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

[user 4756]

Hi all. here's one for you.

I know it is not really a Home Machine Shop question but it is about a prototype...

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

 

[portlandron]

The people here might be able to give you an answer

http://www.smokstak.com/forum/forumdisplay.php?f=7

 

[bezalel2000]

Hi Andy

From your description I can't work out whether the rope is a typical 3 strand cable lay rope or a kermantle rope.

Of these two only a kermantle has outer strands. A cable lay rope really doesn't because the outer fibers at any given point on a cable lay rope are in the middle of the rope 1" - 2" further down the rope.

If the rope is cable lay it is relatively simple. Use a hardwood conical peg with 1 to 2 degrees of taper. Drive the apex of the cone into the hole in the piston between two of the strands of the cable (already in the hole). This will cause the fibers to rearrange them selves to conform to the shape of the hole around the peg. It is assumed the edges of the hole are nicely rounded so the rope fibers don't get damaged.

If you have a kermantle rope I'm not sure I can help.

It is likely the kermantle, that contains the inner fibers, would prevent the rope from deforming to the shape around the peg.

Perhaps in that case, if you made a hardwood dowel the same diameter as the hole in the piston. sand and seal smooth, cut along the length of the dowel from one side to the other at say 2 deg. from the axis. Drive the thin end into the hole with the rope already in the hole.
At some point the hole will be part full of wood / part full of rope with no room for any more of either. At that point saw off the surplus wood.

Good luck

Bez

 

[user 4756]

Hi guys,

Ron; thanks, I will try them. I have also emailed the people who have the twin to this engine (they were built as a pair working side by side, this one is ours: http://www.geograph.org.uk/photo/1992633 ) but have heard nothing from them.

Here are some more pictures showing the dismantling and some of the story:
http://oldenginehouse.users.btopenworld.com/hop1.htm

Bez; thank you for the info, I didn't know what the types were called. It is a 3 strand cable lay rope. The problem is that the rope is thicker than the hole. The old boy who used to do this job is too ill to do it anymore, and too ill to give instruction as well (as I can make out, I never met him) but the others know that he used to trim the rope somehow.

I was thinking of whipping the end about 1.5" from the end, keeping the outer strands (as they lay at the end) and trimming back the strands that lay in the middle.

Andy

My reasoning is that the outer strands pulled down into the hole and plugged would stop the others from unwinding in use.

I don't want to rely on the whipping to hold the rope together as it is thin enough to wear away quite quickly.

 

[tel]

Put a packing piece in the bottom of the groove and use thinner rope?

 

[user 4756]

Thanks Tel,

Unfortunatey the boss has already bought the rope to spec and gone away for a couple of months.

I don't want to drill the hole bigger to make life easy. :big:

I would like to find out how to do it properly as it appears (I have asked on a couple of other forums too) that this is a dying (if not already deceased) art.

I feel that the point of museums is to keep not just the machines for prosperity but also the skills required to run them.

You never know, when the oil runs out we may be back to steam (in a much more efficient form)

I will be worth something then :big: :big: :big:

Andy

 

[bezalel2000]

HI Andy

My first thought was the other end of tel's - the hole too small
Let's assume that they are both right to work out why the other guy trimmed the rope
My guess would be that the rope is actually full size in the hole but a very tight fit
To achieve this the rope needs to be whipped. Doing this makes the rope Evan thicker. So shave each strand of the cable such that you reduce the thickness by a fiber or two every millimetre along the rope so that when you re twist and whip the rope, it tapers over the last couple of feet.
The whippin needs to start at point where the rope plus whipping is the same size as the hole.
With a taper on the rope end pull the rope through the hole - use plenty off pulling force as the rope must deform into the shape of the hole. A cable rope is not a circle.

 

[Maryak]

My way would be tie off the end of the rope with a piece of twine at two times the length required to be tapered.

Now split the rope into its' three strands.

At one third the length remove one third the fibres on each strand.

At two thirds the length remove two thirds the fibres on each strand.

Re-lay the rope which should now have a tapered end and tie off the small end with another piece of twine.

Drive this end into the hole with the peg and a dolly to ensure the peg is level with the full sized rope.

The peg and rope ring should bed in together when the engine is run.

Hope this helps.

Best Regards
Bob

 

[champ2run]

Her Majesty's Stationary Office (HMSO) has a Royal Navy publication which included information on rope work. It described how to make a pointed end about three inches long on the end of a hammock rope. The pointed end is made quite stiff and can be made to any custom taper. This will go in the hole smaller than the rope ready for wedging. I did this on my hammock a very long time ago. Hope this helps. EMB ex R.N.

 

[user 4756]

Ahh...now it sounds like we are getting somewhere I want to be (please don't the others take offence, I am grateful for all ideas...and many of those can get me through smaller engine builds)

My father is also ex RN, '43 - '46, but all he can remember is that Thursday was his turn in the barrel... :big: :big: :big: :big: :big: :big: :big:

I will look for the information on...what would you call it? Reduce splicing?

Many thanks Bob and EMB

Andy

 

[tel]

'All you ever wanted to know.....' dept!

http://doit101.com/Knots/knots.htm

 

[portlandron]

For pointing a rope these explanation is a little easier to follow:


Pointing A Rope

Pointing a ropeThe rope is unlaid and a tie put on to prevent it unlaying further. The strands are thinned down gradually, and relaid again. The end may be stiffened with a small stick or piece of wire. The end can be finished off with any of the crown or wall knots.

 

[user 4756]

Thanks Tel!!!
I have saved that as a favourite!

Ron, thank you too, that is a great idea, though I doubt there will be enough room for the crown or wall.

Andy