Keep Tenons Grensed
Keep the corks on the tenons greased with cork grease or tallow and you will avoid much trouble and expense from broken tenons and damaged key action. Cork grease not only retains the resiliency of the cork and preserves it, but it makes the joints easier to put together and take apart. Nine broken tenons out of every 10 are the result of tight, "frozen" tenons. Of course, some of this tightness may have been due to expansion of the wood from excess moisture, but many cases are due only to lack of grease on the corks. Be especially careful of the middle tenon, for it is thin and is located in between two long joints where the force of leverage is greatest. It is the one most often broken. When tenons are not greased and do not work freely,
not only are you liable to break tenons off but in your effort to force the joints together or pull them apart you may twist the keys and rods. The "death grip" you take on the joints and the twisting and pulling motions are bound to bend a key, twist a post, or spring a hinge rod. Then you will wonder why the key mechanism doesn't work perfectly!
Grease will not solve all difficulties. It may be the cork has swelled and is too large. If so, sand the cork down a little with some fine sandpaper and grease it. Don't sand down too much, or when dry weather returns the wood and cork will both shrink and the fit will be too loose. Then you'll have to have new cork put on the tenons. If the cork on a tenon comes unglued and breaks, wind string around the cork to hold it in place. If the cork is badly broken, it may be best to peel it all off and substitute string entirely until you can have a repairman recork the tenon. Grease the string as you would the cork, to make it work easily.
It is expensive to replace a tenon and in a percentage of the cases it is impossible to replace it. It is then necessary to obtain from the factory an entirely new joint — and that is doubly expensive. Why not avoid all these troubles by greasing the tenons so they will work freely?