How to cut a curve?

[paul]

Just been thinking about a support for my boiler and quite like the idea of a tripod - I white-tack'ed some legs in place to see how it would look and it's not vastly unpleasant (the boiler has slipped downwards a little in this pic!).

I plan to bolt the legs through the 10mm or so of the boiler tube that extends beyond the lower flanged plate. I could just bolt them on as is but I think it might look better (and be more stable) if the legs had a curve on the inside edge to match that of the boiler - trouble is I can't think how I could do that accurately! Can anyone make any suggestions please?

[ron]

Hi Paul
The two methods that come to mind are either a fly cutter or a boring head set at the diameter of the boiler, first one cheap, second one not so cheap.
Ron

[havoc]

Turn it on the lathe.

- mount the tool in the jaws with the tip at the radius of the boiler, and mount the feet where you would mount the tool normally. Advance workpiece with the cross slide into the slowly running tool until satisfied.

- mount the feet in the 4-jaw excentrically so that the tool when coming in from the middle of the lathe will cut the desired radius.

The first will require making an adaptor to hold your boilerfeet in the toolholder at centerheight. But once the bit is adjusted in the jaws, it will always cut the desired radius. The second method will require a bit more setup (I feel).

[spurley]

Hi Paul

Just looking at your boiler picture this morning; how are the bushes and joints assembled? It looks to me like soft solder in the picture you have posted.

I am a little concerned, for your safety, if that is the case as steam under pressure can be at a higher temperature than that type of solder and you potentially face a joint opening up under steam pressure. Boilers for Mamod and the like were soldered together in this way and were safe due to the low(ish) pressures involved and that some of the joints were below water level and hence at a lower temp than the steam. Tubal Cain's Model Engineer's Handbook, amongst others, lists the relationship of steam pressure to temperatures and will allow you to decide if there might be a problem.

Please understand I am in no way attempting to criticise your work I hope to avoid you being involved in a potentially nasty accident.

With the very best of intentions

Brian

[paul]

Thanks all!

Ron: I don't know what a fly cutter is!

Havoc: I've yet to use the 4 jaw chuck - maybe this would be a good time to try it out, your first suggestion sounds easier (but not easy)!

Brian: Thanks for taking the time to add that note of caution! You're right, I have used soft solder but I don't think it will be a problem because...

I intend to keep the pressure below 35-40 psi - according to a table I've got that would make the temperature 140 degrees max and the solder is rated at 220 or so.

I've tested it (cautiously!) under steam at or slightly above that pressure.

Stan Bray's book that I'm using as a guide recommends silver soldering but says that soft solder should be ok.

When I made the boiler itself at the start of the year I had very limited equipment/experience hence the reason for soft soldering. I'd feel happier now about silver soldering instead - who knows, now you've put the fear of god in me I might just desolder the fittings and start over!

[Tel]

How to cut a curve? Try to cut a straight line! ;D

[chris vine]

Hi Paul,

If you have threaded the fittings into the shell before soft soldering them, I think you should be OK, but be very careful as there will not be a lot of thread anyway.

If you have not threaded them and want to re silver solder them, you will have to get every last trace of the soft solder off the components or the silver solder won't run. That means even getting the inside of the shell completely clear....

Chris.

[paul]

tel said:

How to cut a curve? Try to cut a straight line! ;D

It'd work every time but all three would be different!!

[paul]

cvine said:

Hi Paul,

If you have threaded the fittings into the shell before soft soldering them, I think you should be OK, but be very careful as there will not be a lot of thread anyway.

Nope, that wasn't suggested in the book so they're not threaded - maybe re-soldering is on the cards...

[havoc]

and that some of the joints were below water level and hence at a lower temp than the steam.

Water and steam that are together in a vessel are at the same temperature and pressure. To get the steam hotter than the boiling water you need a superheater. That heats the steam above the equilibrium temp while keeping it a the same pressure as the steam in the boiler.

Not to be confused with a steam drier. That only evaporates the last droplets.

Lately a lot of those gauge 1 boilers get build with 2% silver solder. This is a soft solder with a slightly higher melting point, but increased creep resistance. I find brazing easier than soldering these days. Don't know why.

[baggo]

Paul,

I don't know what soft solder you have used on the boiler. If you have used ordinary tin/lead solder be aware that it loses a lot of it's strength at quite a low temperature i.e. 100 degrees C. What you could do, and it's only a suggestion, is to unsolder as much as you can, clean off the old solder and redo with Comsol. That melts at 296 degrees C and is the solder used for caulking threaded stays in boilers if it is not possible to silver solder them. It contains a small amount of silver which makes it stronger than the ordinary stuff. If you use that you should be able to get away with not having to remove every bit of the old solder.

John

[paul]

Thanks again John! I'm umming and aahing on this one at present; desoldering it wouldn't be that big a deal so I might go that way. Mind you I might just chuck it all in the scrap box and start over!

[spurley]

Paul

Sorry to have opened such a can of worms and possibly scared you about your boiler! The overall workmanship looks fine it was just the jointing material, and your safety, that concerned me.

