A Smaller Steam Engine For A Smaller Boat

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
Project of the Month Winner
Jun 28, 2011
Reaction score
Well my steam powered sternwheeler http://www.homemodelenginemachinist.com/showthread.php?t=22191 is fun to run, but it is a real event to get 50lbs and 6ft of boat out to the water and back. I want something I can toss into the car and steam on a pond with little effort and support equipment.

I am going to start with the running gear to get an idea of weight and from there I will find some kind of hull that will hold the running gear and be able to handle a little bit of waves. Right now I have to go out on glass smooth days for the Liberty Belle.

So here goes...

I have a chunk of 3 inch copper pipe stamped with an 'L' left over from the first boiler I built. I want to make a vertical fire tube boiler this time. I cut off a chunk of the pipe, heated it up and formed that plate into the end caps. It took many heating cycles to get the metal to bend around the wood form blocks. I used a flush set in my rivet gun to do the work for me. They seemed to come out pretty good. It sure is amazing how much the copper will bend and form. I am basing the boiler on drawings in a book called Model Boilers and Boilermaking by K.N. Harris. It will have a 3" dia x 5" tall shell with 37 1/4 OD fire tubes.

Here are the pictures
















Looking good Pete, I think I’ll pull up a chair and tag along. That piece of 3” tube looks a lot like the one I have our in the garage but I think mine might have more spiders
I'll pull up a chair too. Looking great so far.
That's funny mine had a lot of web before I cleaned it up guess it makes a nice home

Next up was riveting the end plates on the shell. I know they aren't necessarily but they look pretty neat and they sure can't hurt for added strength. I used 1/8 copper rivets from McMaster Carr. My rivet set wasn't quite the right profile but after bucking them they looked fine.

I also drilled holes for the bronze bushings for all the anticipated fittings that will be needed later.










Next up was brazing up the ends with 45% silver. I went and got a weed burner torch to attach to my barbeque propane bottle to heat the whole shell, and then used a smaller mapp torch in the local area I wanted the solder to melt.





I needed to solder in all 37 fire tubes at the same time so I set up the lathe to wind the solder into a coil so I could cut rings to place around each tube at each end. I fluxed it all, heated everything up and it came out pretty good. A dip in citric acid and it was all back to a pretty copper color.









I turned the bushings out of 544 bronze and tapped them to 1/8-27 NPT and then secured them with more silver. That stuff is not cheap !! I did a low pressure leak check under water and found a couple of leaks on the fire tubes one one side with a couple of tubes. I refluxed and added a little more solder, recheck at low psi. Once that was done I checked the boiler at 130psi, I hope to run it around 30-40 psi but this leaves me room to up the working pressure if I need to.





I didn't know they would do that, I guess the metal expands and stops tiny leaks.

These few post are coming fast because I have been working on this project a little while before I got around to posting my work. I'll be caught up soon and the updates will slow up considerably.

I switched gears and started the steam engine next because I had to order a tap to work on the burner for the boiler. I cant continue the boiler till I see how big the burner will turn out and where it needs to be positioned to work well.

The vee twin engine I am going to build is called Modelldampfmaschine V10/12. I found these plans on the internet here - http://www.plans-for-everything.com/downloads/steam_engines/SE VGerman.pdf

I am using google translate to understand the directions. I haven't worked with metric dimensions in the little experience I have machining so that has been a new challenge.

The first part in the plans is the engine base. It calls for two concave cutouts with a 16mm radius, and I sat around staring at my mill for a while wondering how I would pull off this cut. I looked into buying a 32mm T-slot cutter, but that was 30-40$ for a cheap ebay cutter and the less I spend the better so I had to try something else. I came up with a homemade setup that used a 5/8" piece of cold rolled steel with a hole drilled near the end and a set screw to hold a HSS #21 drill bit shank that was repurposed to form a 3mm cutting edge. I was able to set the cutting radius to 16mm and made a few test cuts on scrap, and it worked great. Everything else was straight forward, I just went real slow to get the part exactly to the plans. I haven't built an engine using real plans before, it sure is nice to just build what is called for and not have to wing it the whole time !

Starting so square up the stock

Testing the new cutter on scrap

All done with the radius cutouts. What isn't in the pictures is the scrapped version that almost got this far but the cutouts were messed up. I forgot to take into consideration the thickness of the tool when I was watching my DRO when cutting the length of the cutout. It was 3mm to long when I pulled it off the vise !!! Lots of time down the drain...

Drilling the holes very carefully because there isnt way to match drill the bearing blocks that will sit on it. Which is my usual practice. This is the better way but its hard for me, my skills, and my loose chinese tooling !!


First part complete


I live in a railway town where there is a loco museum which was set up by the famous record producer, Pete Waterman, It is called " The Crewe Heritage Centre".


Anyway, back to the reason for this note.
We used to go to the supermarket right next door to it, and it sometimes had locos steaming up in the yards. When you first saw them, there were rivets leaking all over the boilers, but after finishing shopping, they were all leak free. Expansion and rust had sealed everything up.

But unfortunately here in the UK, we are not allowed any leaks on the small boilers we make.

A really great job you've done with yours.

