K3s Progress 2015 - The inside cylinders
This page describes the work done from February to October 2015 and takes the inside cylinders to the beginning of the final silver soldering operation. As the work progressed I realised the risks of each operation were becoming greater and that any error could cost my considerable investment in time and materials if it was not recoverable, so each step was made only after a lot of thought, making sure that no part had been overlooked before it was impossible to go back and correct the omission. Each machining operation was also carefully planned in my head before committing to cutting metal. Hopefully I've got it right and I'm not ending this project with a glass case model.
I spent many hours pondering how to draw the inside cylinder, let alone build it. Having a copy of the full size cylinder drawing helped with the detail, but actually getting my head around putting together a cylinder that was inclined in relation to its valve chest was really challenging. I followed the concept used for the outside cylinders, but the construction needed to be different, not least because the internal support plates were inclined in relation to the ends.
The process begins in the obvious way with the preparation and machining of the end plates
Two cylinder back plates mounted on the mill for sizing and squaring
Same plates with centres drilled for cylinder and steam chest (small holes) and the mounting holes for the steam passage casing (see below)
The steam passages were machined next from a block of gunmetal. Mounted on the rotary table the outside shape was simple to machine after drilling pilot holes for the centre of the steam chest and the outer radius and the holes for the mounting pins.
The top edge was finished using a corner rounding cutter
The piece was cut off using a hacksaw rather than setting up for a slitting saw.
The pieces were set up in the four jaw and after centering on the steam passage pilot , faced off and bored part depth to form the steam passage.
Once all were done, they were each put back in the mill to open out the steam passage for the connection to the cylinder
The parts were then attached to the front and back plates by lightly riveting them using brazing rod, followed by silver soldering
The front and back plates were then set up in the lathe for boring out the holes for the cylinders
As the valve chests are not parallel with the cylinders a different technique was required for boring the holes in the endplates. The plates were set up on an angle plate on the rotary table on the mill. Slightly precarious, hence the blocks on the edge to stabilize the workpiece, and carefully bored to the require size.
Here they are temporarily mounted in the frames to show where they go.
Two side plates are needed to fix the inside cylinder to the outside cylinders. There are no bolts connecting the inside cylinder to the frame plates. the three cylinders can be bolted together to form a complete cylinder block, the traction forces being transmitted to the frames through the cylinder bolts and via the cut outs in the frame plates that closely fit the inside cylinder side plates. The side plate bolt holes are being drilled
The drawing for the side plates.
Milling the outside profile if the side plates using MNC (manual numerical control)
Slotting a side plate for locating the back and front plates and the longitudinal support
Slotting for the two internal support plates
Two side plates slotted ready for trial assembly
Unlike to outside cylinders there are no ribs on the inside cylinder barrel, seen here being bored.
The bore is opened up at each end and the internal chamfer made as the outside cylinders and set up with the end plugs so the outside can be turned between centres, concentric with the bore.
The outside is finished by rebating the ends, and reducing the middle to give the required wall thickness and then put on the rotary table to machine the locating slot for the longitudinal support.
With the same set up the steam passages are milled into the cylinder wall
An inside cylinder begins to take shape
The internal support plates are machined as the end plates but the valve opening is square to the plate and can be bored in the lathe. The valve bore is big enough to cut out at the side and a sacrificial piece of brass plate is provided so the tool does not collide with the adjacent chuck jaw.
The cylinder opening needs to be bored as before on the milling machine at the correct angle and here the holes are being drilled for the assembly rods before the main bore is started
The cylinder opening is bored to size
A trial assembly of the supporting components to check that it all goes together as intended
The internal support plates have to be split across the centre to allow assembly because the cylinder ends are a larger diameter than the barrel. A horizontal slot is machined at the half height of the cylinder corresponding with the longitudinal support plate leaving just a narrow connection between the two bores
On assembly a thin blade is used to cut the internal support plates so they can be fitted either side of the cylinder, valve chest and longitudinal support plate.
The trial assembly shows the cylinder and it's back cover (made with the outside cylinder covers) in position.
The valve housing or steam chest is made exactly as those for the outside cylinders that was seen on Page 6, except at one end the flange for the crosshead guides is omitted and fitted after the part is inserted into the assembly.
Also a flat is machined along the length where the side mounting plate abuts the steam chest
The valve housing is shown in place in the assembly
The inside cylinder assembly temporarily positioned in the frames showing how close the valve is to the inside face of the frame.
Before proceeding to the first soldering operation the exhaust passages from the outside cylinders are machined in the side plates
A side plate temporarily fixed with steel screws having run out of brass ones - again, showing the exhaust passage holes filed out so they point
in something like the right direction
The top half of the internal support plates also support the underside of the exhaust passages which all meet under the blast pipe
They are shown here in what was expected to be there final position
The inside cylinders are nearly ready for the first silver soldering with the end plates roughly cut to shape for the smokebox saddle plate and the openings made for the exhaust passages from the front and back of the valve housing. Correcting fluid has been applied to those places where silver solder is not wanted.
The two cylinders are fluxed ready for the first silver soldering.
A cylinder in position in the frames after being silver soldered and pickled.
Machining the sides of the cylinder block to ensure the bore is exactly in the centre. The cylinder is mounted on the mandrel made from the pressure testing gear shown earlier and mounted between centres on the rotary table. The sides can then be progressively machined to close to the required spacing and the final cut to each side made with the sane tool setting. The same set up is also used for spotting the cylinder drain positions and spot facing for the flange plates to be located.
The curve for the saddle plate and the final machining of the exhaust passage supports was also done using this set up and step machining with a ball nose cutter utilising the DROs to produce the profiles.
The side walls for the exhaust passages were made up from brass sheet, cut to follow the cylinder and valve chest reasonably closely after being bent to shape in the horizontal plane. 10 BA brass screws were used to fix these in position for the next silver soldering operation.
The exhaust passage walls are seen passing through the side plates with the 10BA fixings angling through. The Dremel is a very useful tool for drilling the holes for these, but temporary clamping is challenging.
The passage from the end of the valve housing has been made and the corner stiffeners fitted
The slide bar support has been fixed to the back if the cylinder, hopefully in the correct position, as there is little room for error at this point.
Finally the flanges for the cylinder drains are put on, and all is ready for the next phase of silver soldering.
The cylinders carefully treated with correcting fluid and fluxed ready to be silver soldered
After silver soldering and pickling
Templates being made for the floors of the exhaust passages
All floor sections in place for silver soldering
After silver soldering
Machining surplus material from the exhaust port walls and profiling the centre fin of the blast pipe base
The oval blast pipe flanges were machined from a block of bronze mounted on the rotary table in the milling machine
Opening up the centre with the boring bar
Using the slitting saw to part off the two blast pipe bases and two flanges
A blastpipe base in position
Blast pipe base drilled for studs and the first exhaust passage tops in position.
I'll leave it here for the next instalment , which will start with the making of the smokebox saddle plate, an integral part of the inside cylinder structure