machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment.

Making Springs and Other Stuff

Other stuff first.


SWMBO has always considered that having a winch on a vehicle is a bit of a wank, but I have used it many times getting out of bogs, getting other people out of bogs more often, moving machinery, pulling down/moving trees, straining fences etc etc.   SWMBO was intending to replace these concrete steps, because they were crooked with respect to the house which she is fixing up.  I said that I could straighten them.


This is after straightening.  I jackhammered the path slab, lifted the floor slab with the 4WD high lift jack, and pulled the steps with the Landcruiser winch.  Easy as.  Took 30 minutes.  SWMBO was delighted!   


And I used my new spring tool.  Brilliant!  Recorded on videos.  Again, apologies for my lousy video technique.  I had forgotten to bring the spring making instructions, so it was all trial and error.


This was my first effort.  Aluminium wire, just to try the tool.  As you can see, there were multiple errors.   Feed rate too slow for the RPM, forgot to enter a stop command at the end, feed rate much too slow at the beginning on the left.

So I started with aluminium, making many mistakes, sometimes repeatedly, but eventually learning.  Progressed to soft iron wire, and eventually to stainless steel spring wire.

Following is a series of pics and videos.



The mandrel was 4mm diameter, and there was a bit of spring back, with the final ID of 4.4-5.0 mm.


Initially I secured the end of the wire by catching it in the collet, but quickly replaced that method, and drilled a 1.5mm hole in the mandrel.  Again, I forgot to issue a stop command in time.   The starting coils were hand wound by manually turning the spindle and jogging the feed.  If I was making multiples of the same size spring that would be simple to program on the CNC.


Ah!  Getting the hang of this!  That one looks good!

In the next video, a good spring is made.  The mandrel wobble is occurring because I had bent the mandrel, when the steady was not hard enough against it.  Bend straightened afterwards.







And the safety valve with its new spring…



But screwing in the safety valve was a bit of a struggle…



And re-installing the safety valve lever was almost comic..



So, that’s it for this post.

How did you like the videos?  I suppose that I should have stitched them together into one long video.  Maybe I will do that later for YouTube.   And to edit out all of the errors.

Later today I will post another video, this time a longer one, a tour of the Trevithick engine.

Well, what a nice day!

Wednesday is always a good day.  That is when our model engineering group has its weekly meetings.  Mostly a 2-3 hour informal gathering around a large table, chatting about current projects, new tools, the weather, rarely politics or religion.  Coffee.   And once each month a more formal evening meeting, involving discussion of club business, “models on the table” and usually a guest speaker.   Today was the informal 2-3 hour chat variety.

I used the opportunity to ask about methods of making a rectangularish water tank for the Trevithick dredger engine, riveting, folding brass, caulking with solder, etc etc.    And Stuart T, knowing that I had to make a stainless steel compression spring for the safety valve of the Trevithick, brought in his tools for making springs.

This is one of the tools.  It was designed by Dwight Giles, and made by Stuart.


Published in Model Engine Builder 2007.

The tool is mounted in the lathe tool post.  The V supports the chuck mounted mandrel, and the brass washers apply drag to the spring wire.  The lathe threading gears supply the pitch to the spring.  Looks excellent, and I was hoping that Stuart was intending to lend it to me.  Otherwise I would make one of these tools.   But why were there two of the tools?   “Oh, one is for you!  I was making one for myself, and it was just as easy to make two.”

Not the first time have I been the recipient of Stuart’s generosity.  When I make the spring (soon) I will take some pics, and post them here.

Later in the meeting, Swen Pettig, recently returned from a fabulous trip to Scandinavia and UK, called for shoosh, and stood up to make a presentation.  Some people knew what was coming.  I didn’t.  But in “recognition for writing about his model making” (now my ears pricked up), Swen had picked up an item in the UK which he thought I might find interesting.  Knowing of my current interest, some might say obsession, with Richard Trevithick, he had looked for and found the following item.


