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|Main Page and Introduction||Head Button Construction|
|Head Construction||Jet Construction|
|Body Construction||Final Assembly and Operation|
|It All Starts With A Brass Blank:
The Hero Reaction Turbine Engine starts life as a blank brass cylinder 1 7/16" diameter and 1 3/4" long. Aluminum can also be used for the engine, but the extra mass of the brass results in better performance.
|Mounting the Blank in the Lathe:
The blank is first mounted in the lathe so that the sides and ends can be cleaned up. The standard jaws on my lathe chuck would not hold the blank, so I had to switch to the external jaws.
Some would say that you should use a steady rest for a piece this size, but this arrangement worked out fine.
|Centering the Blank in the
Before the blank can be turned, it must first be centered in the lathe. (In this photo, the blank has already been cleaned up. Yours will still be rough.)
To center the blank, mount it in the chuck just tight enough to hold it, but not so tight that it can't be moved by tapping with a hammer. A dial indicator is then brought into contact with the end of the blank as shown in the picture. (My indicator mounts on the lathe headstock, but it could also be mounted on the lathe bed.) The chuck is then turned by hand to find the highest and lowest readings on the indicator.
Once the highest and lowest readings are found, the chuck is turned to obtain the highest reading possible. A small hammer is then used to tap the top of the blank until the indicator reads halfway between the highest and lowest readings. The chuck is rotated again to find a new set of high and low readings, and the entire process is then repeated until the indicator variation is minimized. It may take several tries to minimize the indicator variation. Once the variation is minimized, the check is firmly tightened. (Make sure that tightening the chuck doesn't affect the centering. If it does, you will have to repeat the centering process.)
It is doubtful that you will be able to bring the variation down to zero, since the blank is not yet perfectly round. The goal is to minimize the variation.)
|Facing the Blank:
Once the blank has been centered, the exposed end can be faced to produce a smooth surface. Remove only enough material to clean up the end. Your final cut should be a very light cut (perhaps 0.002") with a slow feed to obtain the smoothest surface possible.
|Turning the Side of the Blank:
Once the end of the blank has been faced, the side needs to be turned. As before, remove only enough material to clean up the side. Your final cut should remove only a couple of thousandths of an inch and you should use a slow feed. The goal is a clean, smooth surface. (You will not be able to clean up the entire side because the chuck will get in the way. Just do as much as you can.)
Be sure to note the position of the cross slide on your last cut, and do not change the orientation of the tool post or cutter until the next step is completed.
|Turning the Other End of the Blank:
In this picture, the front and side of the blank have been cleaned up. The blank is now removed from the chuck and turned around so that the remaining portions can be turned. When the blank is placed back in the chuck, it must be recentered. (When centering the blank this time, the dial indicator should ride on the finished part of the blank furthest from the chuck. It should be possible to bring the indicator variation down to zero this time.)
Once the blank is again centered, the remaining end and side are cleaned up as before. For the final cut on the side, the cross slide position should be the same as noted earlier. If you did a good job recentering the blank, the two side cuts should meet seamlessly.
|Cutting the Head Relief:
Once the blank ends and sides are finished the head relief needs to be cut on the exposed end. The relief is 1/4" wide and 1/16" deep. The relief is cut in several passes, removing around 0.010" per pass. Your last cut should only remove about 0.002". The relief must be very smooth and flat to insure a good seal against the body.
|Chamfering the Edges of the Head:
Once the relief is cut, rotate the piece on the lathe and use a smooth file to chamfer the edges of your cut. This removes any burrs or sharp edges, and insures a good seal against the body.
|Center Drilling The Head:
The engine is supported by a button that screws into the middle of the head. A hole must be drilled and threaded in the center of the head to take the head button. The first step is to use a center drill to drill a pilot hole in the exact center of the head. Don't drill in too far. Drill only far enough to guide the drill in the next step.
|Drilling the Head:
Once the pilot hole has been drilled, use a #21 drill to drill a hole about 5/16" deep. (The edges of the drill should go about 5/16" into the piece.)
|Threading the Head:
After drilling a hole with a #21 drill, use a 10-32 plug tap to tap the hole. In this photo the tap is being held in the tailstock chuck, but the piece is turned by hand. The tailstock chuck is only used to guide the tap. Do not use the lathe to turn the piece. (To do so will most likely result in a broken tap and ruined piece!)
After threading with a plug tap, blow any chips out of the hole and then use a 10-32 bottoming tap to finish the threading process. (If you haven't got a bottoming tap, just finish threading the hole after the head has been cut off.)
|Cutting Off the Head:
After threading the center hole, use a cutoff tool to cut the head off the end of the blank. Position the tool so the edge of the head will be 1/8" thick.
After cutting in a short distance, remove the cutoff tool, rotate the piece in the lathe, and use a file to chamfer to inside edge of the head. Then reinsert the cutoff tool and finish cutting off the head.
In this picture the head is finished except for drilling the four holes that will mount it to the body. Note how chamfering the edges produces a smooth, burr free finish.
|Drilling the Head Mounting Holes:
The final step in making the head is to drill four holes exactly 1/8" in from the edge with a #32 drill. These holes with hold the head on the body. The holes should be equally spaced around the head.
In this picture I am using a rotary table to drill the holes, but a rotary table is hardly necessary. The holes don't need to be perfect, but they must perfectly match the holes in the body. One way to insure this is to use the completed head as a template when drilling the holes in the body.
|Completed Head with Head Button:
This picture of the completed head also shows the head button screwed onto the head. The hole in the head button to attach it to the swivel has not yet been drilled. (When I built the Hero engine, I saved all of the drilling on my milling/drilling machine for last, rather than finishing each piece in sequence. This saved a lot of time.)
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