Boesy Capo Problem

[David Love]

Mike:

I appreciate all that.  The bolts are steel and the nuts are brass.  I'll
look again at the bolts since they were slightly painted and it was hard to
see exactly just how compromised the threads were.  The threads on the brass
nuts were almost smoothed over but since the brass is quite soft, hopefully
they took most of the abuse.

  

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of MICHAEL MORVAN
Sent: Friday, December 14, 2007 10:18 AM
To: Pianotech List
Subject: Re: Boesy Capo Problem

David,
    It's better that the nuts appear to be the problem not the bolts. But 
still,  you state " Apparently in the rebuilding of this, the threads on 
both bolt and nut  were compromised" This is worrisome considering the 
stresses they will be under when brought to pitch.
You asked, "That being said (forgive my machinist ignorance) can you not 
simply cut the threads on the bolt to a slightly smaller size and replace 
the nuts with something appropriate."
Answer, yes you can, but when you reduce your bolt to a slightly smaller 
size and replace the nuts, you reduce it's strength to the strength of the 
new size. For example if a 5/16ths 18 bolt (5/16ths being the diameter, 18 
being threads per inch) is stripped and one reduces the diameter slightly 
and re threads it to a 1/4 20, your newly threaded bolt will only be as 
strong as a 1/4 20 bolt not the original 5/16ths 18. So you will lose some 
strength, whether it be enough to be an issue is dependent upon how much of 
a safety factor was engineered into the application.
The device you want is called a thread pitch gauge, this will tell you the 
threads per inch, the threads per inch and diameter of the stud will tell 
you what it is, 1/4 20, 5/16ths 18, whatever, in this case I would guess 
that we are dealing with a metric size.
You stated the decimal size was about 0.268, if that is correct you probably

have about a  7mm diameter (slightly stripped 7mm), the thread pitch can be 
fine or coarse. You could go down to a 6mm, but again, who would know if it 
will be okay, not me.   Good luck,   Mike

----- Original Message ----- 
From: "David Love" <davidlovepianos at comcast.net>
To: "'Pianotech List'" <pianotech at ptg.org>
Sent: Friday, December 14, 2007 12:16 PM
Subject: RE: Boesy Capo Problem


> It does appear that the threads are more of a problem on the nuts than the
> bolts so I might get away with it.  I'd like to avoid replacing the bolts 
> if
> possible as not only do they have to fit the plate but they are bent at
> rather strange angles in order to align with the capo bar.
>
> That being said (forgive my machinist ignorance) can you not simply cut 
> the
> threads on the bolt to a slightly smaller size and replace the nuts with
> something appropriate.  Also, what is the gauge called that you use to
> measure the thread counter per...?
>
> David Love
> davidlovepianos at comcast.net
> www.davidlovepianos.com
>
> -----Original Message-----
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On 
> Behalf
> Of MICHAEL MORVAN
> Sent: Friday, December 14, 2007 8:23 AM
> To: Pianotech List
> Subject: Re: Boesy Capo Problem
>
> David,
>    Referring back to my machinist days I can suggest/explain the 
> following.
> 1. If the threads were simply ripped/stripped out of the "nut", and the
> threads on the "stud/bolt" are still intact, you can "chase" the threads 
> on
> the stud with the appropriate die to clean them up, and then replace the
> nuts.  HOWEVER
> 2. If the threads were ripped/stripped off the stud/bolt, you have a
> problem, and will need to replace the studs and bolts. If you chase 
> threads
> that are ripped off a stud, you can get a nut to go on well but, there 
> won't
>
> be enough material left to hold the nut, and as soon as you put a load on 
> it
>
> watch out, it will fail.
> 3. For further information type "class of fit" in any search engine, and 
> you
>
> will find many articles referring to the relationship of nuts and bolts
> concerning threads and strength.   Good Luck,    Mike
>
> Michael A. Morvan
> Blackstone Valley Piano
> Dedicated To Advancing The Art Of Keyboard Restoration
> 76 Sutton Street
> Uxbridge, Ma. 01569
> (508) 278-9762
> Keymaestro at verizon.net
> www.pianoandorgankeys.com
> www.thepianorebuilders.com
> ----- Original Message ----- 
> From: "David Love" <davidlovepianos at comcast.net>
> To: "'Pianotech List'" <pianotech at ptg.org>
> Sent: Friday, December 14, 2007 10:31 AM
> Subject: Boesy Capo Problem
>
>
>> Interesting problem.  1890's Boesy.  The heavy metal capo bar is held in
>> place by several bolts running through it and held down by some cap nuts.
>> Apparently in the rebuilding of this, the threads on both bolt and nut
>> were
>> compromised so that as the piano was being tuned the nuts let go and
>> popped
>> (probably shot) off.  So the bolts need to have the threads recut and the
>> nuts replaced.  Not a big deal but I need some advice on re cutting the
>> threads.  The outer dimension of the bolts is .268".  Can anyone suggest
>> the
>> best approach for this, tools, thread count, etc..  Machining type work 
>> is
>> not exactly my area.  BTW  I'll have to send some photos of the bass
>> stringing (eastern European rebuilding job).  You won't believe it.
>>
>> David Love
>> davidlovepianos at comcast.net
>> www.davidlovepianos.com
>>
>>
>>
>>
>
>
>
>
>