Date:         Wed, 14 Jul 2010 18:22:18 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: drilling into pop top
Comments: To: "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
In-Reply-To:  <4C3E2D2F.8040100@gmail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 05:33 PM 7/14/2010 Wednesday, Mike \"Rocket J Squirrel\" wrote:
>Perfect timing. I am drilling a couple holes in my poptop for gas shock
>lifts. High speed metal type twist drill? Step drill? Them versions of
>twist drills that are used for wood that have the real pointy tip and
>the two pointy shoulders?

Well, here's one man's opinion:
http://www.ehow.com/how_4425956_drill-fiberglass.html

A few thoughts:

Any time you're enlarging an existing hole, brad-point (your
pointy-shoulders bit) or pilot-point drills will tend to misbehave
because since they cut at the outside first, they don't have any
centering effect from the walls of the existing hole.  A standard
drill will tend to center on the lip of the existing hole act more civilized.

OTOH the pilot-point ones are effectively two drills in one, they
don't *usually* wander much, and they are designed to make a clean
exit leaving a tapered disk of material on the drill -- something to
watch for if you're drilling two things at once.

Step drill is an intriguing thought.  I wonder if there might not be
a lot of splintering, but I'm not sure why.

The fellow at ehow seems most concerned about gel-coat chipping at
the entrance. The way to get a clean exit is to clamp ideally the
same material behind the work so the edge of the workpiece becomes in
essence an internal part of the hole.  The pilot-point drill will
notice though, and pretty much stop drilling until you get the disk
off its tip.  But here we don't care about drilling into the backing,
so the hole should be complete at that point.

Yrs,
David