Downbearing...,

[jamesp]

Hi folks, it's been a while, but I've finally found some time and inclination to get on with my piano restoration project. I've got 2 questions; firstly I would like an idea of the amount of downbearing to aim for at the front and back edge of the bridge. Reblitz suggests about 1-2mm from the front of the bridge but (unless I'm being stupid and can't see it) I'm not sure what to aim for at the back. I'm asking because I'm in the process of re-capping the bridges and whilst I've got them in the right ballpark I think they are too high still:

New treble bridge:




Closeup - bit too much downbearing I think - at the rear at least:



As I had good crown in the soundboard and the old bridges had reasonable downbearing I've copied them as close as possible but I'd say that there is definitely too much bearing at the moment. How much would you expect to raise the thread at the back and front before it lifted off the bridge?

The second question concerns the agraffes/studs. They appear to be a strange size (1/4" x 32 threads per inch). Does anyone know where I may possibly be able to get some more? The old ones may well not need replacing but I've read (I think on this forum) that new ones can improve the sound and after all the effort I'm going to with the bridges, and everything else I don't want them to be the weak link.

Thanks for your time.

James

[Barrie Heaton]

Each model of each make has its own specks, I trust you did take lots of measurements before you removed the bridge with tension and without tension on the soundboard

Get the speaking side of the bridge right and the back end will follow as you can pack the bearing edge with card under the felt too much and you will kill the sustain to little and it will be false as hell and again no sustain



Supply houses will stock the agraffes or ones close failing that a stiff pipe cleaner in a drill to polish the holes smooth do the DB after you change the agraffes



Barrie,

[vernon]

Barrie
don't understand that

[Barrie Heaton]

Which bit

[vernon]

about packing the bearing edge with card.

[Barrie Heaton]

OK

What he should have done is take lots of measurements and only take off 30mm of the capping at most as the DB was OK he should put the capping back to the same hight across the bridge. Next he should do his marking-off from the template he made, then drill the holes. Making sure that the side draft is the same as before. Then do some test string to check the SD and DB if the DB is too great then he can add thinker felt on the hitch pin bearing edge and if he has got it very bad he can add card under the felt - but he must put the new studs in before any test. the angle from the stud to the bridge is determined by the hight of the bridge But you can reduce it with a few washers under the studs (but it is better to get it to the correct hight in the first place ). the important line is the one from the stud to the bridge the bridge to the hitch pin is small and some times to steep on small grands look at good makes the DB is normally equal on both sides

if a piano has poor DB making the bridge thicker will make the soundboard more ridged and make the piano dull if the piano has poor DB then re-rib or change the soundboard.

Also the hight of the frame to the soundboard should be the same as before and that need to be bolted down first to get the correct measurement

Barrie,

[vernon]

The cap will need to be glued AND screwed throughout it's length. Any attempt to use the original go-bars will buckle the belly.
Doe's the correspondent know the intricacies of the marking off?
The bridge carving has got to be done in one continuous session for accuracy and consistency and artistic finish.
In our factory, Archie Dores had the only ancient stubby 2" chisel that kept it's edge from start to finish, which we all had to borrow.
I remember at Welmars seeing the boy routing a bridge BEFORE fitting.I asked where was the marker-off and was told the boy, who was unskilled, could do it on the router 10 times faster.
Who said all of us dinosaurs are extinct.

[Barrie Heaton]

The cap will need to be glued AND screwed throughout it's length. Any attempt to use the original go-bars will buckle the belly.
Doe's the correspondent know the intricacies of the marking off?
.

Not if he is getting most of is input from Reblitz I would be surprised but the only way to learn is to do it. I remember doing my first cap made a complete dogs dinner of it had to replace the cap and do it again.

Did they not use a jug at Welmars which was bolted to the cap

Barrie,

[vernon]

Barrie.
What dat mean?
A jug bolted to the cap?

[Barrie Heaton]

Barrie.
What dat mean?
A jug bolted to the cap?

typo fingers not doing as brain says should have been Jig

but there again the quality of some of the last ones it may as well been a jug

Barrie,

[jamesp]

Hi folks, thanks for the answers. I didn't make a template of the old bridge since I was not confident I could do it well enough and I was reluctant to machine away the tops of the bridges as I would lose my only reference so I got a special router cutter and machined the tops off so that I could lift the caps away and have something to measure endlessly and copy. I spent hours over several days endlessly scraping the bridge roots to fit the new cap material closely and having screwed it down tight from underneath used a trimmer to get the profile right to the bridge roots. I then trimmed down the height and it is within 0.5mm of the old bridge all the way along. But... when I originally unscrewed the frame it rocked in the piano horribly. I've fitted a new pinblock and adjusted the frame mounting points so that it sits in nicely without rocking (I was worried the rocking would put pressure on the frame in the wrong axes). It all fits nicely now except that I'm going to have to marginally reduce the height of the bridge to get the bearing right. As far as the notching is concerned - yeah, I'm worried as hell about it!! I've never done this before...

[Barrie Heaton]

O dear the roking will have been on the piller bolts quite common on a lot of pianos, what you should have done is turn the piller bolts down and count how many turns, then with the frame bolted, you turn up the piller bolts (takes a lot of Bottle) some frames are bent a tad with no tension, when tension in on they go straight we are only taking 1mm at most but it seems more the way the frame rocks (piller bolts are the ones with the nut on top)

Template for marking off, cut a strip of tracing paper to match the bridge tack it to the old bridge making a note where your tack holes are. Run a crayon over the the top of the paper the pins will show up as spots put the tack holes in the same place on the new bridge and with a pin punch mark the centre of the pins for drilling.

Take new piece of tracing paper and place on top of the old pins and tack it in the same place as you did with the other With very light sand paper sand the top of the paper this will make holes were the pins are, gently push the paper down and with a penile mark the chisel lines place the template on the tack pins on the new bridge you can mark the side of the of your bridge transfer the line to the top of the bridge. This will give you a line to aim for when you start to chisel out

I would also put new bridge pins in there are 3 sizes that the supply houses stock. Drill the holes before you chisel you need to spend day sharpening your chisels Visit Ytube see if there are any vids of folk doing bridges this will give you some idea to the way it is done

Barrie

[vernon]

excellent guidance from Barrie.
However, instead of a single pin punch make a punch with the 3 points on it to match the pattern;thereby you will mark 3 holes at a time all exactly equidistant and tidy. then your bridge pins won't have any untidy aberrations.
Barrie mentions sharpeneing your chiselS.
As previously I said, you should aim to have one excellent chisel that will hold it's edge for a whole section. At least measuring 1 1/2"( 1.5 in) which will give it weight to keep the bridge carving(notching) even as you will have more control.
You must carve each section in one session for evenness. Previously you must saw all the downcuts in one session for the same reason and to keep the same angle. Most important be confident.Start thr chisel cut halfway thru' the row of 3 holes Strike the chisel with the heel of your hand only resting both your elbows on the belly throughout the section without moving them.and get a rhythm going and don't stop. Practice on a mock up first.