Axle bearings

[weldsol]

I'm at the stage now where I need to look at what type of bearings to use for the axles on the 7 1/4 Shay I'm building
I'm building it from the Kozo Hiraoka book using his scaling calcs,
Note he uses bronze for all scales from 3 1/2" up to 7 1/2"

Anybody got any thoughts on this ??

[Tel]

You would do well to follow his example.

[weldsol]

I did think that but he never built in 7 1/4"
When I looked at the American site for the Shay they are using ballrace bearings.
The sizes that would fit the Hiraoka design would reduce the dia, of the axle shaft at the bearing by quite a considerable amount (16mm down to 10mm).
I did contemplate using needle roller but then there is the problem of ingress of dirt.

Paul

[Shawki Shlemon]

There are sealed roller (needle ) bearings , I used them on 5" c38 but this engine was designed for bearings , they were supplied by the casting supplier ( winters ) and they were made in the US .This was more than 20 years ago . For all the other engines I used bronze or cast iron as per the drawings and they work fine .
The choice is yours but I would follow the plans .

[Tel]

The use of ball races seems to be an American thing - an unnesessary complication, in my opinion.

[weldsol]

Thanks for the reply
There are no plans for 7 1/4" just a scaling factor to get from his 3 1/2" to 7 1/4" you multiply (major dim's) by 2.07
So I have drawn in CAD his drawings from the book and rescaled them by 2.07
The question is the weight will not be scaled at x 2.07

Paul

[baggo]

Hi Paul,

Having used drawn cup needle roller bearings on my 2½" Helen Long I don't think I will be using anything else in the future. I shall certainly be fitting them to my Simplex. The needles run straight on the axles which are just plain silver steel. This seems to be a combination used by quite a few loco designers nowadays. The only 'problem' is that you may need to increase the width of the axleboxes to accommodate the bearings. The bearings also need to be a press fit in the boxes as the bearing shells are very thin and rely on the fit to maintain the shape.

The larger sizes of bearings are available with rubber seals which will prevent any ingress of dirt. For Helen the bearings were without seals so I turned some plain PTFE washers fitted either side of the bearings to do the job.

If you do decide to use them (and it's your choice) you'll need to anchor the chassis down once you get the wheels on as it will roll down the slightest incline!

John

[jgb7573]

Hi Paul,
I'm not clear from your posts why you are thinking of changing from Bronze. Plain bronze bearings have been used for axleboxes in all scales for many years with great success. They've also been used in other applications where the loadings are far greater than you would get with your Shay. They work fine. If you fancy having a go with rollers, then Baggo's approach sounds good.
Have fun,
John

[charles]

i am a firm believe in ball-races ,,, theres some very small balls bearings around ,,,, using some in a 2.5 gauge on a bullied merchant navy rebuilt.....ok needle rolers are good wont disagree on that but rather expensive and can be a little bulky metric sizes give your more choice to choose from,,,some of these little barings are rated up to 50,000 revs and more altho these bearings are very narrow in the smaller sizes,, using 2 side by side will give you more load baring area ,, i am talking about bogie's and pony trucks here ,,in 2.5 gauge engine and smaller and they are not expensive most of these bearings get sold in packs of 20 vxb bearings e-bay in the states ,, and you will be spoiled for choice,,by using bearings that means i can get away from using gunmetal axle boxes and go to steel yep i am all for bearings
make sure you have some good chocks otherwise when you ain't looking it will disappear of the end of the bench
Charles ;D

[alanstepney]

Apr 25, 2008 10:24:50 GMT weldsol said:

Thanks for the reply
...
The question is the weight will not be scaled at x 2.07

Paul

Length will be 2.07 x the original, area will be 2.07 squrd x the original and volume will be 2.07 cubed times the original.

As weight relates to volume, reckon on roughly 8 times the original figure.

[weldsol]

That was my thought as the bearing area is not 8 times greater to match the weight
Hence the question
Paul

[alanstepney]

The problem with scaling existing drawings is twofold.
Firstly, many items wont come out to "nice" sizes.
Threads, for example may come out to odd figures, and then need to be adjusted to a standard size. Materials too can scale to a dimension that doesnt fit in a standard size. Making something from the next size up is always possible, but may not be the best option.

The bigger problem is strength of parts.
When scaling down from, say, full size, it works in our favour and most parts will be stronger than they need to be.
Going the other way might result in parts not being sufficiently strong for the duty required.

Hence the x 2 or x 2.07 or whatever, should really be the first step. The second should be to consider each part and see that it is right for the job.

[gilesengineer]

Just for interests sake, RS do a very wide range of needle roller bearings, and give data on static and dynamic loads. They're not really so expensive, and I bought a pile for my valve gear. More of a complication are the drillings to keep them lubricated! Arc Eurotrade also do a (more limited) range at a good price.

Giles

[weldsol]

Thank you all for your thoughts on the subject.
I will go the bronze route and see what wear rate I get, it should be ok as the loco will not be running 24 /7 if it turns out to be excessive then I can go to needle rollers without to much modification.

Paul

[ianengr]

Would someone like to tell me who "RS" is in gilesengineer's last post.

Regards,

Ian.

[baggo]

R S Components - used to be Radio Spares

[Boadicea]

Try this RS
They have been the company for others to aspire to on stock and delivery for years. However, they are not cheap.

[charles]

just another thought on bearings for the larger engin....are the self aligning type,,,if you have a frame that is not quite,,, the bees knees these roler barings will get you out of a lot of trouble

[weldsol]

I did look at those but there is not enough meat in the wheel boxes to allow them.

Hiraoka design uses a bronze block with a radius top & bottom to take up the movement from the sprung block on the other side
and at the same time keep the pivot on centreline with the bevel gears

Paul

[weldsol]

Try looking at Ondrives site
Paul