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