Machine Threads in Pinblock, was WD-40

[Fenton Murray]

Terry and Ron. O.
Thanks for the replies and information, especially the formulas from Ron O. I'm planing to use machine screws on my next block. Would you recommend a fine or coarse thread?
Fenton

Fenton and Michael,


We use machine screws to fix our pin block to the plate. We use 8 mm countersunk machine screws and the pin block holes are threaded in the maple before we fit the screws. The tapping drill size we use is the same as is used for threading metal with the same thread size.


Speaking of tapping drill sizes, I have a short formula which has been kicking around in my head for couple decades which I use for calculating the tapping size for a thread. The formula is handy because it is sometimes more convenient than looking up tapping tables. The formula for the minor diameter of a thread is;


        (major diameter in thou) - (1220/tpi)


This is handy when tapping for agraffes for example, when we're dealing with an unusual thread that we won't find on a tapping chart. For example, lets take an agraffe with a 1/4" diameter and 36 threads per inch. The tapping drill size for this thread can be found using the following;


        Diameter of major diameter in thou is 250
        Threads per inch is 36


Substituting the above into the formula we get;


        250 - (1220/36)


        250 - 33.88


        216.11


So 216 thou is the minor diameter of this thread. The nearest nominal tapping drill will be 7/32", which has a diameter of 218 thou.    The tapping drill should always be slightly larger than the actual minor diameter of the thread, to allow for better clearance of the swarf.


The same formula can be used for metric threads also, but the major diameter in mm needs to be converted to thou by multiplying the diameter by 39.37, and the thread pitch in mm needs to be converted to threads per inch. To do this divide the metric pitch into 25.4. For example, a 0.7 metric pitch, expressed as threads per inch is;


        25.4/0.7


        36.285 threads per inch


For those of your who might be rebuilding grands, and sometimes need to use replacement agraffes with a new thread size, when the original agraffes are no longer available, these formulae can quite useful.


Ron O.


  Micheal,
  I know some of this thread was meant as a joke, but I'm interested in your comment regarding machine threads in the pin block, if you were serious. I've diffenately used machine treads in maple, but nothing as critical as a pin block. Please comment on thread size, drill size, ect. I assume you might use a smaller drill than recomended for metal. Or maybe I missed the joke.
  Thanks,
  Fenton

  ----- Original Message ----- 
  From: Farrell 
  To: Pianotech List 
  Sent: Monday, June 16, 2008 1:32 PM
  Subject: Re: Machine Threads in Pinblock, was WD-40


  I hadn't followed the WD-40 thread, so I don't know who (Michael) you are referring to Fenton, but I also routinely use machine screws in pinblocks. I really can't tell you exactly what size/bit/etc. I use - just whatever size machine screw fits and I use coarse thread and drill as small a hole as I can screw a nicely buttered-up machine screw in there.

  Just seems to me that a machine screw is more secure than a wood screw- you have full length of the machine screw with treads locked into the wood. If I'm not mistaken, Ron Overs is doing this also - probably others.

  Terry Farrell
    ----- Original Message ----- 
    From: Fenton Murray 
    To: Pianotech List 
    Sent: Monday, June 16, 2008 1:10 PM
    Subject: Machine Threads in Pinblock, was WD-40


    >to thread machine screws into the pinblocks

    Micheal,
    I know some of this thread was meant as a joke, but I'm interested in your comment regarding machine threads in the pin block, if you were serious. I've diffenately used machine treads in maple, but nothing as critical as a pin block. Please comment on thread size, drill size, ect. I assume you might use a smaller drill than recomended for metal. Or maybe I missed the joke.
    Thanks,
    Fenton
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