Loctite 680 and its use in a press fit application?

[Charles Lamont]

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.

A push fit is fine for Loctite. Reducing the central portion to provide the 'necessary gap' is unlikely to be an improvement: a gap is not necessary, and you may well be weakening the joint.
The main reasons I often use Loctite instead of a press fit are because it is easier - the tolerances are wider, and I don't have to worry about dimensions (of a bush, say) being altered.

 

[William May]

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.

Those are EXCELLENT points that I had not even considered, but are VERY important when talking about hobby machining, and small engines, whether they are steam or petroleum.)

 

[chrsbrbnk]

But how can you prove that its the loctite working as opposed to the press-fit? surely any loctite applied is squeezed out with the press-fit, yes?

well after building hundreds and hundreds of lamination plates and trying out several methods of assembly like just press fit , no loctite or loctite with a gap and different gaps turns out the superior method was .0005 press with loctite applied to both hole and bushing and prepping with a light sand blasting on the bushing and really clean holes kept the bushings in the plate best

 

[ICEpeter]

I understand that Loctite when used for retaining purposes in conjunction with different metals, other than steel, like for bronce / brass / aluminum, etc. has varying retaining characteristics / strenght depending on the metal combination. Typically lower of what the retaining strength for steel is as indicated on their application data sheet. What is the experience of forum members in this respect?

Peter J.

 

[Chiptosser]

No ferric, (iron based) metals are treated differently for activation.
Activator is needed for some applications and the application of heat.
This was communicated in a seminar presented by the manufacture of locktite retaining products, previous to Henkel purchase.
For retaining stainless steels aluminum and brasses, apply material to both surfaces, assemble and apply heat, roughly, heat to around 150 degree F.
I used 660 for a retaining brass to SS, Alum. to SS, ect. This is threads ,bore fits, Bearing retaining, lots of different appictions, up to .020 gaps.
The application of heat helps to excellerate the set-up with out loss of strength.

 

[petertha]

I will volunteer some other Loctite comments/experiences, although kind of a tangent issue. Recently I volunteered to help a fellow who was restoring a vintage drill press. He had a fit issue where the bearing ID was 0.001-0.002" oversize the spindle shaft. And it was also a convoluted sequential assembly procedure to pre-assemble the bearings on the shaft which are spaced out about 12, then into the spindle cartridge, then anti-backlash nut...some other constraints. I had 0.001 & 0.002" brass shim stock & was using it mostly to size the gap & verify bearing fit.

I had an idea to simply pre bond the shim stock to the arbor & then slid the bearings down over it. I was more concerned by the permanence of bonding. Both parts were given about 600g light sanding treatment & cleaned with acetone. Loctite 680 was applied, securely taped & left it overnight. Next day checked it over - if I lifted the end of the shim just slightly, it peeled off very easily. I had tried 2 flavors of retainer, I think 0.005" gap & 0.015". These worked excellent on my prior bonding but were completely 'failing here'. I suspected maybe brass shim stock is some other alloy? I tried some red & blue Loctite with/withou primer, same results.

 

[petertha]

Then I tried what I had done before, bonding regular C360 brass to the end of a makeshift arbor, one steel, one aluminum, same variety of Loctite. I could turn it in the lathe & it was difficult to pop off even with a chisel. Usually this requires heat.

 

[petertha]

Eventually I found some carbon steel shim & tried that with same Loctite's & also JB weld. JB actually held pretty good, I was able to turn the brass down until it was quite thin foil.

 

[petertha]

So what is going on? Bearings can be very difficult & sometimes impossible to remove from shafts with the exact same Loctite even without interference fit. You can see on my tester pics the green film adhesive remnant is fully hardened & has to be filed or sanded off the steel.

Here is graph from #680 spec sheet, steel pins & collars at different controlled gaps. I interpret this to mean the annulus is 100% adhesive filled, no metal contact. The middle blue line of 0.25mm ~ 0.006" gap cures slower for sure. Only 75% strength is achieved after 24 hours vs say 90% strength for the black line 0.05mm = 0.002" gap over the same period.

Here is my opinion, maybe you have other thoughts. I think the 'peeling back' action of the shim is putting very high localized stress on the adhesive, because its basically a teeny pencil line width of equivalent area. Once it lifts up a bit (fails), it easily perpetuates along the joint. The joint stress is also mostly tension & adhesives are generally weaker in this mode vs. shear. I don't think its related to the material itself at all, but purely to this effect.

Contrast that with a rigid bearing or collar. It could never never be peeled back like this which is why we don't see parts dropping off in real life. It needs to be pushed off axially, therefore the entire bonded surface area is resisting and doing so in shear mode not tensile, which is more favorable to the adhesive. And I think that also explains why my mandrel turning in the lathe didn't fail the glue. Its again acting more in shear & the parts are thicker so not easily allowing the peel up like shim stock. At least that's my armchair engineering notion.

