Date: Fri, 17 Aug 2012 19:40:24 -0700
Reply-To: Alistair Bell <albell@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Alistair Bell <albell@SHAW.CA>
Subject: Re: windshield wiper repair
In-Reply-To: <502ecdd3.5284cd0a.7719.594c@mx.google.com>
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I want to add to this excellent description, maybe differing a bit...
I'd use a fine prick punch to mark the hole, then if you want punch again with 60 degree point puch. Then as Bill Monk has said, use a small (1/16") drill to enlarge punch divot. The small flexible drill does a better job in this case than a centre or spotting drill. You do not need to drill very deeply with the 1/16" bit, just make the punch mark a hole. Then go on to the 1/8" bit and follow with tap drill size.
Tapping the hole in situ is tricky. Hard to keep tap perfectly aligned, as is it is hard to keep drill bit aligned.
All in all, I'd say it is a tricky job to get a good tapped hole in shaft.
alistair
On 2012-08-17, at 4:03 PM, David Beierl wrote:
> 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
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