Material for tyres - 946 alloy

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andrewnummelin
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Material for tyres - 946 alloy

Postby andrewnummelin » Wed Aug 07, 2013 7:02 pm

I am thinking about having a go at turning some tyres and was wondering what material to use when I remembered an article (J. M. Davidson, Model Railways, January 1973 p 28) with a recommendation to use Alcoa Superspeed 946, a corrosion resistant free-cutting alloy. Perhaps not surprisingly after such a long time, I've not been able to find a source of this material - does anyone know of anything similar that is currently available from the model (engineering) trade?
Regards,

Andrew Nummelin

JFS
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Re: Material for tyres - 946 alloy

Postby JFS » Wed Aug 07, 2013 9:32 pm

An aluminium alloy? I wonder what reasons were given for suggesting such a thing?

I recall the Stephen Poole Aluminium-tyred wagon wheels from about 40 years ago - it quickly became clear why no one else used such a solution!!

Surely a free-cutting stainless steel would be better?


Cheers,

Terry Bendall
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Re: Material for tyres - 946 alloy

Postby Terry Bendall » Thu Aug 08, 2013 6:12 am

It is possible to obtain free cutting mild (ie low carbon, below 0.3% carbon content) steel as well as free cutting stainless steels.
see http://www.metals4u.co.uk/EN1A-Free-Cut ... oducts.asp for more details.

Traditionally free cutting steel contained a small amount of lead but lead free freecutting steels are now available. Mind you, for the small amounts that anyone would need, I have no idea where you would go to obtain the material.

The lathe of course would need to be sufficiently robust to do the job.

Terry Bendall

JFS
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Re: Material for tyres - 946 alloy

Postby JFS » Thu Aug 08, 2013 5:52 pm

Andrew,

If, as Terry suggests, you would be happy to use EN1A, just pm me and I can give you a foot or two of bar about 25/28mm dia - it was left over from when I re-stayed my ploughing engine boiler and I have a fair bit of it. Should do most wheels up to a Duchess!

It is very soft and turns like a dream but I would still go for stainless though - mild steel rusts!

Best wishes,

Howard.

ScottW
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Re: Material for tyres - 946 alloy

Postby ScottW » Thu Aug 08, 2013 9:02 pm

Andrew,

I have just completed turning a set of 3' 2" bogie wheels for an S-Scale locomotive. The wheels started out as a 3' 8" wheel casting, the outer rim was reduced in the lathe to a suitable size for a 3' 2" wheel. A tyre was then turned from free cutting mild steel EN1A, into which the casting was soldered. I would certainly recommend the use of EN1A, it cuts freely and solders very easily.

DSCN0366.JPG


Good luck with the wheels.

Scott

andrewnummelin
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Re: Material for tyres - 946 alloy

Postby andrewnummelin » Sun Aug 11, 2013 8:17 pm

Many thanks everyone for the very useful comments and the inspiration from the S scale wheel.
Although I have turned steel on my Unimat I've always been concerned about lubrication (I'm not set up for it) and I wondered if working with an aluminium alloy might be easier. I did wonder about the wear characteristics of Al wheels but for the occasional use for which they are intended (not locos) I would be happy to experiment.
For those of you who may not have seen Mr Davidson's article his essential conclusions of the comparison of EN1A steel, nickel silver, 249 brass and the 946 Al alloy were:

colour - steel best, nickel silver and Al nearly as good
electrical properties - Al best, steel worst
friction (traction) - Al slightly better than the others
corrosion - Al and nickel silver best, steel worst
wear - steel and nickel silver best, Al slightly poorer

He tested wear by running a chassis for 12 hours with the wheels slipping on the rails and found that the wear in the brass axle bearings was twice that of the wheel treads.

I won't be experimenting for a while - first comes trying to finish something for Scaleforum, then it's Great Missenden.
Regards,

Andrew Nummelin

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Guy Rixon
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Re: Material for tyres - 946 alloy

Postby Guy Rixon » Mon Aug 12, 2013 2:14 pm

When I asked about aluminium wheels for locomotives in the 2mm Association forum, I was told that it had been tried and pitting due to electrical arcing was a big problem.

Natalie Graham
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Re: Material for tyres - 946 alloy

Postby Natalie Graham » Mon Aug 12, 2013 7:20 pm

Pitting was certainly a big problem with the Stephen Poole wheels mentioned earlier. I suppose wagon wheels might not have suffered but I had a set of their Manning Wardle drivers. Very nicely moulded centres but the tyres were terrible. A very odd profile to start with but it got even odder with the pitting.

