Reply To: Building a Rob Roy

[stephen goodbodyParticipant @stephengoodbody77352]

Hi Pete,

It occurred to me that the late Alan Stepney set up a website that included compiled lists of errors for several locomotive designs. Alan's website is still extant at: https://web.archive.org/web/20130811220810/http://alanstepney.info/index.html

I have unashamedly copied Alan's Rob Roy error list at the bottom of this message and can personally attest that the crosshead pump fouls the cylinder jacket, I ended up cutting away a small portion of the jacket to clear. While I didn't use different valve spindle threads, or add gland locknuts, the suggestion is good.

One other thing that comes to mind is that the mechanical lubricator linkage causes the lubricator to pump far too much oil as designed. I ended up using a slotted rather than pinned connecting arm between the crosshead arm and the pump arm, meaning that the pump is rotated by two ratchet teeth with every wheel rotation. That's still plenty enough oil to get your face dirty!

In addition to this forum you may also want to check out the Chaski.org/homemachinist/ forum (live steam) which has good information for North American model engineers such as ourselves.

Here's a cut and paste of Alan Stepney's Rob Roy error list:

• "If built to the drawings (and I don't think they have been corrected yet), the valve gear and the valve spindles don't line up. The difference is 1/8" (?), and the solution is either to make a stepped valve crosshead, or to make the valve face 1/16" further out from the cylinder, and the valve spindle 1/16" higher in the steam chest. (Thanks, to Steve Papworth.)

• Change the pitch of the thread on one end of the valve spindle, to allow the setting of the valves to be more easily modified.

• Fit thin locknuts to both valve and piston glands.

• The bottom section of the crosshead pump is too close to the cylinders.

• The blast pipe is in the wrong position. Increasing the height of the blast pipe by about 3/8" seems to improve draughting.

• The dome bushing on the boiler should be 3/4" diameter bore!

Best regards

Steve