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Steam Engine Number One

A Build Log (hopefully)

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Iain Downs08/05/2020 16:31:11
649 forum posts
570 photos

A little more done today after various distractions. I've honed the cylinder with a cylinder hone. Which took a few minutes. It took a good deal longer to find the cylinder hone as I'd put it away 'somewhere sensible'.

Also trimmed the piston on the piston rod down to be a close fit in the cylinder. There was a slightly lumpy bit at one end, which the cylinder hone also took care of.

Finally, I took a little bit off the inside of the piston gland so that the cap would screw down a little more. about 20 seconds work, but a good 10 minutes of random walk trying to get a good register on the 4 jaw chuck. Still that's an improvement!

Next steps would seem to be soldering the piston gland to the bottom cylinder plate and millling the valve ports.

I'm not sure whether to break and heat treat the piston rings at this point or if I should leave them intact until final assembly. I will probably leave them for now. I'm still a long way from having it ready to run.


Iain Downs10/05/2020 17:41:58
649 forum posts
570 photos

Valve ports yesterday. Though clearly a little bit too much of happiness juice as I appear to have uploaded the pictures twice. Or it's just old age...

On the whole this went well, though I was attempting to do the cutting by eye against marks made with a scriber. The marks were fine, but I hadn't take into account the difficulty of seeing the work piece with a great big spindle in the way and a whole bunch of cast iron grit. Made me wish my DRO had arrived.

Here is the piece being setup to be accurately held in the vice. Turn it upside down on the surface plate can clamp some 20 40 80 blocks to it, then sit it on those.

valveports setting up.jpg

This then gets gripped in my new big vice - though I'm realising that I how need to get some bigger parallels. It never stops, does it?

valveports on the mill.jpg

I was quite worried about milling 11 mm deep slots in the face and even more worried about the 25 mm deep slots at the end, but I had no dramas at all, cutting about 1.5mm deep each time. The DRO on the spindle is a joy. At one point Madam returned from some shopping exhibition (tip - queue too long and waitrose queue too long) and had to tell me about it. With my old mill I would have no idea how deep I'd gone and need to start again.

valveports milling.jpg

When I said, no dramas, That was true of the actual deep cuts, but when milling the end of the face there were some odd noises and a ping as the cutter gave way. I have no idea what I did. the replacement cutter finished it off fine.

And here are the results.

valveports milled.jpg

valveports end.jpg

In truth they could have come out cleaner, but I'm mainly content that I haven't ruined the cylinder. It would have made me deeply sad to have to start this again!

Next step is probably to drill and bold the end caps in place or possibly a trial fit even without out that. If it turns out that the throw is longer than the cylinder.... Well, I;ll probably make a clock.


Iain Downs11/05/2020 16:55:41
649 forum posts
570 photos

I find myself a bit of a fair-weather modeller. If it's sunny outside, it's nice to be in the shed. If it's grey, cold and drizzly, then the armchair has some attractions.

Today was spent doing a bit more work on the design for the engine. I know, a bit late to be messing with it now...

However, I decided that I might as well add some valve gear as it won't add a huge amount to the time I've already spent - and better now than trying to add it later.

Here are some drawings. The first giving an overall impression of the engine and the second for the valve gear.


valvegear drawing01.jpg

I might make some cosmetic changes such as rounding the eccentric straps. Also the straps will be split and bolted together and the eccentrics have grubscrews to fix then to the crank.

My main concern is about sizes. I see in some engines that the eccentric rods are fat things, whereas I didn't see the point. Mine are 5mm, but perhaps that's too small, particularly in EN1b - would silver steel be better. By the same token the eccentrics are quite thin, but equally they don't have a huge load.

I'm also not sure of the best material. I was thinking of cast iron for the eccentrics and mild steel for the straps.

Broadly, the two eccentrics are fixed to the crank with grubscrews. The eccentric straps are connected to the Stevensons link and the bearing connects to the top eccentric rod (bottom, middle, unlabelled) which passes through the valve guide bearing that is secured to the valve guide and thence passes into the valve chest. Please ignore the rod at the top of the top eccentric rod. That will end up a thread that ultimately connects to the D Valve.

OH and I will need to work out some way of locking the Stevenson's control lever. Probably something from the bottom cylinder plat, but not sure what exactly.

The other thing I wanted to check is the way I'm securing the cylinder to the top and bottom ends. I'm planning 7 M5 bolts at 50 degrees apart, except for a 60 degree gap where the valve ports are. top and bottom to be held by thread into the cast iron (5mm thick) of cylinder flange. Is that enough and will bolting directly into cast iron be strong enough.

On the practical front I've made some hold-downs for my rotary table so I can secure the cylinder to it.


JasonB11/05/2020 17:12:55
18103 forum posts
1994 photos
1 articles

5mm dia rods should be OK but your dimensioned 4mm straps sound a bit thin and are actually shown thicker than the 5mm rods, 6-8mm would be better.

Thread the top end of the valve rod and have a rectangular bar that screws onto it so you have some adjustment

5 x M5 should be OK.

Iain Downs13/05/2020 18:01:50
649 forum posts
570 photos

Thanks very much, Jason.

