3/4" Raritan 2-4-0 build.

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shild
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Re: 3/4" Raritan 2-4-0 build.

Post by shild »

I don't really have to worry too much about what I've already done cause a pilot truck and a 15 pound tender don't see a lot of load do they?. But when it's time to do the wheels for the riding car I've got to do a better job cause those see a heavy load don't they? Well anyway I think I'm going to work on the journal bearings for the tender now. Once I find a 1/2" x 1/2" piece of square stock I probably want to do all operations with the stick method then saw each journal off one at a time to finish don't I?
jcbrock
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Re: 3/4" Raritan 2-4-0 build.

Post by jcbrock »

shild wrote: Sat Mar 27, 2021 4:13 pm If I'm able to press the wheel on by hand is that the fit I want to use with loctite?
Retaining compound manufacturers specify a fit for each product they sell. For example, for Loctite 638 it is 0.25 mm and for 648 it is 0.15 mm. You can go here for 638, then hit the Information tab: https://www.henkel-adhesives.com/us/en/ ... e_638.html. I believe this is the max desired size and the compound can handle a little variance, but I couldn't find that stated anywhere. There was a graph of cure speed vs bond gap in the Technical Data Sheet and for 638 it had graphs for 0.05 mm, 0.15 mm, and 0.25mm, thus my conclusion the 0.25 mm is the maximum recommended size for 638.
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Greg_Lewis
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Re: 3/4" Raritan 2-4-0 build.

Post by Greg_Lewis »

Shild:
To expand a bit on what others have written about Loctite, you use it instead of a press fit. You need a small amount of clearance for the Loctite to reside between the bore and the axle. Thus John's references above. A fine finish on the bore or the rod isn't needed; actually a little roughness will help the Loctite hold. Just go with the machined surfaces.

Loctite is an anaerobic material; it hardens in the absence of oxygen. So what happens is you clean the mating surfaces, clean, clean, and if possible use the Loctite primer. You apply the proper Loctite (note that there are different formulas of Loctite for different applications), assemble the parts and let the Loctite cure. The Loctite catalog lists the shear strength of the various formulae. Just as an example, the 620 has a maximum gap fill of .015 and a shear strength of 3000 psi, far, far more than our projects will ever put to it.

I have seen mention of using Loctite for press fits, but the company says, "Finding wide acceptance as a standard method for assembling press and slip-fitted parts, Loctite retaining and securing compounds fill the 'inner-space' between components...." So this means that a press fit with some minute gaps in it could benefit from Loctite. I suspect this is aimed more at maintenance and repair situations where things are less perfect than desirable.

So in the end, in the future, leave just less than the maximum clearance as specified by the Loctite, apply the compound, assemble, and you're done.
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Bill Shields
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Re: 3/4" Raritan 2-4-0 build.

Post by Bill Shields »

What you are describing is THREADLOCK ...similar to but not the same as the loctite we are recommending.. see earlier comments with specific loctite product codes.

As I mentioned earlier...take it all apart and make new axles to lit your wheels and loctite them together properly.
Too many things going on to bother listing them.
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Greg_Lewis
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Re: 3/4" Raritan 2-4-0 build.

Post by Greg_Lewis »

Bill:
I'm not sure what you're referring to. What I posted above is from the Loctite catalog pages on cylindrical retaining compounds.

loctite1_20210327_0005.jpg
loctite2_20210327_0001.jpg
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
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Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
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Harold_V
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Re: 3/4" Raritan 2-4-0 build.

Post by Harold_V »

shild wrote: Sat Mar 27, 2021 4:13 pm After I did the finishing pass for the place to mount those wheels I held sandpaper against it to smooth it off. You're saying I don't need it too smooth because the loctite needs a place to be?
No. What I'm saying is if the parts were a snug fit, there's no place for the LocTite. It can't help if it isn't there.

