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Nylon for axle boxes ?

Will is work

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Pete White04/01/2019 19:36:37
25 forum posts
3 photos

I have a project in the way of a 0-4-0 5 inch gauge loco to be made for our grandsons............and me. Design is well underway and am keen to move towards doing some cutting.

I have done some research but not found the answers, so a bit of input would be appreciated.

1 How about nylon for the axle boxes?

2 I am old fashioned and favour, "proper" bearing set into the nylon?

3 Springs......... Bearings of 26 - 28mm od do not leave much room in "normal" 50mm horn blocks for the springs. Is 19mm enough ?

Sorry for the dumb questions, but this is not my "area of expertise" lol

With Thanks

Pete


Nick Clarke 304/01/2019 19:47:23
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135 forum posts
2 photos

I can't add anything to the question of suitability of nylon for axleboxes from experience. I suspect it may deform under load.

However my experience does tell me that it is easier to machine metal to a good working finish than nylon which tended to whisker and score badly the one time I tried it.

Brian Sweeting04/01/2019 21:14:54
311 forum posts
1 photos

Try looking at Acetal.

Jeff Dayman04/01/2019 21:29:49
1340 forum posts
34 photos

If the loco is to be a steam powered machine the heat from the boiler and firebox may cause trouble with deformation over time of acetal or nylon plastic bearings. Water exposure will cause nylon to expand and also lose strength. If electric or gas/petrol powered, not so much.

You mention 26-28 od bearings- are you planning to use sealed ball bearings? In that case metal axle boxes would be best to securely hold the bearings - ball bearings may come loose if held in plastic axle boxes. Steel axle boxes in cast iron horn blocks, well greased, will work well. Same for bronze axleboxes in steel horn blocks or guides.

Springs can be placed over or under frames and operated with a push rod to the axle box, to minimize room needed above axle box in frames.

Have a look in youtube for J E Nystrom's Quickie engine and other locomotives for good, simple, proven ideas for building inexpensive and fast-build locomotives. J E is in Finland . Youtube "Finnish live steam" will yield some videos too.

Pete White05/01/2019 10:30:09
25 forum posts
3 photos

Thanks to all for the input. Yes its a quickie battery project. So not keen on nylon/plastic then! I was after a cheap easy solution, but might as well do the job properly on reflection.

I have found in my stock a large bar on cast iron, so cast axle boxes in steel horns would be good I assume? Might as well put in pb bushes as well !

Pete

ega05/01/2019 10:53:35
995 forum posts
85 photos
Posted by Brian Sweeting on 04/01/2019 21:14:54:

Try looking at Acetal.

Or Nylatron.

Pete White05/01/2019 13:14:23
25 forum posts
3 photos

Thanks ega, for keeping the ball rolling !

Query number three ?...................how much room would be reasonable for the springs if I want them at the top of the horn blocks.

Jeff Dayman06/01/2019 03:49:08
1340 forum posts
34 photos

Did you think about query 3 at all? How would anyone guess space for springs without knowing anything about the weight of the locomotive and all other factors affecting the design of the springing?

Pete White06/01/2019 13:28:54
25 forum posts
3 photos

YES, I did think about question 3 quite alot , but my reasearch did not give me an answer that I understood.!

As follows

If using compression springs for suspension on locos, bogies, etc we recommend you decide what weight you need that item to be able to carry (or its resting weight in the case of locos) then double it for the lb at full compression. If you then put a spring (or multiple if need be) on each axlebox to meet that maximum compression then when on the track the axleboxes will sit halfway up in their slots/ on the spring meaning they have movement both up and down to follow the track.

springs

so if my loco weighs say 100 - 120 lb doubled gives 240 lb = eight springs at 30 lb ?

So ref. no. 47 springs needing 0.75 inches in th hornblock?

The above description was not very clear to me, have I now got my understanding correct?

I still do not understand max solid length or lb / Lb

With Thanks

Pete

Edited By Pete White on 06/01/2019 13:39:20

Keith Long06/01/2019 14:45:13
776 forum posts
10 photos

Pete the data in the spring table gives you the following.

OD - simply the outside diameter of the wound spring, the Free Length is the overall length (or height if it's vertical) of the wound spring just sitting there with no load on it. The Max solid length is the length of the fully compressed spring with all it coils touching - "coli bound". It won't get any shorter and it won't fit into a smaller space. The Lb/in is the "spring rate" ie how much load you'd have to apply to shorten the spring by 1 inch. So the "load for full compression" is the maximum load that any of those springs will support when JUST fully compressed. Taking the first line the difference between the free length and the max solid length is 0.75-0.3 inch or 0.45 inch. Now the spring rate in 21 lbs/in so 0.45 x 21lbs give you the 9.45 lbs that the spring will need for full compression - and still be a spring. If you loaded that particular spring up beyond 9.45lbs it would still support that load but would in effect be a solid tube with no spring in it until the load dropped below the 9.45lbs at which point it would start to extend again.

From that table you can work out what length any of those springs would be at a given load and then you can see which of them will fit your application or conversely how much room you need to allow in order to be able to fit springs.

Another point to bear in mind is that for springs used in parallel (side by side) you add the individual spring rates to get the overall rate, for springs used in series (end to end) things get more complicated and you have to use

(R1 x R2)/(R1+R2) to get the effective rate where R1 and R2 are the spring rates of the separate springs. The overall effect of springs in series is that the net spring rate is lower than that of either of the individual springs

Keith

Pete White06/01/2019 15:47:35
25 forum posts
3 photos

Thank you Keith for that detailed explanation, I understand the table now.

What I am seeing is that with say the short 0.75 springs there is not much difference between free and solid length. In the case of type 47 on 0.23.

So what I think I was originally trying to find out, in hind sight, was how much suspension travel is a reason amount to design for.

I am working from drawing form 5g drawings in M.E. which show horn brackets at 2 inches and as I said with bearings at 26-28mm only leaves 19 ish mm for the springs to live in. This is not exactly my area of expertise but understand that "proper" loco builder do use ball bearing?

With Thanks

Pete

Pete White06/01/2019 15:48:44
25 forum posts
3 photos

Thank you Keith for that detailed explanation, I understand the table now.

What I am seeing is that with say the short 0.75 springs there is not much difference between free and solid length. In the case of type 47 on 0.23.

So what I think I was originally trying to find out, in hind sight, was how much suspension travel is a reason amount to design for.

I am working from drawing form 5g drawings in M.E. which show horn brackets at 2 inches and as I said with bearings at 26-28mm only leaves 19 ish mm for the springs to live in. This is not exactly my area of expertise but understand that "proper" loco builder do use ball bearing?

With Thanks

Pete

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