A Two pound coin.  I did not get the significance, until I looked more closely.  Holy Shit!  That is a Trevithick engine on the coin.  The Pen-y-Darren railway engine if I am not mistaken.  Made in 1804.  And using many recognisable features which are in my slightly later dredger engine.  The coin was minted in 2004, 200 years later.  Wow!!

I did not even know about the coin until today.  But I am honoured and very grateful for this lovely gift and thought, Swen.

One wag suggested that I should make another gas knob for the engine, and mount the coin in the knob. (thankyou for the suggestion, President Brendan.  I will do no such thing).  It will be a  valued possession.

Incidentally, the reverse of the coin has an image of the Head of State of Australia.







Gas control on an historic model?

Well, no likes and no comments on this morning’s post… no picture the problem????   hmmm???

So, this afternoon, the weather was windy and wet, and unsuitable for winching concrete steps, so I retreated to the workshop.  Much to SWMBO’s disapproval.

And did a bit more with the gas supply and control.


And that is what it looked like.


OK, except that Primus knob does not appeal.  And the wooden base is looking decidedly wonky.  More about the base later.  I have some improvements in mind.


This wheel was a reject from my triple expansion steam engine model.  I wondered if it would look OK on the Trevithick.  It certainly looks better than the Primus knob Yes/No?

Possibly not historically accurate, but maybe yes for 1850-60?


Historic Model Compromised?

I was attempting to model the Trevithick Dredger Engine as true as possible to the original.  But, I also wanted it to run, so the flywheel would spin and the crosshead move up and down and the unusual valve control lever flick up and down.

There are several problems with this approach.

  1. The 1 in 8 scale.  This is the biggest problem with making a model.  Since the scale applies only to linear dimensions (e.g. the boiler is 6″ diameter compared to 48″ for the original), surface areas are at a scale of 1 in 8×8 (1:64) and volumes and weights are at a scale of 1 in 8x8x8 (1:512).  So my little model weighs a few kilograms (not actually weighed it yet) compared to 4 -6 tons for the original.   It does mean that there is a safety advantage in scaling down, in terms of boiler explosion risk, despite the fact that the model will be run at roughly the same boiler pressure as the original (50 psi).
  2. Some components do not scale well.  For example, the square nuts.  To my eye, they look too big.  If I was to make another of this model, I would make the fasteners smaller.
  3. The requirement of the model actually running.  The original was fired with coal, or in some situations wood, and even dried animal dung (in Peru, look it up.  There was no coal and no trees in the silver mines area).  I have made my model so that it could run on coal, but to be honest, that is unlikely to happen.  So I have made a gas burner.  And that involves gas pipes and regulator valve, which are impossible to conceal, and detract, IMO, from the appearance.
  4. Boiler regulations.  I want to run the model at club exhibitions, which means that the boiler must be certified.  The boiler certification regulations make no special allowance for historic models, so several compromises have been made.  For example a pressure gauge has been installed, and the water level taps must be replaced by a glass sight tube.  Not a biggie I guess, but it all adds up.  I will keep a separate set of parts which can be used when it is displayed as a static model, which will be most of the time.
  5.  Is this a model dredger engine or a model factory or mine engine?  I still have not decided.  Hence the rather ambiguous base.  I do not intend to build a dredger or section of a dredger, or a factory or mine or parts thereof.  But I have to admit that the base which is appearing in the photos so far does not look “right”.  Still pondering that one.
  6. And finally the colours.  Although Trevithick was a brilliant engineer, he was no artist.  I doubt that beauty, or attractiveness of line, ever entered his thoughts when he was designing.  If his engines were painted, the colour was probably utilitarian black.  Not that we know.  I can find no reference to colour in any of the works about Trevithick and his engines.  And there is not a skerrick  of original paint on the original engine in the London Science Museum, as far as I know.  Later engines, in the Victorian era, were painted in gorgeous colours, and I am tempted to paint my model as if it were a Trevithick engine which was being used in the Victorian era.  That is not so silly.  It is known that Watt engines, and even Newcomen engines were still being made in the 19th century, and Francis Trevithick records that many of his father’s engines were in use in the mid 19th century.  That little subterfuge could also explain why my model has a pressure gauge and sight glass!

