Loctite, Brass & Steel

[petertha]

Maybe. I pre-curled the shim strip so it was maybe 90% conformed to the steel blank already. Very little tension & brass is ductile. Steel feeler gauge material I agree 100% it would be working against you right off the bat. The consecutive winds of tape under tension should have been lots of clamping force. I was actually worried about squeezing out the adhesive. But you can see an even film of cured green film completely around the shaft. Now the test with C360 brass was simpler yet. Just a drop of Loctite on the end of the shaft spread around, lay the brass slug on top & allow to cure.

Its made me re-think slight press fit bearings using Loctite. One would think a slight interference would scrape away all the adhesive, but obviously there is a microfilm between the surfaces & enough to make it a pretty permanent bond.

 

[Weldingrod1]

I would try rubber toughened cyanoacrylate; loctite black max. Strong, tough bond.

Sent from my SM-G892A using Tapatalk

 

[Flyinfool]

K&S is not what it used to be. It is all now made in china out of who knows what.

Is this something that is to be a tempory bond or is the brass to be permanently attached?

 

[petertha]

Kind of a long story but the application was an elderly restored drill press with a spindle that no longer fits original IMP bearings, which were themselves a bit of oddball size. So one option considered was stepping a next larger ID metric bearing which is very common & available. But it would leave an annular gap to make up of 2-3 thou depending on how the shaft was measured. (I'd only seen pictures of the assembly until just recently). Anyways the thought was to bond a strip of shim stock onto the shaft as a kind of uniform sleeve & the bearing would then go on top of that slip fit with LT retainer. There are other intermediary assembly steps, buts that's the nub of the problem.

Steel shim would probably be a be better choice from a material & LT bonding perspective IMO. But most of the steel shim stock I've seen is stiffer so likely be even more difficult to stay put; the tension would want to break the bond. Brass (which I had handy) was easily lightly rolled to the shaft so it was 90% of the circular shape already before bonding. Judging by the size & bearing layout, I don't think radial loads are super high. I think any metal would suffice, its more about the proper fit & just juggling the assembly issues.

Black CA I have experience with & lots of temporary fixtures like my posted pics using CA glue. Setup time would be too fast for this particular assembly, a few more components have to come together along with the 2 bearings. That's kind of the nice thing about LT retaining fluid, you can get it applied & still have some wiggle room time wise. Even something like JB weld might work, but the gap might be too small relative to its viscosity. I'm aware of other methods like knurling an enlarged section. Lots of ideas, we were just proceeding with what seemed easiest first.

 

[savarin]

Could you not soft solder the brass shim to the shaft?
The low heat requirement shouldnt cause any problems with the shaft.
I would dip the end of the shaft in an acid flux when hot enough then re heat and dip into a small pot of the liquid solder and wipe the surplus off with a dry rag, or just let sit in the hot solder till it sticks and wipe.
The brass will take the solder very easily and the same process of wiping the surplus off to get a smooth surface.
Wrap around the shaft, hold in place with tightened iron wire, re heat to melt solder and allow to cool.
The wire will peel off and the brass shim wont move.

 

[petertha]

Yes I bet it that would work too.

 

[Flyinfool]

That is why I asked if it was a permanent thing, I was also going to suggest soldering it on.

 

[hman]

A couple years ago, I bought a mini sand blast cabinet thru Craigslist (previously owned by a dental technician, I believe to smooth and "adjust" restorations). It is meant for very fine abrasives. 20 micron is a typical size.

Anyway, I've discovered that by sandblasting the mating surfaces to get a "toothed" surface (and then cleaning off the dust with alcohol), JB Weld and other epoxies stick tremendously well. This, with a good wrap of tape to hold your shim tightly to the steel shaft while curing, might well work for you. You might also want to use black electrical tape instead of Kapton. The vinyl tape is more elastic, so it should provide more even clamping pressure, and thus a better cylindrical brass surface, while the epoxy cures.



Here's a photo of a random piece of stainless steel I partially blasted, just to show the texture. I'm pretty sure that just about any kind of sandblasted surface would work.

 

[pontiac428]

I think it is cool that you did a good test to see if brass were the cause of non-sticking.

I'm not surprised you had failure when wrapping a shim around a shaft and hoping loctite cures like glue.

Loctite is an anaerobic curing polymer. It cures in the absence of oxygen, like on the threads of a torqued bolt and nut. If you hand-thread a nut onto a bolt with loctite and leave it, it won't cure. It needs the pressure of torque to kick off.

By wrapping a shim around a shaft and taping it, you are not creating the right environment for loctite to cure. If you used a 2-part epoxy, you would have completely different results (parts might not stick without a blast profile either). The only way I could see this working would be if you wrapped the shaft with your shim and glue goo, then press-fit it into a hole. That'd set the loctite off, but it doesn't change the fact that loctite is a poor tension adhesive and is a superior shear adhesive. So it may not do what you want. I suggest epoxy or J-B for what you are doing, that will fill the gap and stick.

 

[petertha]

I hear you pontiac428. I have lots of composites experience & familiar with cyanoacrylate's which are also anaerobic. I'm not saying CA is identical, but similar. Look at the pictures posted in #8 and #18. It is a sandwich of metal + Loctite + metal. None of which wee aggressively clamped. It is obviously bonded to some reasonably high degree because the assembly is firmly stuck together, at least to the extent it resists machining forces. Also the Loctite film remaining adhered to the steel shaft when the parts were forced apart is as cured as anything I've seen on a dislodged bearing. It wasn't still liquid or gooey or partially cured. As I said, it needed to be aggressively scraped or sanded off. I've used both Loctite & CA interchangeably on fixture jigs. Usually its the opposite problem. Needs a lot of heat or a sharp hit to remove the two.

Going back to post #19 showing Loctite's own data sheet for that particular product#. If we had a bearing race of 0.500" ID and centered a pin with 0.006" annular gap (pin diameter = 0.488") the data is saying it will cure. There is no metal to metal contact by definition. Yes it takes longer to cure or achieves reduced strength within X hours compared to smaller gap. It has a teeny bit of air exposure via the 0.006" wide gap times circumference (just assume the bottom is air tight). So how is this different than a strip of metal tightly bound to the surface of a shaft? I would think radially clamping it like this would be equivalent to a incredibly small annular gap, I dunno say 0.0002" on a matte finished surface? Thats orders of magnitude smaller than the 0.006" test example.

So I'll do some more testing steel on steel just for fun & to eliminate the brass as a variable altogether. I don't think brass gets bonded in this manner nearly as often which is probably why its a strange combination to even speculate on. I agree there are better choices of bonding agents in this application. But in my own mind the C360 brass vs ?alloy? shim brass behaved very differently all things being equal so the 'shim brass' in bad JuJu in this application.

Here is CA chuck in action. I think its an aluminum fixture & brass but I didn't listen closely if he specified alloys. My results are identical to this.