Havoc

My point about the temperatures below water level in a boiler is based on the circulation effect carrying heat away from the joint material(s). Full sized loco boilers, in Britain anyway, are protected by one or more fusible plugs in the firebox crown (depending on the size/boiler pressure of the locomotive). These are bronze plugs with approx 1/2" hole filled with a lead plug or some have a bronze plug soldered into the screwed plug. These plugs will melt if the firebox crown is uncovered for a time in the case of low boiler water level. The subsequent rush of steam/remaining boiler water will provide a warning to the enginemen and assist in extinguishing the fire and releasing a portion of the boiler pressure. It was considered a very serious misdemeanor if an engineman allowed the plugs to melt, known as 'dropping a plug' and I believe was usually followed by the Driver being demoted or dismissed!

Cheers

Brian

[paul]

No problem Brian, as a newcomer I appreciate it if people 'ask questions of me' - it's the only way to improve.

Waaaay off topic but in response to your bit about fusible plugs it would certainly have been a fine for the driver/fireman and maybe even a demotion...

For anyone interested in this sort of thing I can recommend the book "Engine-Driving Life or stirring adventures and incidents in the lives of locomotive engine drivers" by Michael Reynolds (what a title!). Published in 1881 it was re-printed in abridged form in the 1960's.

I bought an immaculate original copy earlier this year (at £80) - from Canada! Why? Because Mr Reynolds was born, and retired to write this book, just a few hundred yards from my home. The first railway casualty mentioned in the book is also buried in our village churchyard.

[spurley]

Hi Paul

Michael Reynolds wrote some excellent books about steam engines both stationary and locomotives. He was an early protagonist of standard operating practices and proposed a National Qualification for enginemen! I have a great admiration for the man particularly as he was an inspector on the LBSCR, my particular favourite line. Not a major player in Britain's Railways but one with an enviable reputation for locomotives, William Stroudley, Douglas Marsh and the Billinton's RJ and LB (Father and son) produced some fine machines with only a few falling short of expectations! My favourites being the I3 4-4-2T or the J2 4-6-2T, love big tank engines as well as the BR STD 4!

I was born in Sussex and although too young to have worked on mainline steam served from the age of twelve on the Bluebell Railway as a volunteer in the Loco dept. I made it to Fireman but ceased footplate work when I worked on the restorations of the North London Tank, the Adams Radial and the C class through the 80's. Moved to Ireland in 1991 so regrettably my association came to an end.

Cheers

Brian

[havoc]

The reason the fusible plug melts is when it is uncovered, the temperature can be raised above that of the water. So as long as there is water in the boiler, ther won't be a problem. It is the heat of the fire that melts them, not the steam.

The problem is that if a soft-soldered boiler is boiled dry, then it is ready for the scrap. A silver soldered one has a chance to survive, if you let it cool and give it a hydraulic test (and it passes).

But fusible plugs are notorious for not blowing. Very often, there was enough deposits on the plug hindering to blow out the fire.

Are there model boilers with fusible plugs?

[Phil Sutton]

My Winson 1400 has one,and I expect all their other kits will have them too.I suspect that H&SE and litigious public will ensure that this is so.

Phil

[chameleonrob]

they're certainly available (http://www.steamfittings.co.uk/asp/components_subcats.asp?CatID=2) and I know that our club loco (Thomas II steel boiler) has one. as it just means one extra bush in an area you are soldering anyway why leave it out?

rob

[wayne]

[glow=red,2,300][/glow]
Hi Paul
The following lists the safe operating tempratures/ pressure for soft solder copper joints (the type of solder you buy from plumbers merchants)

Size 30°C 65°C 110°C
6 – 54mm 16 bar 10 bar 6 bar
67mm 10 bar 6 bar 4 bar

Note soft solder should not be used in any circumstances above 110 degrees. and for steam or gas a de-rating factor will also apply as the table applies to hydraulic pressures.

As you can see the safe strength of a joint failing is well below the melitng point of the solder.

Soft solder is not normally used above 85 degrease in industry for good reason. I strongly recommend that you use an appropriate jointing meduim for a steam pressure vestal.

On a secondary note dose any body Know why you can not use the Rothenberg Rollot s3 for jointing copper boilers. This stuff is brilliant, as its a copper based rod no flux for copper to copper joints, suitable for very high pressure and temp joints and its reasonably free flowing. Of course the drawback, at work we all use oxy-acetylene with it, although i have heard of people using the high tem map gas.

[spurley]

Havoc

If a soft soldered boiler boils dry you are corect it is ready for scrap and will probably have 'let go' in a fairly exciting way as well. I speak from experience ; I once foolishly refilled the meths in a Mamod boiler without adding any water to the boiler. Result one of the ends desoldered itself and flew past my face at a high rate of knots! This was caused by there being no further cooling action from the water, which is exactly what I was trying to put across in my initial post to Paul. Wayne has also agreed with my concerns.

Cheers

Brian