Axles

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JTolan
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Axles

Post by JTolan »

Hi guys,

I recently bought some 1 1/2" scale wheels with the hole in the wheel reamed to .5". What would be the recomended OD for the axle and the size of the shoulder on the axle?
Also, should the axle rod be tapered or just pressed on with lock tight?
Thanks for your help in advance.
Jeff
Last edited by JTolan on Fri Mar 26, 2010 10:25 pm, edited 1 time in total.
Happy Steaming
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ALCOSTEAM
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Post by ALCOSTEAM »

.5 is a pretty small hole. It might be ok if this was for a non-riding type car but if its for a car with people riding on it I would be a bit concerned about overall weight carrying capacity.

I would shoot for .001 interference fit. General rule of thumb is .001 per 1.00 of diameter. For wheel and axle assemblies I like a good snug fit.

For axle stock I would go with at least 3/4. That will give you a shoulder of .125 unless you up size the axle hole in your wheels.

tim
Andy Rafferty
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Post by Andy Rafferty »

I may have missed this detail but may we assume these are riding car wheels? Sounds like I would be using 1/2" bore bearings in the side frames and loctite the wheels in the approprate slip fit. But lets see how the others feel. Congrats on geting ready to run wheels. AR
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Fred_V
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Re: Axles

Post by Fred_V »

JTolan wrote:Hi guys,
Also, should the axle rod be tapered or just pressed on with lock tight?
Thanks for your help in advance.
Jeff
press fit and LocTite require different tolerances. for LocTite you need to leave a couple of thou. clearance space for the glue. it's like gluing up 2 boards. if you clamp them too tight and squeeze out all the glue they will fall apart easily.
Fred V
Pensacola, Fl.
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Harold_V
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Post by Harold_V »

If you have little or no experience with press fits, use caution. For starters, do NOT use a caliper (vernier, dial or digital) for measurements. Such an instrument is not capable of resolving the true size of either the axle or the bore.

Finish is important, as is the amount of press. The thou per inch rule is good, but if your finish is poor, that may not be adequate to keep the wheel in place. Key to success is a decent surface finish.

If both the axle and wheel are made of the same material (mild steel), be certain to lubricate the two surfaces before pressing, and don't expect the pressing action to align the axle with the hole. If you start off crooked, it's likely to end up with some run-out. You can facilitate alignment by machining a short lead (1/16") on the axle, which would be an easy fit with the bore size.

An arbor press can work to great advantage, or a heat shrink fit is even better. With that process, you need no lubrication, and the axle should be dead aligned because it will bottom before gripping. You should heat the wheel until the axle is an easy fit. Chill the axle and heat the wheel. Assembly quickly, in one smooth operation. You get no second chances with this process. Be certain that the axle fits to the shoulder. It should grip (permanently) almost instantly.

Harold
pat1027
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Post by pat1027 »

Harold_V wrote:

Chill the axle and heat the wheel. Assembly quickly, in one smooth operation. You get no second chances with this process. Be certain that the axle fits to the shoulder. It should grip (permanently) almost instantly.

Harold
I used the heat shrink fit to put my drivers one. Worked pretty slick. I packed the axles in dry ice and heated the drivers in my kitchen oven. I started the axles into the hole, gave them a good whack with a shot filled mallet just to make sure and they were set. You do have to work quick.

I found dry ice at the supermarket. The store has to get it out of the freezer for you. The kid took my piece out with an insulated glove then grabbed it in his bare hands. Before I could say anything he started yeowing and took off for the checkout...still carrying the dry ice. As he rang me up he kept looking at his hands complaing they burned and asked "What do you use that stuff for?"

What could I say but, "To make things really cold."
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Dick_Morris
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Post by Dick_Morris »

grabbed it in his bare hands.
Which gives evidence that the workplace signs we tend to think are pretty stupid . . . overestimate the audience.
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Fender
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Re: Axles

Post by Fender »

JTolan wrote:Also, should the axle rod be tapered or just pressed on with lock tight?
Jeff
Jeff,
If I understand your question, the axle surface that the wheel fits on should not be tapered; it should be straight. If you are going to use loctite, then the axle will need to be a few thousands undersize to provide room for the loctite to work. If you are going to use a press fit, then the axle will be (as others have said) a little larger than the hole in the wheel to provide an interference fit.

The first time I attempted a press fit of a wheel on an axle, it was a pretty crummy job. The axle finish was rough, and the axle was too large (about .002 interference). It required a HUGE amount of pressure to get the wheel on! Good thing the wheel casting didn't break! Subsequent attempts have been much better, using the method described below.