I had a full day in the workshop yesterday, so I had better front up and straighten those steps for SWMBO.   Actually, it will an interesting job.  I will use a 4WD high lift jack(s) under the house to free the steps, then use the Landcruiser winch with a snatch block to pull the concrete steps into position.  Might be worth a photo.  How the steps ended up out of position is a mystery.



Fitting the Boiler Feed Pump to the Trevithick Dredger Engine.

The feed pump is attached to the base, and since I had not decided on the final form of the base I had to leave the pump sitting all alone on my messy bench.

But I have now decided to proceed with a wooden base, made of 32x32mm hardwood beams, and a solid wooden top to which the engine and the feed pump are attached.

So today I attached the feed pump.  The engine itself is still just sitting, not attached.  And the bits of the base are still a loose pile of beams of wood, not bolted glued or screwed together.

One minor problem was that there were incomplete dimensions on the plans for the feed pump and its supporting column.   Fair enough.  I assumed that the dimensions would be measured on the job.

First I had to make the steel beam which attaches to the cross head, and the column at the other end, and the pump… 3 attachment points.  I had cut out the beam last week, but it needed a couple of bends.   It was 4mm thick steel, so I did the bending in the workshop press.


Bending the feed pump beam.

Of course one of the bends was too angular, so a bit of cold blacksmithing to flatten it.

And fitted everything to the engine sitting on the base.


The holes which were drilled in the top of the base were a bit of a guess, because the distance between them was not on the plans.  I drilled them 28mm apart, but it was clear after assembly that they were too close together.

Then the penny dropped.  The holes in the base should be the same as the corresponding holes in the steel beam… 32mm.  so I filled one of the holes with epoxy filler, redrilled it, re-tapped it and reassembled everything.


The re-drilled hole and filler are hidden beneath the feed pump.  The space in front of the boiler face is now occupied by gas piping and a gas control knob.  Not quite finished so no pics yet.  Notice the boiler pressure gauge on top of the boiler.  Not as per R Trevithick, because the Bourdon tube type pressure gauge was not invented until 1849, but it is required for boiler certification.   Maybe I will label this as a model of a Trevithick engine which was updated in 1850.

Next to make the pipe between the feed pump and the boiler feed pre-heater, and a bypass tube with valve.   I have not decided on the size or form of the water supply tank. A riveted squarish tank, or even a riveted cylinder would be nice.   Probably make do with a plastic bottle for the time being.

I also need to fasten together those base beams.  Have still not decided how to do that.

There are 4 types of wood in the base.  I might have mentioned one or two of them.  One is the top, one is the beam under the front of the boiler, the base beams is another, and there is a sizeable block underneath everything.  I doubt that anyone will be able to identify all of the wood types.  2 are Australian, one is European, and one is Asian (I cut up a breadboard for that one).

And thinking about a colour scheme.  Flat black is the favoured colour in most other models, but I want to include some Georgian reds blues greens or yellows.  And leave a bit of brass and copper for polishing.

Oh, and I made a ring for the top of the chimney.  Seen in the second pic.

A Day In The Workshop.

One of those days.

Warm night.   Restless sleep.  Woke at 4:30am.  Got up.  Dressed.  checked the emails, blog, Facebook.  Dozed until 8am.

Went to workshop. (15km drive).   SWMBO a bit peeved because she assumed that I would install some laundry cupboards and straighten some outside steps at the property which she is preparing for sale.  Baby sitting yesterday was fun, but I was thinking about the burner on the Trevithick.   So I told SWMBO that I would do an hour or two at her job at the end of the day.

