Letter to the Editor May 2009

I write in response to your intention to have a “Letters” column in your magazine; I fear that this would not be particularly successful in a publication that only appears every three months. In all other respects I consider you produce an excellent magazine, a most interesting read from cover to cover. I have particularly enjoyed the reminiscences by “The Old Yeovilian” and hope he has many more to come.

However, I did find it surprising that the Spring 2009 Issue No 97 published only a matter of weeks before the Exhibition, probably our major event of the year, contained no mention of its location or its dates or its time of opening. Perhaps there has been other extensive publicity, but a new member or a non member on picking up “The Oily Rag” would scarcely know there was one on at all.

You are quite right as far as the Exhibition is concerned, Chris - the further details that you mention should have been included for the benefit of not only the members that we do not always see at meetings but for anybody reading this magazine on the internet. In our defence, I would say that details of the exhibition are included separately on the Society’s website, and the members that we do see at meetings are constantly reminded of it and of our requirements from them. The deficiency that you have mentioned will apply to members that we do not regularly see and do not have a computer. We will try to do better next year!

As far as your thoughts are concerned about a Letters page not being successful, then I do not think that I agree with you on that one. It is an opportunity for members to air their thoughts and also to raise points or questions that they do not wish or are unable to raise elsewhere. I think the following letter is perhaps an example of this where we have been able to answer the technical questions raised before publication and which accompany it.

Dear Tony,

Having read the last issue of “The Oily Rag”, I thought that I would help start the ball rolling by asking the following questions as I have been unable to find answers in the current range of books available to Model engineers.

Riveting - Most explanations of riveting include reference to using a Rivet Set to draw the two pieces of metal together. My question is - are these still available as all model engineering suppliers seem only to sell Rivet Snaps? Also in only one book I have read there is a mention to the effect that the rivet will need to be pressed through the material, which to me sounds as if it should be slightly bigger, or exactly the same size as the hole it is going through in order that the Rivet Set will work in ‘drawing the two parts together’. If my understanding is correct then I assume that the rivet has to be ‘an interference fit’ in the hole and also how does one judge/obtain such a fit for a rivet?

Silver Soldering - Most, if not all books I have or have read suggest that one needs a very large Paraffin Blow Torch to obtain enough heat to Silver Solder effectively. These seem only to be available at the likes of boot sales these days and their safety/suitability has to be in question as most seem to be at least 30 years old! Can I use one of the hand held butane or propane gas powered torches advertised for plumbers use, or can someone recommend the correct type of torch I can use for silver soldering small strips of brass together to make strapping for 5” gauge rolling stock?

Brazing - I am confused as to the difference between Silver Soldering and Brazing. Several books I have read use the titling of Silver Brazing and Silver Soldering over a list of ‘solders’ such as ‘Easyflo’ and ‘Silverflo’. When does the difference between the two methods take effect when using these materials and what is the difference between the two methods/ when would one braze rather than solder?

Sincerely, Dave Harris.

Our Member “Aquarius” offers this reply:-

There is some confusion in the books I have concerning rivet “snaps” and rivet “sets” as they appear to be interchangeable. I prefer to regard the “snap” as the tool for forming the head of the rivet - hence “snap” head (round head) rivets and the “set” as the tool for forcing the plates together before the rivet head is formed.

Rivets are normally a loose fit in the hole - when closed hot the shank of the rivet swells and fills the hole.

Brazing and Silver Soldering are very similar processes differing only in the filler material used to make the joint. Traditional brazing uses copper zinc alloys (brass) known as spelter and borax as a flux.

The melting point of the spelter is around 875 degrees C - near the limit of the capacity of a blowlamp or LPG torch - hence brazing is seldom used by model engineers. Silver soldering - brazing for the better off - also called “hard soldering” as distinct from “soft soldering”, uses alloys of silver, copper and zinc. Commercial silver solders are available with a wide range of melting points - the lowest being Easyflo No. 2, melting at 610 degrees C - barely red hot and easily reached with a small butane or propane torch making it very popular with model engineers.

The types of silver solder available include very fluid alloys with the capacity to flow into close joints, some have a wide melting range and the ability to form fillets and the range of melting points available make step brazing possible.