adhesives for loose bearings

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil A on 07/12/2017 12:06:06:

Maximum gap fill on diameter for LOCTITE 641 is quoted as 0,2mm or 0.008" .

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Sorry to labour this, Neil, but may I ask how you came to that conclusion.

My working assumption is that you must have mis-interpreted this graph from the Technical DataSheet:

• Bondline gap is [in a typical repair situation] a radial measurement, not a diametral one.
• Three representative examples of curing behaviour are shown … but these do not represent the extremes of its useability.

​If you have supporting evidence for your claim, I would be very keen to see it.

Until then, I remain very confident that 641 would do what Frank needs.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by bricky on 07/12/2017 15:38:26:

… Jason has drawn exactly what I have ended up with.

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Thanks for the clarification, Frank [and for the drawing, Jason]

I've been off-line today, so have only just returned to this discussion.

What I would do is use Loctite 641, and insert a couple of brass pins in the larger part of the gap.

… These would 'pack' the bearing into the correct position, and also catalyse the curing process.

MichaelG.

[Jeff DaymanParticipant @jeffdayman43397]

Posted by JasonB on 07/12/2017 18:25:12:

Jeff, how do you get the bearing and a tolerance ring in an undersize hole

Sorry Jason, cockup corner here, should have written OVERsize hole.

(however, with a big enough press and enough heat, you might be able to do it…. Just kidding, sorry for cockup typo)

[Neil AParticipant @neila]

Hi Michael, that's a very good question and I hope that I can answer it.

If you follow the link in my previous post it will take you to the LOCTITE Retaining Compound Design Guide. If you look at the bottom of page 14 you will find a paragraph on joint gap where it refers to the gap as being "diametrical". Also the chart on page 17 refers to "maximum gap fill diameter".

My personal view, and it is only my personal view, is that the graph on the data sheet for cure time against gap is misleading, unfortunately there is no graph for bond strength against gap, which would be more informative. Yes, LOCTITE will cure in large gaps, but its bond strength decreases with increased gap.

In my work and in my contacts with LOCTITE it has always been understood that the gap figures were diametrical as we were usually discussing the fitting of cylindrical components.

Of course, what we do in industry may not always applied in a home workshop. In industry "might be alright" is not an option, but at home, where you can monitor the success or otherwise of your work it is a different matter.

You will understand that the opinion I offer is from my own experiences in specifying LOCTITE in industrial applications. But, as my old boss would say, "design specifications are not tablets of stone". If you find that the larger gaps work for you, then go with it, there is probably some latitude in the LOCTITE specification, but not for industrial use where the product has to perform to the specification or you might be in trouble.

Well Michael, I hope that has explained my statement, sorry if I have rambled on too much.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Very interesting, Neil Thanks for going into some detail.

… Further investigation is obviously required !!

All I can say is that I have used Bearing Fit, both at work and at home, on some pretty big gaps, and have never [Yet!] had a problem with it.

MichaelG.

[brickyParticipant @bricky]

Way to go Michael that is what I will do thanks for your solution.

Frank

[Michael GilliganParticipant @michaelgilligan61133]

Strangely, Neil, there appear to be inconsistencies within the Loctite documentation.

In the document that you linked:

On page 14 is a general statement regarding "Joint Gap:

Joint Gap: LOCTITE® Retaining Compounds are versatile. They are recommended for gaps ranging from zero (interference fit) to 0.5 mm (0.02 in.) diametrical. Optimal bond strength is typically achieved at a diametrical bond gap of 0.075 mm (0.003 in.) or less. Total strength decreases as diametrical gap is increased.

Page 16 shows a 'Clearance' of up to 0.15mm for 641

Page 17 shows a 'Maximum Gap Fill Diameter' of 0.2mm for 641

… and neither of these terms is defined.

Any offers ?

MichaelG.

Edited By Michael Gilligan on 07/12/2017 21:24:23

[Neil AParticipant @neila]

Hi Michael,

I suspect that I'm being over cautious, probably comes from working on the design of large high speed diesels engines. They are not very forgiving and will always find any weakness if you let them.

All I can really say on the subject is that the success of these retainers is down to the people machining the parts and applying it to the cleaned surfaces, not the people like me who only specify where to use it.

Neil

Just spotted you last post. It does look as if the left hand does not know what the right hand is doing!

Perhaps we should both say that these data sheets seem to be more of a rough guide and go by our own experiences on how we decide to use them. I suspect Loctite would hedge their bets if asked them directly.

All that I am really sure of is that any solvent you use to degrease the surface needs to have evaporated completely, otherwise you end up with a sticky mess, and that's from experience!

