Start Model Engineering

The Completed Engine Running

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And there is the finished (or at least completed) engine. It should now run.  And here it is with the chamber sealed up with tape and running. But it is running more slowly than I would like. It should do better than that; about 60rpm on recently boiled water. The problem is that the crankshaft bearings are squeezed up a bit too tight. They need a small amount of endplay to stop them from binding. The solution is to make a new crank disk Item 7 or flywheel centre Item 9. But in fact, I am not happy with the join between these items being in the middle of the crankshaft. So change of design and make new crank disk and new flywheel centre.

A New Bearing Group

First turning the outside to diameter, then the flywheel mount and check for fit.  Then the bearing mount with its built-in washer, and check for fit.  Then spot drill, drill the 6mm hole for the crank disk and drill through 3.2mm.  Lastly, the flywheel centre is parted off, reversed in the chuck and bored for the cap screw.  The crank disk is turned to diameter followed by the bearing mount with the built-in washer and the bearing checked for fit.  When the spigot for the flywheel centre has been turned, the bearing assembly can be checked for fit, including the all-important end play that was missing before.  All that remains now is to drill and tap the crank disk, part it off and drill for the crank pin.

The Modified Engine Running More Freely

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And the complete engine doesn’t look any different, but the reduced friction lets it run faster.

The Glass Cylinder Liner

Now it is time to cut the glass syringe to make the cylinder liner. I used a diamond wheel in an air grinder with the syringe held very gently in the lathe (and with suitable protection for the lathe). It takes a long time and must be done gently. The diamond wheel heats the glass quite a bit and I later learned that applying water with a small brush will cause the glass to break (fairly) cleanly. It can then be cleaned up on a diamond lapping plate. Not knowing this at the time, I had to cut almost all the way through and then to clean up the edge with the face of the wheel before using the diamond lapping plate. The cylinder was then set in the cylinder block with silicone sealer to allow a little room for differential expansion.

The Piston

The piston is turned from aluminium bar, checked for size, spot drilled and counterbored. Photos 660 – 680 The piston is then transferred to the mill/drill for cross-drilling before going back to the lathe to be parted off from the bar stock. The piston fits nicely in the cylinder.

The Displacer Assembly

The displacer core is simply turned and checked for size with the CD that will form the displacer disk. But it is not parted off yet because it can be used as a mandrel for turning the displacer disk to size.  The displacer disk is held on the mandrel using the core that was used to centre the bearing block pressed up with the live centre. My indexable parting tool has a sort of vee shape that holds the disk in the centre of the tool while it is being turned to size. The size in this case is about 4mm smaller in diameter than the inside diameter of the acrylic cylinder.  Putting the displacer disk together with the core and stem completes the displacer assembly.

The Acrylic Cylinder

Once the displacer assembly is fitted to the engine, its stroke can be measured. We need about 2mm clearance from the plates at the top and bottom of the stroke so the width of the acrylic cylinder can be measured, remembering to account for the rebate on the top and bottom plates. And then it is back to the mill with the kitchen canister pressed up to the slitting saw to cut off the cylinder. Once again being very careful and holding on very tightly. And here is the engine sitting on its cylinder.

The Crank Disk

The outside diameter of the crank disk was next turned from a length of bar in the 4 jaw chuck (again, just because the 4 jaw was in situ).  Then the bearing mount was turned leaving the small built-in washer to stop the outside of the bearing from rubbing on the disk. And, of course, the bearing was tried to ensure that it fitted.  Then it remains to drill the 6mm hole, drill for the M3 thread, part it off and tap M3

The Flywheel Centre

The outside diameter of the flywheel centre is next turned to size followed by the section on which the flywheel will sit, and then the bearing mount. Again, there is a small built-in washer to stop the bearing from rubbing.  The spigot for the crank disk is turned to fit the hole in the crank disk and then it is possible to check the assembly to ensure that the bearings and spacer fit between the crank disk and flywheel centre.  Then the flywheel centre can be spotted, drilled through and parted off. And we have a bearing group to add to the engine.  Here is the engine with the bearing group fitted.

A New Vertical Plate

The misaligned holes in the vertical plate were annoying me so I decided to make another one. This time, instead of marking it out, I used the indexing facility on the mill/drill (dunno why I didn’t do that before). The plate was squared and dimensioned, the mounting holes drilled and countersunk, and the hole drilled for the start of the bore.  Two clamps were not enough. When I started to bore the hole, the plate moved. So it had to be indexed again and more clamps added. With the new setup, the hole was bored, the bearing mount tested in the hole and the new plate fitted to the engine. And this time, the bearing mount fits much better.

For some reason, it now seemed like a good time to mark out the new vertical plate. Note the use of the guide cut from the bearing block.  Back to the top and bottom plates. The first task is to cut the rim from the kitchen canister to get an accurate measurement of the diameter and the thickness. This was done by holding the canister to a slitting saw in the milling machine. I have not found an alternative to this process which feels very awkward as the saw tries to whisk the canister out of my hands and/or to weld itself to the plastic. The canister has to be held very tightly with both hands at all times.

The Top and Bottom Plates

Once the dimensions are obtained, the top and bottom plates are stuck together with double sided sticky tape and a rough outline drawn on them (mainly to check that they are big enough). After the edges of the plates are roughed out with the hacksaw and disk sander, they are held on the chuck using Bogs’ method and turned to the outside diameter.

John (Bogstandard) Moore showed that plates like these can be simply held by the friction of masking tape on the chuck jaws and the plates, with the plates being pressed against the chuck with a revolving centre. As long as light cuts are taken, even with the interrupted cuts on this job, the tape does provide enough drive. A problem arose when I attempted to cut the rebate in the plates. By this time, the plates had become quite hot due all the work on the circumference. In retrospect, I should have realised this and given them time to cool down. Instead, I pressed on and the double sided sticky tape let go and allowed the plates to slip.  Rather than mess about, I pulled them apart and attached each one separately to the chuck using Bogs’ method and turned the rebate on them. And ended up with two plates that fitted nicely on the canister.