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Author Topic: NMO Mounting  (Read 6313 times)
KD7WNJ
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« on: October 03, 2011, 04:58:24 PM »

Hey all, just wondering what you guys use to drill the NMO holes. I have a standard 3/4" hole saw, anybody on here use one for mounting?? I know that Laird and a select few others make pricey specialty hole saws for the job, and have also heard of people using stepped drill bits. Just curious what anyone on here uses.

I have my radio installed in my car (2005 Ford Focus) and am using a mag mount, but want to get a permanent install in.

Here's a link to my install: http://s819.photobucket.com/albums/zz118/avdrummerboy/

Thanks,

KD7WNJ
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KG4NEL
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« Reply #1 on: October 03, 2011, 05:23:26 PM »

I used a 3/4" hole saw for mine, but make sure to go sloooowly Smiley

My drill of choice for these sort of things is a 1/2" Hitachi corded beast that's older than me - no worries about running out of battery power halfway through.

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K3GM
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« Reply #2 on: October 04, 2011, 04:52:49 AM »

I use a 3/4" Greenlee punch.  It's a 2 piece affair.  A small hole is required to allow a bolt to pass thru the sheet metal to connect the punch to the anvil.  Then it's just a matter of cranking down on the bolt which draws the punch thru the sheet metal.  The resulting hole is perfect with a razor sharp edge, and no surrounding paint damage.  The downside to punching is the fact that you need to access both sides of the sheet metal.  I've used some creative methods to thread the 2 halves together when I didn't want to take the headliner down.  My favorite method is  to tape the one half to a coathanger, and go up thru a dome light while my lovely assistant (aka. XYL) is outside ready to thread the bolt into it.  It's a bit more challenging than a saw, but the results are perfect.

Your installation looks good.  If we ever get a rain free weekend, I'm going to put an NMO mount into the trunk lid of my just purchased 2012 Ford Fusion, and get some VHF gear in there for my daily ride.
« Last Edit: October 04, 2011, 08:17:14 AM by K3GM » Logged
KJ4ADN
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Posts: 39




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« Reply #3 on: October 04, 2011, 05:41:51 AM »

I must have some other kind of NMO mount - it's a 3/8" hole.  There's a small backer plate, and on it goes.
Used a stepper bit the last time, and cleaned up the underside real good, doped it up with Nox, worked fine for the almost 2 years I owned the car.

I'll be putting another one on this week, same deal.   But, also a 90 degree 3/8 stud (makes a 1/2" hole) for some 7' HF whips.  That's the biggest hole through the roof I can think of.  On the last car (2010 I just traded in..), I used a plastic plug and JB weld to plug, looked nice and neat.

The NMO mount I've used is for 2m/70cm antennas, pretty small, and quick to dismount for the car washes.   These have a rubber gasket on the surface that mates with the top-side of the car roof.

KJ4ADN - Bill
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KE4DRN
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« Reply #4 on: October 04, 2011, 05:36:02 PM »

hi,

the trusty Antenex HS34 with replaceable cutting blade.

http://kollmanradio.com/antenex-hs34-hole-p-7688.html

73 james
« Last Edit: October 05, 2011, 05:45:45 PM by KE4DRN » Logged
K5LXP
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« Reply #5 on: October 05, 2011, 06:55:25 AM »

Punches aren't the ideal tool because they need access from both sides of the panel, which means in the case of a roof install you're dropping the headliner.  There's a lot of hassle and risk of damage doing that.  Additionally, the metal on a roof is thin and the torque from twisting on the draw stud can cause a crease.  A punch also doesn't remove the paint around the hole to ensure a solid groundplane connection, so that's an extra step.

An antenna hole saw can do everything from the outside - drill the hole, remove the paint and the collar prevents the saw from going too far in and damaging anything underneath.  And, it does it in about 10 seconds.  From there it's a simple matter to run a fish tape to a convenient pillar, pull the coax through and secure the mount.  Usually you never even have to touch the headliner.

Why you'd want to bother with the time and trouble to use a punch, or risk damage using a standard hole saw is beyond me.  Given the number of holes a ham typically drills, buying the purpose built tool is a lifetime investment.  It turns out the right tool is no more expensive than a punch, so why argue with it. Do it once, do it right.


Mark K5LXP
Albuquerque, NM
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K3GM
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« Reply #6 on: October 05, 2011, 08:14:42 AM »

.........Why you'd want to bother with the time and trouble to use a punch, or risk damage using a standard hole saw is beyond me.  Given the number of holes a ham typically drills, buying the purpose built tool is a lifetime investment.  It turns out the right tool is no more expensive than a punch, so why argue with it. Do it once, do it right.


Mark K5LXP
Albuquerque, NM

Mark, for over 30 years, I've punched many holes in my new vehicles, as well as those of my friends and from my experience, your claims of creasing are baseless.  I mentioned above the hassle of using a punch when it involves headliners, but I have two NMO mounts in my Tahoe that were both done without taking down the headliner, which nowadays is typically a foam shell as opposed to the cloth type used years ago.  Pictures of my installation in the Tahoe can be fouund on K0BG's site, and include the punch process. I've seen the results of a hole saw and while acceptable don't approach the precision of using a punch.  A hole in my '12 Fusion is up next.  If you're happy with the results of a hole saw, be my guest. <g>
« Last Edit: October 05, 2011, 08:17:31 AM by K3GM » Logged
VA3WXM
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Posts: 277




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« Reply #7 on: October 05, 2011, 11:19:38 AM »

One has to be careful and not use just any old 3/4" hole saw.  The ones you find at the big box hardware stores will give you a hole slightly bigger than 3/4".  The 3/4" NMO mount is very precise in what size opening it needs (I have no experience with the 3/8" mounts).  I use a dedicated 3/4" Antenex NMO hole saw and have had zero issues.
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K5LXP
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« Reply #8 on: October 05, 2011, 11:51:50 AM »

OK, let's look at it another way - what's the advantage of using a punch?  Precision?  Just how precise does an NMO mount hole need to be?  As I mentioned, creasing is just a risk.  I've seen panels thin enough that wrinkled just from torquing the NMO brass ring, so I don't think the crease risk is far fetched.

