Here's an e-mail I received from George Waterman on July 17, 2014. Please note: Dad sold these plans for 15+ years before he passed away, and I'm sure he would have fixed any errors reported. This e-mail is posted to offer a different perspective and solutions to the author's understanding of the plans:
My modifications are either to fix simple errors, or to suggest ways to make the design work better – I will list here the ones I should be able to send in a form that can be understood.
1. The little lubricator that fits under the slide rail of the crosshead is too big in diameter and height – my little layout that shows the problem and my modified design. See the attached sketch in both JPG and DRW formats “Small Lubricator for Displacer rod end”. The other rod ends could be made to the original design but I made them like this (except 0.150 high) so they would look similar. You can decide for yourself.
2. The rear cap for the displacer has serious problems with staying aligned with the rod. With Jerry’s design the displacer tilts at an angle and scrapes the bore when the thread is tightened. I designed three improved versions. The Mod 1 seemed logical but still allowed too much flex. Mod 2 with the threads also tilted too much when the threads were tightened so I reamed out the threads and made it a press fit with the rod – this is the version in my Vickie now. I designed the Mod 3 as what I would do if I were making it again – it’s the one I recommend but I haven’t make it yet. In all cases the rod need to be extended as appropriate to fit the modified rear cap selected. Note also JPG and DRW’s attached for each.
3. When Installing the rod into the crosshead, it seemed risky to try to machine them as an assembly so I drilled the crosshead for a #2-56 setscrew which allows final fine tuning of the length if necessary. Jerry’s method would also work if you can do the drilling as an assembly – I didn’t think I could.
4. When I made the hot cap, I machined it from a single piece of stainless steel – to avoid the brazing operation – I used 304 stainless but it is a bit “gummy” to machine so I would use 303 stainless next time – free machining type.
5. Also important – on sheet #18 the instructions for the crosshead say machine to 0.5 “ dia – this is too small, causes the sides to be too short. The diameter should be at least 0.576” diameter to allow full sides. See attached study sketch “Crosshead 0.5 vs 0.576 study” in JPG and DRW formats.
Good Luck with your model