LBSC's Doris versus the Code

[runner42]

Hi Julian,

thanks for the very sound advice. Unfortunately the barrel is away awaiting to be rolled, it is one feature that I think requires rollers to do a satisfactory job so I am comfortable at allowing some assistance in this area. However, the copper sheet for the barrel was cut out and the ends profiled so that when it is rolled the two ends will be perpendicular to the bottom edge. Basically this requires curves to be established at both ends, instead of straight edges, which I am sure you already know. This was facilitated using an Excel spreadsheet provided by a very experienced model locomotive builder at SASMEE. If anyone building a tapered barrel boiler who would like this Excel spreadsheet then I would ask if I am able to pass it on.

The smokebox tubeplate OD is 0.015" oversize and I think a small amount of machining of the flange is allowed by the boiler inspector, so this may help in mating the smokebox tubeplate to the barrel.

Brian

[Kevin]

Brian
Hows the boiler coming on

[runner42]

Hi Kevin,

I hadn't realised that this thread included your last post until today. Well I have rolled the barrel, made the flange-plates and formed the firebox and outer wrappers. I purchased the tubes and flues from EJW because he provides the thickness gauge required by the code, also rivets and foundation ring material. I thought I could get away with 22swg but no. I'm still waiting for delivery of the item from EJW. So I have done most of the metal bashing and awaiting delivery so I can rivet the barrel and start the silver soldering the boiler.

I haven't taken pictures of all the flange plates but here is a few pictures of the barrel with its transition piece into the smokebox. This is required because I reversed the smokebox tubeplate.

Brian


 

PS I have had the flange plates inspected by the boiler inspector and they are OK.

[runner42]

Got to rework the firebox ring flange plate

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[Shawki Shlemon]

Very nice job , clean and well shaped , good luck .

[jma1009]

hi brian,
what are those backhead bushes made of?
cheers,
julian

[runner42]

Hi Shawki,
 
thanks for the encouraging words. Annealing the outer wrapper was a struggle with my 8kW propane torch, I need something much bigger before I start silver soldering. BOC advertise an 80mm (85kW) but don't appear to provide the other bits that are required to make a complete burner. The M20 x 1mm FM connection doesn't fit my tradeflame propane torch.

Hi Julian,

they are made of LG2 Gunmetal.

Brian

[jma1009]

hi brian,
i only use hard drawn phos bronze for boiler bushes. ive never liked the idea of gunmetal bushes in any application in boiler work if to be silver soldered to the boiler. low melting point plus porosity and lots of gunmetal has zinc in it, and the threads are nothing like as strong as phos bronze. much harder to make out of hard drawn phos bronze compared to gunmetal, but well worth the extra effort!
cheers,
julian

[suctionhose]

Oct 21, 2014 23:33:34 GMT jma1009 said:

hi brian,
i only use hard drawn phos bronze for boiler bushes. ive never liked the idea of gunmetal bushes in any application in boiler work if to be silver soldered to the boiler. low melting point plus porosity and lots of gunmetal has zinc in it, and the threads are nothing like as strong as phos bronze. much harder to make out of hard drawn phos bronze compared to gunmetal, but well worth the extra effort!
cheers,
julian

Availability is the problem here Julian. We're pretty much settled on Gunmetal. No problems with it really. Some people use copper bushes. I'd treat those threads very carefully!

[runner42]

In keeping with Doris' changes to comply with the code, I noted that the somewhat inaccessible wash out plug in the throatplate if placed central as I have depicted in the drawing will interfere with the axle driven pump. This time I was clever and did a trial assembly of the boiler and found the potential problem before drilling the throatplate. So the wash out plug will be set off to one side, still inaccessible but not affecting anything else.