So I went to my workshop, and started mounting the permanent pressure gauge on the Trevithick dredger engine.   It was fiddly, not totally satisfactory.  I dropped things.  I burnt my fingers several times.  I could not remember where I had put things 5 minutes earlier.  The workshop is really in a mess and I should have just tidied it up.  But I didn’t.  I had not had breakfast because the bread was mouldy and my normal cereal was empty so I skipped breakfast.  Except for coffee of course.  I cannot skip that.

Eventually the pressure gauge was mounted.  I thought about running the engine on steam and making a video for the blog, but I was just not in the right mood.

I packed up, and went to where SWMBO wanted me, and installed some cupboards.  Oddly satisfying.  Only took an hour or so.  SWMBO was happy.  I made some lame excuse why I could not straighten the steps, and went home and had a few reds.

Shit day in the workshop.  But sure beats working.

Trevithick Dredger Engine Burner

Reader Huib suggested that I would need to modify the gas burner for my model steam engine even before I had tried it.

He was absolutely correct.  The burner was difficult to light and keep going, unless I blocked off at least half of it. (see previous post).

So, today, I modified the burner along the lines suggested by Huib.


I added this stainless steel tube with drilled holes to the bottom of the burner, underneath the fire clay burner.  It is wedged into position.

And this was the result.  The burner li up easily when gas was admitted.


From above you can see that the fireclay burner is red hot over most of its surface.  And hottest at the end which is deep inside the boiler.

I measured the temperature of the burner, and it was 790ºc.  I think that it will do nicely. After that, I sealed the fire clay burner into the brass container with a high temperature boiler sealant.

Yesterday I received in the mail a tiny pressure gauge.  3/4″ diameter, 0-80psi.  from EJ Winter, Sydney.  Order was placed Wed, arrived Thurs.  Great service.  Thanks Ben deGabriel.

Trevithick would not have had a pressure gauge in 1803, but modern boiler regs insist on one, so I have bowed to the inevitable, and will install this gauge on top of the boiler.  Photos to follow.   I expect to be running the engine on steam next time I am in the workshop.   WooHoo!   Not tomorrow though.  Baby sitting.


Trevithick Gas Burner Problems

Today I connected the gas burner to a propane bottle, and it would not light.


The jet, tubing, control knob, and connectors were removed from an old gas camping stove.  The camping stove burner is in the picture above.

The only way that I could get the engine burner to light up was to block off about half of the outlets in the ceramic burner.


With half of the burner blocked, the other half produced a nice hot flame, but whenever I increased the open area the flamed spluttered, and died.


The more area exposed, the worse the flame.


..And eventually it died.  Adjusting the gas settings made no difference.  Blocking the other end of the ceramic burner resulted in being unable to light it at all.

It appears that that the gas air mixture is being blown to the distal end of the burner, where it will burn.  But if too many holes in the burner are exposed, it just will not function.

So, I came home to ask for advice from my readers, and lo and behold, before I even opened up the blog I checked my emails, and there was a message from reader Huib who predicted the problems after looking at yesterday’s post, and told me how to overcome it.

Huibs letter,

Hi John,

I have read your blog about the gasburner, I  suggest that you  make a brass pipe with small holes in it to spread the gas all under the ceramic stone, otherwise I think the stone will only fire up at the beginning of the stone.

Or as I did, fill the space unther the stone with stainless steel wool, this material will also ensure a spread of the gas under the stone, but not as much as a brass pipe with holes.

I have the stone sealed in the holder with stove kit, this kit is heat resistant.   I think that is available in your area.


Regards Huib

2019-02-06 07.47.18.jpg

There are some aspects of this blogging business that I really like!!  I will let you know how the suggestion works in a couple of days.   Thanks Huib!!!


A Gas Burner for the Trevithick Dredger Engine

Last post I asked if anyone could guess what the redgum pieces were going to be used for.


Today I turned up another piece of the puzzle, which might be helpful..



And look where it fits..with a 1mm gap.



Just to bend a piece of annealed brass in the press.   Hmm.. I wonder where this will fit..


