small steam engine for a model boat.

[optima21]

the flywheels were made from an offcut of 1/8" thick brass plate, the holes for mounting the crankpins and axle were reamed using precision ground stainless steel rod with three flats filed on them, to get the best fit possible.

and a m2 hole was drilled and tapped for a allen screw in one of the flywheels so that it can be mounted to the axle, the other flywheel would be loctited to the axle. this 2mm grub screw was the only part of this engine not made by me.

the flywheels were then clocked up on the centre bore and the outside was machined. The flywheel blank was superglued some aluminium so that I could machine it.

I also needed a couple of tensions springs and a compression spring, so here's me making them using a transfer punch as a mandrel and they are hardened, so that would minimise the flexing as the spring coils get further from the chuck. small compression and tension springs are easy to make and only take a few minutes. heres my way of doing it.

Making Small Compression Springs

today I had a go at making some small compression springs as I wasn't prepared to pay the minimum order quantities for half a dozen so thought I'd have a go at making my own. I need stainless steel springs so got some hard drawn stainless steel. this is available from the far east via ebay etc...

www.mig-welding.co.uk

as this engine was being assembled using loctite, I needed to make some grooves on the shafts for it. this is making the groove on a 2.00mm diameter shaft using a 0.6mm wide parting tool.

then a couple of weeks ago I went to a steam punk event at Leeds Industrial Museum with a stand for a model engineering club. so I though it would be good to take it in pieces in a small container so people could see the parts, and later that day I was given an airbrush and the display box for perfect for doing this. The 5mm squared paper just made it easier for me to position the parts.

the engine was then assembled, using Loctite 648, to hold it together, and ended up using it like superglue, using a wooden cocktail stick to apply it to the grooves, then assembling it. After a couple of minutes the excess Loctite was then wiped off, which gave a very clean finish, and the final engine looks like this (on a pound coin for scale).

and compared to the original engine that its a smaller version of

it runs very nicely on compressed air, just need to get on with trying it out on steam and making a new boiler for it. The drive for a propeller shaft is taken from the extended crank pin. on the propeller shaft there will be a disk the the same size as the flywheels but has a slot in it to take up the drive. this also makes it very easy to remove the steam plant from the boat if required.

 

[Dilkris]

Incredible

 

[optima21]

time for another quick update, and it does run on steam too, although it does run better on air, but after a few run it is getting better. Im using wet steam from the boiler as that should provide some lubrication.

and speaking of boilers, this is the boiler that I was using, which is from a small steam plant. the original engine that it came with will be used as a decoration on a Christmas tree. I'll be using the barrel from this boiler to make a new boiler with. I could have bought some new tubing to make a boiler from but the wall thickness is much thicker (well over twice as thick) and I need to keep the weight down. I'll also be silver soldering the boiler as soft soldered joints seem to disintegrate over time. A new boiler casing will be required that will fully encase the boiler to keep the heat in.

as for fueling, I ran this engine on 50cc of water using 10cc of methylated spirits for 20 minutes just as a benchmark. the twin wick burner is an original one for this boiler. I also tried 50cc of water using 15g of fuel gel using a Mamod car burner. this gave a hotter flame but only 10 minutes running time and left 10cc of water in the boiler, so I think experimenting with burner tray shapes may give a longer burn time.

as Ive just been using wet steam, I can also play about with using a steam dryer (a steam pipe going though the flames) as this will increase the power output of the boiler, but the lubricating properties of the steam may be reduced, so I may also need to fit a lubricator. What has surprised me is how thermally insulting silicone as the silicone tube shown here can be easily held with the steam going through it, and you cant do that with a copper steam pipe.

 

[optima21]

I bent a piece of 3mm copper tube to make a steam drier, it was a bit of a failure though as it went around the wicks rather than though the flames, so didn't pick up any heat. To have any kind of effect, I think it needs to wrap closely round the bottom half of the boiler with as much of it a possible being in the flames of the wicks.

I also made a tiny displacement lubricator, they work by allowing steam into them by a small hole, the steam then condenses into water, this then displaces the water and the oil goes into the steam pipe.

the cross tube was silver soldered to the main body of it, then a 0.4mm hole was drilled though the cross tube. this was then enlarged to 0.5mm

the top for the lubricator was made, Im not a fan of knurling for gripping things, but prefer the feel and look for a fluted grip

and the competed parts for the lubricator, the collar for the body was loctited into place rather than silver soldering.

I got some wick chafing fuel (diethylene glycol (DEG)) and tried to see what it was like for burning, well it burns ok, once you get it lit, but its less viscous than methylated spirts (MS), so needed to use a 6mm diameter wick rather than a 4mm wick (that I would use for MS). if I was trying to burn MS like this, i think the liquid in the container at the bottom would be burning too.

I then needed to make a new burner for the wider wicks. this was made from 0.25mm thick brass. the wick tubes were flared at the ends to stop them falling through the holes when I soft soldered them to the top

and then it time to test how the 3 fuels burn (from left to right) MS, DEG and fuel gel ( some form of alcohol, water calcium acetate). both the DEG and fuel gel are used by restaurants to keep food warm at tables so are readily available.

and one of the fuels under test, there is a probe thermometer at the back to measure the temperature between the wicks to show how hot the burner may get, as I didnt want a soft soldered burner to melt if it got too hot. the pressure gauge was a 0 to 15psi gauge and the engine was run at full speed continiously.

rather that post a lot of figures, 10ml of DEG gives slightly more heat energy than 10ml of MS with 15cc of fuel gel coming in 3rd place.

