Unusual Corliss

[Caber]

I have been thinking about building the MEM Corliss for a while. The nearest real Corliss to me is at the National Museum of Scotland. This is a reasonably locally built example, middling to small size. I was rather astonished to see that rather than the usual oscillating disk operating the valve there are instead two eccentrics with shafts directly operating the inlet and exhaust valves.







Does anyone know about this type of gear and what is the collected opinion on whether this would be simpler to make for the MEM Corliss than the designed version?

Cheers😃🏴󠁧󠁢󠁳󠁣󠁴󠁿

[Jo]

American Corliss engines normally have the disc whereas British engines have the two shafts. There are various flavours of mechanisms used to get the quick cut off on full sized engines but on models you need something chunky/simple like the disc or the Throp Corliss model engine it uses Musgrave trip gear.

The Douglas and Grant Engine's valve gear could be a bit tricky to scale down and have it work. Another view of the trip mechanism:



Notice that only the inlet valves "trip".

<a href="https://www.youtube.com/watch?v=4BoDp8dSFTg" target="_blank">http://www.youtube.com/watch?v=4BoDp8dSFTg</a>

Jo

[Charles Lamont]

I don't know that the oscillating plate arrangement is actually 'usual' in UK practice. The Pollitt & Wigzell engines at Markham Grange & Blists Hill have disks, but the steam and exhaust are separate, with the smaller steam disc partially hidden behind the exhaust one. I have also seen running in the flesh the the corliss valved engines at The Bratch and Mill Meece pumping stations, the Ellenroad Ring Mill engine and the 'big red engine' at The Science Museum. None of these engines has a disk, and all have independent steam and exhaust gear. There is reasonable YouTube coverage of all these engines running.

[Caber]

Ok I have started my Corlis build. I am not yet decided whether to use the rocking plate or the two eccentric type gear but it is going to be based on the MEM drawings. I have started with the cylinder block being carved out of a lump of Mehanite cast iron. I roughed it to size with a shell cutter and finished with a fly cutter though surface finish still not good enough. I bored the cylinder on the lathe, unfortunately gone slightly oversize as I mis allowed dimension allowing for spring in the boring bar as it is stuck out just over 2.5”

I am proposing to drill the valve ways next maybe tomorrow though I realised I don’t have a 1/4 reamer so ordering one today. Is it better doing this before the valve chests and passages?

Caber:)

[crueby]

Great to see the build start, will be watching along. For me, I like the rocking plate version just since it adds an intriguing visual dance to the engine operation, great eye candy. But, as said, there are lots of variations over time and between countries.

 

[Caber]

Progress today drilling the valve bores. All the quarter inch stainless stock is seemingly just undersize so rattled in the test drilling reamed to quarter inch. My quarter inch drill however matched the stock so I drilled the holes to 7/64 then ran the quarter drill through very slowly which gives a very nice fit and finish in the bores is excellent. While on this set up I plan to drill the holes for fixing the valve caps.

[Caber]

This weekend’s progress was a bit hampered by the installation of a new central heating boiler! What I have achieved is drilling the fixing points for the valve bonnets , all 32 of them and carving out the exhaust valve chest both exercises in learning the circle and array functions of my new DRO.

I also paid another visit to the NMS to look at the Corliss there. I am going to see if I can adapt the MEM design to look more like this engine. One aspect will be mirroring  the design so the valve gear and flywheel will be on the other side, the next task will be to rearrange the slide bar tunnel and connection to the main crank bearing. The final and most challenging  change will be replacing the wrist plate with a second eccentric and valve rod. If anyone who has built the MEM Corliss can tell me what the rotation angle of the valve is when the engine runs that would be a great help to determine the required  eccentric throw as there is no intermediate lever in this design!

[Caber]

So I am some 16 hours of workshop time and have now drilled all the holes except cylinder covers into the cylinder block. Touch wood no broken drills or significant errors. The most nerve racking bit is the 20 holes for the steam ports. As these are in the curved surface of the valve guides I decided to create a flat area with a 3/32” end mill then went straight in with 1/16” drill. I used a sensitive drill attachment in a collet with an expensive sharp HSS drill which all went surprisingly well. Now a ton of tapping 6BA for the 1/8” holes and 9 BA for the 1/16” Experimenting on my scrap cast iron it seems I need to go straight in with a bottoming tap as a number 2 bottoms on the 3/16” hole without forming enough of a thread.

[Caber]

Another weekend on the Corliss. I made the cylinder covers and as I am looking to get more location for the cross head guide the back end cover is somewhat deeper. The intention is to bury the heads of the bolts to get full contact between the guide and cover. I used the DRO hole circle function but could not realign this after I took the cover off.

I then started work on the cross head trunk guide. This is being made from some 2” scrap steel bar that seems to be cutting quite well but needs support in my lathe.