Another potential problem is the lack of separation distance between the lower tubes and the inside butt strap. I have used 1/8" copper rivets which have a half round head, inside the barrel of course, that further adds to the intrusion of the butt strap into the space occupied by the lower tubes. LBSC unfortunately doesn't show the butt strap in the boiler drawing and the closeness of the lower tubes to the bottom of the barrel indicate that this is a general problem for all Doris boiler makers. Although the code doesn't specifically address the separation distance of tubes from the barrel, implicit in the code is a requirement for a minimum ligament distance between tubes of 3mm -0.5mm. This requirement could also mean the distance from the tubes to the barrel. The rationale for a minimum ligament distance is that hot spots can occur due to vapour pockets and scale deposition if too close. I don't know what the resolution is likely to be unless and until I progress the build further.

Does the UK boiler regulations address tube to barrel separation distance?

Brian

[ejparrott]

Nope

[uuu]

Does the butt strap have to be at the bottom? How about at two o'clock?

Edit: I see you have the dome hole in the top already. So not a good idea to swivel the barrel - the dome would look silly sticking out of the side.

Wilf

[runner42]

Thanks Ed for the short but unequivocal reply.

Hi Wilf, yes your right the butt strap must stay at 6 o'clock because of the dome hole being already made, also I have made a cut-out at the end of the barrel where the throatplate is fixed (see the crude sketch at the beginning).
 
I may be being overcautious and probably incorrect in my connecting the ligament issue to the tube to barrel separation problem. On reflection the hot spots usually occur only at the firebox tubeplate as you would expect and not within the barrel. The question I should have asked is what is the distance of the tubes to barrel that one should aim for to prevent problems such as stresses on the tubes due to relative movement of these occuring when contacting the barrel?
 
Brian

PS yes I know that I should speak to my boiler inspector.

[jma1009]

hi brian,
i dont like any restriction between bottom of the barrel and bottom of the throatplate as water circulation is very important at this point, hence my preference for double flanged throatplates rather than an internal strengthening ring. havent seen a pic of your throatplate yet and would be very interested in same.
cheers,
julian

[ejparrott]

The UK code is shockingly bad. There is no mention in it anywhere of most of the critical things, like tube spacing. That's why I bought a copy of the Oz code and I've been trying to push the UK to do the same thing.

[runner42]

Hi Julian,

here's the throatplate and it shows the principle of overcoming the need for a full size double flanged throatplate. Here the barrel goes into the outer wrapper by 9mm and the half size throatplate is double flanged to connect to the barrel and outer wrapper. The second picture shows the 9mm thick shaped copper pieces that complete the sealing of the wrapper to barrel. You see that I have already used screws to test the assembly which will have to substituted for rivets. Had I realised the pain of silver soldering over rivets both sides I would have had second thoughts.

Brian

[jma1009]

hi brian,
that looks excellent and note you've already silver soldered the barrel together - so worst job done! you may find a bit of a 'joggle' necessary on the firebox outer wrapper where it meets the 'ears' (as don young used to call them) of the top of the thoatplate flange. just a few judicious taps with a hammer!
i would silver solder the throatplate to the barrel next, or if you are keen do the outer wrapper and top corner segments at the same time
cheers,
julian

[runner42]

Hi Julian,

before I start silver soldering, I want to make sure that there are no surprises along the way so I attempted a dry assembly as far as possible before making things permanent. I had diffulculty in determining the length of the inner wrapper and the angle of the firebox hole ring flanged plate because of the change to LBSC's design, ie a foundation ring between the throat plate and firebox tube plate. The code requires that there is a minimum of 6mm all around. So I elected to have 5/16" at the front, the same as at the rear. So that I would have the inner wrapper too long I used the LBSC dimension and at dry assembly marked the position of the flange plate on the wrapper. This needs to be trimmed since it is as expected about a 1/4" too long

Brian

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[ejparrott]

I always make my wrappers and flanged plates longer, I find it much easier to trim them and get them right at this stage

[runner42]

Hi Ed,

thinking ahead a little it is particularly important on the inner wrapper that the wrapper sides just meet the curve in the flanged plate and not go beyond it because it would make the foundation ring at the front and rear very diffulcult to form. As it is it needs to be shaped at these positions to follow the curves of in the case of the front, the throatplate and the firebox tube plate and at the rear, the firebox hole flange plate and the backhead. A careful bit of filing is required. 

Brian.

P.S. I know you already know this, I am just thinking aloud.