Building Don Young's Doncaster

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Pic260

Before fitting I did a test to check all was ok, here you can see the water flowing through the holes once the cock had been opened which is a simple 90 degree operation.

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Pic261

The water gauge fitted, other parts here are the bracket and the tube swan neck soldered to the top of the tube. The gauge is shown in it's closed position, to open the tube is turned 90 degrees to the front so that the holes face forward.

I have to admit to enjoying making this little thing, it was fun but more importantly was good practise for those small cones I'll be making when I tackle those important injector cones for the loco at some point in the future.

Not sure what I'll do next but rest assured I'll be back soon..

Pete

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[Shawki Shlemon]

Fantastic , Pete I envy your patience , keep up the good work .

[Deleted]

Thanks Shawki although I have to say my patience gets severly tested at times..

Small update for today, vacuum brake reservoir tank and it's protection shield.

Pic262

The picture shows the components made ready for making the tank, I've deviated from the drawings again to make use of the materials that I have. The 1 1/2" copper tube is to drawing, the end caps are supposed to be 3mm copper sheet of which I have none but I do have some brass billet left over from the filler neck so I made use of it. Rather than just turning up two plain 3mm discs I decided to include a 2mm step to be a tight fit inside the tube ends, one of which was centre drilled and tapped 3/16x40T for the brake line. I small bush was also made , drilled and tapped 3/16x40T for the drain plug, which fits into the hole in the tube centre.

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Pic263

The finished tank after silver soldering together, now Dons words and music contradict themselves when it comes to pressure testing the vessel. The words say test to 100 psi, the drawing says test to 150psi so a little confusing although both seem a little high to my inexperience in such things. Mind you I have no way of testing either so testing will have to wait for now. I did however plug one hole and forced compressed air into the other with the only escaping air coming from the poor seal where the air nozzle was forced into the hole.

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Pic264

Last picture for tonight, the tank shield that protects it from the coupling. This was a simple item, 1/16 brass sheet, 2 1/2 long and 1 7/16 high with a 90 degree bend at the top. This has 5 No.44 holes drilled which are then transferred to the bottom of the drag box and drilled and tapped 8BA. Final thing was the 3/16 hole as seem for the rear vacuum pipe to be fitted later.

Tomorrow I hope to make the two bands and wooden packing for fitting the tank to the drag box.


Pete

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[pault]

Hi Pete
Testing to both 100 and 150 psi seem a bit extreme for a vacuum tank. The reality is that you will probably be using it at a vacuum equivalent to 7 to 12 psi. Not only that but the loads under vacuum will be the other way so to speak. Personally I use a small electric vacuum pump attached by a bit of silicon tube with a vacuum gauge on the tank. Pull the highest vacuum you can and put a bulldog clip on the silicon tube and turn the pump off. If there has been drop in vacuum over night then it is PDG
Regards
Paul

[pault]

I should have said no drop in vacuum overnight

[Deleted]

Hi Paul

Thanks for the info, it confirms what my head was telling me. I have no vacuum pump so all I could do was test it the other way so to speak with compressed air just to see if there were any obvious leaks. I guess I need to start looking at some new workshop testing gear for this build as I'm sure they'll be more things like this down the line.

Many thanks

Pete

[stubee]

Hi Pete,

Just like to congratulate you on your thread - really informative and a real inspiration to us other builders. If I can get my work looking half as good as yours I'll be extremely pleased .. you should be proud

Keep up the good work my man ;D

Stu

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Hi Stu

Thanks for the kind words, I get just as much inspiration from reading others building threads, perhaps more. There are many ways of doing a job and by stating how we each tackle a particular problem we all learn, I've certainly learnt a lot by reading other build threads and state in my build when I've used others ideas. I look forward to following your 7 1/4 build and take my hat off to you forming your own frames, there's a lot of work involved in those which I'm sure you'll make a great job off, happy building....


Ok guys here's the tank fitted as promised

Pic265

Don listed 1.2mm thick 1/4 bands for this but I've used something a lot thinner, easier to form and nicer looking to me. Because I've used such thin section the bent tab that's attached under the rear of the drag box I fabricated rather than just bending the band at 90 degrees, so here I've used 1.2mm brass that's been soldered to the end of each band and had a No.43 hole drilled in the middle. Two 1.8mm holes have been drilled at 2 11/16 centres and then tapped 8BA for securing the bands. 4 pieces of 1/8 thick oak planks ( left overs from the tender planking) are used as packing between the tank and drag box. Later these will be glued to the bottom of the drag box but that will have to wait until the chassis has been painted , so are loose for now.
With the tank in situ the bands were pulled tight over and then marked for a slot to be drilled/filed , at the same time the drag box is marked, drilled and tapped 8 BA on it's front face to hold the bands via the slots.

This picture was taken from underneath to try and show what was involved rather than taking pictures of each stage for what is a straight forward job.

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Pic266

And a picture the right way up. Something that comes up here is whether I'll be able to get a fitting in between the tank and it's protector, there is some room but not much so I'll have to tackle that when I get to it.
It's important as I do plan on having a working vacuum conection here. If I do get around to making a full Flying Scotsman train ( which is the plan) I think I'll need working vacuum brakes throughout if hauling 12 coaches, " to much fun" as Jack would say...


