[modeleng] Re: Modern Material

Hi John,

Thanks for this. I have gone ahead and made a  pair of slide valves out of 
"the black stuff". It's very easy to machine but it's fairly abrasive on the 
cutting tools. I used HSS and they required sharpening a few times although 
it wasn't very obvious as the stuff imparts a terrific shine on the tool.
Anyway, if these high tech valves fail to do the bizzo - you will be held 
responsible! Of course, if they are a resounding success, you can rest 
assured that you won't even get a mention!

Cheers,


Barrie

> Hi Barry,
>
> I've made solid piston valves from PEEK HPV which is a high performance
> bearing grade plastic filled with PTFE, Carbon, and Graphite with some
> success, apart from the difficulty of getting the correct fit at working
> temperature due to the expansion (not a problem with slide valves!).
> Using this for slide valves should be no problem as it will stand the
> temperatures involved and it's very easy to machine. I've used it for
> all sorts of bearings including coupling rod bushes etc.
> I made a set of slide valves for my brother's Rob Roy from solid PTFE
> which seem to be ok so far although it hasn't run a great distance yet.
> I have heard mention of PTFE valves distorting but as mentioned above,
> the ones I made haven't. The carbon filled variety would probably be
> more rigid and perhaps more suitable.
>
> John
>
> Barrie Purslow wrote:
>> I am currently refurbishing a 5" gauge Simplex which has non ferrous 
>> cylinders. The slide valves are rather badly scored so I have skimmed the 
>> top of the cylinder block no problem but I am reluctant to skim the valve 
>> itself as it is obviously not made of a material with good rubbing 
>> characteristics against the cylinder block.
>> I have it in mind to make new valves out of carbon filled ptfe which I 
>> have previously used for a regulator valve with good results but this 
>> duty is a little more onerous.
>> Any thoughts anybody?
>> Barrie
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>>
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