[Caber]

I finished the trunk guide roughing today. Next challenge is to fit it to the cylinder block all fully aligned. After several different ideas I am planning on a couple of stout dowels and clamping them with bolts through the side of the trunk guide. I will start on this tomorrow!

[Dalboy]

Some great progress I enjoy watching other people produce some fine workmanship. I will be following this build keep up the good work

[Kim]

Enjoying watching your build. Nice work on your block and trunk guide.   

Kim

[Caber]

I don’t know what happened to last weeks report so this covers 2 weekends work. Last weekend saw the cylinder and trunk guide united and aligned. I also made feet for the cylinder and commenced the bearing pedestals. This week has been trying to incorporate the bearing pedestal and the trunk guide extension. This has involved a number of “interesting” set ups to preserve alignment. I have tried creating splices between the bearing pedestal and trunk extension that have not worked out as expected. I think I may need to rethink some of this so gave up early this afternoon to get some headspace for fresh ideas.

[Caber]

Further progress has been limited however the crank bearings and supports are complete as is the crank disk. First attempt at the crank shaft failed as I was pushing myself at the end of a session and consequently mid setting the DRO and made what should have been an interference fit with the crank disk a sloppy slip fit☹️ I have been working on the set out of eccentric and valve rods. Making eccentric’s and straps is next on the list. I am trying to figure out valve travel. I think I need 90degree movement at the valve and decide on length of valve cranks.

[Dalboy]

Looking good I have been following what you have done so far. Keep up the good work.

I have yet to get into the workshop but then the first job sort out space for the new toys tools

[Caber]

So more work has been completed. Getting the engine erected on the baseplate complete with flywheel has to be some kind of a milestone and is pretty much essential to setting out the valve gear. I have made a pair of eccentrics but I am really confused by the angle required for the valve operation. I was working back from the MEM drawings and concluded I needed 90degrees of movement however having spent today looking further at video of operating engines I am coming to believe 45 degrees is nearer. If anyone who has built the MEM engine to the drawings can help me out here it would be appreciated.

The next job will be the eccentric sheaves. I happen to have some castings for the RobRoy locomotive and the eccentric dimensions are very close so these are next weekends task unless I need to remake the eccentrics with less throw!

[crueby]

Hi Caber,


I just looked at my Mem Corliss, and the travel on the valve cranks at the end of each valve is more like 30 degrees from center at most, and the travel on the center plate each one connects to is about half that. I built mine at about half size, so the angles might be slightly different than  full size, but not much.


Chris

[Caber]

Chris

Thanks. That is quite a surprise I am not sure where my calculations have erred. Literally back to the drawing board!

[Caber]

Making the eccentrics and straps has been most challenging but so far. After the false start with incorrect throws I remade the eccentrics only to have one grab the tool and fly out of the chuck on the finishing pass destroying the flange. The strap’s weren’t any easier. I started with some castings I had for a Rob Roy . These were horrible with too much draft and a very out of centre and I discovered not round core. After spending a full day trying to get one to size I realised it wasn’t happening so ordered some 1/4” sheet brass. I then needed to do the conversion on my portable band saw to a table type. A project that had been hanging around so I could reasonably accurately rough out the shapes from the sheet. First one went OK second one not so much!  It slipped on the rotary table so I had to redo the set up. Then I broke the carbide cutter that had done the first one without complaint. Then the second cutter broke for no apparent reason. I broke the third by stupidity not lifting the cutter before moving the table which left only one to finish the job. Despite being good on dimensions I needed a lot of fitting to get the straps running nicely on the eccentrics. I think my tolerances on measurement are not good enough anyway done for now but I may remake the straps so they look better once I have sorted the valve events.

[Kim]

Wow, Caber!  You had quite a time with those straps!     Hope you have a better time with the next part you tackle.  That could get expensive going through three cutters for each part!   But they do look good in the end so you persevered. 

Kim

[crueby]

Bummer about the cutters!  One thing for future reference  in case you don't know , most sheet brass is alloy 260, sometimes  called yellow or cartridge  brass. Its a lot grabbier and pushes before cutting than the alloy 360 that most flat and round stock comes in. The 260 still works, but its tougher to cut cleanly, seams to act more like copper does.


 

[Caber]

It looks like I may have been using cutters intended for fibreglass PCB rather than metal! I got them a year ago at a show rather cheap and looking online to replace them the only ones that look similar are not meant for metalwork so maybe the wrong tool. However where can I get 3/32nd" and 1/8th" milling cutters that will work with brass phosphor bronze and steel?

[crueby]

What country are you in, and what type of end mill holders do you have? Collet, Weldon shank? What diameters? Many choices out there!

