Grotrian 128 captive nuts

[John Delacour]

At 9:26 PM +0200 12/6/01, nirran wrote:

>I'm working on an upright Grotrian 128 No.38251.
>
>Is any body knows how to remove the plate to get access to the soundboard?  
>
>There are "blank" bolts on the upper side of the plate.

Sounds like the old J&P Schiedmayer trick at the corners of the 
grands.  Don't worry -- it's possible but you have to work 
methodically.


Get it on its back so you can work easily.  There is a square captive 
nut in among the beech there that you can't see and it was done up 
with a wrench before they glued all the bits on, so those bolts are 
tight.  You will be replacing them maybe with suitable special 
wood-screws or with new bolts that you are going to have specially 
made.  It's just possible you'll be able to re-use the bolts, but I 
doubt it.

Carefully cut a slot in the domed head as deep as you can go and 
think about which screwdriver you're going to use or buy.  I use an 
18" London pattern screwdriver for this sort of work as I can lean on 
it and turn the flat shank with a pair of long grips, but that comes 
later.

Once you've cut the slots, get a strongish screwdriver with a through 
shank and hammer downwards into the slot, firmly but not too hard. 
This is to send shocks through the bolt and free it up as much as 
possible, but that's not much.

Now get a good strong and fairly sharp-angled nail punch or centre 
punch and a medium lump-hammer.  Position the point of the punch in 
the slot just outside where you imagine the shank of the bolt to be 
and hammer first downwards and then gradually at an increasingly 
acute angle to make a good impression for the punch to work against.

Now you are ready to drive the head round driving the punch 
tangentially with very firm blows of the hammer.  Don't try to do it 
all in one go;  the first attempts will help to free the head and the 
thread and you will soon feel that you've started the head turning. 
You can now lighten up on the hammer and move it round by slow 
degrees until you get the feeling the screwdriver will do the rest of 
the work.

In my experience, to attempt the job without a punch is pointless. 
You will destroy your slot with the screwdriver before anything moves.

If you are not going to use the nut but replace the bolt with a 
normal screw, make sure you pour something in there to prevent it 
rattling.  Beeswax springs to mind but epoxy something would do too. 
Don't use glue or anything that'll shrink.

JD

PS.  I bet that soundboard's looking far better already :-)  All it 
needs is a good dusting.