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Hello, as most likely a lot of different offering materials for the displacer,
I thought and I propose you to derive the displacer (without the use of regenerator) from a porcelain mug cup.
The mugs cups are not many used in Italy, but I've used they in my travels in Anglo-Saxon countries.
Obtained by turning, with the correct equipment.
Of course the shape of the cup may be does not have the right dimensions, and (of course) must be removed by grinding the handle.
The cup is too thick and heavy, and may easily have deformities in shape (cylindrical, round)
So I propose by placing the cup on the lathe, turning the inside, bottom, and the cylindrical, (Or a bit conical) interior of the cup.
So in the mouth of the cup is obtained a internal recess (to put the cap), diameter greater than 4/1000 of an inch of the cylindrical, and deep 16/1000.

Is then turned a plug of hard wood, diameter of the inside diameter of the cup, then puts the cup (as an hat) on the plug, slightly forced on.

You can now turn the outer cylinder and the outside bottom of the cup until you have an approx. Thicknesses of about 8/1000 of an inch.

Is prepared now the plug closing the cup, stainless plate 1/16”, fixed, welding or mechanically, to driveshaft – stem - (tube, or full rod). In the plate/plug may be performed for the tiny hole for pressure equilibration.

The driveshaft (stem) is fixed in the lathe spindle and the plate is machined to the diameter of the opening of the cup recess, so it's slightly forced.
The plug is mounted in the cup recess, checking (by comparator) the alignment to the stem to the outside of the cup.
Setting up the cup, to weld, soft soldering. with alloy of silver, the plug with the cup.

Small differences in alignment between the displacer stem and the outer of the displacer (cup), after the welding, may be corrected with adjustment by grinding on lathe the displacer, and monitored with a comparator.

Please consider my difficulty in explication in English;
This solution is foreseen for a dedicated level of technology, excuse me if the level is not uniform enough.
Being me a starter, excuse me if the matter is yet develloped and, (as we say in Italy), if I 've re-invented the "hot water".
Your observations are wellcome,

CORRECTION:
ernal recess (to put the PLUG), diameter great....

I'm not sure, is your mug enamalled steel? it's not unusual to use stainless mugs, and similar containers. A large test tube, or Pyrex beaker would be ok, but a porcilane mug thinned down may not stand the shock of heating and cooling, and moving back and forth at great speed. Ian S C

Ian S C wrote:I'm not sure, is your mug enamalled steel? it's not unusual to use stainless mugs, and similar containers. A large test tube, or Pyrex beaker would be ok, but a porcilane mug thinned down may not stand the shock of heating and cooling, and moving back and forth at great speed. Ian S C

I think he is talking about using a porcilane mug. I personally would not use it.

Ian,
I considered a porcelain mug cup, (of course) or similar material (like tile or ceramics).
Then you say that it will not sustain the rapid changes in heat, and I think you should say for an experience on the matter.
However there are not many wide variations in heating and cooling, being the displacer work as an inert body, without flow all round: not as heat-regenerator; and we should see the solicitations for the fast movement and the strengh.
Instead I checked out (after writing) the coefficients of expansion, and should not be very good idea a metal plug (the metal expands so much more) than it should be a plug of the same material).
My proposal is derived from the fact that near my town there is an abandoned factory which produced high quality ceramics, insulators, for high voltage transmission lines. The stores of ceramic materials of high quality (mechanical and physical) have been emptied and everything was disposed of.

There is a big difference between the normal earthenware, porcelain and ceramics.

I refuse to believe for the use for a Stirling engine homebuilt, of special hi-tech ceramics, (also resistant to internal parts of IC engines, shock resistant and the greatest pressure), but may be there are simply more resistant than glass, and to be worked better.
Displacers in glass are yet used for the Stirling engine, also if not of great characteristics.
Thank for answers