Heisler Cross Compound Compressor Construction I
Nelson Riedel, Nelson@NelsonsLocomotive.com
11/15/2005, last updated 04/08/2006

The Cross Compound Design Details are located at the following links:

The construction doesn't follow the design sequence exactly.  Instead, I started with the larger pieces first.  The fabrication of the cylinders and the main parts of the center piece are described in this part. The construction of the  pistons, heads and center piece are described in Part II.  The compressor is finished in Part III.  

Heads & Cylinder Ends: The first step was to fabricate the heads (HM542, HM548, HM555) and cylinders ends (4 - HM533).  The bolt patterns and outside shape are the same for all 7 pieces.  (Note that the upper steam head HM562 was also initially fabricated at this time.  The design was later changed and a new upper steam head was made as discussed in Construction Part III.)   Eight pieces of 2.5" X 4.062" brass were cut from 2.5" X 1/8" bar stock.  The eight (seven with later design) pieces were stacked and a couple 3/16" holes drilled in the outside waste area and then expansion pins were driven into the holes to keep everything aligned.    The stack were then clamped in the vise on the mill table and the mill indexing used to center drill and then drill the 18 head bolt holes.  Next,   1/2" holes were drilled through  the center location of each cylinder.
The four (three with later design)  heads were removed from the stack.  The boring head was then used to enlarge the cylinder holes in the four cylinder ends.    The photo shows the boring operation.
This photo shows the heads on the left and the cylinder ends on the right.  The eight (seven in later design) pieces were stacked together again and the outside finished using a band saw, the mill and the belt sander.
Finally, the 4 cylinder ends and the 4 heads. (Recall that the upper steam head made here was discarded and a different upper head made as discussed in Construction Part III)
Cylinder Units: The cylinders (HM530, HM531 & HM532) were machined from bronze bearing stock per the drawings and the brass filler bar  HM535 was cut to length.  A hole was then drilled through each cylinder end into the filler and the part in the filler tapped 2-56. The hole in each cylinder end was countersunk for a flat head screw.  These two screws hold the cylinder unit together when everything is silver soldered.  The photo shows a unit being prepared for soldering.  Pieces of flat silver solder and flux were placed between the cylinder ends and the lip on the cylinders and the end of the filler.
This photo shows shows one of the units being heated.  The solder hasn't flowed yet in this photo.
This photo shows one of the units after the soldering.  Additional solder was added at the joints between the filler and the side of the cylinders.
Mount: The mounts (HM534)  were made next.  Two pieces of 0.5" X 1.25" bar stock were joined at the end with a couple spacers made from 0.75" length of 3/4" diameter brass rod.   The end holes were drilled in the bars and also though the spacer.  Screws through the bars and spacer held everything together while the spacers and bars were silver soldered together.   The screws were then removed
The cylinder holes were bored through the mount bars using the boring bar in the same way the holes were bored in the cylinder ends.  The photo shows the mounts after the boring operation.  The pieces were then cut in half and the ends finished on the mill to match the drawing.

The mounts were attached to the cylinder units with a recessed 2-56 screw through the mount into the filler.   This screw holds the mount to the cylinder unit when the mount is silver soldered to the cylinder unit.   These screws as well as those from the cylinder ends into the filler hold everything together when the unit is reheated.  One more reheating is required for the output air port (compressor cylinder unit) and steam ports (steam cylinder unit).  The photo above shows the units after mounts have been soldered but before the steam and air ports have been attached.    The pink color of the brass & bronze is from the pickling solution.  In this early design the large steam and air cylinders were both 1.75" ID.  The design was later changed to have a 1.5" ID for the large air cylinder.  A sleeve was inserted in the large air cylinder to reduce the ID to 1.5"

