broken screw

[Paul]

Richard
Sorry for the delayed reply. My daughter got married and we hosted the
reception at our home. Whew! What a "to do list". Anyway: A cap screw is the
retaining bolt that we used in the machine shop to anchor bearing caps to
machinery. They are very strong- usually grade 8 or higher. The ones we used
were usually tightened with an "Allen" hex wrench. Young Chang uses these to
attach their legs on grands ( I think that's the right piano). The small
groove can probably be filed in with a triangular file but a moto tool
fitted with a metal cut-off disc seems to work the best. The leading edge of
the thread or "lead of the thread is the very beginning of the thread that
you can see at the end of the bolt which "leads" the screw into the nut. I
like to place the groove just ahead of this lead. Look at the threaded end
of the bolt straight on and mark the center. From there draw or visualize
the x-y axis'. The groove is cut in on the left side of the y axis to a
depth of approx. 2x the thread depth, and across the threads (vertically as
you say) for about 8 to 10 threads, tapering to infinity. The finished
groove should leave a vertical cut on the threads along the y axis to make
the "tap".  Carefully start the "tap" into the damaged nut. Work slowly.
Sometimes a quarter turn in and a smaller amount out will help cut  the
threads easier. It is helpful to make the "tap" from another matching
thread. My choice for this is a tougher bolt such as the grade 8. I've been
able to get by with this most of the time. Severely damaged threads are hard
to restore without retapping, and the loss of additional material can
seriously compromise the strength of the fasteners. The moto tool (Dremel)
cut off wheels are available at Sears or other stores carrying Dremel
products.
----- Original Message -----
> Subject: Re: broken screw
>
>
>
> >  No luck finding a replacement
> > screw, but the hardware store clerk said he could make a "tap" out of
the
> > original.
> >
> > Paul Chick
>
> This sounds really interesting, but I am kinda lost.     Cap screw.....  A
> cap screw is......?       So from the cross threaded screw he ground a
small
> grove.    What did he grind with?   A moto tool? or a bench grinder?
Would
> a triagular file work?  "just to the right of center on the leading edge
of
> the screw"   If the screw is round, where is the "right of center" ?  Did
he
> grind the grove verticaly or horizontaly?  To make a tap I assume he
ground
> verticaly across the threads?   Intersting idea, if grove is vertical.
So
> it really makes a tap if I am imagining right?    ---ric i magen
>
>
>