Boxhill Boiler Construction

[Robert Thompson 3Participant @robertthompson3]

position of stays

[Robert Thompson 3Participant @robertthompson3]

Hi all,

I have been pawing over my Boxhill drawings in particular the boiler drawing and realise that this is obviously different to the little boilers ive been making so far. I am struggling to identify where all of the stays start and finish, The 23 per side I assume bridge between the inner and outer sections of the fire box, but im not sure about the longtitudal stays( 7 or 8), the crown plate stays, and the tube plate stays.

Can someone point me in the right direction please??

thanks in anticipation

Bob T

[julian atkinsParticipant @julianatkins58923]

hi bob,

the BOXHILL boiler is unorthodox. there are no longitudinal stays or crown stay girders that connect with the outer wrapper or crown rod stays. the longitudinal stays are replaced with 'palm' stays – the strip of material on the backhead and smokebox tubeplate to strengthen it. (incidentally the new boiler for DOLGOCH built recently by the SVR for the TR has these type of stays). the lack of proper girder stays between crown of the inner firebox and the outer firebox wrapper was a new departure by martin evans in 1963 using instead a curved inner firebox wrapper crown with girder stays that only fit to the inner wrapper. he reckoned that this design avoided the need for proper girder stays and the 'difficulty' of fitting them to the inner and outer wrapper.

i have never had a problem silver soldering proper girder stays to the inner and outer wrapper, so i dont know why martin evans did this. bearing in mind that the BOXHILL boiler has quite a high working pressure because of the small cylinders, and the inner wrapper is shown to be only 1/16" thick, i think his boiler design can be improved upon. (i dont like the BOXHILL boiler design AT ALL!)

see my post of 21/02/2012

http://www.model-engineer.co.uk/forums/postings.asp?th=56115

it is quite a small boiler so poses no problems being a small round topped boiler.

however as you will note from the above link, i have made my TERRIER boiler to be what i think is both an improvement on martin evans' design, and far more like the prototype boiler.

there is no reason whatsoever why you shouldnt fit proper girder stays and longitudinal stays to martin evans' boiler as designed.

cheers,

julian

[Robert Thompson 3Participant @robertthompson3]

Thanks Julian, that removes some of the haze but one of my biggest problems was the stays that are shown on Martins drawing? namely 23 on each side, 8 shown on the firebox tubeplate and seven on the backhead and where these connect at the other ends? sorry if that sounds a bit of a thick question but most of out little gas fired boilers ive been used to have no stays and even the coal fired 16mm boilers may have at most 2.

Cheers

Bob T

[julian atkinsParticipant @julianatkins58923]

hi bob,

you are quite correct about the boiler drawing, and it is a pity that martin evans' drawings show no detail of the firebox stays which can lead to confusion, though if you can obtain copies of the MEs for the contruction series all may become clearer (martin is a bit vague about staying BOXHILL and the methods to be employed). 2 methods of staying are described in the construction series, and there are various methods of making and fitting stays. they connect between the inner and outer plates and on the drawings are shown as 4BA but no detail provided as to material or how to fix them on the drawings. my stays are 1/8" snaphead copper rivets with the snaphead on the inside of the firebox, silver soldered in place with a slightly smaller stay spacing than martin evans at 5/8" pitch on mine, so more stays. i added a few 5BA threaded stays near the backhead on the sides of the wrapper and foundation ring, these stays being made out of 1/8" hard drawn phosphur bronze rod which is easily obtainable. the threaded stays stop the risk of anything shifting when silversoldering it all up! i left my inner firebox doorplate off when silver soldering up the inner firebox. this can be a bit complicated when fitting the inner firehole door and backhead to everything else, and i made up some 3/16" x 40 tpi special stays to go in the inner firebox doorplate when silver soldering the firehole ring to it. the special stays then had a plain 5/32" dia portion to fit in holes very carefully positioned and drilled in the backhead. all fun and games!

the alternative is to use copper or phosphor bronze threaded rod and fit nuts on the inside of the firebox and 'caulk' the stays with a high melting point soft solder such as 'comsol'. with this method the boiler plates are drilled, threaded, and stayed after all silver soldering has been carried out and the boiler is otherwise complete. martin evans sometimes specified gunmetal rod for stays but 3/16 x 40 tpi threaded phosphor bronze rod is IMHO much better and easier to obtain and make. the threaded stays have a plain unthreaded length on the outside of the wrapper.

there are quite a few good books on the subject (one by martin evans and the other by alec farmer) but if you can obtain the MEs for 1968 Don Young provides what i think is one of the best descriptions of boilermaking for beginners in his RAILMOTOR construction series. far better than martin evan's description for BOXHILL IMHO!

the other point about BOXHILL's boiler is the side extension pieces on the outer firebox wrapper. if you think about it there is no need for one each side if you cut and bend the wrapper accordingly…only one side needs an extension piece which simplifies things, and make it the right hand side of the boiler coz the reverser is on the left hand side. this also avoids the extension piece getting in the way of the foundation ring if you are otherwise making the boiler to martin evans' drawings. the extension piece should IMHO be done with quite a high melting point silver solder such as silverflo 24 and you need the appropriate flux for it too. the rest of the boiler can be done with silverflo 55.

i flanged all my own plates, and Don Young had a better method for the dome bush recommended by alec farmer using only a small register compared to the dome bush outer diameter.

hope this is some help!

cheers,

julian

 

Edited By julian atkins on 03/03/2012 11:54:30

[Robert Thompson 3Participant @robertthompson3]

Hi Julian, and thanks for taking the trouble to expand so thoroughly on the subject . By coincidence Ihave just received the construction notes very kindly copied and sent to me by Dennis Rayner so now I should have a much better idea on what is needed. No doubt i will be on again in the future but once again many thanks, this really is uncharted territory for me.

Regards

BobT

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