Ah… now I see…


Silver soldered.  Ceramic burner needs to be cut.  Diamond saw?  Maybe I will try the bandsaw..


Well, that is surprising.  I expected that the ceramic material would laugh at the bandsaw blade.  But no problem at all.  Like a hot knife through butter.


After sawing the burner roughly to size, the edges were given the curved contour with a belt sander.  Again, easy as.  It is sitting in position, but needs the edges sealed with some heat resistant goo.   Any suggestions?

The gas burner will be easy to remove if I ever run the Trevithick engine on coal.  I am still fiddling with gas jets, hoses and connections.

Trevithick Dredger Engine – Base -4

Reader Jenny asked about original mounting methods for the dredger engine.

This picture appeared in the Rees Cyclopedia of 1819, and as far as I know, is the only picture exisiting of the engine in its use as a dredger engine.

Trevithick dredger on Thames - Rees.jpg

Gun boats had no method of propulsion, so they were towed into position.  They were very strongly constructed to withstand the enormous forces of firing cannons, mortars and siege guns.  Often they carried only one very large blackpowder gun.  Trevithick chose one of these vessels to mount his steam engine to dredge the Thames.  Somewhere I have seen a drawing of the construction of one of these vessels, showing the massive oak beams and thick deck.  At this time I cannot relocate the drawing, but when I find it I will post it.

Many more of Trevithick’s “strong steam” engines were used to pump out mines, and operate factories and mills.  We can assume that those engines would have been mounted on a base of bricks, stone blocks, or large wooden beams.  The engines weighed about 4 tonnes, so it is possible that they just sat on the strongly constructed factory floor, with a slot for the flywheel and driving gear.

And in writing this I have come across another drawing from the Trevithick era of one of his engines mounted for use in a factory.  This layout drawing was by John Rastrick, an engineer at Hazeldines, who made the engine which is in the London Science Museum.  It shows a 4 hp Trevithick puffer engine, driving 2 “scouring barrels” and “a set of polishing lathes”.

Screen Shot 2019-02-04 at 5.55.27 am.png

Screen Shot 2019-02-04 at 5.56.25 am.png

This is very interesting to me.  First, the engine mounts are likely to be masonry, possibly topped with wooden beams.  The flywheel is mounted not on the crankshaft, but on a separate, extra shaft.  The connecting rods are straight, and rather too thin to be wood;  more likely steel or cast iron.  The safety valve weight is suspended on a long shaft, well away from the front of the boiler.  The front boiler support has angled ends, not squared. The crosshead has tapered edges, not parallel.  And the firebox door is approximately as I had guessed it, although rather smaller proportionately than the firebox than I have made it.

I am sure that this is not intended to be an accurate representation of the details of the Trevithick engine, but I suspect the engineer who drew it would have got the proportions approximately correct.


Now I have to decide whether I have made a model dredger engine, or a model factory engine.


Trevithick Dredger Engine Base.- 3

Just a quickie.

One of our GSMEE members, Stuart Tankard, solved the base issue on his most recent engine build like this….


Those bricks are CNC’d out of aluminium bar.

Reader Huib suggested that if I follow suit, I should program in some imperfections!

Maybe I will ask Stuart to make my base.  (relax Stuart.  I wouldn’t do it to you.)

Trevithick Dredger Engine Base -2

It is odd how the most trivial part of the model dredger engine, the base, seems to have occupied more consideration than any other parts of the entire boiler and engine.

Thankyou to those readers who have offered opinions about the base options.  The most common design preferred, including SWMBO,  was the brick base.  I am still thinking about that one.  Meanwhile, here is a photo of the engine sitting on the blocks of wood which I had cut yesterday.   Not joined yet.


SWMBO opined that it looks a bit “bitsy” and clunky – (I always get an honest opinion from that one). To me it looks sturdy and believable and functional.  And it would be darker when finished.

Another really hot day here, so just an hour or so was enough in the workshop.  And this is what I made.    Can you guess what it is for?  It is made of redgum, a very hard dense Australian eucalypt.


