On 10/07/2019 18:07, harry wrote:
On Wednesday, 10 July 2019 16:16:19 UTC+1, Adrian Caspersz wrote:
The sort that looks a bit like decorators masking tape, but used in
engineering to establish what clearances lie between mating surfaces by
looking at indentations when parts are assembled?

Replica tape.

https://www.corrosionpedia.com/defin...5/replica-tape

Never heard of that (although I spent years measuring rough surfaces,
including taking replicas).

Our replica material of choice was Acrulite, this is just methyl
methacrylate monomer which you mix with powdered polymer. It sets in a
couple of minutes.

You can also get replicas using RTV silicone, either two pack putty as
used by dentists for replication, or creamy liquids dispensed from a
double tube syringe through a mixing nozzle.

Metallurgists have a clever technique for large, immovable plant. They
grind and polish the surface finishing with micron diamond paste, then
etch, then apply a drop of acetone and press a thin piece of acetate
sheet on to the surface, and allow it to dry. Done well, the resulting
replica, examined in a metallurgical microscope, gives almost as good an
image as could be obtained from the original metal.