I find I've dimensioned the inside of the strap not the outside, so it is actually 8mm. Revised drawing below.

valvegear drawing02.jpg


Iain Downs14/05/2020 20:59:07
649 forum posts
570 photos

Today was about starting the assembly process for the cylinder. What I needed to do was to drill 7 holes in just the right place in the cylinder cap and cylinder. Errors would be disastrous!

Here's how I went about it.

Firstly, I put a rotary table on the mill and centred it with a co-axial indicator.

cylindercap rotary table.jpg

The blurry bright thing is actually a co-axial indicator and I love it!

Next with rotary table centred, I mounted the cylinder clamped it to the rotary table and proceeded to centre that with the coaxial indicator and judicious taps from a hammer. This only just fitted (and I can see a bigger rotary table sometime in my future, but probably not soon) and I'd had to make new clamps to clamp it.

cylindercap cylinder centreing.jpg

II was able to centre the table pretty much spot on (under 0.01mm), but I only managed about 0.05mm (2 thou) with the cylinder. I was pretty happy with that, actually.

The next step was to align the valve face along the mill axis so I had a registration point for the rotation. This meant unlocking the mill table and winding back, turning the rotary table so that the face was at the front and then clocking it, getting the face parallel to the mill by turning the rotary table.

cylindercap clocking valve face.jpg

The, back to the coaxial indicator to re-centre the cylinder, now I have the face parallel to the X axis and the whole shebang under the spindle.

Lock the X axis and wind forward 35 mm.

cylindercap ready to drill.jpg

Oh and clamp the cap on lining up registration marks on the cap and cylinder and taking care to avoid where the holes will go using a printed template.

What I actually did next was to do a trial run. 7.5 turns, 12.5 turns (and another 6 like that) then 7.5 to bring me back to the registration mark at the front. At each point I marked the cap gently with the drill bit. Since I ended up where I started I thought my practice had gone well!

Also when actually drilling I could check my counts against the previous marks to make sure they were correct. They were (much to my relief).

First hole drilled

cylindercap first hole drilled.jpg

Then the rest

cylindercap all holes drilled.jpg

And taking the cap off, all the holes in the cylinder are nicely inline.

cylindercap cylinder drilled.jpg

I'm trying to decide if I should use the same process to tap the holes (in this case not under power), or do them by hand off the mill. Provided I can line up and don't miss my counts it would probably be better to tap on the mill, so I think I'll do that.

Next is to do much the same with the bottom cylinder plate.


Chris Gunn14/05/2020 22:24:34
326 forum posts
24 photos

Ian, if the cylinder is still set up, I would put a centre in your drill chuck and use this to locate the tap wrench to hold the tap straight, and then tap by hand.

Chris Gunn

Iain Downs15/05/2020 08:05:13
649 forum posts
570 photos

Hi, Chris, I've got a tailstock tapping thing which is basically a centre on a spring and I use that in the manner you've described. It saves worrying about pulling the quill down whilst turning the tap.

Same basic idea, just a bit easier. I may even have a go at power tapping, but certainly not on the blind holes!


Edited By Iain Downs on 15/05/2020 08:17:37

Iain Downs16/05/2020 20:15:36
649 forum posts
570 photos

Do you every have one of those days when you start off feeling you're pretty good and then your incompetence swipes you in the face?

Well, I've been expecting this and, to be honest, I'm astonished it's taken this long...

I followed Chris's advice and tapped my cylinder in situ.

cylindercap tapping.jpg

And found the sight of a cleanly secured top cap quite satistying

cylindercap bolted.jpg

Nice, innit?

But then I turned the cylinder upside down to process the bottom plate. Oh dear.

The spigot to hold the cylinder was off centre....


The spigot is 1mm off centre with respect to the edges of the bottom plate.

At this point, I shut down the shed and went indoors. Unusually, not for a glass of comfort (as I occasionally feel a need to let my body recover that this was that day. Sadly).

My first reaction was, Oh bugger!

My second was I can just drill and tap and if it doesn't work I can make a new plate and drill it afterwards.

The third was, 'Did I do this on purpose and have forgotten the reason?' Even I realised that was wishful thinking.

Fortunately a night's sleep put paid to that and I had the thought that I should see if that 1mm actually made a difference.

So (for the first time!) I assembled the engine.


I found two things (well two bad things).

I put the piston gland in place with some superglue, by the way so I can get it out easily if it turns out the plate is gash.

The main one was that if I put the cylinder on, it is fine at the top part of the cycle, but jams near the bottom. This is because the piston position is to far to the back at the bottom. Two possible reasons. One is the 1mm offset and the second is that somehow the piston gland bore is NOT in line with the cylinder registration. By about 0.3mm.

I really don't know how I managed that as the two were machined on a superglue chuck which was never removed in the same machining operation (Possibly several days apart, but even so..).

So I've stuffed up the bottom plate well and truly.

Oh, the other minor thing is that my piston gland is to long It stops the piston rising to TDC.


That, at least is an easy fix!

In a perverted way I'm almost pleased this has happened. It's the first major component I'll have to rework and I expected a major screw up much earlier in the process. I'm still terrified I'll accidentally drill a hole in the wrong part of the cylinder. That would be a trial.

So a chastened Downs is going to buy another bit of steel and see if he can learn from his mistakes.

In the meantime, there are the eccentrics to cock up....


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