BTW I've used this same arbor technique with CA glue & it works quite well. Not my idea, saw it on YouTube (Clickspring).

 

[petertha]

Some pics of the spindle assembly. Eventually all it too was some TLC & steel shim stock carefully put in (dry) & he has a very nice low runout classic machine.

 

[Ken I]

FWIW - My tip for repairing an undersize (worn) press fit shaft is to clock it dead true in a four jaw, diamond knurl it, skim back to press fit diameter and assemble with Locktite.
The residual knurling grooves are filled / wicked by the locktite - works great.
Regards - Ken

 

[ajoeiam]

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.

Interesting reading!
Having been involved with some serious interference fits I'm a little confused.
The fits we were doing were assembled with the internal part being cooled by dry ice and the exterior part was at 300 F.
Just dunno how you would get that 'compound' to actually help.
In fact I'd bet using a compound would likely hurt your assembly.
Now if you're talking room temperature press fit then maybe but you can't press fit a 0.004" interference on a 2" shaft.
If you do that without a serious delta T - - - well you just gall the crap out of everything which would mean that you're going to be making those parts again.

 

[Steamchick]

Thanks Tom. There are plenty of jokes about various professonals. E.g. "a doctor buries his mistakes", or "a bad doctor has many undertaker friends...". Or - from a Civil Engineer friend - "what is the difference between a Builder and a Civil Engineer? The builder suckling his teeth when he tells you how many thousands it will cost. The Civil Engineer sends it in writing, so you can count the letters after his name to know how many zeros will be on the end of his bill!" - or something like that.
What's the difference between a fitter and an Engineer? The fitter will fix it with gaffer tape, the Engineer will use the gaffer tape to fix a notice on it saying "condemned".
Etc.....
Incidentally, I ride Moto Guzzi... and don't need Loctite products to affix everything against vibration... But it used to blow the tail bulb frequently, when I rode it at anything over 6000 rpm... can't get the Loctite to fix that!
Ya pees ya money.... n teks yer choice!

 

[Steamchick]

I have to agree with you all. The correct application of the Designed fit of parts can sometimes include anaerobic adhesives - and sometimes not. I certainly would not knowingly risk my life in a car held together with an adhesive holding the wheel to the shaft/spindle unless that was the proven design. (So far, I have only experienced hubs held onto spindles using a precision taper fit and a very large nut, locked with a steel pin). But almost all cars use a lot of adhesives - especially holding the body together as it spreads the load better than spot welds - and I'm sure that there were well over a dozen different adhesive materials used in the car factory I worked in for 30-odd years...
Square pegs must be used in square holes....

 

[len1042]

All of the above is very useful and informative but keep in mind that the strength of "locktite" type of adhesives is dramatically effected by elevated temperatures. I am not sure of the limits, see the spec sheets, but I do know that you must apply heat to disassemble some slip joints. Do not heat that high as to effect the strength of the metal though.

 

[Paul Gibeault]

As a high performance model airplane engine aficionado, I was wondering if say a slightly worn (less than a hard press fit) steel crankshaft ball bearing can be installed in an aluminum crankcase with Loctite red (stud & bearing mount) adhesive. Same with a lower connecting rod bronze bushing pressed into an aluminum rod. Obviously they can. My main concern here is I understand these Loctite's are forms or cyanoacrylate adhesives ( CA glue). I run my engines on fuels with up to 70% nitromethane. Nitromethane is debonder to CA glues. So I am querying anybody who uses nitromethane fuels. Would use of such fuel ( just nitromethane and synthetic oil) cause Loctite adhesives to eventually fail in these part applications?? Thank you.

 

[SmithDoor]

A press fit I use light oil.
I know they a loctie that say will work for gap filling.
I had employees machine wheels and from time to time they would miss one. So try locktie filler it did not work. Wath work is DOM tube for mistakes. The locktie may work for 0.000,5" but any great just buy a bar of DOM tube and make sleeve.

Dave

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

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

 

[LorenOtto]

Well said!

 

[holmes_ca]

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

Tom, no I am talking real full size where the shaft has highs and lows and as it's pressed on the wheel, the highs roll into the lows giving filling the gaps giving a press-fit, or could it be a cold shrink? not sure, I toured the shops of Canadian Pacific in Winnipeg in the 80s

 

[holmes_ca]

I made contact with Loctite.com here is their reply, straight from the horse's mouth so to speak,

Walter, the optimum design to maximize the shear strength is a slip fit of approximately 0.002-0.004" for both products. Also, you reduce the chance of shearing too much product off upon assembly since they're both higher viscosity formulations. However, they have still been used for closer fitting parts including press-fit and shrink fit assemblies. With a press fit, we would suggest applying it to both parts instead of what is typically one to compensate for what you may lose. Ideally, though, thinner products like 609 or 648 work better for snug fits. With a shrink fit, you heat or cool one part down and shrink the parts together.