A punch is guaranteed to take longer.  Not every antenna will be directly above a dome light like your Tahoe, which means you need to get under the headliner.  The foam headliners can crease or crack if bent too far, and risk staining from handling. 

I've been very happy with the results of using an antenna hole saw the thousands of times I've used one.  You won't find any 2-way shop that uses punches for antenna installs.  More often than not the place you need to put an antenna can only be accessed from the outside like on top of a rib, double panel or somewhere you can't get your hand into. Yes, you can use a punch in some circumstances.  I just can't see any reason that makes it better, faster, easier, or more versatile.


Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #9 on: October 05, 2011, 02:24:19 PM »

There is another issue with punches. Most places which sell punches, don't sell chassis punches, but rather pipe size punches. Some unsuspecting poor amateur who doesn't know the difference, and goes ahead and punches his proposed 3/4 inch hole will suddenly have a really big (pun intended) awakening!

If there is a drawback to NMO hole saws, it is the depth they drill (≈3/8 inch worse case). But oh! One of the cheapest cars on the market is the Nissan Versa at just under $11k. Just wait until you see how the headliner it mounted!
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KC7YRA
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« Reply #10 on: October 05, 2011, 10:36:51 PM »

After punching quite literally THOUSANDS of holes in vehicles, and using every method imaginable, I just us a step bit. 

You have to be careful and not hit the headliner, but thats the worst of it.  It does send lots of sharp, hot shavings into the vehicle.  I personally try to snake a shop vac nozzle in the headliner beneath the hole.  It works great.  In the field, I make a duct tape hammock that catches the shavings.

But as has been said, it isn't rocket science.  Any 3/4 inch ish hole will work.  My favorite was going to a rural SD fire department for a leaky NMO mount.  Turns out the fire chief had tried the install.  But since 3/4 inch bits are hard to come by in the middle of nowhere, he held an arc welder rod the the roof and burned something resembling a hole in the roof.  Sad thing is, it kinda worked.  A few minutes with a dremel fixed it up.

Just don't overthink it and do whatever you need to make a 3/4 inch hole.

Brad
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K3GM
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« Reply #11 on: October 11, 2011, 09:35:02 AM »

I added some pix of my recent install in my 2012 Ford Fusion (a few weeks old).  I'm a measure three times, drill once kinda guy.  Speed is not an factor in my installations.  When you're drilling a hole in a brand automobile, I want it to be right:

First I drill a little pilot hole.  If I really screw up, a tiny hole is easier to fill.  I never had to fortunately!
http://i9.photobucket.com/albums/a96/TwoSevenRight/nmo1.jpg

Then I drill the clearance hole that allows the punch bolt to pass thru and thread into the die.
http://i9.photobucket.com/albums/a96/TwoSevenRight/nmo2.jpg

Next I thread the punch onto the bolt.
http://i9.photobucket.com/albums/a96/TwoSevenRight/nmo5.jpg

Now it's just a simple matter of CAREFULLY wrenching the the punch up thru the material.  The finished hole is razor sharp, and is within several thousandths of 0.750"  (3/4")
http://i9.photobucket.com/albums/a96/TwoSevenRight/nmo3.jpg

Here is the finished installation.  I place this antenna off-center to allow the installation of a second antenna later.
http://i9.photobucket.com/albums/a96/TwoSevenRight/nmo4.jpg
« Last Edit: October 11, 2011, 09:36:43 AM by K3GM » Logged
K5LXP
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« Reply #12 on: October 11, 2011, 11:27:58 AM »

I added some pix of my recent install in my 2012 Ford Fusion

Where's the smoke?  Cutting a hole in a brand new car just isn't the same unless there's that waft of freshly burnt factory paint coming out of it.  :-)


Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #13 on: October 12, 2011, 08:27:36 AM »

You're right Mark. And isn't it unique? There is something less exciting about drilling through old paint.
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K1CJS
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« Reply #14 on: October 13, 2011, 01:30:49 PM »

...As I mentioned, creasing is just a risk.  I've seen panels thin enough that wrinkled just from torquing the NMO brass ring, so I don't think the crease risk is far fetched....

If the sheet metal is that thin, even the use of a hole saw is a risk.  Once more, one slip with that hole saw, and you've got more of a crease or worse, a pulled panel!

I have a greenlee 'D' punch that I use regularly.  The fact that that makes it a two person job isn't really germane--if it's a two person job, use two people!  If done correctly and carefully, a hole punch leave a result that is just about impossible to beat. 

It comes down to personal preference.  If you like the hole saw better, go for it.  I happen to think that the hole saw is the more dangerous of the two methods.  BTW, the paint removal shouldn't be done on the outside of the hole as a hole saw does, it should be done on the INSIDE, where the serrated grippers of the mount are. 
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