Miniature Injectors by D A G Brown.

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

Post Reply
David Powell
Posts: 523
Joined: Thu Mar 13, 2003 10:38 pm
Location: Pickering Ontario Canada.

Miniature Injectors by D A G Brown.

Post by David Powell »

I am tempted to have a go at making my own injectors,
I guess I am only what you would call an average machinist, I bought the book, read it a couple of years ago, put it on one side as the processes seemed to need extreme accuracy,
However, I now need some injectors to replace some very old and cranky ones.
It would be an immense help if anyone has followedthe advice and details in the book, or any other injector making instructions, and would offer advice.
I am not cheap, I will buy if necessary, but wonder how hard the challenge to make my own would be.
Regards to all David Powell.
User avatar
gwrdriver
Posts: 3439
Joined: Mon Jan 06, 2003 10:31 am
Location: Nashville Tennessee

Re: Miniature Injectors by D A G Brown.

Post by gwrdriver »

Hello David,
I have not yet attempted an injector but over time I've collected a number of resources for doing so when I am up to the challenge, or my back's up against a wall. Here's my list of respected authors on the subject which you find to be hjelpful. You'll note that LBSC is absent.

1) Making Small Live Steam Injectors D.E. "Laurie" Lawrence
Part 1: Model Engineer 18 April 1975
Part 2: M.E. 02 May 1975
Part 3: M.E. 16 May 1975
Part 4: M.E. 06 June 1975
Part 5: M.E. 20 June 1975
Part 6: M.E. 04 July 1975
Part 7: M.E. 18 July 1975.

2) Laurie's Standard Steam Injectors - D.E. Lawrence
ME April 04, 1986, pp.370-451

3) Miniature Live Steam Injectors Basil Palmer (South Africa) ME Vol.142
Part 1: ME #3536 07 May 1976. pp.437
Part 2: M.E.#3537 21 May 1976 pp.508

4) Injectors D.A.G.Brown (ME Vol.184)
Part 1 ME #4111 pp. 89 14 Jan 2000
Part 2 ME #4113 pp.213 11 Feb 2000
Part 3 ME #4115 pp.309 10 Mar 2000
Part 4 ME #4117 pp.410 07 Apr 2000

5) Making Laurie's Injectors (The easy way) - Geoff King
ME July 18, 1997. pp.78-82

6) How to Make'em - Boiler Fittings (A look at injectors) - Keith Wilson
ME July 21, 1995 pp.111-115

7) Safety Valves & Other Odds and Ends D.E. Laurie Lawrence
Part 1 ME 21 April 1989
Part 2 ME 19 May 1989
Part 3 ME 16 June 1989
GWRdriver
Nashville TN
Steve Goodbody
Posts: 219
Joined: Thu May 25, 2006 7:16 am

Re: Miniature Injectors by D A G Brown.

Post by Steve Goodbody »

David,

I've built three injectors to DAG's Brown's design and largely following the methods in his book. All worked first time and I cannot recommend them highly enough.

I used slightly a different method to Mr. Brown to arrive at the accurate nozzle diameter and depth for the steam and exit cones, using aluminum plug gauges turned to the exact nozzle throat diameter and depth as a go/no-go test. There's nothing wrong with Mr. Brown's methods, but I found my plug-gauge method to be a bit more straightforward to achieve the result. I recently wrote it up to help another builder and can regurgitate it if helpful.

The trickiest part is drilling the tiny nozzle holes so that all nozzles are exactly concentric and aligned. Start by making a tiny dimple using a sharp tool rather than using a center drill (even my smallest center drill - 1/16" - was too big to get an accurate start for the drill). A "pecking" method works best, I did this by moving the entire tailstock back and forth by hand rather than using the tailstock handwheel.

Best regards
Steve
Steve Goodbody
Posts: 219
Joined: Thu May 25, 2006 7:16 am

Re: Miniature Injectors by D A G Brown.