I think the sealing on steel boilers is rust, but a copper boiler won't rust. Tiny leaks can be 'caulked' with soft solder which is much easier to apply. But do NOT get any soft solder around if you ever expect to silver solder again. The lead will contaminate the work and you will never get it clean.
John - That looks like a neat place to live near. It seems like it would be really interesting to be a working volunteer and see full scale steam equipment up close and personal !!

RonGinger - Thats good to know about the softer solder, I didnt know that would happen.

I did get this boiler sealed up completely, but the other boiler I have seemed like it seeped a very tiny amount when I first fired it up years ago. I thought I saw a few wisps of steam from the flue tubes that have cross drilled water tubes in them. It was so small I just left it alone, but I never saw that trace moisture again after a few firings. I dont know if it was a leak that healed, or just water from condensation during the heating up. It passed a couple pressure checks with water and low air pressure under water looking for bubbles. Who knows but it works great now.
Next items were the bearing blocks. The plans call for the blocks to be made from brass. I don't have any that thick but I have plenty of aluminum so I decided to just make brass bushings for the crankshaft to ride on.
View attachment ImageUploadedByModel Engines1478480646.513272.jpg
View attachment ImageUploadedByModel Engines1478480676.880235.jpg

The plans call for a radius on the top corners of the blocks but that's another tool I don't have so I just made steps instead
View attachment ImageUploadedByModel Engines1478480784.854139.jpg

I drilled the blocks to accept a .001 interference fit bushing
View attachment ImageUploadedByModel Engines1478480850.193023.jpg
View attachment ImageUploadedByModel Engines1478480865.494406.jpg
View attachment ImageUploadedByModel Engines1478480886.195533.jpg

I know that any day now we here in the US are going to switch over to the metric system but for now all I have is inch based stock so my crank shaft will be built up from 3/16 stainless rod. I drilled and reamed the bushings for that diameter.
View attachment ImageUploadedByModel Engines1478481193.534190.jpg
View attachment ImageUploadedByModel Engines1478481210.366837.jpg

The mount holes took a long time to locate, I didn't want to mess them up so I rechecked it many times before drilling and tapping for 2-56 cap screws ( another deviation )
View attachment ImageUploadedByModel Engines1478481332.721635.jpg
View attachment ImageUploadedByModel Engines1478481348.109593.jpg

Last hole was for oiling the bushings
View attachment ImageUploadedByModel Engines1478481388.260510.jpg

This is how they mount up
View attachment ImageUploadedByModel Engines1478481425.179550.jpg
View attachment ImageUploadedByModel Engines1478481449.532444.jpg

Almost caught up
You guys south of the 49th parallel will probably go metric the same way as we have in the great white north. Officially Canada went metric in the 70’s but to this day it’s a mix and if I go to my local metal supplier other than some metric drill rod it’s all imperial. Some hardware stores call it 12.7mm copper tube instead of ½” or 121.92cm x 243.84cm sheets of plywood instead of 4’ x 8’ but the problem is you’ve got over 100 years of existing stuff that’s all imperial and a new part or addition has to fit.
I’m enjoying your build and for what it’s worth I think the bearing blocks look better with the steps. Good job on the alignment. That sort of thing always gives me fits.
The US went metric in the 70's as well, but Regan cancelled all the budget for the change over and no one followed through.
It seems like they only got half of the hardware in the engines of the cars I own converted. My guess is the tool mfgs lobbied to keep it mixed up to sell more sockets and wrenches :):)

Thanks for the kind words, I am really slow and still produce plenty of scrap or "changes" to the design. I would be hard pressed to make just a simple 1"x1"x1" perfect cube, like I was told a buddy of mine had to make for a test when he was learning machining.

I would be hard pressed to make just a simple 1"x1"x1" perfect cube, like I was told a buddy of mine had to make for a test when he was learning machining.


We went metric in the 70's and I still use both. Done a Fitter/Machining apprenticeship, in the late 70's in imperial, (no metric) I remember the test with the 1" cube, was given a 2"dia ball in cast iron, hammer, chisel, and a file and told to make it, could not do it now to save my life.
I use what I have, saves money buying new tools unless needed.
Keep up the great work, Just following along

Ok I had another scrapping event but I don't know what happened mabey you guys have seen this. I don't want it to happen again. The crankshaft is a built up 3 piece design and it called for pins to be pressed into the three shafts through the brass. I don't have good pinning material and bits to get a good press fit so I tried running 2-56 cap screws through everything. Well that still allowed some movement so I went to soldering it together. That didn't go well and here is why. For some reason the solder/flux ate into the brass !! I haven't had that happen before and I was using hard solder not silver solder so it wasn't even that hot. I'm at a loss. A redesign is in order too. I don't like how this is built.
View attachment ImageUploadedByModel Engines1478653952.266657.jpg
The file marks are from me making sure the solder was really below the face of the brass

It was going so well and now I've got to start over. This hobby can be hard on a person huh. This is what it was lookin like before disaster struck
View attachment ImageUploadedByModel Engines1478654472.926374.jpg

My approach on these crankshafts has been to loctite them together. Once cured, I drill cross holes with 1/16" bit and press some 1/16 drill rod also with loctite. I use gauge blocks during assemly to ensure everything is parallel.