BJ is quite right pointing out the disadvantage of using a scraper or
sandpaper on jacks, I would not wish that done on my work but I have
found the removal of rack wood by far the best way! Again I can see
why Bill does not like that move simply because he makes a lot of block
racks with more wood working than I do; his work would be very fine and
he would not want that disturbed. I purposely make my racks so the
jack blank is only working on a 1mm bead front and back, the thickness
of the face area of the rack is again about 1mm and I always angle the
jack when setting up so that the flat areas of jack blank are contacting
virtually no wood! The tapered surface of the jack blank when planed
to the rack has been done with great care and with very sharp tools, so
like Bill I would not like that surface altered! Now I make a file
for the very rare occasions I need it from a strip of pear, beech will
do just as well, and with copydex I glue on one surface 1000 wet-and dry
paper; 3M is the best if you can get it. Trim the edges with a very
sharp knife or chisel and very carefully remove a little from one face
of the rack, preferably the face that the back of the jack works on.
The file must be made on a fraction narrower that the width of the
mortise (jack blank) in order to have control and can be well thinner.
Best to not have to do it at all but we have little control on what
happens when the instrument leave our workshops.
Finally Jack Peters referred to clicking wood jacks; Bill and I make
silent wood jacks that work to perfection, the only acoustics are the
sound of a plucked string :-) Pray to God!
Have a good day,