Date: Sat, 18 Aug 2012 17:38:09 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: windshield wiper repair
In-Reply-To: <20120818134815.2V3XK.1264425.imail@eastrmwml114>
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At 01:48 PM 8/18/2012, mcneely4@cox.net wrote:
>Once I had a good hole with the drill (and I did), I had no trouble
>with tapping. I did not use a jig. My tap set includes a double
>handled handle (hows that for mangling the language). The tap fits
>into a center clamp and one turns the tap from two sides to keep
>even pressure. That is the only kind of tap handle I've ever seen,
>but I'm no machinist.
For small taps there are collet-type chucks with and without
ratchets, a few inches long with a (usually sliding) tee handle. For
larger ones solid-handled affairs resembling die stocks, with a
two-jaw chuck operated by screwing in one of the handles. My
Craftsman tap/die set which has hexagonal dies, came with an insert
for the die stock with several square holes in it for different size
tap ends (don't think I've ever used it).
Where people run into trouble is using a tee-handled one with the
handle all to one side, or using a wrench. It's an interesting
paradox that very hard materials like taps have high tensile
strength; but it takes very little energy to break them because once
a crack forms it has astonishingly high stress at its extremely
narrow end, and it propagates like lightning. In a softer/tougher
material the material at the point of the crack deforms, both
absorbing energy and widening the point which rapidly reduces the
stress and slows/stops propagation. Glass is a special case -
extremely high strength in tension, but the surface will form cracks
if you give it a dirty look. Hence tempered glass, where the surface
is caused to swell, stretching the core but squeezing all the cracks
closed under great force.
> Working very slowly, with oil, I was able to keep the tap moving
> without it going off course.
Good on you, as they say in Oz.
> After flushing the hole repeatedly with oil until I could get no
> debris to rise out of it, a 6 mm bolt turned in smoothly. It did
> not bottom on the threads, shimming with a washer was required to
> get the bolt to tighten on the wiper arm axle. I just think the
> washer arm axle is too worn to have enough metal left to respond
> properly to the splines.
This is purely a matter of dimensions. The socket is a solid
casting; there's no point where the soft metal stops and hard takes
over. If you have a small enough hole left to marry to the splines
without them sticking out too far or the arm bottoming on something,
it will work.
Were you certain that the splines were shiny-clean? The old splines
from the arm shear off and stay in the grooves between the splines on
the shaft, and must be removed.
>BTW, Alistair, I did use a prick punch and then a larger center
>punch. The stud (which was cut down actually into the conical shaft
>in order to get a flat surface to work with) showed no tendency to
>move, though I whacked pretty good, but with a light ball peen hammer.
Light hammer is the key - you want to upset the surface of the shaft,
not move it. In electronics terms you're matching the impedance of
the driver to the load.
>So far as center is concerned, I hit what I perceived as center with
>the prick punch, and examined the stud with a 3x botanist's field
>lens. I accepted that I had hit center,
For a mounting bolt that has to be plenty good.
>Though I did not accomplish this job as I'd hoped, I really do
>appreciate all the pointers and advice given.
Re-check those male splines before you give up. There is a
deterministic reason why you didn't get splines cut on the female
part, and it's not that you ran out of cuttable metal. It has
something to do with dimensions/interference or insufficient clamping pressure.
Yours,
David