Post by Steve Goodbody »

I should also mention that I consider myself an average machinist too, and use fairly basic tooling and equipment. I don't have a milling machine, and my lathe is pre-1910 and relatively small. Hence if I can do it with my limitations then I think that most folks should be able as well - they will probably make a better job of it too! Planning, patience and persistence is the key, in my view..

That said, it would be difficult to make these injectors without collets of the right size - you really do need to ensure that the cones are running dead true at each stage, including when they're reversed, and that would be tricky (but not impossible) to achieve without collets.

Best regards
Steve
User avatar
baggo
Posts: 161
Joined: Mon Jan 12, 2009 6:25 am
Location: Derby, UK

Re: Miniature Injectors by D A G Brown.

Post by baggo »

When I was building my Helen Long I had a go at making some small injectors for it. The smallest we can buy are 11 or 12oz and even those are a bit too big for most 2½" Gauge locos so I had a go at making some 8oz and even a 4oz (just to see if I could).

I pretty much followed Derek Brown's 'Words and Music' and documented my trials and tribulations here:

http://www.modeng.johnbaguley.info/inje ... ctors1.htm

Unfortunately, I wasn't as lucky as Steve and had to do quite a bit of work to get them to work but I got there in the end. No one was more surprised than me when the 4oz one worked!

These very small injectors are very fiddly and temperamental in use and I eventually replaced them with two commercial 11oz injectors. I would imagine that the larger sizes are a lot less critical on dimensions and water quality.

I would say that the most critcal aspect of making them is probably making the cone reamers. You need a very good finish on them or else any imperfections are transferred to the surfaces of the cones. I just turned mine in the lathe but next time I would grind them on a tool and cutter grinder.

I would also recommend the articles mentioned by Harry and I read them all. There are also two other books that I found useful -

The Model Injector by Ted Crawford (I think it's an Australian publication?)

All You Need To Know About Miniature Injectors And Ejectors by Bob Branson - Available from Taunton Model Engineers in the UK.

Bob's injectors use end regulation for the steam cone to combining cone gap which is a lot easier to achieve than the usual method of having the end of the steam cone narrowed down so that it goes inside the entrance to the combining cone. That makes the steam cones very fragile and easy to damage and getting the gap right is not easy.

John
Secretary of The National 2½" Gauge Association
Member of North West Liecestershire SME

http://www.modeng.johnbaguley.info
Steve Goodbody
Posts: 219
Joined: Thu May 25, 2006 7:16 am

Re: Miniature Injectors by D A G Brown.

Post by Steve Goodbody »

John -
All my injectors were to the 26 oz/minute design. I applaud you for getting a 4oz injector to work under any circumstances!

David -
FYI, one of my injectors is on a 3" Allchin TE and the other two are on a 3" scale Hunslet with a similar-sized boiler to the Allchin and hence giving a redundant feed. That may help you get an idea of your target capacity.

As an aside, while I followed the critical DAG Brown cone and body dimensions exactly, I went with my own body design rather than copying the DAG Brown design. There were four reasons for this:

1. I must admit that I'm not a fan of the aesthetics of the overflow cover in the DAG Brown design.

2. For 3" scale, the bodies needed to be beefier to be in aesthetic proportion to the engines.

3. For the Hunslet, I wanted side-entry water inlets that could be screwed directly into the water valves from the saddle tank

4. It avoided the need for a fabrication assembly jig.


Some pictures below of the injectors on the loco.
P1013171.jpg
P1013084.jpg

Best regards
Steve
User avatar
baggo
Posts: 161
Joined: Mon Jan 12, 2009 6:25 am
Location: Derby, UK

Re: Miniature Injectors by D A G Brown.

Post by baggo »

Thanks Steve but I think the fact it worked was more luck than skill!

I agree that the bodies are a pain to make, especially the overflow cover. I've thought about getting some lost wax castings made if I make anymore!

Image

John
Secretary of The National 2½" Gauge Association
Member of North West Liecestershire SME

http://www.modeng.johnbaguley.info
Post Reply