Thompson Class B1 Springbok

[jones1972]

in reply to Mr Ashton return crank cheat i must hold my hand up and say i followed Mr Evans drawings! in my defense the loco is being built for a friend who produced the drawings but after acquiring a rather nice side photo of full size machine he requested alterations! The cheat is pinched from an article in model engineer dated @ 1968 a solution for me as wheel sets finished by this time . However i did set the return crank up by using a jig set up as follows which enabled the return crank to be set at right throw from axle centre. The jig consisted of a plate with a hole bore thro, one side had a location to fit axle centre and other side, a button of 1" dia.also a bored hole to correct throw for valve travel was put in ,in line with axle centre. on the crankpin i placed a nice wring fitted collar on crankpin of 1" dia which allowed me when the crankpin at 6 o clock to place a square alongside collars to establish axle centre and crankpin aligned this being done with wheel sets on surface plate. the wheels then clamped to an angle plate also on surface table to secure wheels rigid.I then using a clock in surface stand clocked up jig level or parallel to surface plate and clamped this to wheel. by using a nice fitting pin trough eccentric rod hole in return crank i simply assembled return crank on crankpin by pushing setting pin thro return crank and then into the throw hole postion in jig plate. return crank then tightened up and taper pinned. i have air tested chassis and very pleased with results valve cracks lovely in mid /for and reverse postions and valve openings vary by .008" from forward gear to reverse. as a matter of interest a friend also building a B1 not far from here set his return crank by axle jig with wheel off axle and he has proper square fitting of his return crank and his valve events are slightly worse than mine so i was lucky!! Hope you find this interesting and many thanks for your work on valve gears your books were used on all my engines you even have an input into this B1 regards valve travel !
I will try and put up a picture of chassis when i get 5 mins!
Regards
jones 1972

[donashton]

Jones1972,

Well done and I'm glad you are so pleased with the results. My genuine congratulations are not just directed to your achievements, but also to the fact that you realised the necessity for the jig work. The designer should draw and dimension precisely, and 'words and music' should include the methodology, but there are plenty of horrors awaiting the keen tyro who's just hacked out his frames in a burst of enthusiasm.

Ignorance is bliss for a time. Thompson's B1 is a cracking machine both at 12" to the foot and at 0.0885 to the inch, but I should hate to get well on the way only to discover that many leading dimensions have been deliberately altered for the worse. Try Highlander, which is nothing like a Class 5. I can philosophically pass over a mistake on the drawing of such a complex thing but not major alterations that affect the visual aspects for no good reason.

Yes, please post a pic - I always like to see what good work some people are doing and it is inspirational to most viewers. Thanks for sharing your jig explanation.

Don

[chris vine]

Hi Don and Jones 1927,

I had some problems with the Martin Evans' valve gear for my B1 in 7.25" gauge. The main problem (apart from wrong appearances etc.) was that the valve travel in full gear was long enough to make the rings on the valve bobbins overrun their working diameters and run into the slightly bigger diameters at the ends.

You could hear the rings clicking as they went up and down the taper lead ins.

I am afraid my solution was to slightly limit the movement of the reverser so that they just stay in the correct operating area. Had I known Don when I was at that stage of the build, I would undoubtedly asked for his assistance.

It was interesting to look at Martin Evans' drawings for the valve gear because he never showed what the full gear valve travel was. I suspect he did not know it!!

Also when he was describing setting the valves in the ME series, he explained that the little spy holes should be opened and the amount of lead set by adjusting the valve on its rod. This clearly is wrong as the only thing you can do by moving the valve on its rod is to centralise it, or offset it one way or the other.

Of course I am now fully prepared for Don to tell me that it is I who have misunderstood it all!!!.....

Best to all,
Chris.

[springbok]

Chris,
When I spoke to you at sandown I said got my B1 running on air but that was the evening before the show running forward when I tried reverse a day later nothing it will attempt to turn over have been fiddling with it for about a week no luch please everyone what am I doing wrong. This is my first time of building a train with this type of valve gear.
Also I did not realise there were so many people building a B1, I have had mail from all over the world.
Thank you all
Bob

[jones1972]

Hello Mr Ashton,Mr Vine,Springbok,
I would like to say in reply thanks for kind words from Mr Ashton and two things to Mr Vine that you have a fabulous B1 and that my user name is Jones 1972 last part is my date of birth had a chuckle i am 40 in December not 85!! On a serious note i am finding that most loco designs i have come across so far mainly from Keith Wilson and the late Martin Evans a lot is left to the builders understanding of steam engine theory and practice.I myself have been lucky as my father started making engines over 40 years ago plus i have served a toolmaking apprenticeship and indeed still in the engineering game. My own experience of steam has been through playing around with full size steam engines mainly traction engines and been involved with couple of railway engines. I am going to have a guess without seeing springbok chassis that three things are not right his length of eccentric rod,return crank setting or indeed the actual valve itself. I will leave the final word with Mr Ashton on the matter and will be interested in his reply.
jones 1972

[jones1972]

[img src="[/img]"] Pictures of B1 motion
regards
jones 1972

Attachments:

[jones1972]

[/img] return crank fitting now pinned.
jones 1972

Attachments:

[jones1972]

[/img] picture of crosshead valve spindle guide etc
jones 1972

Attachments:

[jones1972]

[/img] pic of expansion link etc but note link brackets to drawings they are not like this in full size! well not according to mayflower and 61264 !
jones 1972