Diethylene glycol - 10ml ran the engine for 14 minutes with the steam pressure being 2.5psi average and no water left in the boiler

Methylated spirits - 10ml ran the engine for 13 minutes with the steam pressure being 2psi average and 10ml of water left in the boiler

Fuel Gel - 15grams ran the engine for 12 minutes with the steam pressure being 2.25psi average and 15ml of water left in the boiler

so for me thats good news as for fueling a small boiler like this the DEG gives a better performance than the MS, but it works out at being twice the price of MS but for the quantity that I'll be using, its small change still. the DEG is safer as it has a flash point of 124C and a boiling point of 244C when compared MS which has a flash point of 11C and a boiling point of 78C. I guess its a bit like comparing diesel and petrol, both are fuels, but diesel is a lot harder to burn than petrol. I did put some DEG on a teaspoon and try to burn it, but I could not get it to burn. the temperature between the wicks got up to 100c , so soft soldered fuel tank should be ok as the it wont get hot enough to melt the normal soft solder (170 to 180C melting point).

the DEG is also fairly clean burning as this shows the carbon deposits on the bottom of the boiler after about 6 hours total running time

so next I need to make a new boiler using a cut down tube from this boiler. I need to use this tubing as it is thin walled so will save me some weight.

 

[Bullet2012]

I bent a piece of 3mm copper tube to make a steam drier, it was a bit of a failure though

failure ! your work is awesome, if thats a failure !

 

[davenport]

Cool as fuuuuuuuuuuuu**

 

[optima21]

Ive now made the boiler, and to save weight, I reused the boiler from the Signal Equipment Limited 1540 steam engine that I was testing the steam engine that I made with. The tubing for this boiler was 0.5mm thick, with the thinnest commercially available copper or brass tubing having a minimum wall thickness of 1.0mm. the toy steam engine isnt a rare model, so I didn't have and issues cutting it up. its not clamped in the vice, its just used to steady it.

then a hole needed to be "drilled" for the filler /safety valve bush to be fitted. Due to the delicate nature of the tube I find that using a milling cutter in a milling machine works better than using a drill, but go up in stages, like I used a 4mm drill then a 6mm end mill them a 8mm end mill.

then I needed to make some new end caps for the boiler, these were made from 0.6mm copper, I would have used brass but didnt have any in that thickness. for smaller end caps, using a lathe to "spin" them is easier and more accurate than beating the blank with a hammer. I first made a wooden blank so I could push the copper blank against the former, there is a gap so I had clearance for the small faceplate that I used.

a mandrel was then turned to form the end cap around, there is a hole in the centre of the end cap so that makes it easier to locate the centre.

as the copper was relatively soft to begin with I started to for the flange using a ball bearing in a steel bar to apply the pressure. The angle changed about 15 degrees each time and the lathe was cranked over by hand for this rather than using power.

when it got to roughly 45 degrees, I annealed it

then continued to form the flange, and tidying up the end, but as this is soft copper, it needed cleaning up with files

then we have the pieces that are need to make a boiler with, a boiler tube, two endcaps, two mounting bushes, a filling/safety valve bush and a steam pipe. The steam pipe is that shape so it will pass through the wick flames to pick up some heat to tr and improve the efficiency of the steam.

the original boiler was soft soldered together as it was a commercial toy, and I could have soft soldered this together, but Ive had issues with soft soldered joints on old steam engines disintegrating when you look at them, so I decided that I would silver solder this boiler. As I only make small models, I normally use 0.5mm silver solder wire, in 3 variations, most model engineers use silverflo 55 which melts at 630 to 660C, but I also use silver solders used for jewellery making, with easy grade melting at 670 to 718C and hard grade melting at 741 to 788C. this comes in handy for making sub assemblies with higher temperature solder and then using them in later assemblies with a lower temperature solder. I also use Easyflo flux and Tenacity No.5 flux, as the Easyflo works to slightly over 800C, but the Tenacity is good up to 900C and also suitable for silver soldering stainless steels.

when Im silver soldering I use refractory tiles and bricks and the are good for over 1200C,

the boiler mounting bushes were soldered to end plates first using hard grade jewellery silver solder as I didnt want the bush falling out later if the solder got too hot. The rest of the silver soldering was done with Silverflo 55, and where possible I like to use solder rings as it heats up consistently with the part and doesnt take heat from the joint (if adding i as a rod later) the boiler tube was turned over and the second endcap was fitted and then soldered in place. the tile that the boiler is shown was on top of a "lazy susan" bearing so that the tile can be rotate to heat the bottom of the boiler evenly.

and final assembly to solder the steam pipe and filling/safety valve bush to the boiler tube. this is supported on pieces of scrap brass to support the tube and steam pipe in position. A chunk of brass was also used to hold the filling/safety valve bush in place due to its weight.

 

[optima21]

and with silver soldering its a good idea to have the parts clean, the normal method to do this is to use an acid pickle to remove the oxides from silver soldering previous joints. The acid pickle was traditionally a weak sulphuric acid was used but this is the first time Ive used citric acid as a pickle. I used 3 teaspoons to 1 litre of water and it worked well. You can also use citric acid on your pancakes if you run out of lemon juice as it is readily available for use in the food industry.

so after the final silver soldering session, the boiler looked like this.

and after cleaning in the weak acid pickle solution it looks like this, and nice and shiny again. The boiler weights 67 grams, if it was made from commercial tubing it would have weighed over 100 grams. it can hold 70ml of water, so 50ml should be fine when using it on a model boat.