Britannia 70047 "Derek Stokes"

[JonL]

Excellent, thank you John.

[JonL]

My castings, petticoat pipe and chimney.


Lots of fun trying to find a way of giving myself a reference machined portion the rest could be measured and centred from. Using my rotating centre to hold the casting against my chuck seemed to do it, after a fair bit of clocking first to make it run as true as possible.



Using the boring bar for the inside of the petticoat pipe. My limited experience from tuning internal combustion engines suggests this should ideally be fairly smooth (I'm not going into the depths of laminar flow etc!).



A nice smooth finish for some reason looks dreadful as soon as I use the camera. I knew I should have stuck with the blurry phone.



Machined out the centre of the chimney to fit the petticoat pipe. I think made a mandrel and pushed the chimney onto it.


A little hard to see but the mandrel is in there, I promise. Now I can take the cuts to make this look like the real thing.



But thats a job for another day, I don't want to risk getting tired and making a clumsy error. 

Thanks to everyone who has given advice on the other thread.

[barlowworks]

Hi Nobby

Here is a nice shot of the chimney in profile. Its cropped, I think from Britannia, masquerading as The Territorial Army. I hope its useful.

Mike

chimney crop by Michael Cawthorne, on Flickr

[mbrown]

ES Cox records that he chose a chimney profile for the BR Standards which followed the old Lancashire & Yorkshire profile (Cox trained at Horwich).

So a good drawing of a L&Y prototype (maybe Don Young's Lanky or Crab, or from a book) would give you the correct contours for a Brit.

Malcolm

[Cro]

Nice work so far Nobby, You have a fairly well shaped casting to start with which is good. The one thing you see quite often is quite a thick rim/flange so if you can try get it closer to a scale thickness all the way around as it changes the look drastically!

Keep up the great work.

Adam

[timb]

Looks like you are doing a good job of an awkward casting there Nobby! I generally have a break for a think when things get tricky. Your decision to leave it for another day after a good deal of success is sound by my way of thinking!!

Keep it up!

Tim

[JonL]

Great shot, thank you. I'll have a crack at the narrow rim, here's hoping....

The casting does seem quite nice quality, I was worried about how thin I was making the petticoat pipe but it seems ok.

Thanks for all the compliments.

[JonL]

I had a crack at the thin lip but wasn't very brave!











I am quite proud of that, with my modest skill set I feel like I've achieved something. Thanks to everyone who gave me tips and reference photos. I ended up profiling it to fit the smokebox by wrapping the smokebox in coarse emery cloth and rubbing it until it took the correct profile. Some minor finishing still to go but otherwise a great success.

Thanks to all who assisted. 

[JonL]

A better look at the profile of the lip. Close but no cigar...

[mbrown]

Nicely done. If you can bear it, it would look even better with a tighter radius to the bottom flange, maybe done with a small round file? Another tip that came from Don Young years ago - look at the diameter of the top rim and the "trunk" of the chimney - they are usually about the same diameter but models often have the top too large in diameter. Don did this with his IoW O2 and was chided by LBSC who told him to compare his chimney with a picture of a real Drummond chimney - Don spotted his error immediately (although I don't think he ever changed it!)

Keep up the good work (and the posts)

Malcolm

[JonL]

Thank you. I think I'd happily do hand finishing to it, but I don't think I'd like to risk re-mounting it! I looked at the photo posted above and it appears to have a narrower trunk than rim, that could be an optical illusion though.

Thanks for the support.

[barlowworks]

Looking good Nobby, I agree that the bottom radius could do with a bit of fine tuning but the important thing is it doesn't shout out "this doesn't look right". If it did it would nag at you every time you saw it. Only the fixing bolts to do now.    

Mike

[JonL]

Apr 24, 2019 22:26:41 GMT barlowworks said:

Only the fixing bolts to do now.    

I had an idea about that, using a threaded ring to clamp the smokebox onto the petticoat pipe, but I don't see how I can make it work. I think I will have to do it conventionally.

[timb]

As Mike says it certainly does not look out of place. I would get the mounting sorted out then re-visit it later if you feel the need to adjust. You are moving the build along well and it appears your confidence is building with it. Keep it up!!

Tim

[JonL]

Thank you Tim

[David]

Great work Nobby, on a tricky part to make.

[don9f]

+1

Cheers Don

[JonL]

...and suddenly I feel like a complete and utter beginner again...

I'm making the Y-piece that becomes the blast pipe in the smokebox. My intention was to make a bending machine to bend the pipe to the radius I wanted, then slit and solder the pipes like so:




I made a die to the internal radius, and fitted some ball races to an arm that rotated around the centre point to the external radius. This means the ball bearing rollers would bend the pipe to the exact size and shape I wanted. To prevent deformation (or reduce it at least) I firmly packed the copper tube with sand after annealing. All for naught. The pipe collapsed to a horrible shape, flattened the tube. I made adjustments to my new tool for about half an hour before it went in the scrap bin. Back to the laborious process of annealing, gently hand bending, annealing, and repeat until the bend was the right size and shape. Downside is, although the radius and shape was there, there was also the odd shallow kink too. I think my problem was that I chose to go for slightly oversized pipe thinking it would make my life easier. This turned out to not be the case. The only advantage being the larger diameter should mean I haven't impeded the gas flow compared to the smaller diameter LBSC spec pipes.

Anyway, I cut out the tubes to the above pattern using a slitting saw. That went beautifully, as did cleaning them up prior to soldering. I then did my first bit of proper soldering using my new hearth and good quality flux. What a revelation, it worked a treat! Filleted nicely where I wanted it to, the only issue I had was I put too much on, so its not as pretty as it should be. A quick test showed a watertight seal. I then soldered on the brass flanges that fit to the cylinders. With a little minor fettling it went in a treat. LBSC calls for threading the pipe to fit the blower to it directly; I plan to solder an internal boss on (the other advantage to being slightly oversized pipe) and attach the blower to that. I don't trust threads on copper pipe. 



You can see one of my dimples on the inside of the right hand pipe. That was my third attempt at bending those. Although it doesn't matter in the grand scheme of things I'm annoyed I couldn't seem to do better; what you can see there was my best attempt. I'm going to get some more practise in, maybe revise my pipe bending design, and just be thankful no-one will be able to see this part once constructed.

[weary]

When using a bending machine it may be worth trying as an experiment bending your pipe without annealing, that is to say with copper tube/pipe in 'half-hard' state, especially if using thin-wall pipe. Hopefully your bending-machine is rigid enough and strong enough to take it. I do a lot of pipe-bending, albeit 12" to the foot scale, using bending machines, and annealed (copper) pipe in a machine is guaranteed collapse. A single relatively slow smooth and continual pull in the bender gives best effect.

Hand-bending copper will require annealed tube.

But, what you have done works....so, another good job done!

Regards,
Phil

[JonL]

Thanks Phil, as you say it has worked, I'm just glad it's hidden.

It's a good point about not annealing, I didn't even think about it.