KS 28: Gauging the Plan - Part 2

KS 28: Gauging the Plan - Part 2

So next, the worn backchecks come out and new backchecks go in. WNG backchecks are very height-sensitive with their checking surface abbreviated for better clearance and closer-to-string catching. To determine their optimum height, I compared old and new and ran samples. The original backchecks were higher in the bass and lower in the treble to work with hammer tails longer in the bass and shorter in the treble. Since I'll be custom boring the replacement hammers, I'll make all tails one inch. And all the new backchecks will then be the same height.  I removed the old backchecks using a shop-scrap jig and pry bar, then drilled holes larger for greater-diameter WNG backcheck wires.


The backchecks were inserted using the WNG installation kit (see photo below). Because the pusher part had been previously modified to work with larger old-style backchecks, a bushing of backcheck buckskin was added to help retain backchecks being aimed for insertion. Then, each was pressed part way and eased a little to let stresses out (what David Rubenstein calls "pecking"), sometimes more than once, before pressing home. This process offered enough positioning forgiveness to not get far astray on the way in. Backcheck wires are strong, but soft enough to bend for regulating, which means soft enough to bend back, forth, or to one side if force and hole don't quite line up.


Some backchecks did tip a little one way or the other (see below), which was  safely and easily adjustable with key clamped and square as reference. The original bore angle stood backchecks up a little too straight, but with protractor as guide, they roughed in to a more accurate tilt. Finally, some height tweaking was needed, a slight backing out of those that went too far and a nudging in as needed. Medium CA glue was added to reinforce.


The balance holes all had degrees of backchucking. I sized them using hot hide glue water-thinned modestly enough to stay on brush from jar to key. Without correction, loose balance holes get looser as they're played. And they can arbitrarily shift position and geometry on innocent regulators, undermining efforts at accuracy. When topstack comes off for the last time, I will do a touchup round. This I do with Dampp-chaser additive if no glue-sizing was needed, taking up slack created during regulating. Either way, plenty of drying time is key: the DC-treated ones on their pins to self-size or the glue-sized ones off for all they can swell before being eased onto their pins the following day.


Glidebolt contact surfaces can be polished and keytops cleaned (for which I use a damp cloth with a tiny amount of soap and a dry cloth to follow). If the keyframe has return-spring indentations, use 80 grit sandpaper on a sanding block and a single-edged razor to dress it flat, smooth, and vertical. Much sanding brought me to the photo below, with about the same again to finish. The return spring will need to be shimmed vertical at reinstallation.

This week's offering and the last one looped back into prepping steps but say something about choices to be made, tradeoffs to be negotiated, and cost-benefits to be considered, all essential to good planning. The original parts had excessive friction, nearly 100 years of wear, played like a truck, and the tone was harsh. New parts will save lengthy efforts to improve details with a completely fresh start: New Ronsen Weikert hammers will provide a huge tonal upgrade. New backchecks will play better than originals restored. New capstans will help reduce weight and inertia. And new hard bushings will offer more stability with less friction. For letoff buttons and key bushing cloth, money was saved to little disadvantage by not changing materials, and all this is well-aimed to optimize the customer's investment in new board, block, and strings!

Next time: Where Rubber Meets the Road (Stiff Keyframe)

(Index of all articles in this series)

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