Tag Archives: marine steam engine

Tube Expanding and Economiser Headers

Just an update on progress with the boiler and other (interrupting) activities.

Tube Expanding

Nigel was good enough to make the trip north and assist with the tubing of the first boiler.

This was actually a simple, if repetitive, job.

Fitting the tubes

We firstly supported the three drums in the casing end plates, which were temporarily joined with lengths of timber. When fitting the tubes the game plan is to first locate the “centre” row of straight tubes, then fit the outer rows.

In practice there is not enough clearance to insert the first end of the tube with the drums in their correct orientation, so one firstly turns one of the drums in the casing to allow one end of each of the first row of tubes to be slid into this drum, and then the drum can be rotated back to its correct orientation and the free end of the tube inserted into the other drum.   (Hint: Insert them into the mud drum first, we actually started by inserting them into the steam drum first, but they fall out as you rotate this drum).

Once the straight tubes are in place then the outer rows can be inserted by inserting the tube into one drum and pushing it in as far as the first bend, this then provides the clearance to allow the  tub to be swung into place and then you can slide the free end back into the other drum.

Once the tubes are in place you can commence expanding (in fact we expanded the straight tubes into place before inserting the bent ones. Drilling all the holes with a 12.1mm drill actually worked well and provided just enough clearance to allow assembly – any tighter and it would have been a real struggle.

How much expansion?

Before expanding we did the maths on how much expansion was needed. The idea is that firstly you expand the tube to take up the slack between the tube and the hole (12mm OD, 12.15mm hole) so this was 0.15mm on diameter, then you expand the tube by 5% of its wall thickness. So given a wall thickness of 0.7mm this meant expanding the tubes a further 0.07mm. So the resulting ID of the tube was 10.82mm.  We did this by test expanding one tube in stages and checking the diameter, and when it was right we measured the free-length of the mandrel still showing. This proved to be about 20mm, so we then made a 20mm collar for the mandrel which stopped the expanding at the right point.

This worked very well, the load on the drill driving the expander could be heard to change as the expander reached the collar, thus making it simple to know when each tube was tight, without a lot of squinting down the drums. It’s really a two man job, as one needs to hold the tube so that the required 3mm+ of the tube is extended into the drum, while the other drives the expander and “contraption”. A video of the process in action:

We actually fitted about three-quarters of the tubes that we could reach from one end and then turned the boiler around and did the tubes at the other end. It might have been better to work from both ends, as by the time we had finished the mud drums had been pushed out sideways in the casing by about 1mm – no big issue, but information we will use when expanding the other boilers.

One other issue was that the “contraption” and expander proved too long to be assembled inside the smaller mud drums. We solved this by shortening the “chuck” on the “contraption” and by shortening and regrinding the square drive on the expander.

Here are some pictures showing the process. About 14hrs work to expand the tubes for one boiler.

Interruptions

The next part of the job was to turn up the ends for the drum, and also the economiser and superheater ends.

I decided to start with the economiser and superheater ends. Having first drilled another 12.1mm hole in the centre of the blanks for the inner headers (to take one of the super heater tubes), this was initially a simple turning job with the blanks held on a mandrel pre-turned in a 3-jaw chuck – this lead to Interruption 1, the clutch on the Harrison started slipping when confronted with the loads of highspeed turning with the insert tooling I was using. So an hour of so cleaning and refilling the parts washer followed by getting all the oil off  the clutch plates solved the problem.

Then we needed to cut 70mm diameter 12mm deep recesses in the centre of each part – I started by boring one of these, but it was slow work, so I decided to change over to milling these – here two more interruptions intervened in progress. Firstly the Mill started a rather worrying clicking noise from the gearbox – trying to ignore it didn’t seem to work, so I concluded I needed to strip it and investigate, as any major failure would be catastrophic as there very few parts available if anything broke.

Rambaudi Mill Gearbox Servicing

Rambaudi Mill Gearbox Servicing

This was simple to do, but hard on the nerves  – more parts washing, lots of inspecting and new grease restored the machine to full (quiet) operation. I think small bits of dirt and swarf had migrated into the gears and spindle bearings, and the cleaning sorted things.

 

Lastly, I spent a while trying to resharpen a bunch of broken and worn milling cutters with pretty limited success – so I bit-the-bullet and purchased some new cutters, including a 16mm “ripping” cutter designed to rough out at higher speed – a good choice.

Recess Milling and PCD drilling

I decided to mount the header blanks on a rotary table and then mill the 70mm recesses with the ripping cutter, then remount the blanks on the table with a stud through the centre hole, located between a set of stops to drill the 12 M8 tapping holes using the DRO’s PCD program – nice and simple and accurate. More pics.

