White metal v. resin. Model Rail Mag. No. 27 Page 52
- I must first of all declare my interest as I am the proprietor of a small,
but hopefully growing, cast resin kit business. Some of the points put
forward in the letter from Mr. Bridger appear to be somewhat out of date. As
he must know 'Resin' in the context he uses it, is a generic term for an
ever increasing number of different polymer and catalyst combinations. This
may take a while but I would like to comment on his letter item by item,
bearing in mind that these are only my opinions gathered over the last 5 or
6 years as a maker, but some time longer as a builder of resin kits.
The first point is that there has been a lot of progress and development
of resins since he worked with them 15 to 18 years ago. I use a fast setting
poly-urethane resin that uses no filler at all and has a dry smooth finish
when taken out of the mould.
The only time that I have had problems with paint adhesion is when I have
failed to clean off the slight silicon residue left on the casting by the
mould rubber. Some of my kits have been in fairly heavy use on layouts and
handled by the public on my trade stand without ill effect. My kits carry a
note to this effect in the instructions. I would agree that the casting of
thick sections is not advised, but only because of the distortion caused by
the different rates of cure. As far as flexibility is concerned, my
customers seem amazed by just how flexible the castings are, obviously they
are nothing like as flexible as most injection moulded plastics. As to the
powdery finish ,this is something I have not experienced at all.
The comment about always being a liquid I can only answer by drawing
attention to the fact that in theory so is glass. I have had no experience
of loss of detail either.
I have also met and had conversations with 'experts on resin' whilst
selling my products and demonstrating resin casting at exhibitions. One such
'expert' assured me that it was impossible to make air bubble free castings
without the use of a vacuum degassing chamber, he continued on in this vein
for some time while I continued to make a table full of bubble free castings
as I was holding the conversation with him. He could not tell me how to
vacuum degas a mix with a pouring life of only 90 seconds either!
The medical problems associated with resin affect the person mixing and
pouring the resin rather than the person using the casting. As with any
process, casting hot metal, etching sheets of brass or casting resin,
sensible precautions need to be taken. In the case of resin, a well
ventilated work space, protective gloves and glasses to protect eyes from
splashes whilst mixing are what I use.
I think it's really a case of horses for courses and whatever medium you
feel happy in rather than A versus B. My own opinion on materials is, for
thin sections ,sides, ends, floors and cosmetic bogie side frames and sole
bars resin is fine, for delicate brake gear etched brass is ideal, and I
like white metal for all the heavier below sole bar items. For low sales
volume, obscure prototype vehicles, resin seems to me, and my customers the
ideal answer, not least because they can provide me with patterns made from
cheap easy to work materials such as styrene sheet and wood as the mould
rubber is cold vulcanising.
Sorry about the length of the letter, but I feel better now!
Port Wynnstay Models