How do I fit a rope piston ring to a beam engine condenser?

Hi all.
Here's one for you. Not model engineering I know, but working on the prototype, so I guess that it counts...

I help out at a local industrial steam museum and, among other things (it is a constant work in progress), we are renovating the self-contained condenser on an 1879 Gimson & Co beam engine.

We have got to fit a new piston ring which is made of rope wound 3 or 4 times round the piston and which is secured by the ends in two holes in the ring groove held by pegs hammered in.

My question is; how do you/I trim the ends of the rope so that the outer strands are retained by the peg while making the rope thin enough to go in the hole and be held by the peg?

My thoughts are to 'paint' the outer strands (to identify them when winding it all back up) and then undo the whipping, then use scissors to trim out the inner strands. I feel that the inner should be cut to a taper, cutting a cone into the rope about 1 inch long, ending up at a point in the middle in order to keep the profile of the rope to as close to the hole as possible while giving the peg a chance at fitting the hole to give a start.

Having thought this out, is it then possible to 'drill' out the centre using a cone cutter that I could make? The whipping on the ends of the rope could, maybe, hold the outer strands in place while this is being done.

The rope looks and feels like sisal (the original was) although it is a man-made fibre.
Just to let you know, PTFE rope to do the job is nearly £2000!

Does anyone have any experience or ideas please?

Just something to get the grey cells working.

Many thanks

Andy

 

 

Andy I fear that you will have to learn the secrets of making ‘Square Sennit (or Sinnet)’. Hmm! From memory its making involved many strange oaths, ‘sippers’ of ‘Jamaican Nectar’ (real rum the nearest thing is Woods usual disclaimer) and a baccy pipe.

Two stands of Sisal, Hemp or Manila are whipped at each end and are then ‘middled’ into 4 strands and then plaited just like normal Sennit (or Sinnet) except that the right most strand is tucked ‘round the back’ and over the left most strand. The result is an almost square shaped plait. Square.

I have found two reasonable videos. The first one http://www.youtube.com/watch?v=1lWFn3iyH0I used 4 strands or rather two strands middled. The second one http://www.youtube.com/watch?v=fCcMBl6ecSc uses a single strand and is complicated. For your job I would use the first 4 strand method. There is an excellent diagram at http://home.tiscali.nl/knotsandknottying/knots7.htm#vierkanteplatting4streng .Have a go with some old boot laces first

The strange oaths occurred when the man noticed he had made a ‘Goof’ and had to undo his work.

Square Sennit (or Sinnet)’ was not only used for decorative work but for gaskets, joint washers, piston ‘rings’ and other seals. When stuffed into the place where it is going any slackness in the weave is taken up, and if you are cunning it can be woven on the lines of a ‘Turks Head’. This would be woven loose and then put in place and then tightened up.
Good luck
Dick

I like the square sennet. I have a feeling that the basic material is important, and modern synthetics will not work. Sisal, hemp etc. change properties when wet, and also absorb moisture and oil etc. Just a thought.

Manila, Sisal, and Hemp were all used. They were soaked in oil/grease as they were fitted. The stuff used was some sort of ‘Black Gunge’ (Graphite Grease?) and a thick brown mineral oil.
I saw it done twice the first time was in the form of a Turks head which was woven round a large wooden former with a single strand. It was slipped over the shaft and then tightened up by partly by doubling (that is following the original single line it was woven from. It was then I learned the strange oaths.

 

The second was to act as a large joint washer and that was woven from 4 strands. The trickery bit was butting the ends together. It was sort of ‘interwoven’.

I can imagine all sorts of problems with platics picking up or smearing.

Richard your description of square sinnet reminds me of the 'square knot' (not an American reef knot) we used to tie in our neckerchiefs when I was a Sea Scout - we were a woggle-free zone. Moly grease might be a good (and suitably messy) substitute for tallow.

 

Neil

Hi Dick and everyone,

 

Thank you for the ideas.

 

Sorry, I should have mentioned that the holes are about 3/8 diameter and the rope about 1/2 or 5/8 inch, while the piston is about 2 feet across.

 

I am guilty of what I criticise others for, not asking an accurate question!

 

Anyway, this should then give you my problem...

 

I will try and get photos and proper dimensions next Sunday which will illustrate my problem.

 

Please keep the ideas coming.

 

Andy

Silly question, but do you know what came out of the hole?

 

Neil

If it is any help, this is the engine; one of a matched pair that worked side by side

 

 

And some of the story and dismantling

 

 

Andy

Hi Neil,

 

Yes, we have the plugs and, although I didn't take them out, the chap who did says that there weren't many strands held in.

 

Andy

You may be worrying too much - once in the cylinder there isn't anywhere for the rope to go, so perhaps it isn't a critical job.

 

Neil

Hi Neil,

 

That is true.

However, I have been told that the Navy has a way of reducing a rope to a point in use with hammocks so I will chase that up.

 

Many thanks to all who have offered advice and suggestions...I will keep you posted.

 

Andy

Dear Andy,

 

The penny dropped with your comment about the Navy. Much of my miss spent youth was taken up with sailing. The technique is called 'pointing a rope'. I can send you a scan of the relevant pages from 'Knots & Splices' by Charles Gibson if you like. These days Mr Google can probably help too - once you know what you are looking for.

 

Bill.

 

 

Dear Andy,

 

Should have looked things up before my previous post. Try these:-

 

and

 

 

All you ever wanted to know ....

 

Bill.

-Oh my! The project Guttenberg site contains at least one error. If it contains one error there will be others. The illustration of ‘worming and parcelling’ is wrong. The rule is “Worm and Parcel with lay then turn and serve the other way”!

Shaving down a rope was done for two reasons. These are ‘Looks’ and to guide the rope into or over a pulley. it is done a few stranda at a timeafter each 'tuck'.

Back to the ‘holes in the piston and the ‘pegs' These are there so that the ‘Square Sennit’ can be held and tightened into the piston groove whilst you are fitting it. One strand of the sennit would be ‘shaved down’ and poked into the hole and pegged so the fitter could pull the well greased sennit tight as he worked pushing it into the groove and knocking it down with a mallet and wooden punches. When he had nearly finished he would shave the end strand down and peg it into the other hole to stop it coming undone as the piston was put back into the cylinder.

By the way I have found error 2 in the Guttenberg site. The finishing knot in the illustration of the ‘necklace tie’ is a GRANNEY it must be a REEF. The ‘Badgey’ who taught me and several others would have thrown a fit if we had done that (and keel hauled the culprit).
Where are you Ady 1 this stuff is all nauticians work

looks as though the 'long link' problem has not yet been sorted out yet.  Some one needs to have a good 'Growl' at the system suppliers!" 

Hi Bill,

 

That's great, thanks; the beers are on me at Stalham...if you can wait that long. Haha Hopefully Ramon will be able to be with us too.

 

Richard, thank you for the errata; it does help to clarify.

 

Incidently I was given this link also:

 

 

Andy

 

 

Dear Andy,

 

You're on. Meanwhile happy splicing. Don't forget to post some pictures of your efforts. It's a part of an engine not often seen.

 

Better explain that it is planned to hold a Steam Day at the Museum of the Broads at Stalham on 10th June. I hope it may also be a mid-season meet for people interested in the Model Engineers' Day Out at the Forncett Steam Museum, next one will be 7th October. More details of either/both on request.

 

Bill.