joy valve gear (Derby 4f)

[David Bothwell 1Participant @davidbothwell1]

Building a three and a half inch Derby 4f and experiencing some difficulty with the parts attached to the motion viz the anchor link. I have carefully measured the parts according to the drawings but the loco will not turn over, removing the anchor link and it will. Tried a different size (both longer and shorter) most frustrating, any suggestion very welcome!

[David Bothwell 1Participant @davidbothwell1]

very tight

[MikelkieParticipant @mikelkie]

Wanted to build a Derby 4f myself experience difficulties with the drawing some 25 years ago, gave it away and did a Simplex instead. I suspect Don Young's drawings had some incorrect measurements

[David Bothwell 1Participant @davidbothwell1]

Hi Mike, Thanks for your reply, nobody seems to have built the Derby!!

[BazParticipant @baz89810]

You couldn’t be more wrong, lots of Derby 4f locos built also quite a few 2P both Dons designs and both having identical Joy valve gear. Never seen any criticism of the valve gear in fact the only criticism I can recall of the 4f was the use of imperial decimal dimensions, seem to recall there was a lot of bad feeling between Don and Martin Evans over the dimensioning.

[David Bothwell 1Participant @davidbothwell1]

Sorry for the delay in making a reply, Could not be more happy to be wrong! Prefer that than having to remake parts.

Thanks for your response.

[RedsetterParticipant @redsetter]

OP- Removing the anchor link effectively disconnects the valve gear, so I am not sure that proves anything. Does the valve/valve spindle move freely over its designed travel?

[David Bothwell 1Participant @davidbothwell1]

Thanks for your reply, I realise that the anchor link is integral to the valve gear. I also found I had "reversed" the trunnions i.e. it is a triangular shape and I had placed these the wrong way round. This has made a difference and I am still assembling it all. The valve spindle moves freely. I made the main part (forgot its name) slightly longer and although it did not seem to help it now is rotating (the part that attaches to the anchor linketc.,

[Bruce VoelkerdingParticipant @brucevoelkerding91659]

I remember Don Young mentioned something about the Derby 4F & 2P valve gear, but was not sure what it was. I had subscribed to his magazine LLAS for a year or two. This morning I came across LLAS magazine #26, dated Feb 86, mixed in with my ME back issues. In this issue Don was describing the building of the 2P. Here are some extracts –

"Just one point to be mentioned for those who have purchased drawings ahead of Sheet No. 3 appearing in LLAS, in that the slideshaft has been moved from the center line of the slides to the top of them. I put the slideshaft on the center line originally because this was the approximate position full size on all engines fitted with Joy valve gear, plus this helped mask the presence of said Joy valve gear in lieu of the authentic Stephenson gear with rockers, but it meant in practice that the .16 inch dimension of metal to be removed between the slides had to be exceded to achieve working clearance for the vibrating links, and although the end result was perfectly satisfactory, moving the slideshaft upwards to what I would call the "LBSC position" means the drawing dimension can be adhered to, thus saving me a query or two."

Note in the text above "slideshaft" refers only to the .38 x .38 x 2.75 bar which is a component of the "slideshaft assembly". The fulcrum pin location was not altered.

In the same issue referring to the Slide Valve –

"Incidentally, when my 4F pencil drawing was traced back in 1974, a poor 6 became a 0, so what should have read .561 inch became .501 inch, something that was perpetuated initially on the 2P. It was in fact a 2P builder who advised me of my error, I guess that by the number of 4F's already running at the time it was a rather obvious mistake, so I simply corrected the drawings and forgot about it. Unknown to me, however, the designer of the Clayton Steam Waggon that has become very popular through a series in "Model Engineer", used those 4F cylinders and repeated my dimensional error."

I hope I didn't make any transcription errors.

Moderator – could you add these comments in the drawing errors section ?

Bruce

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