Proper Way to Layout an Axle?

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EOsteam
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Location: Pendleton, Oregon

Proper Way to Layout an Axle?

Post by EOsteam » Sun Mar 04, 2018 4:07 pm

What is the proper way to layout an axle? Specifically, what is the way to set the Z dimensions?

Here is where I am:
Givens:
1) Trailer truck axles for a live steam locomotive
2 They are 12.25 inches long and have journals that are .9375" and 1.625" measured from the end of the shaft.
3) I'm nailing the widths of the journals, it's the lengths of the journals that are problematic.

The procedure so far:
1) Cut and face off the lengths of the axles to 12.25" The lengths have been accurate to 2 tenths.
2) Working between centers, the journals have been turned using a dial indicator to measure the carriage travel from the end closest to the tail stock. After an end has the axle journal and the wheel journal turned, the axle was dismounted and flipped around so the opposite end could then be turned.

The Problem:
1) The measurement of the length of the axle that determines back to back wheel spacing is really off on the second and the replacement axle. In fact the dimension is off by .010" on one of the axles. This dimension needs to be accurate and before I waste any more time and material, I'm soliciting advice. I'm 1 for 3 at this point and very open to suggestions.

Thanks,

Harper

John Hasler
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Re: Proper Way to Layout an Axle?

Post by John Hasler » Sun Mar 04, 2018 5:21 pm

I'm not a railroad person so I may not understand what you are doing, but I'd start with the axle over-length, do all the turning between centers with one setup (measuring that critical back-to-back distance directly) and then face the axle ends to length measuring off the completed journals.

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GlennW
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Re: Proper Way to Layout an Axle?

Post by GlennW » Sun Mar 04, 2018 7:18 pm

EOsteam wrote:
Sun Mar 04, 2018 4:07 pm
The Problem:
1) The measurement of the length of the axle that determines back to back wheel spacing is really off on the second and the replacement axle. In fact the dimension is off by .010" on one of the axles. This dimension needs to be accurate and before I waste any more time and material, I'm soliciting advice. I'm 1 for 3 at this point and very open to suggestions.
Are you flipping the axle end for end and not re-zeroing the indicator to what is now the end of the axle?

If so, it sounds like the issue is that your center drill depths differ and are throwing off your length.

You need to touch off with your cutting tool and re-zero the indicator each time you change or flip the axle.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

pete
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Re: Proper Way to Layout an Axle?

Post by pete » Sun Mar 04, 2018 7:24 pm

Like John I'm not a loco person either so I may not be reading your problem correctly. My understanding is your having issues edge finding the face of the axle shaft and then missing your target lengths with the lathes longitudinal travel?

Since you can apparently measure your axle finished lengths to within 10ths then getting each journals length correct is the problem? Easy to do to less than .0005" if that will work for you. Old machinist trick for use on a lathe or mill is to use cigarrette rolling papers as an edge finder. Mount the axle between centers as your doing. Since you know the exact axle length to close limits then simple subtraction gives you your lengths on each end. Zig Zag rolling papers in the light blue package are almost exactly .001" thick. Run your chosen cutting tool up so it's very close to the face of the axle and as close to the axles C/L as you can get with the tailstocks center supporting it. Now hold one of those rolling papers between the tool tip and the axle face, very carefuly and slowly advance the carriage towards the axle face as you move the paper up and down until the tool tip catches the paper. That's your tool zero point. Then attach a dial indicator so it's tip registers against somewhere on the carriage and zero it. Now you know exactly where the tool tip is in relation to the axle face. Need more than the indicators 1" of travel? Use something like a micrometer 1",2"3" etc setting rod between the carriage and the indicator tip and again zero the indicator. For example, lets say your journal length needs to be 2.565" long, use a 2" long mike setting rod and with the indicator zeroed with maybe .010" of preload, remove the setting rod and then advance the carriage until the indicator reads .565" The indicator and setting rod do have to be set up at least by eye so there as close to being square in both the horizontal and vertical directions as possible so the measurement is accurate.

No mike setting rods? Just make your own length out of any rod, as long as you know it's actual length then it can still be done. Other ways the same job can be done of course, an internal spindle stop for one end of the axle if it will fit into the spindle. But that cigarrette rolling paper is the key to finding exactly where your tool tip is in relation to the axle face. There's 3 or 4 packages of those rolling papers that are kept with my precision measuring tools. I also have proper edge finders and even a very expensive Haimer 3D edge finder. Neither will work on a lathe so those known thickness papers give me a way to find that part face with the tool tip and then setting any part features to very close limits using the part face as a datum point. Thicker paper can be used, but it gets less accurate since you then don't know how much the tool tip is compressing the paper. Known thickness shim stock could be used, but again you don't know by how much the tool is pushing against it. If I was extremely careful and took my time I'd bet I could get the tool tip zero down to less than .0005" and be confident it was accurate to at least being within .0001" - .0003". It is a slow method but it's one I've used a lot if a part feature had a important accuracy length.

Any HSM sized lathe is going to have a certain amount of flex so what you measure under travel while cutting will likely be slightly less than what the indicator says it should be. Since your doing it correctly and working between centers then measureing the first axle you do might give you an idea if a few more thou is needed to hit your numbers by putting the part back in the lathe and recutting until you hit your exact target dimension.

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NP317
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Re: Proper Way to Layout an Axle?

Post by NP317 » Sun Mar 04, 2018 9:05 pm

My opinion:
An error of 0.010" in wheel gauge length is well within normal operating parameters, especially given the variability in track gauge.
This of the error as less than the thickness of 3 pieces of regular printer paper.
Don't worry about that.
~RN

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