cleaned will chemically adhere to the components being assembled, thus increasing the shear strength of the joint.
N.B. LOCTITE is a Company name, not a product, as with many other Chemical companies... But we write with a Biro, clean carpets with a Hoover, but we don't light our rooms with a Swan or Edison....
As Loctite et al produce MANY products, as well as "Industrial adhesives": I read this thread as referring to Anaerobic Adhesives, and the title of product gives the game away. They are adhesives, when used correctly. Although they may only provide a few percent extra in the shear strength of some joints, in other joints you go from "zero" to "Something" - which is an infinite improvement if that's what you need. What these liquid products cannot do is correct alignment - as with taper-on-taper assemblies that are badly worn, or 10 thou gaps between wheels and axles. Precision Fitting is the proper Engineering (I mean that in it's truest definition of "problem solving") that should be adequate (because that's why the Engineer that designed it did it that way!). The use of "vibration resistant" and "gap filling" materials" can and does increase the strength of joints, and is used widely by Design Engineers to resolve such problems and make assembly easier and CHEAPER. But please don't confuse a 10 thou clearance bonded with sticky stuff with Engineering, as it is a bodge (However you spell it.). For "Bodge" read "A repair", which may have a long life if performed correctly, but is usually likely to fail after a short lifetime compared to the "proper" Engineered assembly. So if you pride yourselves in your machining and assembly work - and the resulting Models - then you will use liquid adhesives etc. with the respect and caution in their intended applications, which mostly rely upon very precise dimensional control for their strength and durability, as do press fitting, silver soldering, friction welding, riveting, etc. and many other joining methods.
Model Engineering designers may not always follow the "traditional" assembly method - particularly due to scale and strength not always being simple and linear - but anyone associated with making steam plant will be very aware of the laws for following assembly methods correctly where steam is used at pressure. But that does not mean that for other models we should not be responsible in our model making for considerations of Safety, as well as simple personal integrity that we have made "the best we can".
So please use Anaerobic Adhesives wisely, carefully, and as intended for your assemblies.
Sorry to preach, but it seemed a bit appropriate here, although there are some very sensible comments already.
K
 
I think that Loctite 648 is the one to use for interference fits
 
FWIW When the only practical method to lock a round part in a hole is Loctite I machine the male part for a slide tight fit and then reduce the diameter in the center portion to provide the necessary gap. The untouched shoulder guarantee the alignment and concentricity. For model work a well made press fit has all the strength one needs. If the press fit is not enough to handle the torque, counting on a minimal gain from the adhesive seems irrational. Find a better design approach. If one needs to fix something and Loctite is the most practical solution anything goes, just get her done.
 
Holmes
If you are talking about a real locomotive axle and wheel combo. You can not use anything besides Castrol oil or actual wheel lube that’s made for pressing wheels on. This is per FRA and AAR rules anything else is not approved. But after writing this I have a feeling you are talking about small gauge stuff instead of the big boys. Lol wouldn’t be the first time my mouth over rode my ass
Tom
 
Loctite even makes a wicking formula that is used after bolts and nuts are assembled and torqued. They also make a formula that is made for a slip fit and a formula that is for a press fit. A sleeve retainer and a bearing retaining formula. The only thing better then all this stuff is sliced bread. Lol lol lol
 
Read the instructions and specs, they do make a product for nearly every application, and I have seen some remarkable repairs done with anaerobic products that out perform the expectations. I have also seen failures when not done properly, but generally anaerobic is pretty good insurance on assemblies.
 
I have worked on aircraft for 44 years, and since I was a tadpole, Loctite products such as 635 and 680 have been an approved and REQUIRED item in assembly of nearly any aircraft part. Nearly all of them are press fit applications, such as the installation of uni-ball bearings in flap arm assemblies, bushings in forgings, etc. If it is not a nut or a bolt with a cotter pin, when you put it together, there is nearly always an engineering requirement for one grade of Loctite or another. It is in the manuals and on the blueprints. The inspectors always checked to see what was required, and what had been used.
I was shown early on that, even with a press fit, the addition of Loctite-type products gives a BIG increase in retaining friction, sometimes as much as 200% over the simple press fit. It may sound like "snake-oil" but having used it for many years, I can attest to it's effectiveness. I have yet to see a Loctite-assembled press fit assembly ever come loose or wallow out. The bearing assembly may be rough or even failed, but it stays where it is installed. until it is pressed out so a new bearing bushing, or stud can be pressed in.
 
Just my 1.414 cents worth. With .0625" wall thickness cast iron cylinders after being perfectly
bored and pressed in are no longer perfect and have to be honed back to size.
With a good slip fit and 680 no problem. Also some castings are not perfect, and if you
have porosity that needs to be water/gas tight Loctite solved that problem also.
Just IMO.
 
Glad to know many of you professionals have had success with these products. That's the same as my experience.
But I was cautioning against use where the "consequences are not understood!" - or the designer intended a different assembly as suitable. (Designers and professional Engineers make their money by getting it right.... despite abuse from many quarters).
Hats-off in respect to Aircraft people - the best certified, disciplined and safe people in my experience. (As someone once told me, you can get a ladder up the side of a building, a ship usually won't sink, but when an aircraft goes wrong even prayers can't stop gravity from working while you fix it!).
Enjoy!
K
 
The thing about aircraft techs are the reason they don’t have comebacks is because they don’t make it past the thud of hitting the ground. Now I only say that because it came from a aircraft tech of 35 + yrs that told me that joke. As for the loctite repairs I have personally on the professional side used about every formula they produce and always had great success with their products. As long as the proper cleaning procedures and the proper formula was used for the repair. The stuff really is as good as sliced bread when used within its own boundaries. I also own 3 Harleys so I think I might be a part owner in the loctite company
Lol lol
Tom
 
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