Edited By Neil A on 07/12/2017 21:38:43

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil A on 07/12/2017 21:27:23:

Hi Michael,

I suspect that I'm being over cautious, probably comes from working on the design of large high speed diesels engines. They are not very forgiving and will always find any weakness if you let them.

.

Your cautious approach seems very wise in those circumstances, Neil

MichaelG.

[vintagengineerParticipant @vintagengineer]

Bugatti gearboxes have eccentric bearing housings so you can adjust the mesh between the layshaft and first motion shaft.

[JasonBModerator @jasonb]

So give the gaps quoted above will the stuff actually go off in a 0.47mm gap? My thoughts are that it will remain sticky for ages and possibly set up in a week or so. That is provided you can stop it all running out of the large gap in the mean time.

I suppose if you have some 641 to hand then give it a try, if it won't set it can be cleaned out and you can go and buy some 660 that is made for the job of large gap filling..

[jimmy bParticipant @jimmyb]

Posted by Mike Poole on 07/12/2017 17:33:38:

A tolerance ring is a thin piece of Spring steel with a pressed in design to grip the housing and the bearing. Concentricity should be good as long as the housing is true. They can be useful where there is not enough housing to bore and fit a sleeve and also it is not critical to bore the housing to the quite tight tolerance needed for a correct fit of a bearing.

Learnt something there, thank you. I've taken up slop in fits with shim steel before. These look quite useful

JIm

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 08/12/2017 07:28:44:

So give the gaps quoted above will the stuff actually go off in a 0.47mm gap? My thoughts are that it will remain sticky for ages and possibly set up in a week or so.

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No guarantee expressed or implied [!] but I have every confidence that it would.

The brass locating pins that I proposed would:

1. locally reduce the bondline gap, and
2. introduce a copper catalyst into the area

MichaelG.

.

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Note: In case there is any confusion about the pins:

Looking at Jason's sketch two pins would be pushed 'into the page' to maintain 'three point' location of the bearing whilst the 641 is curing.

[Howard LewisParticipant @howardlewis46836]

Looking at the OP and the sketch, it seems to me that what now exists is a correctly positioned hole, of the right size, but with a arc at the bottom, 0.018" deep. Can't see a tolerance ring being a viable solution for this situation.

On the basis of what has already been posted, the bearing should locate in the rebored hole, and hopefully the right grade of Loctite will fill the gap, at the bottom, and cure off.

Michael Gilligan's suggestion of using brass or copper pins to hold the bearing against the correct side of the bore, and initiate cure of the anaerobic is a good one. If this does not work, the only solution would seem to be, as already proposed, to bore out the housing oversize, press/loctite in a bush, and finally, to bore the hole for the bearing in the right position, and to the right size. This assumes that the housing has sufficient wall thickness to allow rebushing in this way.

Howard

[Mike PooleParticipant @mikepoole82104]

Howard I think you missed that the housing must be true to use a tolerance ring, the case in question would need to be machined to a circular true shape and size suitable for a tolerance ring. The advantage is that the increase in housing size is minimal, so if there is not much meat in the housing to fit a sleeve type repair they can help. They are also useful next time the bearing needs replacing or the equipment needs dismantling. The adhesive solution as has been mentioned will need to address the concentricity problem and dismantling will be more difficult. We seem to be close to the limit of the adhesive solution and my personal preference in this case would be to use a tolerance ring even though the housing will need to be machined again.

Mike

[Howard LewisParticipant @howardlewis46836]

My thought was that a tolerance ring would not be ideal for use in a non circular bore.

If the tolerance ring will work in (nearly typed tolerate!) a bore 0.018" oversize, then by all means, bore out, on correct centre until it just cleans up, and use a tolerance ring..

Howard

[Tim StevensParticipant @timstevens64731]

Might there be a relevant factor which has not been considered above? That is – what does the bearing actually do? There is a difference, in the (excellent) drawing between the top/bottom clearance and the side/side. So, if the bearing has to resist shaking side to side (as well as rotating, eg a crankshaft) then a bit of top & bottom slack fixed with Loctite is likely to last OK. If the shaking is in line with the over-boring, then this is much less likely. Another factor is 'what happens if the bearing does loosen?' In some applications this will be a disaster at once, in others it might make more noise but hold together, and the new noise would be a warning to have a look.

So, whatever we advise, there will always be some 'it all depends' as it is not possible, in the space here, to show, or to see, the whole picture.

And while I'm here, how about plating the overbored bore and boring it again, perhaps by grinding to avoid peeling the plating?

Cheers, Tim

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