steel tires

[hoppercar]

looks like I will need to put some steel tires over some cast iron drivers. ...I'm sure there guys out there who have some this....just wanting some input, o n how much to allow for shrinkage and a tight fit

[amadlinger]

Hi Hoppercar,

I have applied steel tires on three locomotives now and have had great success with 0.001" of interference for each inch of diameter. So, for example, 0.007" of interference on my 7" dia 2-8-0 drivers.

Sincerely,
Adam

[NP317]

Same here. 0.001" interference per 1" diameter of wheel.
RN

[rkcarguy]

The rings will expand a lot if heated and dropped over the centers, so there is no harm is using a fair amount of interference in the .005-.008" range. My experience comes from heat shrinking starter ring gears onto various flywheels.

[hoppercar]

do the rings need to go against a shoulder, like the prototype, or can the iron center, just be turned straight across ?

[JBodenmann]

Hello My Friends
Here is link to some info on fitting steel tires. It is from the Disney American thread here on Chaski.
Jack

http://www.chaski.org/homemachinist/vie ... 1&start=36

[hoppercar]

thanks, I'm not planning on pressing the drivers off of the axles, gonna turn them down between centers, and drop the tires on, so the axle bore, shouldn't be a problem ?

[amadlinger]

Hi Hoppercar,

That's exactly how i do the tires, after the wheels are already pressed onto the axles. I also do include a shoulder to give the tire a place to sit nice and squarely when you drop it on hot. If - for whatever reason - it goes on crooked and cools down before you catch it, there is nothing I have found to get the tire off again short of cutting it off. I speak from unfortunate experience!

Sincerely,
Adam

[Asteamhead]

Hello Hoppercar,
Yes, 0.001 x diameter for shrinkage will do perfectly. As recommended above a shoulder will help to achive a precise seat.
Just recommend to turn the raw outside profile of the tires, too once they are on the lathe to turn the inside fit.
Makes finishing the complete axles between centers a lot easier.
A (small) adjustable electric oven will work perfectly to warm up the tires (as is intended to toasts or pizzas )

Asteamhead

[KarlKobel]

Adam,
I had a similar experience with dropping two of the tires on the wheels, however mine didn't get stuck.
While they were on risers cooling on the floor I heard a very loud WHACK and I thought the tire crushed the wheel - it was that loud. The wheels looked fine.
Then a second WHACK.
The only explanation I have is that when they went on crooked, there were two points that got cooled. Then as the tire started to shrink, they were slightly mis-alinged, and the sound was the tire re-orienting itself on the wheel.

BTW - I did leave a flange on the tire so it would seat squarely, and the shrinkage factor was 0.001 per inch as stated above.

http://www.karlkobel.com/Wheels/Tires/Tires.html
Karl

[daves1459]

My experience is the same as the other responders that .001" interference per 1" diameter works very well. Heating to 400 F for a half hour will allow a few seconds to seat the tire after it is served up to the wheel. I prefer a shoulder on tire so during those few seconds before it shrinks onto the wheel I can spin the tire while pushing down to make sure it is seated. A make shift fixture to hold the wheel stationary as the tire is attached is very desirable.

Finish machining the tire after the wheel is pressed on the axle or on the loose wheel is a matter of personal preference. Although, even though with the wheel on the axle and between centers ensures precise concentricity the wheel set assembly can be "springy" making getting a good finish difficult, particularly with larger diameter wheels. I prefer to rigidly mount the loose wheel with tire piloted on a solid fixture.

To assist assembly and get a consistent grip on the wheel when the tire is shrunk on a round bore is necessary. Three jaw chuck work is fine for roughing the tire and finishing the bore for small wheels. Appropriately machine soft jaws in the three jaw are even better. But, for larger diameter thin wall tires mounting the tire on the lathe face plate, properly clamped will ensure size and a round bore when the tire is removed from the lathe.

I took the time to look up locomotive tire strength in my 1925 encyclopedia. In those days they listed tensile strength instead of hardness. For passenger locomotives 105,000 psi was specified, 115,000 psi for freight locos, and 125,000 psi for switchers. (Why a lowly switcher is higher than a passenger loco stumps me.) Those tensile strengths correspond to rather low Rockwell C scale hardness of 18, 22, and 25 respectively. Any decent heat treat shop can get those hardness out of SAE 1018 or 1020 steel. The usual steel source for larger diameter tires is hot rolled plate torch burn outs which is classified as A36 and is same as 1018. Problem is the burning cost money and you have to pay for all the steel including the inside disc and some outside. A good alternative is D.O.M. tubing which is usually 1018 or 1020 and slices are often cheaper than burn outs. You can probably tell by now I'm pushing heat treating. It's not really necessary for tire life on most models. But, after heating, quenching, and drawing the tire is stress free so will be easier to machine to dimension, again particularly for large diameter tire say over 8" diameter. Also the moderately hardened steel actually machines easier and gives a better finish than gummy raw steel.

Anyway, good luck, Dave

[Harold_V]

Those tensile strengths correspond to rather low Rockwell C scale hardness of 18, 22, and 25 respectively. Any decent heat treat shop can get those hardness out of SAE 1018 or 1020 steel.

Unless there's something I don't know, that isn't true. Mild steel is not heat-treatable by conventional means, as the carbon content is too low to achieve the desired hardness. One does have the option of pack hardening, or having carbon infused by a carbon rich heat treat furnace atmosphere, but it most likely would be simpler to use 1045 steel instead.

I suspect the vast majority of steel tires are not heat treated. They will provide considerably longer life in the annealed condition than will cast iron, be it gray or ductile.

H