Date: Fri, 17 Aug 2012 19:03:43 -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: <20120817161817.YBUA1.1290694.imail@eastrmwml205>
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At 04:18 PM 8/17/2012, Dave Mcneely wrote:
>Well, I worked on the "simple" fix for the broken windshield wiper
>shaft stud. Despite punching a good, centered dimple on the tip of
>the stud after filing it flat, I was unable to keep the drill bit
>from slipping sideways and so removed too much metal on one side.
That's too bad. If I'd known you were going right ahead with it I'd
have said some more.
Things that can help keep your point from walking:
Triangular point on the center punch, nice deep punch. Light punch
first so you can walk it sideways if need be; then a good deep one
when it's definitely in the right place. The three triangular faces
should be reasonably even.
First drill bit used should be very small. A 1/8" pilot-point drill
(1/8" is as small as is practical to put the much smaller pilot point
on) is probably ideal for hand use on this size hole; otherwise start
with a 1/16". You could probably start with the correct size of
pilot-point bit, but not nearly so likely that you could find one the
correct size for tapping an M6x1 hole (which without doing the
calculations I've seen listed as 5.2 mm (or #5 in the US numbered
series of drills) or a 5 mm or #5, incidentally. Pilot-point drills
around here come in the US fractional-inch series, by 64ths. So I'm
wrong, a 13/64" is about right.
Alternatively you can start the hole with a small (Nos 0-2, say)
center drill of the type used with lathes, which have a very short
straight-flute pilot point followed by a sixty-degree cone which
makes a good starting hole for a drill bit. This is the conventional
method, so to say, but they tend not to sell center drills in
hardware stores, more's the pity.
Second (and possible subsequent) drill bits, the chisel point of a
standard bit (the flat line across the end of the point) must be
shorter than the width of the existing hole. Conversely with a
pilot-point bit the pilot must be large enough to be drilling into
metal and not air, as with that type of bit the outer edges cut first
rather than the inner, and they'll simply fling the bit away if the
point isn't solidly anchored.
Pull the bit frequently to clear chips, more frequently as the hole
is deeper; use cutting fluid of some sort, slow speed and heavy
pressure relative to the bit diameter.
A jig can help immensely to keep the hole direction along the shaft
axis. I have one where a second drill chuck slides up and down in a
frame. A jig is also the best way to keep the tap from choosing its
own direction of travel which it will very readily, being in effect a
tunneling machine on its own. There are more angled holes tapped in
this world than straight ones.
Yours,
David
