In common with Tornado, Prince of Wales will not have many rivets in its structure, the majority of assembly is by driven bolts, where a machined bolt is made very slightly bigger than the hole it fits in and is driven in, either using a hydraulic jack, or if not practicable, a large copper mallet. A self locking nut is then fitted. This way the bolts act as dowels and are very resistant to shear forces which tend to be the predominant loads in locomotive frames. The nuts provide a strong clamping force as well. The resultant joint is very predictable in terms of forces and quality.
In the original construction two types of rivet were used:
1) hot rivets where the hole the rivet is fitted into is typically 1/16″ larger than the rivet, to allow the white hot rivet to be easily inserted. The rivet is then turned over by a pneumatic rivet gun to form the desired rivet head – typically countersunk if the finished rivet is to be flush with the surface, or snap head which produces the classic hemispherical rivet head. As the rivet cools it pulls the two plates very tightly together, however it is not particularly good in shear as the rivet is a loose fit in the hole.
2) cold turned rivets  – these were used where heavy shear forces are encountered, for example on spring hanger brackets. In this case as per driven bolts they are made to be an interference fit in the holes but are inserted cold. The protruding end is then heated to white heat and the head formed as per hot rivets. Whilst they react well in shear, it is not possible to achieve high clamping forces.
When applied on a large scale, rivets are cheaper and quicker to make and fit than bolts, however the less predictable joint strength and the lack of highly skilled riveters makes the bolt solution more attractive today.
09151401Warming up rivetsDE
Ian Matthews heats up a rivet prior to fitting – David Elliott
09151402Rivet in holeDE
Mick Robinson inserts the rivet – David Elliott
09151403Hammering over rivetDE
Reg Rossiter supports the jack as Mick applies the rivet gun – David Elliott
The only places where we are retaining rivets is in areas where the bolt heads and nuts would be in the way of other equipment. The frame doubler plates under the front of the firebox are just such an area, where a number of pipes have to be routed along the inside of the frames past the ash pan. Thus we have used rivets with a snap head on one end a countersink head on the other. The photos show the countersunk heads extending proud of the plates, these will be ground back flush as necessary to clear the pipework.  Mick Robinson has experience with using large pneumatic rivet guns so we have done the work “in house” with assistance from Ian Matthews who when not painting engines (including Tornado) does a lot of riveting on 1/8th and 1/12th scale models, and volunteer Reg Rossiter whose background is ship and oil rig engineering, so is used to big pieces of metal. Thanks are due to M Machine for the loan of their diesel compressor and to Rail Restorations North East for the loan of the rivet gun