Terry Bendall
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Re: Material for tyres - 946 alloy

Postby Terry Bendall » Tue Aug 13, 2013 6:33 am

andrewnummelin wrote:Although I have turned steel on my Unimat I've always been concerned about lubrication


It is perfectly reasonable to turn steel without the use of a lubricant, altough it will probably give a better finish if you do. The traditional lubricant is soluble oil because it is mixed with water, but some people will use the term cutting oil to mean the same thing and they may not be. Some suppilers make the distinction between soluble oil used on machine tools, and cutting oil used when making screw threads in steel.

On large lathes there will often be a pump which will supply a constant stream of oil which is better than the occasinal dab with a brush that most of us will do. It can of course make a lot of mess which most of us will not want in our model making area. I usually turn steel dry unless taking heavy cuts but the use of a lubricant is essential when drilling steel in the lathe.

Both types of lubricant can be obtained from:

Maidstone Engineering http://www.maidstone-engineering.com/in ... ommon/home

who have on their web site soluble oil 1 litre at £5.60 and cutting oil 500ml at £3.53

or from
Chronos Ltd http://www.chronos.ltd.uk/ who show I litre of soluble oil at £8.09 and 1 litre of cutting and tapping fluid also at £8.09. i litre will last a very long time for most of us.

When needed, I tend to use soluble oil for all turning, drilling or thread cutting jobs in steel although at times I have used a thin lubricating oil such as 3 in 1.

Terry Bendall

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jayell
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Re: Material for tyres - 946 alloy

Postby jayell » Tue Aug 13, 2013 7:25 am

The problem with using soluble cutting oil (usually called suds if memory serves me right) is that the lathe needs to recirculate it so you a metal tray under the lathe with a drain hole, a tank, a pump and pipework to feed the oil back to the tool.

When I had a 3 1/2" lathe I decided it was too much work to add all all that to the very solid wooden stand I had made to support the lathe (the first illustration here: http://www.lathes.co.uk/warwick/ was the one I had) so I used a cutting oil as my only lubricant applied with a brush. OK, I got a mass of oily swarf on top of the bench but that was preferable to soluble oil running all over the floor, especially in a wooden shed.

For tapping I used a thick lubricant specially made for that job that was supplied in a plastic 'tube' and could be squeezed out in small quantities. No idea what this was called but it was probably not the ideal medium as it didn't allow of clearing chips easily.

John

billbedford
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Re: Material for tyres - 946 alloy

Postby billbedford » Tue Aug 13, 2013 7:40 am

Has no one thought of using stainless steel for tyres? I believe this is what the Exactoscale wheels have.
Bill Bedford
Mousa Models
http://www.mousa.biz

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jayell
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Re: Material for tyres - 946 alloy

Postby jayell » Tue Aug 13, 2013 8:33 am

ScottW wrote:Andrew,
A tyre was then turned from free cutting mild steel EN1A, into which the casting was soldered. I would certainly recommend the use of EN1A, it cuts freely and solders very easily.


reading that made me wonder if adding a tyre to a cast centre could be done the way wheelrights put tyres on wooden wheels, by heating the tyre so it expands then inserting the wheel centre and letting it all cool, wheelwrights cool the tyre with lots of water so it doesn't burn the wooden feloes.

Finish turning the tread when it is on the centre perhaps.

John

ScottW
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Re: Material for tyres - 946 alloy

Postby ScottW » Tue Aug 13, 2013 2:34 pm

johnlewis wrote:reading that made me wonder if adding a tyre to a cast centre could be done the way wheelrights put tyres on wooden wheels, by heating the tyre so it expands then inserting the wheel centre and letting it all cool, wheelwrights cool the tyre with lots of water so it doesn't burn the wooden feloes.

Finish turning the tread when it is on the centre perhaps.


Alternatively you could make the casting a little over size and press it into the tyre.

Scott

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grovenor-2685
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Re: Material for tyres - 946 alloy

Postby grovenor-2685 » Tue Aug 13, 2013 4:25 pm

made me wonder if adding a tyre to a cast centre could be done the way wheelrights put tyres on wooden wheels

Railway engineers put tyres on cast centres of Locomotive wheels in just that way, there are films on You tube showing the process. I have read descriptions of modellers doing the same.
Keith

nigelcliffe
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Re: Material for tyres - 946 alloy

Postby nigelcliffe » Tue Aug 13, 2013 5:45 pm

johnlewis wrote:
reading that made me wonder if adding a tyre to a cast centre could be done the way wheelrights put tyres on wooden wheels, by heating the tyre so it expands then inserting the wheel centre and letting it all cool, wheelwrights cool the tyre with lots of water so it doesn't burn the wooden feloes.



