Harold Hall

Workshop Projects

The Valve Assembly 21, 22, 24 and 26

Part 21 was covered earlier

Unfortunately, these are only drawn as an assembly with a few dimensions omitted though it is not a major problem but does require the reader to study it carefully to ensure it is fully understood.


Valve Block Nut (24)

This is a simple part just a rectangular piece (3/8” x 1/4” x 1/8”) of brass with a central 5BA hole and being cut from 3/8” x 1/8” only the 1/4” dimension needs finishing by filing. The tapped hole does though need to be perpendicular to the parts surface and this can be difficult with such a small component, the following will though eliminate any likely problem.


Mark out and centre punch the position of the hole but then lap this surface on a  fine file to remove the raised portion of the punch mark. Next, place this, punched side down, on a flat surface and place an open drilling vice over this and tighten it. This ensuring as a result that the part is level with the top of the vice's jaws, drill the part and tap using a guide block as illustrated by Photograph 58. The photograph should make the principle clear.


Slide Valve (26)

This is a complex little part but most of the requirements are met by the brass casting as supplied. The valve block nut has to go between the cast in pillars but being tapered they need filing at their base to permit it to enter fully. Do not remove too much metal as the nut should be a close sliding fit. More about this part when finishing is discussed.


Fork End (22)

First make two steel washers 1/4” diameter with a 2.5mm hole and 1/8” thick, purpose detailed later. Next place the 1/4” square brass into the four jaw and set it to run true, drill and tap 5BA 1/4” deep and with the valve rod in the drill chuck screw the parts very securely together, then shaping the end adjacent to the rod as per drawing, part off at just over 13/32” long.  


Fix the length of brass onto the top slide packing it up to centre height and using a 1/8” end mill  machine the slot to make the fork. Do ensure that you only grip the part at the end adjacent to the rod otherwise the fork will collapse as you progress deeper with the slot, see Photograph 59.


Drill and tap the holes in the end of the fork, one being 7BA clear and the other tapped. Now screw in one of the studs and place a washer on either side securing  with nuts. Use these as a guide to produce the radius by filing. Photograph 60 shows the two valve assemblies I am making,  one assembled, the other separate parts. These are for the 10V and 10H engines.

Stuart 10V steam engine machining
Stuart 10V steam engine machining
Stuart 10V steam engine machining











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