Re: Gunmetal

In message <TrudnY-Epr81I77ZRVny0Q@xxxxxxxxx>, davejpc <davejpc@xxxxxxxxxxxxx> writes
I am building RO ROY and many parts call for gunmetal.
Problem is I can't seem to get gunmetal from any of the stockist is there an
equivelant,
and what are the problems with using brass ?
Gunmetal and brass are not always interchangeable so it is best practice to assume that even designers like the notorious Martin Errors has specified the correct material for the specific purpose.

I don't pretend any expertise but I have always assumed that even if phosphor-bronze and gunmetal are not physically identical they are broadly interchangeable insofar as model engineer usage is concerned. Until someone else jumps in and tells me I am wrong I shall continue to use PB as a generic term and continue to believe that gunmetal is a 'casting' grade of PB.

If you really cannot find the material specified in the drawings then it is my understanding that brass is likely to be satisfactory for cold water fittings but when used in the more extreme areas of boiler fittings it can deteriorate through a process called de-zincing. So for 'hot' boiler fittings PB is likely to be 'right' and brass is likely to be 'wrong'.

Certain grades of PB are specifically intended for use on bearings because they work harden. This same property can make for diabolical machining properties as I have recently found (but that's another story). So for wheel bearings, pistons, cylinders or anything where there is a 'sliding role' PB is likely to be 'right' and brass is likely to be 'wrong'.

So unless someone can produce strong evidence that it is total rubbish to assume "gunmetal = PB" and then take a second look at your stockists. In my experience all 'the usual suspects' both specialist model engineer suppliers and also retail metal stockists such as Mallard or College Engineering has someone on the staff who knows what he/she is talking about.

--
Mike Hopkins
CSME <http://goto/cheltsme>
5" gauge (2 1/2" scale) Alice class Hunslet
.