If you are going to make a press fit, what I would suggest is to make a gage to test on the wheels. Turn up a short bar in the lathe to be a few thousandths larger than the hole in the wheels. (So if the holes are .500 then make the bar about .502) Then create some "steps" along its length that are each about .0005 smaller than the previous step. Good finish is important here, so use brass or cast iron if you can't get a good finish on steel. Each step should be long enough that you can measure the diameter with a micrometer. The smallest step should be about .001 smaller than the hole in the wheels (e.g., .499). Mike each step and mark its diameter with a felt-tip pen.

Now, you can use the gage to determine the largest step that will still fit into each hole with hand pressure. (Note that the holes might not all be exactly the same diameter!) You will want to make the axles about .001 larger than that diameter. At least for me, it is easier to accurately measure external diameters with the micrometer, so this method is more reliable than using telescoping gages to measure the internal diameter of the hole.

Good luck!
Dan Watson
Chattanooga, TN
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JTolan
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Post by JTolan »

Thanks for the advice,

What type of jig set up for holding the wheel and axles while pressing and/or heat shrinking them together did you guys use?

Happy Steaming :)
Jeff
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Harold_V
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Post by Harold_V »

It's unlikely any kind of holding fixture will work if you rely on a heat shrink fit (the best possible way to go). The time interval between the beginning assembly and ramming the spindle home may be but a couple seconds, far too short to permit any messing with the two components in the way of helping alignment. The exception to that might be a V block set permanently such that you can drop the axle in the hole with the body of the axle in the V block, and the wheel located on dead center by some means. Any misalignment could prove troublesome.

The design I mentioned, above, would make an excellent alignment fixture for pressing with a hydraulic press, or even a larger arbor press.

The real advantage of heat shrinking, aside from a generally better grip, is that the axle will end up concentric and perpendicular. If you rely on a press fit, there's a good chance that will not be the case. It is especially true if your material choice is mild steel, which is prone to galling.

Harold
Tom_Dininio
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Re: Axles

Post by Tom_Dininio »

Fred_V wrote:press fit and LocTite require different tolerances. for LocTite you need to leave a couple of thou. clearance space for the glue. it's like gluing up 2 boards. if you clamp them too tight and squeeze out all the glue they will fall apart easily.
The voice of experience: Quite true. And pay attention to surface finishes also.

I purchased the frame with assembled drivers from a GM engineer’s widow back in ’92. The work was perfect in 7-1/16 gauge (1 ½ scale). I decided to convert it to the standard 7 ¼ gauge and complete it as a NYC 2-8-2 H10b Mikado. New axles were made to stretch the gauge and to incorporate needle bearings instead of ½ brasses. This required the making of 1/8 wall “hub caps” to go over the smaller diameter axle required of the bearings and get back to the axle bore. Everything worked fine with about a .0015 - .0020 press fit and the engine was run in its incomplete form as a Consolidation (2-8-0) as the rear truck was not yet made.

Over the course of a few years running, the 125 micro finish (good lathe work, but some tool marks still visible) peened over to a mirror like 32 micro finish – the peaks of the tool marks cold flowed into the valleys.

It happened one late afternoon as Jim Leggett’s daughter Liz was literally running the wheels off the engine at the Montreal clubs meet. The Consolidation became a Consugal (2-7-0) as the left rear driver slipped off the axle in a right hand curve.

Mic-ing the bore and axle showed that the .0015 press had become a .001 clearance. A little self-wicking Loc Tite (for the small clearance) and straightening the drive rod and we were back in business. Many years of running without mishap has proven the worth of the poor man’s press fit..

A word of caution. If you’re running on block signal track, you might be a stealth train if ALL axels are Loc Tited. :oops:

Tom
Safety is always preferred over rules.
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cbrew
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Re: Axles

Post by cbrew »

Tom_Dininio wrote:Mic-ing the bore and axle showed that the .0015 press had become a .001 clearance. A little self-wicking Loc Tite (for the small clearance) and straightening the drive rod and we were back in business. Many years of running without mishap has proven the worth of the poor man’s press fit..
What do you think caused the .0025 change?
Tom_Dininio wrote: A word of caution. If you’re running on block signal track, you might be a stealth train if ALL axels are Loc Tited. :oops:
Tom
I wondered about this very problem, I guess i would like to start a new thread on this subject
If it is not live steam. its not worth it.
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