Held as firmly as possible in the 4 jaw, Center drilled, then 16 mm through drilled.  The check does not matter. 


Then 30mm


Then 49mm


Then  bored to 60mm and split.   135mm long.

It will be used in the next workshop session.

Trevithick Dredger Engine Base

This may well not be the final version of the base for the model dredger engine, but of the alternatives it is the simplest to build, so I will put it together and see how it looks.  Most readers who responded to my query for opinions about alternatives opted for the model bricks base, and that remains a possibility.

But the wooden block base is attractive because it is simple, has a reminiscence of the gun boat origin of the dredger, and would be easy for me, a previous woodworker, to build.

This is how it would look..

Trevithick wood blocks.JPG

The top is European oak, chunky, simple.  Has some appeal.  Would look more appealing when fastened and polished.   The top would be grooved, to look like thick oak decking planks.

By no means committed to this option, but considering it.   The square section wood is Australian Mountain Ash, a superb furniture quality hardwood.

Trevithick Boiler Feed Pump, and a base.

Quite a few potential workshop days are being foregone because we in southern Oz are experiencing a very hot summer.  And the few more moderate temperature days are “lost” to essential jobs for SWMBO, and around the house.   Shouldn’t complain about the weather.   Townsville, Queensland, where my brother and family lives, has been declared a disaster area due to torrential floods…  1000mm (39″) rain in the last few days, with more on the way.  And the next ice age has apparently started in USA.

But,  back to the workshop for a few hours here and there, I have made the boiler water feed pump for the Trevithick dredger engine.   As usual, I grossly underestimated the time these few simple components would take to make.


The pump is driven off the crossbar where the stroke is 100mm (4″).  At the pump, the stroke is ~17mm (~5/8″).  The suction side has an 8mm (stainless steel) non return ball valve and the delivery has a 6mm non return SS ball valve.  The plans specified a dummy pump, for appearance only, but I have made it functional.


The 2mm ss cap screw is to limit the ball movement to 0.8mm travel.  Something less conspicuous will replace the cap screw.  Probably a ss grub screw.

The rod driving the pump piston is a piece of bronze brazing filler rod.  Just happened to be the correct diameter.

I will need to add a further pump, hidden somewhere, for boiler approval.  It will probably be a hand pump.

The next step is to design and make the stand for the engine.  The plans specify a large, and in my opinion –  ugly, wooden box.  So that is not on my option list.

Most of these “dredger” engines were used in factories and mills.  Some were used to drive mine pumps, and a few were used on dredgers.  In the factories and mills they would have sat on masonry or wooden bases, and on the dredgers they would have sat on the very solid decks.  (the dredgers in some cases were converted gun ships, designed to mount large black powder cannons,  mortars or seige guns, so they were very solid!)

Now, some pictures of other dredger engine models, and the reconstructed full size one, and their bases.  I have numbered the pictures, and I would be interested in my readers opinion about which would best suit my model.  Please leave a comment.



1. The engine as mounted in The London Science Museum, on large wooden blocks.


2. A Model Dredger Engine on a masonry base.  I could do something similar, but I would used aerated concrete.


3. A very simple wooden base.

Screen Shot 2019-02-01 at 10.39.21 am.png

4. A beautifully crafted model on a cabinet maker’s base.  Acknowledgement to fredyfredy42.                                              I like the colour scheme too!

Screen Shot 2019-01-30 at 5.30.56 am.png

5. Another simple wood block base, reminiscent of the gun boat decking and frame.

odellen 2 137 (69).JPG

6. An elegant wooden base


7. And finally, the modern, aluminium base for the beam engine which I made a few years ago.  I like it on the beam engine, but I doubt that it would look OK under the Trevithick.  The dredger engine is shorter, taller, and narrower.



New Oxy-Propane Torch just watch!