[Caber]

I am in the UK I have R8 collets down to 1/8"and ER32 collets down to 2-3mm. Max speed on the mill is about 1500RPM 

[Caber]

A moderately successful day today two valve spindles complete the other two ready for the valve flats to be cut only one scrap! Sorry no photos as  I had to leave early for dinner guest!

[Caber]

It has been a while since I posted as I have been working on my 5” hunslet austerity in preparation for club portable track duties this summer. Today was a full day on the Corlis. I have completed a lot of the valve linkage. I was intending to make the small bits from silver steel however I somewhat bent the rod so picked up what I thought was silver steel though I think it is stainless given the grief I have had with surface finish and drilling. I am not entirely happy with the valve levers and may need to remake anyway. Tomorrow job are the link rods then it will be back to piston crosshead and connecting rod!

[Caber]

Another workshop day today completing valve linkages. Not much to say just a lot of quite repetitive turning and drilling operations. Putting it together showed the need to shorten the valve rods a bit to centre the valve motion.

Tomorrow will see a start on piston , piston rod, crosshead and connecting rod to complete all the moving parts😃

[Admiral_dk]

I see that you make progress almost daily 

So even if it's only a bit at the time, it all add up 

Per     

[Caber]

Ah yes! The secret is I retired at the end of March so time to access the workshop has significantly increased🤣

[Caber]

Significant progress yesterday and today! The Con Rod! Quite a lot to do starting with 3/4” steel square bar. Also the first significant piece since the cylinder block that I have not had to do twice! I am not saying no cock ups just that they were recoverable and the only remaining bad machining mark cannot be seen as it is buried in the trunk guide!

4 valve bonnets and crank pin to make then it is time to disassemble and paint before fitted assembly and valve timing. That will have to wait for a while as my 5” Hunslet austerity failed with non working hand pump and injector and it is wanted for club running this summer!

[Caber]

Well all the parts are made and engine norms disassembled for paint. I have tried posting a couple of times but the posts have vaporised. Here is assembled engine

[crueby]

Looking great! Really like the details on the valve pieces. 

[Caber]

Thanks!

Next question is what to use as gasket material. The stuff I have is a bit thick for this size of engine and will create some issues with the smaller parts!

[modelsteam]

Hi.  I use .25mm  PTFE sheet. It's easy to cut with a craft knife and punch holes in . It's works for me. Sample quantities are available on Ebay.
        Good luck with your Corliss .
                Chris

[Caber]

I decided to go with oiled paper gasket material that is about 2.5thou for dimensionally critical gaskets I found a small sheet among my existing gaskets.

My next problem is setting up the valve gear. The working end is straight from the MEM drawings but the operating linkage is all to my design. I have struggled a lot with trying to resolve the angular movement required to operate the valves in the cylinder block. My thinking was I needed to open and close the drillings forming the port between valve chest and cylinder but have come to realise that I need the valve to control the opening of the valve chest to the valve shaft. I presume this is a compromise for the model as efficiency wise this massively increases the volume of steam to start moving the piston. Looking at it this way with an angular offset of 15degrees for the ports, a valve chest opening of 45degrees the effective angular movement of the valve is 30 degrees less a bit to stop overrunning the cylinder ports.

When I try and work out the angular displacement at the valve from the  MEM drawings I get 60.1 degrees which seems wrong. The most uncertain measurement is the effective length of the valve lever which is not dimensioned on the drawing. I am scaling that as 0.3”

I would be grateful if anyone could idiot check my thinking on the valve angles or advise how they managed with setting timing and what angular displacement they have on their engine!

[Caber]

So I think I understand how to do this. I made a cut away model of the valve and valve chest to see how it works and realise that the eccentrics need to be at 90 degrees to the crank and advance is controlled by the rotational position of the valve in the chest. In a full size engine the valve would act against the ports but here it acts against the steam chest aperture. In a proper Corlis the advance is fixed by the valve position and cut off by the trip mechanism that I may come back to on mine once it is running. The major issue is setting the exhaust valves as I don’t know what overlap I need to make the valve steam tight. Currently my geometry gives a rotation of about 35degrees which seems adequate to keep the valve open as wide as the port area for most of the stroke. Timing to get the opening close to bottom dead centre but steam  tight during the previous power stroke will be the challenge. As there wants to be marginal advance on the inlet and it is possible to take the inlet cover off when the engine is erected is a bit less of an issue😃

[Admiral_dk]

Aha moment are always revealing  and usually enjoyable too.

Per   

[Caber]

It’s finished! For now. I am contemplating a governor and trip gear but that needs a lot more design thinking as I have strayed so far from the MEM drawings!

I might also add handrails and lubricators like the prototype I have been following but for now it is done.

My workshop compressor is defunct so when that is sorted I will get it running and put up some video.