Air Output Channel:  The air output channel fits on the left side of the of the small compressor cylinder.  The first step was to mill a shallow recess in the side of a length of 5/8" brass rod  This recess is just deep enough to keep a piece of 1/4" square brass bar aligned with the rod.  Strips of  silver solder were laid in the recess and the pieces then soldered together.  The photo shows the rod and bar after they were soldered together and cleaned in a pickling solution.
The piece was then mounted in the three jaw check for finishing.  The photos shows how the jaws grasp the rod and the 1/4" square bar fits between the jaws so that the rod is on center. The ends were then cut to length, the 1/4" bar cut back 1/8" from the end.  The end of the rod was then drilled and threaded to match the drawing.   The bottom of the hole where the check valve rests was made square using an end mill in the lathe tail stock.  After both ends were finished the sides were milled per the drawing and the output port hole was drilled in the side.  A small hole for a 2-56 screw was dilled though the bottom of the hole for the output port.
The channel was carefully aligned and clamped to the side of the air cylinder unit. That small hole for a 2-56 screw in the bottom of the output port hole was then used to mark the side of the cylinder.  The channel was then removed and a 3/32" deep hole was drilled and tapped 2-56 in the side of the cylinder.  Care was taken to assure that the hole didn't go all the way through the channel.   This hole was used to hold the channel to the side of the cylinder during the soldering process and also hold it there if it subsequently must be  reheated.  The photo shows the channel soldered to the cylinder.
Before the channel was soldered to the cylinder, 3/32" air passage holes were drilled though the cylinder side.  The holes are 30 degrees off the horizontal and start at the joint of the cylinder side and the cylinder end.   The photo shows where the hole exits the top (or bottom) of the cylinder.  After the channel was soldered to the side of the cylinder. these holes were extended through the side of the channel into the check valve pocket.
Check Valve Plug:  The check valve plugs were fabricated from 7/16" hex brass stock and a short pieces of 5'8" OD brass rod.  The rod was cut to 0.219" length and drilled 7/16"   The end of the hex rod was turned to 0.43" about 1/4" back from the end.  The rod was then slipped on the turned end of the hex bar and silver soldered in place.  The photo shows plugs were being made on both ends of a length of hex bar.
The bar was then mounted in the 3 jaw chuck and the end turned, drilled and then threaded per the drawing.  A 3/8" end mill was used in the tail stock to finish the bottom of the hole flat.  The plug was then parted off leaving the correct length head.  The photo shows a couple finished plugs.  #109 Buna N O-Rings are used for seals on the plugs
Output Check Valves: The photo shows a couple MCV-1BB check valves modified per the HS530 drawing.  The short length of 10-32 threaded rod was drilled 3/32" and then screwed into the output end of the check valve.  Loctite was used on the threads to assure that the rod will stay in place.  #006 Buna-N O-Rings are used for seals on the 10-32 rod.
This photo shows a check valve installed in the air output channel.  The valve sticks up enough so that it can be tightened with a pair of pliers and also remover later if required.
The check valve plugs are installed in this photo.  This completes the air cylinder unit.
Steam Ports:  The two steam ports are made at the same time.   The photo shows the the 1/4" square bar soldered into slots in short lengths of 1/2" diameter rods.    The center of the rods were drilled with a No 5 drill in preparation to tapping 1/4" MPT.
The next step was to drill and tap holes in each end for #2 screws that hold the rods to the square bar when the parts are subsequently reheated.  The end with the screw heads was then milled flat.  The two parts were cut apart next and the ends machined to the correct length.
The No 5 hole in the port was drilled within about 1/16" of the bottom.  A small hole for a #2 screw was drilled the rest of the way though the port.   The ports were clamped to the cylinder unit and the hole in the port was used to mark the side of the cylinder for a 3/32" deep hole threaded 2-56.  A #2 screw though the the hole in the bottom of the port holds the port to the cylinder while it is silver soldered.    The vertical passages was drilled later after the positions were marked to align with the mating holes in the upper steam head.
Center Piece: The center piece is assembled from a pair of heads and the HM556 spacer. The spacer is made from a pair of bronze cylinders and a brass plate.  One of the spacer cylinders has flared sides.  The flared cylinder is bored 1"  and then mounted on a expanding mandrel for turning the outside flare as shown in photo on right.    After the outer surface was finished the largest part of outer surface was then grasped in the 3-jaw chuck and the flare turned on the inside.  The other cylinder is straight and easily turned.
This photo shows the spacer cylinders after the  wedge has been cut out.  The spacer cylinders have been attached to the lower steam head with a couple 2-56 FH screws per cylinder. (the spacer is upside down in the photo).  The photo shows alignment bushings made from scrap aluminum used to align the cylinders with the holes in the head (each bushing has a 1/2" diameter extension that  fits in the hole in the head.   The flat piece was cut to match the edges of the spacer cylinders and also attached to the head with a FH screw.
The other head was also attached to the spacer with a couple FH screws.  Alignment bushings were also used to align this head. The photo shows the completed center piece. The air passages  and check valve housings must be attached to the upper air cylinder head before everything is soldered together.  The packing glands must also be be soldered to the heads.
Cylinders, Heads and Center Piece:  This photo show the two cylinder units, the center piece and the other two heads all stacked together and held in position by a couple 4-40 screws per section.  Everything seems to fit.          This is a good point to end this section.