Yesterday I took delivery of a tiny oxy torch.  I guess that most buyers would be jewellers,   but if you watched my post about silver soldering the tiny Trevithick dredger engine firebox door hinges, you will understand my interest in this Ebay offering for $AUD28.

I am experimenting with making videos for this post, so please excuse the amateurish faults in the following videos.

And here I am experimenting with the tiny torch.  Frankly, It is probably not up to the job here, but it was interesting trying it.  I can see that it will be very useful for other small jobs.

Please excuse the awful video technique.  I can see that I need a better camera, tripod, and technique.

This little oxy – propane/acetylene/MAPP gas/hydrogen/ etc is pretty awesome.

And BTW, the leak in the water pre-heater was fixed!

Brass Lust

Record hot temperatures in Australia today.  Highest temperature ever recorded in Adelaide 46ºc 114ºf.  And Alice Springs has now had 14 days over 40ºc.  Not so bad in Geelong 39ºc 102ºf,  but too hot for my workshop.

So I decided to celebrate the running of the Trevithick Dredger Engine 1:8 model, by driving to Melbourne and stocking up on round rod brass.

Geelong is 65km from Melbourne, freeway all the way, but the non ferrous supplier is the other side of Melbourne,  in Clayton, 100km away.   About a 2 hour trip.  But what better to do on a hot day.   And I had a new audio book to listen to.   (The book is “A.D   – After Disclosure”.  Yes, I am close to certain that UFO’s are real, of non terrestrial origin, and that their existence has been known to various militaries and governments for up to 70 years.  Another story.)

So I arrived at George White P/L in Clayton, and told the guy that I wanted a 3.6m length of every round brass section, metric and imperial, up to 22.11mm (7/8″) diameter, cut into 1.2m lengths so I could carry them in my car. (I had some 25.4mm 1″ already)

I had told SWMBO that I was going to spend a few hundred dollars, and she just responded “that’s OK, a lot cheaper than joining a golf club”.  So, without really doing a detailed calculation, and with that permission, I just sat back, and waited.

As the bundles of brass rod gradually accumulated on the bench, I was thinking….”Hmmm, that is a lot of brass”.

Then there was the offcuts box.  It was full of chunks of brass and bronze and copper.  At the flat rate price of $AUD6 per kg.   So, as I waited, I made a pile of all the bits that I thought would look good in my bits and pieces bin in my workshop.   It came to 34kg (75lb).   Eeeew.

Needless to say, the final bill came to more than a few hundred dollars.

But you know what?  I am really delighted that I can stop rummaging around and making do with wrong sizes, or machining little parts out of big bits of brass.

I do wonder if I will ever use up all of this round stock.  Some will probably be used by friends and members of my model engineering club.   Some will probably be there when there is a “clearing sale” after I snuff it.

Reminds me of a sign which I saw at a steam meeting   “When I am gone, I hope that my wife does not sell my engines for what I told her I paid for them”.

Timing the Trevithick Dredger engine-4


After the debacle of the valve sleeve rotating because I had not secured it, I secured it with a grub screw, and had another attempt at running the engine today.

But before that I shortened the valve lever blocks by 2-3mm.  I had noticed that air was entering the cylinder well before top and bottom dead centre.  Shortening the bars delayed the entry a bit.   Still a little bit before TDC and BDC, but watch the videos to see the result.


So, it is still not finished, and the timing will need some fine tuning.  But it works!   Phew..

It works in forward and reverse, depending on piston position when it starts, or if the flywheel is given a initial swing.

In the above videos the engine is not bolted to the box, and some of the noise is the cranks hitting the box.  The valve arm being hit by the striker is also contributing to the noise.

I will work on the gas burner next.


Timing the Trevithick dredger engine-3. How embarrassing….

As planned I removed the engine from the boiler, to discover why it would not work with compressed air yesterday.


After yesterday’s failed attempt with compressed air, I removed the cylinder and piston and valve assembly from the boiler to check the steam passages, throttle and rotary valve. 


These components were removed so I could see what was going on.

I wish that I had checked this before going into print yesterday.