If the fit you achieved was snug after polishing, it was too tight for LocTite to be effective. Polishing the resulting turn is a good idea, assuming you don't create excessive clearance, and it's really important when you measure that the surface measured represents the functional surface (that's what you get when you polish). If the cut is coarse with extreme peaks and valleys, or a rough surface due to tearing, the measurement will have little value, and if that type of surface creates a snug slip fit, it will be prone to failure. It's no different from knurling an undersized shaft to create a fit. If it is subjected to any loading, it will fail. It's just a matter of when, as the highs (knurled peaks) displace to the valleys, because the void allows the peaks to collapse easily. Gives them a place to go!

The only saving grace might be if the surface of the mating pieces is so bad that there's enough clearance (the depth of the valleys) to allow some of the LocTite to remain. As a press fit, It will fail without LocTite. It may not with LocTite. All depends on the clearance created by the rough surfaces. You can't rely on a surface finish like that for a press fit, for it fails almost immediately due to the collapse of the peaks, often just from assembly.

Surface finish is critical when it comes to fits that matter. You did the right thing by polishing, but you should have polished enough to provide the required clearance (see the maker's recommendation for the particular grade you used).
If I'm able to press the wheel on by hand is that the fit I want to use with loctite?
I am not a LocTite fan, but then I also have the capability to provide the types of fits I described previously. I might see things differently if that was not the case. So then, as far as the fit you described, it would be my opinion that it was too tight to benefit from the use of a locker. Again, that depends on the maker of the grade you have. You should check their recommendations and adhere to them if you hope to provide fits that won't fail.

That said, I strongly suspect that you'd want about three thou clearance (again, check the maker for specs), and that's not a snug fit at all. If the parts are aligned properly, they slip together without effort.

I'm not trying to alarm you, but you should do things like this as prescribed by the maker. Don't guess, and don't use Kentucky windage. Its much easier than going back after completing the project and experiencing a failure while running. Ask anyone who's had that negative experience. Measure your work carefully. Use a micrometer, NOT A CAILIPER. A caliper is not capable of discerning the readings you need to be effective. For the bores, use a telescoping gauge. NOT A CALIPER. Again, it is not capable of discerning the readings you need to be effective. If you choose to use a caliper, you will achieve success by chance instead of design.

H
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Bill Shields
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Re: 3/4" Raritan 2-4-0 build.

Post by Bill Shields »

Take them all apart and start over
Too many things going on to bother listing them.
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Builder01
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Re: 3/4" Raritan 2-4-0 build.

Post by Builder01 »

So, what is the status with build?
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milwiron
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Re: 3/4" Raritan 2-4-0 build.

Post by milwiron »

I saw the gentleman had posted on one of FB groups asking many of the same questions posted here... hoping for better answers. After a few days the posts stopped. Seemed awfully frustrated about screwing up parts. All I could think was- welcome to the world of machining.
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Greg_Lewis
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Re: 3/4" Raritan 2-4-0 build.

Post by Greg_Lewis »

milwiron wrote: Fri Jun 04, 2021 10:37 am I saw the gentleman had posted on one of FB groups asking many of the same questions posted here... hoping for better answers. After a few days the posts stopped. Seemed awfully frustrated about screwing up parts. All I could think was- welcome to the world of machining.
Denny

I tell people I've built two locomotives — one is in the scrap bin. As my sig line says, "Celebrating 30 years of turning perfectly good metal into bits of useless scrap." I just mangled a part yesterday. The only reason I didn't mangle one today is that I didn't work on it! :roll:
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
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Steamer Al
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Re: 3/4" Raritan 2-4-0 build.

Post by Steamer Al »

Ive started keeping my screwed up parts on a small ledge behind the lathe... to remind me to slow the heck down!! I do keep adding to it however...
jeanluc83
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Re: 3/4" Raritan 2-4-0 build.

Post by jeanluc83 »

Someone told me once that the key to being a good machinist is knowing how to recover from your mistakes.
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