I have just experimented using sealing wax to increase the height of jacks in order to adjust stagger. I must say that I was pleasantly surprised at how easy it was to apply cleanly and adjust if necessary (by removing slithers with a scalpel). Far quicker and less messy than using layers of masking tape and much easier to adjust than a shim of wood.
I suspect that there are varying qualities of wax. I bought mine in England and it has the initials S H stamped on it.
I would attach a photo of the wax on the jack if I could see how to!
Le 06/03/2022 17:06, Matthew Daillie via The Jackrail écrit :
I have just experimented using sealing wax to increase the height of jacks in order to adjust stagger. I must say that I was pleasantly surprised at how easy it was to apply cleanly and adjust if necessary (by removing slithers with a scalpel). Far quicker and less messy than using layers of masking tape and much easier to adjust than a shim of wood.
I suspect that there are varying qualities of wax. I bought mine in England and it has the initials S H stamped on it.
I’ve been using sealing wax since I have screwless wooden jacks. But I
find it easier to use sandpaper to adjust the height if necessary.
I should have thought that once stagger has been set in a new instrument, it should not need to be reset, and certainly not for individual jacks. Presumably the new jacks start off too long, and a fine saw followed by a file, taking care not to over do it, should be adequate to fix the length. On occasions, I have overdone it, but never to the extent that layers of corrective material were needed.To solve the problem I glued a piece of cardboard of the needed thickness to the bottom of the jack. I would certainly not recommend masking tape for the purpose.
The great thing with the sealing wax I bought is that it is easy to apply and even easier to adjust by taking slithers off with a scalpel.
Best,
Matthew
Humidity change can lead to the need to adjust jack heights, as the expansion of the nut bridge in particular raises the string level - or you can adjust the height of the back rail as some do, by means of a machine screw arrangement from the bottom of the instrument. More common is finding several of them cut too short by an amateur maker (thinking here mostly of Zuckermann kits with their I-beam construction).
I agree masking tape is not a good idea. On the Zuckermann design, with its very thin bottom, I have wrapped layers of self-sticking material like address labels from one side to the other around the bottom edge. Another alternative to masking tape is “artist tape” (google it), which has an adhesive that stays soft and removable without residue at least fairly indefinitely (I don’t know about ten years down the line).
Masking tape or indeed anything sticky is to be avoided. Nothing is worse than coming across an instrument where the masking tape has been applied in multiple layers, and become a partially-unstuck mess, or the tape crinkled and adhesive deteriorated to leave a powdery residue.
There’s nothing wrong, though, with carefully glued and trimmed card to lengthen a wooden jack body which is a tad too short.
To correct an amateur regulation of an instrument with plastic jacks of inconsistent height, it is often better to raise the keyboard and trim the jack bottoms to the new height of the key ends.
Sealing wax is certainly an historic method to increase the height of a jack. It was used on both my original Kirckmans. I managed to purchase some red Bank of England sealing wax, supposedly made to the same recipe since the 1770s, which I was able to use to great effect. You have to have it quite hot, and quickly dip the end of the jack in the wax to form a perfect meniscus.
Humidity expansion of the nut must be negligible: I think Fred may be mistaken in thinking global jack height adjustment would be required because of that. Higher humidity will certainly cause the case sides to expand, effectively dropping the keyboard and action 1 or 2mm in relation to the stringband, but also causing the soundboard to (hopefully) rise rather than fall. Unfortunately, soundboard movement does not always occur evenly across the compass, as anyone who has carefully regulated a fortepiano action to a previously-made jig can attest that the stringband of an instrument does not necessarily remain a level line at the strike point in different climatic conditions.
Thank you, Carey, for a comprehensive and very useful answer.
When I built it, RIchard Auber provided me with two large screws that I fitted to the bottom of my Flemish double. Turning these approximately half a turn raises or lowers the keyboards and adjusts the height of the jacks. I have not had problems with this not working across the whole keyboard, though obviously vertical movement of the extreme left and right parts of the soundboard is constrained by their connection to the case.
I am convinced that the best solution is to incorporate Skowroneck Lifters when building an instrument; but unfortunately they cannot be retrofitted. These are flat aluminium strips that hook over the bellyrail and under the keyboard. As humidity increases and the bellyrail rises, it pulls the keyboard up with it. Owen Daly and others incorporate these lifters in their instruments.
I think the stuff I used is also a traditional recipe. Rather than dipping the jack in the heated wax I lit the wick of the wax stick and when a liquified blob started to form I ran it smoothly across the bottom of the jack (which I was obviously holding upwards). If there was not quite enough wax on the far end, I would quickly do a partial run in the opposite direction, stopping as soon as it was level. After waiting for just a few seconds it is really easy to adjust the amount of wax by removing slithers with an Xacto knife if necessary. I was expecting the whole business to be rather messy but if one does it quickly but calmly, it’s surprisingly straightforward.
One can also purchase wax beads and a melting spoon but I haven’t tried that yet.
I used to play with sealing way and seals years ago. It is not messy, as there is not much about it that reminds one of wax – except that it melts! Certainly, modern sealing wax is not sticky like beeswax, as it uses other ingredients. There is a brief, but interesting entry in Wikipedia.
Of course, if one is striving for total authenticity, the beeswax-based version is recommended.
On the subject of humidity rated change in string plane, I have experienced a few instruments coming to my (dry) climate in New Mexico which had been functioning well before coming here (according to their owners), but now the dampers didn’t damp and the plectra didn’t make it back under the strings. Obviously (to me) the string plane was lower in the drier climate. Colleagues in other areas have commented on similar experiences, some of them advocating for an adjustable back rail for the keys, height adjusted by machine screws from the bottom of the case. At least one high quality maker in California installs that system as a matter of course. Much of the US does tend to have higher variances in humidity than other parts of the world, so this kind of experience may not be universal.
I have assumed the most prominent cause would be expansion/contraction of the cross section of the nut bridge, which is close to the end of the string where the jack is and is supported by the relatively stable pinblock. I suppose the pinblock itself would also expand and contract vertically, with the same effect.
The soundboard bridge and the soundboard itself tend to operate in tandem with the downward pressure of the strings, so that the board warps rather than the bridge rising (I see common enough instances of the board warping under the bridge to the extent that speaking lengths of some longer strings buzz against it).