I discovered that the bronze cylindrical insert with the steam ports had never been fixed/Loctited into position.  Clearly it had rotated with the first engine movements yesterday, causing all steam passages to be blocked.  No wonder I couldn’t get the engine to do anything!

And worst was that I had mentally made a note to secure the insert, when I inserted it, a month or so ago.

So today I drilled and tapped a hole for a stainless steel grub screw to hold the insert into position.  I decided not to Loctite it at this time, but will do so when I am sure that the timing is correct.  I might need to alter the shape of the ports, and the insert would need to be removed to do that.


Tapping the thread for the grub screw using the shop built tapping head which I made to Mogen Kilde’s design a couple of years ago.  I have never broken a tap while using this tool.

After reassembling the components I ran another test with compressed air.

Somewhat to my surprise, at 20psi the engine ran for a few revolutions, before  settling down into a back and forth motion.  It still needs to be timed, but hey, it moves.  But by this time it was becoming hot in the workshop, so I left the timing for another day.  Maybe tomorrow pm.   Not Thursday because it will be HOT.  42ºc  (107.6ºf)


Timing the Trevithick Dredger Engine_ 2 making the fittings

Today I made the fittings which would enable timing the dredger engine…


I needed access to the boiler for compressed air, and a temporary installation of a pressure gauge.  I decided to add a valve, so that I could shut off or adjust the compressed air.

I had made a safety valve, with a lead weight, but I had no idea of what pressure the valve would release, hence the gauge.  A spring had been specified in the plans, but I did not know whether it was actually required, so initially I left it out.

So, with the above setup completed, I turned on the compressor, and waited to see when the safety valve would vent.

It vented at about 20psi, a bit low.   So I added a spring.   That pushed the venting pressure up to 30psi.   At 30psi, the engine was still not turning over.

I was expecting that the engine would move at 30psi, but that the timing would need adjusting.   After an initial movement back and forth…. nothing.

The engine is still a bit tight, so maybe more pressure required, so I installed a heavier spring.


So I installed a heavier spring.  Pressure rose to 50psi before venting.  Still no movement in the engine.   Something is wrong.


  1. The throttle is not working properly.  Maybe the plans are back to front, or I have made the throttle back to front.  I have made both of those errors in previous builds.
  2. The steam valve is back to front.  Yes, I have done that before too.
  3. There is a blocked steam-air passage.  Yes, I have managed that one before too.

Next steps…   re-examine the plans.    Do a tear down of the throttle and steam valves.   If no obvious cause for the failure of movement…. call for expert help.   Yep.  I have done that before too.

Timing the Trevithick Dredger Engine – 1. theory.

The plan is this…

  1. Finish constructing and installing all of the components, including gaskets, seals.
  2. Install a pressure gauge, in a temporary position.  Trevithick did not have pressure gauges available, but the current model boiler regulations insist on one.  So my plan is to have one installed eventually on the base, out of the viewing public sight, but where the operator (me) can see it.  For the purposes of the timing, which requires some pressure in the boiler, the gauge location will be on top of the boiler, but moved to its final position later.
  3. Install a fitting to admit compressed air to the boiler.  And a valve to adjust the flow and turn the air on and off.


The lever with the hole controls the entry and exhaust of steam into each end of the cylinder. (The other handle is the throttle.)

The timing is adjusted by removing material from the blocks above and below the lever.  The blocks were made, deliberately, a few millimeters too long.

I will put some compressed air into the boiler, at about 20psi, and slowly move the lever until I hear air entering the cylinder at each end.  The lever position at which  air enters each end of the cylinder will be marked and measured.  Then the blocks will be machined or filed to the correct length.  I will assume that if the entry point is correct, then the exhaust will automatically be correct.

That’s the theory.

I have started making fittings for the pressure gauge and air couplings, and hope to get to the timing in the next day or so.   I will also be checking the pressure at which the safety valve lifts.  I will be aiming for 55-60psi.

%d bloggers like this: