Main stock cup crack

[bobkeenan]

It seemed like I was pumping the bellows too much so I went through my set to see where there might be some leaks. Found a crack or two on the main stock cup that runs along most of a side. That was the leak culprit. But this has led to some questions.

1. Is that part of the set prone to cracking?
2. The wood thickness for the part of the cup that fits on the stock is only about 1/8" or maybe a bit more. Its backed up with a brass sleeve. Is that typical.... it seems like its asking a lot of large wood fitting with a small wall to be structurally sound.
3. I fixed it with some super glue and when it was dry put some thin waxed thread around it as the brass sleeve was a bit loose and figured it needed to be tight to provide the strength. That fixed the leak. But will that last?

I have no doubt that my pipemaker will take care of this but was curious if the thin wall thickness is typical. what drives the thin wall is a very compact stock (which is nice), but then in order for the OD of the cup to be close to the OD of the stock it requires a thin wall cup.

Its also possible that early on, when I first had the set, and I was fixing leaks with thread that I put too much strain on that part and with seasonal changes it cracked. Who knows......

Thoughts?

[PJ]

1. Not normal. Check with the maker.
2. 1/8" seems thin, but there are many variables, notably the type of wood.
3. In my experience, superglu is very brittle. It will flake away over time, particularly with the movement of the wood (expansion/contraction with changes in heat/humidity). Same with wax. You should speak to the maker and see what he recommends.

The seasonal change you mention could be a factor. I usually have to add binding to various parts of my pipes in December, but I have to removed the extra binding in May. If I don't remove the binding in time, the warmer, more humid air causes the wood to expand and can make, for instance, removing the mainstock from the cup very difficult. In general, wood will expand/contract more than metal. So when you're dealing with parts like the mainstock or the chanter (going into the chanter top), then you need to ensure that the fit is just right - not too loose and not too tight.

[bobkeenan]

Thanks.

BTW I looked at another set that I have, different maker, on his the base of the cup is wood. Around that is a brass sleeve. And that brass sleeve is what slides on to the base of the stock. So there is no thin wood wall on that one

[geoff wooff]

A 1/8th inch wall thickness on the Mainstock Cup is a wee bit light but those that I have made which are about 0.2" in the wall have survived ok. I have one I made ,nearly 40 years ago, as a replacement for the old Cow Horn cup on the Harrington set. It has not cracked and has lived in very dry Australia and a very wet Atlantic coast of Ireland. Several things are important here:

Good wood seasoning and stable wood type; I think 5 years is minimum for seasoning and this large diameter piece should be roughed out months before the expected finished date.

The bores of all the stock pieces are better if made slightly tapered because when wood looses moisture through the end grain it tends to shrink more at that end grain area.... thus a stock which has been bored parallel will become slightly smaller at the open end. This can cause a major leak spot because one adds binding to the joint but only enough so the stock can fit in the cup , thus being able to pass that tight spot at the entrance and then the joint becomes slack once inside. The extra pressure caused at the open end by it having shrunk can start a crack running back from the open end grain.

When wood shrinks , a diametral piece will become oval and this will add to the possiblity leaks... again long seasoning is indicated.

If shrinkage is the reason for the crack and you glue it to fix it and pull the crack closed or fill the gap ( and perhaps use some mechanical support like cross pinning... sometimes called "stitching") then the bore will no longer be circular and it could be advisable to re-bore, taking a light skim off the surface to correct ovalities.


Keeping the Ferrule a close fit on the outside will help support the wood to some extent although one would need a very heavy ferrule to be of more than decorative value.

[billh]

I would venture that these cracks are quite common - I have seen many - but are often the result of excessive or unsuitable binding. If you put incompressible binding (waxed thread, plumbers' tape, etc.) inside a wooden cup and wedge it tight, or the cup shrinks due to seasonal changes, you can expect trouble. Players with sets having timber stock cup sockets should stick to dry, uncoated natural fiber binding, and check for over-tightness from time to time IMO.

I agree with Geoff's observations, of course, and he has made many of this sort of cup.

Regards,

B