I think the differences in temperature required are rather difficult to hold for the very small components. The expansion of metal is dependent on the size of the bit of metal - a real wheel of 1.5m diameter will expand, say, 3mm (0.003m) for a certain increase in temperature. But the model wheel of 20mm diameter will expand only 0.04mm for the same temperature rise. To get items to slide over each other there has to be a clearance, and its necessary to hold the centre cool whilst the tyre is hot until everything is in the final position. Might be theoretically possible, but I think you'd just end up with warped or oxidised tyres, or problems with the centres needing liquid nitrogen temperatures, or both !


- Nigel

Terry Bendall
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Re: Material for tyres - 946 alloy

Postby Terry Bendall » Wed Aug 14, 2013 6:12 am

johnlewis wrote:made me wonder if adding a tyre to a cast centre could be done the way wheelrights put tyres on wooden wheels


nigelcliffe wrote:I think the differences in temperature required are rather difficult to hold for the very small components


I think Nigel is correct, and it would be difficult to get the tyre to expand sufficienty.

Some years back, when I was converting Lima diesels to P4, where the axle size was about 2.5mm so Black Beetle wheels would not work, I used to turn down the OO wheels and press fit a P4 profile tyre from Alan Gibson. You do of course have to be a bit careful with the turning to make sure that the tyre is a good press fit. Fairly easy to do with a solid metal wheel but I have not tried it with a spoked wheel. With light cuts it could work. I have successfully re-profiled spoked wheels to P4 so it should be possible.

Terry Bendall

ScottW
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Re: Material for tyres - 946 alloy

Postby ScottW » Wed Aug 14, 2013 10:06 am

Terry Bendall wrote:Some years back, when I was converting Lima diesels to P4, where the axle size was about 2.5mm so Black Beetle wheels would not work, I used to turn down the OO wheels and press fit a P4 profile tyre from Alan Gibson. You do of course have to be a bit careful with the turning to make sure that the tyre is a good press fit. Fairly easy to do with a solid metal wheel but I have not tried it with a spoked wheel. With light cuts it could work. I have successfully re-profiled spoked wheels to P4 so it should be possible.


It is perfectly possible with a spoked wheel and is a tried and test method with S-Scale modellers. As Terry pointed out though you do have to be careful when turning down the spoked casting to insure a good fit within the tyre. Some people also prefer to solder the two together just in case, belts and braces. If I remember correctly I think the new Alan Gibson range of brass wheels are designed to be assembled in much the same way.

Scott

nigelcliffe
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Re: Material for tyres - 946 alloy

Postby nigelcliffe » Wed Aug 14, 2013 12:07 pm

Terry Bendall wrote:Some years back, when I was converting Lima diesels to P4, where the axle size was about 2.5mm so Black Beetle wheels would not work, I used to turn down the OO wheels and press fit a P4 profile tyre from Alan Gibson. You do of course have to be a bit careful with the turning to make sure that the tyre is a good press fit. Fairly easy to do with a solid metal wheel but I have not tried it with a spoked wheel. With light cuts it could work. I have successfully re-profiled spoked wheels to P4 so it should be possible.



Press fits are hard to achieve, much simpler to use retaining compounds, even when you want electrical conductivity.

The 2mm Scale Association wheels are brass centres in steel tyres for split frame. They are turned separately, the brass is a sliding fit into the tyre. The front of the centre has a small flat where the front of the tyre will sit.

They are fixed together with Loctite retainer (it might be the 3M version rather than the Loctite official means). The retaining compound is only spread over 1/3 of the diameter, the remainder is left clean for electrical contact. This fixes all together as the retaining compound will expand to hold everything tight.

The final axle diameter (or axle bore) is done after the tyre is fitted, with the wheel held on its tyre in a special collet. So the axle is concentric with the tyre tread.

The method has worked well for more than 20 years.


- Nigel

Terry Bendall
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Re: Material for tyres - 946 alloy

Postby Terry Bendall » Thu Aug 15, 2013 6:27 am

nigelcliffe wrote:Press fits are hard to achieve, much simpler to use retaining compounds


Depends on how skilled you are with using the lathe Nigel. :D

If you want a sliding fit you still need to be careful to get the correct size, which will be a few thou larger than the size needed for a press fit. It should not be oversize otherwise the tyre will not be concentric to the hub of the wheel. There have been times in the past when I have made the wheel too small and have then had to resort to glue. :(

Terry Bendall


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