Marine Compound Engine

January 2010.


John R. Bentley 2010.

Machining the
Steam Chests
-  for the Stuart Compound Launch Engine  -




The finished steam chests - the low pressure (L.P.) unit is the larger of the two





The LP end fixed into position



These are the castings for the steam chests as supplied




These two units are identical except for the widths, so I will show the work on the LP steam chest with odd shots of the smaller HP unit interspersed among the other photos



Here the casting is clamped into the 3 1/4" Taig chuck






My usual method for rough centering in the chuck is to leave the toolpost loose and turn the cross slide in until the tip touches the workpiece. Then I turn the chuck slowly backwards by hand and note the variation of the gap between the tool and the work. I adjust the jaws accordingly - for a simple job like this one on a rough casting that's as close as you can get.







Taking a facing cut across the top





This is the same scene with the lathe stopped



It is best to remove only what is necessary, it's hard to add metal back on...


I prefer machine this type of valve guide freehand and clean up (carefully) with two small files - a flat file and a round one. (you don't want the file to come in contact with the body of the steam chest or it might just come in contact with your own chest!)








This is a carbide insert for refinishing car brake drums and disks...I made a little holder to fit the Taig



It has a good radius for freehand jobs like this



The completed valve rod guide





Now to the other end - this will become the packing gland





It is easiest to file this smooth while in the chuck





My lathe will function at almost zero RPM so I was able to revolve it slowly and let the file
undulate as it followed the oval surface of the gland packing box.



All done!





At last - I'll get rid of those numbers!





Two 1/4" lathe tool blanks allow clearance for the cutter between the vise jaws





As they say, it is best to get under the crust in the first pass





That looks a little better!





Milling out the 7/8" x 7/8" steam space





I have clamped two strips of steel to protect the body while filing the gland





Starting the stud holes and the packing space





Now.  I am expected to drill through the gland, through the steam space and deep into the valve guide - that is without coming through the end by mistake. I'm good at mistakes so I am ascertaining that there isn't enough of the drill protruding to make it out the other side!



A proper person would simply turn the the steam chest around on edge in the vise so that the tip of the drill is visible...then they would trust to those little numbers on the mill's Z-axis handwheel.



I bored this packing recess in the gland with a 1/4" endmill





Tapping the holes for the 7BA studs which will tighten the gland





Forming the connection for the exchange pipe flange



The exchange conducts the exhaust steam from the High Pressure cylinder to the intake on the low pressure steam chest



The eight mounting holes were located with the mill's X and Y axes then started with a center bit









I tried marking out the holes for the studs as a double-check on my setup in the mill



I just slide the caliper's jaw along the edge as a guide and let the other jaw scribe the line in the toolmaker's ink



Just taking a breather while I contemplate the covers







When I get back to the cylinder block it will be time to tap the eight holes on each end







The covers have a spigot on the back so they can be faced in the lathe







Judging from this cut, the spigot is not exactly square with the cover
(that's OK there is plenty of extra thickness of metal)







Completely under the "crust"







Here is the smaller cover from the HP valve chest





It turned this cover at the same time
It will be drawn over fine silicon carbide paper to remove turning marks







Milling the edges clean while the spigot is still attached
(but not all the way - I am leaving a little extra for endmill clearance in the vise)







Sawing it off



It's gone!







Making a pass





This is a good time to use the depth gauge included on the end of every dial caliper





The plans call for 0.125" thickness







Note the ridges left at the sides to give clearance for the cutter







Now I simply hold it vertically in the vise and mill the edges to bring the cover to specified dimension, thus removing the ridges left in the last step.







I will probably mill off that blemish in the centre while trying to retain that "cast look"







The holes have been drilled through the cover using the body as a drilling guide

A view of some nearly-completed parts








A stark contrast is evident between the casting and a finished valve chest







This much was accomplished over a span of 26 days







Compound Launch main page

or

Castings, Materials and Fastenings

Soleplate

Cylinder Block

Top Cylinder Covers

Lower Cylinder Covers

                 Steam Chests (this page)

Crosshead Guides and Bracket

Crankshaft

Eccentrics

Flywheel

Connecting Rods and Crossheads

Main Bearings

Pistons

Fittings: Oil Cups

Fittings: Drain Cocks

Fittings: Exchange Pipe, Flanges and Glands

Stephenson Link Reversing Gear (5 pages)

Completing and Erecting the Compound Launch Engine

or

Return to main website home page

ModelEngines.info




(c) John R. Bentley 2010.