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Boiler bushes

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john brown 1725/10/2019 19:36:10
114 forum posts
3 photos

My drawings on my model engines copper boiler ,tell me me to use copper for the bushes,l know copper can be a pig to cut an thread but people say using copper to copper is better to silver solder than say copper to brass or bronze ?


Robert Thompson 825/10/2019 19:52:01
48 forum posts

Hello John

The preferred material for boiler bushes is phospher bronze. Certainly not brass because of the de-zincification with time



Paul Lousick25/10/2019 22:57:16
1418 forum posts
542 photos

As Bob has said, Brass should not be used for bushes and components in contact with the boiler water.

Brasses are a family of metal alloys whose main components are the elements copper and zinc. ... Dezincification is the selective leaching and removal of zinc from the brass, and into the water supply. This corrosion process decreases the strength of the brass and increases porosity in the now copper-rich material


john brown 1726/10/2019 05:52:03
114 forum posts
3 photos

Thanks never new that about brass,very helpful,will have a look in the bits box an se if l have some bronze ,l know l have copper,then it comes to cutting the threads in the bushes 5/16" and 1/8" NTP ,am l right in thinking that cutting this type of thread ,you go in until you have 6 threads left on the tap left,having never cut a ntp before l do not know,again many thanks for the help.


Robert Thompson 826/10/2019 06:05:55
48 forum posts

Good morning John

I would normally run a 2nd cut tap right through as the depth of thread on the boiler bush is fairly short anyway.

the important thing is the thread is not slack but you should be able to screw the fitting in by hand and just tighten home with the spanner.

If you are making the fittings yourself then obviously you have more control over the fit, if you are purchasing the fittings then you are to an extent governed by the quality of the the threads on the fitting.


john brown 1726/10/2019 06:50:15
114 forum posts
3 photos

And a very good morning to you bob ,good point about fittings,a couple of the fittings l think l will buy ,but the the one fitting l can not find yet for sale is the safety valve that needs to blow off at 30 psi and has a 5/16" ntp thread or will l have to try an make one?,just do not know yet,ohhhhhhh the learning curve ,l will want to fit a steam whistle on the model as well but will get a mammod type for ease an price,but will get the boiler bits made ready for soldering up then go from there.


Robert Thompson 826/10/2019 06:57:55
48 forum posts

Just a thought John, most commercially available safety valves have an ME thread as you have probably discovered, so why not make the boiler bush to suit what is available i.e 5/16x26tpi 32tpi or 40tpi all you need to do then is invest in additional tap to suit and save the time in making your own valve??


Speedy Builder526/10/2019 07:33:02
2011 forum posts
141 photos

I prefer to make the bronze bush and only start the thread off in the lathe, and finish the thread after silver soldering into the boiler - especially backhead bushes. That allows you to get a 'perfect' clean thread .

JasonB26/10/2019 07:39:30
18154 forum posts
1998 photos
1 articles

5/16 x 26 will not be close to 5/16" NPT, you will want closer to 1/2" x 26. but do agree you should use common UK threads not american which also raises the question is you boiler going to be to a safe UK spec.

Also regarding tapping, the best method it to drill the bush and part tap it in teh lathe so you have the thread started square to the bush and then solder. Once all heating is complete then fully tap the bush. The reason is that if you overheat things which is likely on your first boiler you can burn away the crests of the thread which will be weak

Brian G26/10/2019 08:33:04
701 forum posts
27 photos
Posted by john brown 17 on 26/10/2019 06:50:15:

...,l will want to fit a steam whistle on the model as well but will get a mammod type for ease an price,but will get the boiler bits made ready for soldering up then go from there.



I don't know the size of your boiler, but if the boiler is small enough could you use a Mamod size safety valve (or even two of them?) as you are already making bushes in that size? Dream Steam will supply them set to any pressure between 20 and 60 PSI.

Brian G

Edited By Brian G on 26/10/2019 08:33:17

john brown 1726/10/2019 16:35:34
114 forum posts
3 photos

Ok my boiler is 8" long by 1 5/8" od to be made from 18g seamless copper and to blow off at 30psi .Brian G link looks good,now l have got a safety valve that l got ages ago and it looks like it will came apart so may be able to adjust it to what l need ,but the down side its a bit bigger than the mamod type as far as l can se ,so will not fit under the dome,but l could move it away from the dome and fit a pipe from where the valve should go and fit the whistle there,the other thing l do not like with this model there is no site glass for the water level ,but feel l should try an mount one somewhere ,also after what jason has said will take stock of what fittings to use an keep to uk type fittings,the other two bushes on the boiler in the cab end are for gauge and and testing then to fill the boiler with water,have got a small gauge so will check the thread size and tap bush to that ,the model is rudys steam tractor ,but to be honest l am going to flame licker models after this and mybe ic engines,and yes jason it will be tested way above what the drawings says,before its fired up ,you people on here are great with your help.


Former Member26/10/2019 17:07:03

[This posting has been removed]

john brown 1726/10/2019 17:43:44
114 forum posts
3 photos

Yes have had a look at that build,and even asked him about a few things and he admits the water level is a big problem,he has got some type of valve that he can open to se if there is still water in it ,and a couple of people who have done the engine have said the same,one option would be to mount a site glass on the side of the boiler casing then make a box round it that looks the part with a door,but one thing l did take note from the other builders is to use thicker plate for the horn plates etc as 1/32" thick is way to thin and things like the bull gears bring them up from being 1/8" thick to 3/16",and yes l have introduced errors with the build but get over them as l go,but one way or the other a site glass has to be fitted in my humble opinion .


john brown 1726/10/2019 18:46:37
114 forum posts
3 photos

First off l do not wish to bore you good people,but looking at things with regard to water site glass,now the smoke box end of the boiler expect for the stay nut for the fixing bracket is clear,so why not put a couple more bushes in that end then pipe from them for the site glass,some old usa steamers had chain lockers bolted to the casing ,could then hide the site glass in that ,hows that plan ,Please be honest,there is just no room to put one the cab end as there are already two bushes and yes the safety valve comes apart so will play with the spring and se if l can get it to keep blowing off at 30 psi.


john brown 1727/10/2019 07:09:12
114 forum posts
3 photos

Well its time to put this post to bed before every one gets fed up with it, l had a very nice mail from steve in the states who has made a couple of the steam tractors,the fist one made as the drawings ,and he was never happy with the water situation ,and then made a another one ,this time he put another bush in the smoke box end of the boiler and uses that to fill up with water,that way he had room to fit a level glass in the cab ,its tight but it fits,so will go that way and leave you good people in peace about this matter.


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