1/32 Copper tube for steam boiler barrell

bambuko

Western Thunderer
It seems that the only tubes available from model engineering suppliers in C106 are 1 1/2" , 1 3/4" and 2", with nothing in between these sizes.
It was fine for 10mm, where everything was oversize and it didn't really matter...
but in 1:32 this would not be acceptable, so if you want to use seamless tube for a boiler you are faced with having no (or almost no) cladding/insulation, or accepting reduced boiler volume.
So for a loco I am working on at the moment, 1 3/4" would mean practically no insulation and 1 1/2" would mean accepting 15% reduction in boiler volume.
It gets easier with larger prototypes, but I am into smaller ones ;)
Anybody has any experience in this? or advice?
I suppose I could always "roll my own" to exact diameter I need - is that what you guys do?
 

David Halfpenny

Western Thunderer
There's a lot of people don't insulate boilers this size. Debate goes back and forth online.

Fortunately, you don't have to roll from flat. If you take a slice out of a larger tube, you only need to tighten the curve a bit, which is more Rolling Pin than Slip-Roll. With careful choice of size, the off-cut will be just right to lap the seam, and might even tuck inside what the LMS always called "Clothing".

When buying Mail Order, be aware of Metric versus Imperial, and Pipe versus Tube. (Pipe is sized internally, while tube is sized externally.)
David 1/2d
 

Martin Shaw

Western Thunderer
Bambuko

Look up Holme Dodsworth, they do C106 in 1/8" increments, as I suspect do quite a lot of others. BTW the square area of 1 1/2" is 73% of 1 3/4", quite a bit more than 15% reduction.
Regards
Martin

Edit Following David's post I presume your going to silver solder the boiler together, be aware that in slightly larger scales lap seams are generally not acceptable because of the risk of non penetration of the solder right through the seam. I know it's a low volume and pressure vessel, but none the less. If I'm teaching my granny, sorry.
 
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bambuko

Western Thunderer
Martin,
I am aware of Holme Dodsworth, will try nearest branch, but I am guessing that they don't sell in 6" length :D
I was talking about the change in volume not square area.

David, I know that some people don't use insulation and if it was just an issue of burning fingers than it is up to the owner, but I am using RC and don't fancy melting it... plus I like insulation (not everybody might agree with me...).
Yes, you could use larger tube to downsize to avoid having to roll.
 

bambuko

Western Thunderer
Yes, David
I was after 1 5/8"
Just been told by M-Machine that:
"...We are finding that our suppliers are reducing the range of copper tube available - even some of the regularly used sizes. I'm unable to help..."
 

David Halfpenny

Western Thunderer
Rats.
If you have a sturdy lathe, might you be able to Anneal, then Spin it down onto a mandrel? Or sequential mandrels?
A bit like this (Warning -turn off sound before clicking Play) D

(If the length stays the same, surely the percentage change in cross-sectional area IS the change in volume?)
 

Martin Shaw

Western Thunderer
Bambuko
You must have been taught a different type of geometry to me, for a given length of tube the change in volume is entirely dependent on variation in the square area of the end. For your quoted sizes it will be 27% whether the tube is 6" or a mile long. You could also try P&P Non Ferrous, or Wellington Tube Supplies.
Regards
Martin

David beat me to it.
 

bambuko

Western Thunderer
Guess I was having senior moment :headbang: about my calculations (of course you guys are right).
Thanks for the suggested suppliers.

The idea of "stretching" the tube has occured to me as well :)
 

bambuko

Western Thunderer
...Look up Holme Dodsworth, they do C106 in 1/8" increments...
Just an update on Holme Dodsworth.
Talked to a local (60 miles away :p) branch. They do both 42mm and 1 5/8" , but only if I want 14swg or 9swg

...as I suspect do quite a lot of others ...
That was my assumption as well, but doesn't seem that easy...

...Edit Following David's post I presume your going to silver solder the boiler together, be aware that in slightly larger scales lap seams are generally not acceptable because of the risk of non penetration of the solder right through the seam...

3.3.1 ...Barrels.... may be made... or from flat plates complying with section 2, formed to shape and joined using methods complying with section 4.

4.2.4 ...Silver brazed longitudinal seams in barrels shall be but strap joints as shown in fig 4.2

So, I guess good warning (above fromAMBSC Code Part1)

...I know it's a low volume and pressure vessel, but none the less....
AMBSC Code Part3, for medium pressure sub-miniature boilers:
"...may be made with longitudinal joint.... Such joints shall be made in the manner specified in th AMBSC Code Part1 (see above)

...If I'm teaching my granny, sorry.
Not all!
I appreciate your input.
 
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