[aprssig] Re: I'm gonna drill....

[Chris Rose]

HI,
I just installed two NMO mounts with a "generic" hole
saw (Dewalt yellow).  You just have to be very patient
with the drill.  A piece of masking tape on the barrel
of the saw helps too to use as a sight guage to stop
at a certain depth.  I made some dust of the
insulation between the headliner and the roof steel
but didn't muck up the headliner.  It also helps if
you take off the trim inside the vehicle and drop the
headliner a few inches as well before you drill the
holes.

73,
Chris 
KB8UIH


--- "Stephen H. Smith" <wa8lmf2 at aol.com> wrote:

> yahoo at davidarush.com wrote:
> > I need to do an antenna install for a tracker
> (see, it's 
> > APRS-related), and I'm tired of mucking around. 
> I've ordered an NMO 
> > mount and a hole saw, and the target vehicle has a
> nice, big, flat 
> > roof (and it's even made of metal, steel even).
> >
> > Any tips on installing it?  I'm particularly
> concerned about doing 
> > whatever possible to ward off rust, including from
> the inside, so I 
> > don't want to leave any unprotected bare steel, if
> possible, even on 
> > the inside.
> >
> > Tips?  Suggestions?
> >
> 
> 
> The NMO mount has to have intimate metallic contact
> with the sheet metal 
> for most antennas attached to it to work.  Standard
> NMO mounts contact 
> the sheet metal on the underside of the mount.  You
> can't completely 
> paint the underside or you won't have a ground
> connection.   The locking 
> ring that screws down over the inserted mount, from
> above, has an o-ring 
> seal on it's underside that should, if installed
> correctly, make a 
> waterproof seal between the roof's sheet metal and
> the mount.   The key 
> is to very thoroughly clean the top surface  of the
> roof after drilling 
> or cutting the hole, and before inserting the mount.
>   
> 
> It also helps to have a specialized "Motorola
> antenna cutter" instead of 
> a generic 3/4" hole saw.   This specialized hole saw
> has a very stubby 
> (about 5/8" long) 1/4" drill bit that steps down to
> a 1/8" anti-wander 
> starter bit, in front of the cutter so you you don't
> drill through the 
> headliner below the roof.
> 
> The mandrel that holds the actual hole saw also has
> a couple of flanges 
> that scrape the paint away in a perfect 1/8"-wide
> ring around the hole 
> so the mount gets a perfect metal-to-metal ground.  
> A single tiny ding 
> made with a center punch, before drilling,  will
> guarantee a perfectly 
> placed smooth hole, with the paint removed in
> exactly the right place 
> every time.   
> 
> The back end of this cutter has a hex shaft meant to
> fit neatly in a 
> 3/8" drill chuck without slipping.
>  
-- 
Stephen H. Smith    wa8lmf (at) aol.com