Miniature Traction Engine

[Nigel Taylor]

That is very useful. Interestingly I seem to have the identical clamp set in the red wall mount .
I just rebuild my milling vice. It came with the mill and had 3mm, yes millimetres not thou, of vertical slack in the moving jaw with no adjustment possible. I machined 60 degree tapers on the slides and made gibs for it. It now clamps perfectly.

Drop me a line if you have any additions, I will add them on

 

[Fergie 307]

Before making the boiler I thought I should have a go at just making a standalone boiler - in fact my first boiler.

This tiny boiler is not that simple to assemble, even at 650°C for the lower temperature silver solder it's quite difficult to get the heat in with a smallish butane torch.

Nice job. I use one of the little oxy sets for small brazing stuff. Got fed up with the outrageous amounts BOC want for their cylinders for something I only use once in a while. I use a map torch to get some temperature into it and then the oxy set to just lift it to the final temperature, saves on the oxy bottles by letting the map do most of the work.

 

[Chris4658]

Wow! Lovely craftsmanship there! Really nice work

 

[Nigel Taylor]

I made the little vertical boiler to test myself, but I've got carried away. It is now clad and I've made the siphon tube for the pressure gauge.

I silver soldered the the 1/16th inch diameter copper pipe with easyflo paste. I made the banjo bolt from brass.

I will update with a movie once it is in steam, hopefully this weekend...

 

[Nigel Taylor]

This little boiler has turned back into the test piece it was meant to be. I've been using it to run tests with a methylated spirit burner and got poor results.

So I instrumented the boiler with thermocouples and a Pico Tech logger.

I ended up using 3 thermocouples to record air temperature, water temp and steam temp above the water. As well as I could measure these as I just made a blind hole in the boiler plugs and pushed the thermocouples inside.

I now have quite a lot of data.

I need to have a look at this and see what conclusions I can get to with regards to the boiler design.

 

[Nigel Taylor]

Comparing the cooling curve for the boiler clad and unclad shows there is not actually that big a difference.

Now, these tests were run on different days and I need to go back and repeat some tests to understand what my real errors are.

However, this might make sense as the boiler still radiates heat from a large surface area under and through the centre of the boiler. Plus there are a number of fittings that radiate.

 

[Fitzroy]

Vessel cooling is one of those things that will scale poorly when miniaturising a boiler. The rate of cooling of a vessel to the environment is proportional to the surface area to volume ratio. As you shrink a cylinder this ratio increases dramatically, a 5cm diameter vessel has a ratio 20 times greater than a 1m diameter vessel so it will cool 20times faster.

 

[Nigel Taylor]

Vessel cooling is one of those things that will scale poorly when miniaturising a boiler. The rate of cooling of a vessel to the environment is proportional to the surface area to volume ratio. As you shrink a cylinder this ratio increases dramatically, a 5cm diameter vessel has a ratio 20 times greater than a 1m diameter vessel so it will cool 20times faster.

Agree, the boiler size is similar in size to a Mamod and hence my desire is to improve on that design.

 

[Nigel Taylor]

Here is an image of the traction engine alongside a Mamod Steam Wagon, the vertical boiler is a test before building this boiler.

 

[mcgranag]

Great work, following with interest.

 

[Nigel Taylor]

I've now run a few experiments on the small vertical boiler to understand the optimum distance between the spirit burner and the boiler.

Normal practice is that the hottest point is at the tip of the inner blue flame, however, there is a depth to the boiler surfaces as shown by this cross-sectional diagram.

So, using the simple assumptions, a new firebox and some more measurements on the instrumented boiler I get the following curve:

This plot shows that the peak in heat output is when the burner is around 85mm from the base of the boiler. Also, it shows that this firebox and burner is producing nearly double the amount of heat that the original design generated.

I checked this calculation by looking at the boiler temperature versus time data. The original firebox and burner took just under 8 minutes to take the water from 60°C to 100°C. The new firebox and burner took just over 2 mins 30s for this same temperature change. You have to consider heat losses and heat input, but this makes sense.

PS if anybody wants to use any of the images I've post that is fine, just please add a link to my pages at glue-it.com thanks, Nigel

 

[Nigel Taylor]

I've built and tested an electrical heating system for the boiler, the intention being to calibrate the mathematical model and gain insight into the thermal insulation. The electrical input was 20.2W and the model estimated the electrical input between 17W and 18W over the period that the boiler was heated from 20°C to 120°C. I'm quite pleased with these initial results. This also gives me the tools to develop the insulation of the boiler.

Note: this system is only operating at 10.7V

This image shows the nichrome wire wrap before I wrapped isolation and insulation over the top.

This has also shown me that I could electrically heat the boiler and I have another idea to improve on this deign.

 

[Adam W.]

Wow!

 

[Echo-Star]

Truly a master off your craft Nigel, and what a statement It makes of the skills you possess. The time you must put in to achieve a standard of work off this calibre is awe-inspiring. I am in awe.

Rob

 

[Nigel Taylor]

Truly a master off your craft Nigel, and what a statement It makes of the skills you possess. The time you must put in to achieve a standard of work off this calibre is awe-inspiring. I am in awe.

Rob

Rob, very kind words, but I have been making models for more than 40 years and 10 of those years were as an apprentice to my dad who was exceptional at this. Also, I do make a lot of mistakes, I do post these on my blog and on instagram to show that I'm very much human. I would encourage people to try something and to just take their time (another benefit of growing older ). Thanks, Nigel

 

[Nigel Taylor]

I bought a piece of hex mild steel, but it turned up and I thought it was a shame to turn it into a pile of swarf. So, after a long walk and some thinking time I decided to fabricate the final firebox design from sheet steel:

I think I have a simple way of making some louvres for the air flow

 

[Nigel Taylor]

I finally sorted the issue of getting heat into the small vertical boiler. I used a steam raising blower, then I tested 2 methods back to back and described them both in this video. Along with data that shows this simple technique increases the heat into the boiler from 50W to 350W


Steam raising blowers work rather well, now I just need to be able to finely control the heat input between 50W and 350W.....

 

[Adam W.]

I'm really impressed by your attention to detail Nigel.

This has to be the best project thread on this forum, it's nicely presented and I like that you don't shy away from sharing your research with us.

 

[Nigel Taylor]

I'm really impressed by your attention to detail Nigel.

This has to be the best project thread on this forum, it's nicely presented and I like that you don't shy away from sharing your research with us.

Hi Adam, thanks, very kind. I really enjoy the science and engineering aspect and post things that I hope will help others. Best regards, Nigel

 

[Nigel Taylor]

Just realised that this thread shows a step change in the boiler that I should describe. That is the change from the mid colour oak cladding to the dark bog oak cladding. I removed the original oak cladding as I needed to understand the thermal behaviour of the boiler. This meant that I then had to put the cladding back onto the boiler, this gave me a chance to optimise it.

There are now 6 layers:

1. Teflon sheet – a thin baking sheet wrap
2. Medium weight paper wrap
3. Polythene – this was a thick clear polythene bag
4. Medium weight paper wrap
5. Air gap – created using thin wood veneer strips
6. Bog oak outer layer

The air gap is very small, this image shows me adding the external cladding and underneath you can see the very thin strips of veneer.

I then measured the performance of the final boiler cladding and compared it to the limit cases (ie no cladding and thermal blankets) and to the case where just the cylinder is insulated to a maximum condition (this represents the ultimate thermal cladding).

These performance curves are calculated from the cooling curve, mass and heat capacity of the boiler/water. The cooling curve is a fundamental parameter for any system and is easy to measure and so establish the heat loss to the environment.