Hello,

I'm wondering if some of you folks know what the standard interference fits, in thousandths of inches, were and are for fitting wheels to axles. Both driver centers and tender/freight car wheels. I will be facing this issue soon in having to make axles for new 20" wheels for some of our Maine two foot gauge passenger equipment.

I have a 1932 American Machinists Handbook, which in the press fit section states that a class 7 fit is appropriate for railroad wheels and axles, and is 0.0005" (1/2 a thousandth) per inch of diameter. Then, in the very same book but in the railroad section, it states that the Southern Pacific's standard was 0.004" (4 thousandths) per inch of diameter. This is for cast iron drive wheel centers, but the press fit section said that standard applied to axles in cast iron centers.

Am I reading something wrong? I keep re-reading it...

Thanks for any help you can give!

Jason

jml7@gwi.net

Jason;

I have only made press fits for model live steam equipment. I'd assume that the experiences would
scale up, but I COULD BE WRONG. I have made other press fits for many, many, things, but never something as large as a railroad axle.

The amount of press interference is dependent on a few items; give in materials (both in the material and the area around the material) and the amount of "this had better never come off" you wish.

Note, too, that surface finish matters.

You are doing passenger car wheels? I'd go for a press fit on the loose-ish side; the forces on the interface need only be very small as compared to a driver.

half a thou to a thou per inch diam is a pretty standard amount, especially for steel/steel. 4 thou is one heck of a lot. I'd be wary of cracking cast iron with those pressures.

Also, all of the press fits that I have done have had the first part of the fit relieved slightly to start the two halves together. (ie, interference fit to start, then press fit when pressing home)

The modern equivalent, by the way, is to use Loctite or equivalent for a lot of press fits that one used to see. (I'm still a press fit fan, though)

My 0.02$ - comments welcome.

> I'm wondering if some of you folks know what
> the standard interference fits, in
> thousandths of inches, were and are for
> fitting wheels to axles. Both driver centers
> and tender/freight car wheels. I will be
> facing this issue soon in having to make
> axles for new 20" wheels for some of
> our Maine two foot gauge passenger
> equipment.

> I have a 1932 American Machinists Handbook,
> which in the press fit section states that a
> class 7 fit is appropriate for railroad
> wheels and axles, and is 0.0005" (1/2 a
> thousandth) per inch of diameter. Then, in
> the very same book but in the railroad
> section, it states that the Southern
> Pacific's standard was 0.004" (4
> thousandths) per inch of diameter. This is
> for cast iron drive wheel centers, but the
> press fit section said that standard applied
> to axles in cast iron centers.

> Am I reading something wrong? I keep
> re-reading it...


john.stewart@crc.ca

> Jason;

> I have only made press fits for model live
> steam equipment. I'd assume that the
> experiences would
> scale up, but I COULD BE WRONG. I have made
> other press fits for many, many, things, but
> never something as large as a railroad axle.

> The amount of press interference is
> dependent on a few items; give in materials
> (both in the material and the area around
> the material) and the amount of "this
> had better never come off" you wish.

> Note, too, that surface finish matters.

> You are doing passenger car wheels? I'd go
> for a press fit on the loose-ish side; the
> forces on the interface need only be very
> small as compared to a driver.

> half a thou to a thou per inch diam is a
> pretty standard amount, especially for
> steel/steel. 4 thou is one heck of a lot.
> I'd be wary of cracking cast iron with those
> pressures.

> Also, all of the press fits that I have done
> have had the first part of the fit relieved
> slightly to start the two halves together.
> (ie, interference fit to start, then press
> fit when pressing home)

> The modern equivalent, by the way, is to use
> Loctite or equivalent for a lot of press
> fits that one used to see. (I'm still a
> press fit fan, though)

> My 0.02$ - comments welcome.

FWIW, my version of the good book states
"Engine bogie, Trailing truck and tender bogie axles - .002" per inch of wheel seat dia. - 10 to 12 long Tons/in of dia"
"Engine coupled wheel axles - new centres .004"/in; used centres .003"/in - 12 to 14 long tons/in"

so I guess the SP values are in the right ballpark. These values are for steel castings on steel, so i'd search further afield for CI values (try the carter bros preservation group - they have just had wheels cast and might know)

The typical wheel fit for 5 1/2 x 10 railroad axles is in the 50 ton range, as measured with a recording pressure gage drawing a curve of a specified shape as the wheel is pressed on. If the wheel presses on with the right force but the shape of the curve is wrong, then there has been a mis-mount.

There are two other things involved: white lead, "AAR wheel mounting lubricant"; and that the bore in the wheel should be rather rough, having the appearance of "threads". If you machine a nice-looking smooth bore, a mis-mount is likely to occur.

Sorry I can't translate the fit into thousandths per inch of diameter, but much of my reference material is still in storage. An up-to date AAR wheel and axle manual may have the correct info.

If you're not running the equipment on a US railroad, then AAR specifications don't apply. They are, however, a very good set of guidelines.

If you ever see oil around the axle on the back of the wheel hub on a car with plain bearings, and there is no ready explanation of how this oil got there, this means the wheel is loose on the axle.

> The typical wheel fit for 5 1/2 x 10
> railroad axles is in the 50 ton range, as
> measured with a recording pressure gage
> drawing a curve of a specified shape as the
> wheel is pressed on. If the wheel presses on
> with the right force but the shape of the
> curve is wrong, then there has been a
> mis-mount.

> There are two other things involved: white
> lead, "AAR wheel mounting
> lubricant"; and that the bore in the
> wheel should be rather rough, having the
> appearance of "threads". If you
> machine a nice-looking smooth bore, a
> mis-mount is likely to occur.

> Sorry I can't translate the fit into
> thousandths per inch of diameter, but much
> of my reference material is still in
> storage. An up-to date AAR wheel and axle
> manual may have the correct info.

> If you're not running the equipment on a US
> railroad, then AAR specifications don't
> apply. They are, however, a very good set of
> guidelines.

> If you ever see oil around the axle on the
> back of the wheel hub on a car with plain
> bearings, and there is no ready explanation
> of how this oil got there, this means the
> wheel is loose on the axle.
Jason, I have to agree with John.I work for a bearing and steel manufacturer in their equipment rebuild dept. The standard that is used is .001" press for each inch of bore diameter. Also we use RexLube lubricate,it replaces white lead. hope this helps?????????

jjpfeil@worldnet.att.net

Yes, all of this does indeed help. I've read and heard from several sources that the standard is 0.001" per inch dia. However it seems that most railroad talk is in terms of mounting pressures.

There must be a direct correlation of pressure to interference, based on diameter and material. It also make sense that a driver axle would want to fit to its drivers tighter than a freight or passenger car wheel.

Can anyone point me towards a good reference book with that correlation? I will go after the AAR specs. We are currently an insular 2-foot gauge but we are doing our best to keep ducks in a row for when we someday cross a public road.

Thanks again for all the help, and if anyone has more input, I'm still listening!!

see ya
Jason

> Jason, I have to agree with John.I work for
> a bearing and steel manufacturer in their
> equipment rebuild dept. The standard that is
> used is .001" press for each inch of
> bore diameter. Also we use RexLube
> lubricate,it replaces white lead. hope this
> helps?????????


jml7@gwi.net