Talking of which I think I'll tackle the tenders vacuum cylinders and valves next, another steep learning curve ahead I suspect.. So watch this space guys and any advice for this next stage is very welcome.

Pete

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[pault]

Hi Pete.
A few suggestions for working on the vacuum plumbing/ cylinders. It’s important to remember that vacuum systems often have very little reserves in terms of stored power. So try to minimise the amount of slack that needs to be taken up before the brakes apply. Because of the small reserves any movement of the pistons/diaphragms reduces the amount of brake force available. Any leaks in the system can kill the performance of the brakes. The problem is that vacuum leaks are not easy to detect. I test each component in a similar way to that described earlier or using the vacuum pump and a very low flow, flow meter. To use the flow meter idea you connect the pump to the component under test via the flow meter. If the thing under test is say a pipe fitting you will need to blank off any other openings. When the pump is run initially you will see flow as the air is evacuated. Fairly quickly the flow will drop to zero, unless there is a leak.
One effective way of curing small leaks on say silver soldered joints is to paint them whilst the system is under a vacuum. The paint is drawn into the leak and dries much quicker than it normally would due to the solvents in the paint evaporating quicker due to the vacuum.
Car tyre valves make very good valves for a vacuum system, I normally use the ones which have the springs exposed, you often have to stretch the springs slightly to stop leakage.
I use silicon tube for any flexible connections, it does not need any form of clip, it’s soft enough to grip onto pipes, and it’s very flexible and does not go hard with age. The only problem can be it collapsing in some circumstances, however putting a stretched out spring inside the silicon tube soon stops this.
Are you going to use diaphragms of pistons and seals in your cylinders?
I hope this is not teaching you to suck eggs and is of some help.
Regards
Paul

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Hi Paul

Don't worry about " teaching how to suck eggs" even if I already knew the info it never harms to be reminded or have an understanding confirmed by another, as the saying goes " two heads are better than one".

As far as the cylinders are concerned I'll be following Dons advice and use diaphragms, I'll also make the valves to his design in fact I've spent most of today machining the cylinder castings. I'm aware of the advantages of silicon tube ( my other love is modifying cars and all of the hoses on my highly modified turbo are silicon which handles the -1 bar atmosphere and +2 bar of boost with no problems... ) so yes I will use silicon with confidence for any flexi connections.

Are there pros and cons between diaphragm and pistons? I'd have thought pistons would be more involved to build with not such a good seal as a diaphragm and more likely to wear, or am I missing something?
Another question , the commercial vacuum hoses on the Market by people like Bruce Engineering, are they just for show or do
they work? Could save myself some time if the latter.

Many thanks for the interest and help

Kind regards

Pete

[pault]

Hi Pete
Yes there are pros and cons with both systems. Diaphragm cylinders seal better and have less resistance to movement, but are limited on stroke and don’t tend to be as efficient on a reservoir style system due to the diaphragm stretching and bulging. It might be worth looking at the PNP diaphragms as they have a moulded diaphragm which concertinas to give more stroke. Are you fitting 1 or 2 cylinders if its 2 then the PNP ones would probably be too big. On a cylinder stroke is only limited by how long the cylinder is and they are more efficient on a reservoir style system. On the down side they are more difficult to seal and you have to overcome the friction of the seal.
Yes the vacuum hoses you can buy do work and look good. The only downside to me is they are a little fiddly and delicate so you would not want to be coupling and uncoupling lots of times in a day.
Regards
Paul

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Hi Paul

You've confirmed how I saw the differences between the two although I wasn't aware of the piston being more efficient but it makes sense with more throw according to length of stroke with longer cylinder. According to Don the brake setup is as close as possible to the prototype, their are two cylinders on the tender and two on the loco, I'm building all 4 at the same time. I won't know how efficient they are until I've finished all of the components and piping. However the design looks sound and I am beginning to trust in Dons work, actually it's more than trust I'm very impressed with his attention to detail. I certainly landed on my feet when choosing his drawings although I have a habit of doing that, no secret to it, if it looks right it usually is and that's how I choose things.
I'm happy to hear that the vacuum hoses available are working items, I don't mind fiddly things if they look right and work well, thanks again for the info Paul..

Pete

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Good day all

Vacuum cylinders

I wasn't going to do this update until I had finished the cylinders but I have technical question so I'll update as far as I've got and then ask the question.

Pic267

Dons Doncaster has 4 cylinders , 2 each for the loco and tender. The picture shows the 8 castings which are identical but the tops and bottoms are of course machined differently, although many lathe set ups are shared.

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Pic268

Using the exterior jaws in the 3 jaw all 8 cylinders are held by their periphery's and the spigot is faced and turned to 3/8"

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Pic269

Then faced and turned down to just above 1 5/8 dia.

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Pic270

Now Don makes no mention of cleaning up the inner chamber but I did it anyway, using a suitable length of tool steel I profiled it to the inner radius and cleaned up the chamber as shown here.

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