Shiny Things

While we await the 600+ cut and bent boiler tubes from the other members of the “Boiler Collective” beavering away in Sussex, we went back to the engine to try and close off the final list of “to do” jobs….

Cleading/Lagging/Cladding

I think Cleading is the official word for this, even though WordPress objects!

This is installed around the cylinder block to try to keep the heat in, raise the temperature of the block and reduce power-sapping condensation in the cylinders. (A thin film of condensate on the cylinder walls can apparently eat up to about 50% of the input steam in small (2″) cylinders according to this paper).

While on the face of it the Leak’s cleading can be quite simple, it still took two days of paper templates and careful nibbling of the 40thou stainless sheet I chose to use. This is thicker than often used, but I had discovered in using the same material on the 5″ Nigel Gresley I built, that is produces a far more robust job, and is much less prone to kinks and dents.

This was layed over a sheet of Kaowool blanket (with extra layers stuffed into the spaces) and secured with 2BA screws (temp ones shown in pictures) and I was quite pleased with the overall job.

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Condenser Mounting

The mounting of the ancillaries onto the engine always seems to entail many hours of contemplation and procrastination (see next bit). On the Leak the condenser was not discussed in the original Model Engineer articles, and while the drawings are available the mounting is left to the builder’s discretion.

I opted not to undertake the building of the condenser. and instead managed to purchase a second-hand item (probably for a Stuart Turner 6A) from Simpson’s in Coniston at a very fair price. I eventually decided to build some large “shelf brackets” from some 3mm brass plate in the “stores”, and attached these to the flat faces on the rear of the bed and columns that were originally meant to hold the air/feed pump assemblies and cross-head guide. Having polished them with those fantastic York abrasive rubber blocks that Cromwell stock they looked quite posh!

The Condenser Shelf Brackets

The Condenser Shelf Brackets

Clearly the condenser itself still needs a coat of nice paint!

Displacement Activity

The next task is to find a place to mount the lubricator pump, and this engendered a lot of head scratching and eventually got diverted into some classic “displacement activity” (things you do to avoid doing the thing you need to do!).

So I polished the gauges I plan to use… more abrasive-block work and a nice result…

Shiny Gauge Set

Shiny Gauge Set

Onwards…..

Setting the valve gear ….

Well as the videos below demonstrate we have the valve gear finished, and I managed to time it reasonably. There is some blowby on the HP, and that might need further investigation, but on the whole it’s OK.

I scratched my head a lot on how to set this gear, and while this might not be the “right way” and the setting is certainly not “perfect” – let me tell you how I did this….

Firstly we set the engine up so I could feed each cylinder from compressed air, with “ball-a-fix” valves to allow me to control the amount of flow, and which cylinder is fed. Also fitted a small pressure regulator to allow me to control the pressure fed to the engine.

This set up allowed me to turn the engine over by hand and feel when the air pressure was assisting or hindering this turning, and thereby determine if the gear was feeding the pressure at the right part of the stroke. Then one could simply say “is the gear ahead of the crank position?” (e.g. the air is being fed too soon, or cut off too soon), OR “is the gear behind the crank” (e.g. the air is being fed too late). It was then quite simple to slack off the allen screw locking the eccentric to the crank, use the key to hold the eccentric in place, and manually move the crank ahead or behind (forwards or backwards) to attempt to correct the error. I did this first in full-forward gear and then repeated the same process for the HP  cylinder, and then in full reverse (setting the relevant eccentrics).

Three or four iterations produced the results shown below…

Firstly running in (very) slow forwards

Secondly, a “video tour” providing a more detailed view of the various components?

The &^*$! reversing gear…

Well, if you’re building this engine then I hope the valve gear goes more smoothly for you than me!

The Draglinks

The Drag Link Bearings

Drag Link Bearing Blanks

A handfull of work, drag link bearing blanks ready for drilling boring, fitting and oil-hole drilling

I cannot believe just how long it has taken to complete the reversing gear on the engine – and it’s still not done.

The multitude of little blocks (drag-link bearings) take an age to make – if you had some 7/16″ sq Ph Bronze bar to hand then it might be OK, but I didn’t so decided to hack the blanks out of a piece of 2-inch square bar I had. However, I discovered that my trusty Warco bandsaw did not cut as straight as I hoped, and half of the resulting blocks were undersize. So then you spend a while silver soldering extra bits back on, to bring them to size, and then (literally) DAYS on the shaper, transforming a set of rough cut rhomboids into little cuboid shapes.

Drag Link Pins

Meanwhile a relatively simple turning and pressing job produces the pins for the lifting arms and eccentric pivots.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

I happened to have some EN1A on the shelf that these got cut from – this is lovely free-cutting (leaded) mild steel, but I must confess I worry that this is so “soft” that it might not last well in service.