Attachments:

[jones1972]

[/img] last picture, i will fit a brass cap on eccentric rods !!
for the record this view also shows that the link bracket is nothing like full size in as much the big un has weighshaft bearings incorporated into the expansion link bracket and as i have pointed out a different profile. along side this build i am building a G W star and have over 150 photographs of lode star at swindon and NRM i know that there are certain differences of engine from the same class but as we only have lode star and not western star who will argue well except Taff but i am using his GA also!! so i would when deciding on building a loco if possible get loads of pictures of an example that still survives or drawing etc but mind you if there are no survivors who can argue!!
This B1 for the record has PTFE piston rings and piston valve bobbins and the to be owner is like a dog with three !!!!! it will give the impression of a B1 so he is happy thats what matters i suppose

Attachments:

[springbok]

Hi Jones 1972
Did not think that they did toolmakers apprenticeships in the 90s, but it is nice to hear it. done mine in 63 and then moved on after a while RR college with old "Bully" Bulimore to help found the apprentice unit at Filton. I am aware of the various items you have mentioned.
Also your quote.
My own experience of steam has been through playing around with full size steam engines mainly traction engines and been involved with couple of railway engines. I am going to have a guess without seeing springbok chassis that three things are not right his length of eccentric rod,return crank setting or indeed the actual valve itself. I will leave the final word with Mr Ashton on the matter and will be interested in his reply.
jones 1972.
Jones I am looking forward to ideas not critisisim and I do not think that this will be the final word. What you have refurbished for your client was it a kit and please do not speak to me as "he"
that is just a young persons arrogance.
Now could we just get back to this thread and not a commercial break.
Bob

[donashton]

Gentlemen,

Thanks for your kind words, though I do hope that this is not the final word - a) I wasn't thinking of going just yet and b) everybody should be free to chip in. Come to think, if Chris can produce that wonderful sewing machine of his without my aid I might as well shut up. I do remember stepping aboard the footplate for a ride on Mayflower just as Chris stepped off. Guess what? The full size rides like a well-oiled sewing machine as well.

Regarding Chris's valve overtravel, well I know precisely why! Martin copied his formulae off Henry Greenly, who was also wrong! Without a diatribe, see my website, where there is a dimensioned combination lever to show the vastly different travel of slide and piston valves from the same expansion link input.

At last I know that my EIM article on valve setting should appear in the March issue and there may be some revelations for people, but it cannot put right what the valve gear design cocks up.

Mr Jones takes good pictures, as well as fine work - thanks.

Springbok - your problem will not go away with fiddling or guesswork - read my article carefully and set valves properly. If the design and build is ok the correct setting procedure should assure the best running. I hope you don't mind me pointing out that a 'train' is what your locomotive pulls, and is never used to describe the engine.

Best wishes all,

Don

[springbok]

Hi Don
Will look forward to the article just call me a grumpy old man of to Barbados soon then the Amazon on a boat or should I say ship. but will be back march for your article.
I am presuming from your comments that this is yet another ME bobo as I stuck closely to the drawings. Ah well Egor. We could do with a revelation. Maybe, that I have the same problem that Chris had as it doese clunk when trying to run in reverse. Think I will wait for your article and get on with some other part whilst I am still in this country.
regards
Bob.

[donashton]

Hi Springbok,

Enjoy your trip. If you can't make sense I'm always ready to help. Some people have also had a physical clash in full forward gear - tailpin/lifting arm area on full back swing.

John, have you seen this problem?

Don

[jones1972]

To reply to springbok , firstly i will e mail you my papers regarding toolmaking trained in jig and fixtures for aerospace plus plastic injection moulding and progression press tooling . secondly the b1 is not a kit of parts its been done from a set of castings and thirdly Ivan Law chief judge on seeing my King at thornbury last year invited me to enter it into competition section at sandown!
I think my time is done here gentlemen it seems you cannot be a young toolmaker or indeed be able to build engines !
To quote a well known man in this hobby no longer with us NUFF SAID!!

[Deleted]

Jan 9, 2012 18:01:41 GMT jones1972 said:

I think my time is done here gentlemen it seems you cannot be a young toolmaker or indeed be able to build engines !

Please think again young man: this forum needs all the youthful input it can get.......
JB

[springbok]

Hi Jones
No offence was intended just saying my bit just be like Curly and fight on.
We may meet up at Thornbury and shake hands

Bob

[kenn]

Hi All I am modelling the B1 in 3d cad and I am looking for a cross section profile of the wheel spokes.

[baggo]

Out of interest I dug out the Springbok articles and put the valve gear dimensions into the Wallace simulator. The events are pretty good in forward and reverse, slightly better in reverse.The only thing I needed to tweek was the eccentric rod length to equalise the events. Martin's estimate for the eccentric rod length is a bit short at 6.5" and needs to be 6.6". All other dimensions are as the drawings.

So, if the valve setting is correct and it runs ok in forward gear, it should run ok in reverse as well.

The photo below is taken from the simulator and shows how the events for the front and rear halves of the cylinder compare. The pairs of coloured lines represent the port opening and closing for each half of the cylinder. In an ideal world, they should overlap but these aren't bad. The diagram shows the events over the whole range of cut offs from 0 to 100%.

John

Attachments:

[baggo]

Sorry, that was the diagram for reverse gear. This is the one for forward which is not quite so good.

Attachments: