Monday, May 02, 2011

Axle-Box Dust Seals

Rebuilding is coming on apace and soon we'll install the frame on its wheels. First we must prepare the axle-boxes. The bearing journals are being cast and I spent last Saturday making the dust seals that sit behind the journals, between the bearings and the wheels.

The image shows the pattern that I made first as it fits into the slot in the back of the axle-box, which is upside down in the picture.

I thought we could make the seals out of plywood but Ollie thought that it would delaminate and break across the narrow areas at the sides of the axle. It turns out that the originals probably were made from plywood with an oversize hole for the axle and the actual seal made by having a large leather washer fixed to the plywood and bearing on the axle.

We did a little research and I had a chat with John the engineer about possible alternatives. I suggested something like resin-bonded linen which I remember from my father's engineering days. Old technology, it seems. A search of the engineering catalogue brought us a high temperature, self-lubricating nylon material good for making bearings - at £72 for two small sheets!

I had made a pattern first to check for fitting, that's it in the photos up there.

Now I set about cutting and fitting the (expensive) nylon material.

I'd measured the thickness I needed from one of the axle-boxes and that was my first mistake. The axle-boxes are not identical so the thickness I needed was a nominal half-inch. I'd ordered 12mm thick material, which is just less than half-an-inch so I thought it would fit easily.

I had to file the thickness at the edges so that the seal would slide into the slot in the box, and then I had to thin the end where it goes high up into the box to accommodate the varying thickness of the box itself due to casting imperfections.

In the end it took me several hours to make just two of the seals and we haven't cut the holes in them yet for the axle to pass through. I'll do that when I have the journals set up in the axle-boxes and can accurately mark the centre of the axle. Meanwhile each axle-box is numbered and there's a corresponding number on the seal for that box.


Blogger Flymo said...

Fettling for hours, just like I do with the 4mm ones! I hope that it is just as rewarding (and relaxing) for you when it all goes right :-)

2:17 pm, May 02, 2011  
Blogger frogspawn said...

The size probably makes my life a little easier but you're right about the time.
It is both rewarding and relaxing. Time just slips by.
I'm hoping to learn to use the horizontal mill to trim the next two seals to size. Using an angle-grinder disc on these two became a process of using the friction to melt and move away areas of material which I then filed off at the edge of the piece. Not a pretty nor a very accurate process :-(

7:07 am, May 04, 2011  

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