BTW – Midway thru the gear building I ran short of 1/4MS bar. So I went off to Metal Super Markets in Southampton (metalsupermarkets.com) and stocked up on a variety of bar and plate, that my “stores” were running short of; (these really are great people, and very helpful and economic – I would recommend them to anyone, over the counter service with a smile, for even small quantities) – But they only had EN3B, and when it came to turning and screw-cutting this stuff you really miss the free-cutting EN1A!!!

The only issue with the manufacture of these pins, is that one of the errors in the drawings means these pins need to be longer than drawn, to clear the bolts and lock nuts securing the Expansion Links and Die Blocks. There’s not a lot of space, so take care – I extended mine to 1.5″ overall (I think).

Drilling and Boring Drag-Link Bearings

drilling the bearingsThe next job was to drill the bearing halves for the rods. I did this by clamping them into a small jig (with tool-makers clamps). My normal approach to this would be to soft solder (“sweat”) the bearing halves together and then drill and bore them as one, separating them at the end. But this was not what the ME articles said – so I followed them… The plan was to create a small jig, drill half the blocks 2BA clearance and the other half 2BA tapping – then tap these and use temporary screws to assemble them into pairs while they are bored, and then open out both sides to clearance for the long rods to be fitted.

Jig Drilling DragLink Bearings

Jig Drilling DragLink Bearings

I think this approach was slower.  A better plan would have been to solder them into pairs while they were all still oversize, drill, bore, finish to size and then separate.

As it was I then discovered that despite machining all the blocks to size, the journals on the pins were too tight (only a few thou, but enough to stop them fitting, so yet more fettling was needed)- At this point I discovered that the relevant reamer has gone missing, so more careful hand work on pins and bores (scrapers and emery tape) was needed to get a good fit….

The Valve Rods

This is about to start sounding like the blog of a complete idiot, but at least it’s improving my patience.

LP Valve Rod

Firstly, while assembling and testing the valve gear (prior to first run on air) I found that the LP valve was fouling something and could not accommodate the full travel of the eccentrics, over a couple of hours of assembly, disassembly, reassembly (repeat as needed) I came to the conclusion that the tailrod was too long and clouting the end of the tailrod guide… there being no opportunity to lengthen the guide, I decided to shorten the tail rod – carefully sawed 1/4″ off, and reassembled again, only to find it STILL DOES NOT FIT!!!!!

Further inspection determined that the valve buckle was actually fouling the nut holding the tail-rod guide – and actually the shortened tail-rod was now falling out of the guide at the lower extent of the valve travel!!! So, it now needs lengthening – more work yet to be completed…

HP Valve Rod

The HP valve rod has a “joggle” on the bottom to line up the valve rod with the eccentrics. I decided to make this as a separate part and screw it to the rod proper. This joggle also serves to further widen the already widened drag-link pins resulting from the error in the drawings. I did measure this and allow for it in the longer pins – but I forgot to take account of the lock-nut on the die-block pin….AAAARRRGGG!!!

I concluded I could shave enough off the joggle to accommodate all this, but the amount of metal left for the thread holding the actual valve-rod into the joggle was going to be a bit thin, so I decided to braze the rod into the joggle – this I did (with no distortion), and decided to use the Linisher (belt sander) to just clean the flux and oxide off the joggle…. What I failed to see as I did the final side was that I was holding the assembly slightly out of square and ground a nice 20thou depression in the bally valve rod – thus rendering the whole shooting match scrap! 😐

Either way it provided me the opportunity to screw-cut the 3″ long 3/8″x26 thread on the new rod, using the off-set compound slide method often recommended (but never tried by me) mechanism – and it does a much nicer job (even on the nasty EN3B!), so I conosoled myself that the extra 3 hours work, had resulted in a nicer job (displays a fixed grin)!

BTW, In this process I again reminded myself that under conditions where you need to take fine cuts on tough material a carefully sharpened carbide or carbon steel tool will outperform a indexable tipped tool – as if you check the specs these are not typically made to make a cut of less than 5thou !

The Result….

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Overall these 16 half bearings and eight rods and 4 pins took more than a 10 days of effort (probably about 30 hours! not including the remaking of the vale rod) – a slog…. assembling the whole sh-bang produced something that worked but was too stiff, so more fettling and adjusting needed!

I am really hoping I can bring this all to a good end – sometimes I wonder!

Machining the Air Pump Slideways

I thought I would record this as a video, to show the machines in action.

The machining is being done on my Adcock & Shipley 1AD horizontal mill, that I bought for a fiver back in the early ’80s. I have grafted a Bridgeport J-Type vertical milling head onto this, and fitted with a home-build DRO (Shumatec design) – and I am quite chuffed with the result…