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Author Topic: Cleanest hole?  (Read 5908 times)
K0JEG
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« on: April 12, 2012, 11:13:44 AM »

I'm getting ready to put a hole in the roof. What method works best, punching or drilling? I'd like a minimum of deburring and clean up if possible.

I might also investigate just removing the factory "sharkfin" antenna and seeing what's underneath. I don't listen to broadcast radio anymore (and don't want Satellite), so I won't miss it.
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N5VTU
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« Reply #1 on: April 12, 2012, 11:24:43 AM »

Punching a hole usually leaves a cleaner finished product, but you still have to drill a pilot hole for the punch, so there will be shavings to deal with regardless.

I normally just drill it with a hole saw and use a flexible magentic sign around my work area to catch all of the metal shavings.  If you drill it with a hole saw that's in good condition, deburring probably won't be necessary.  The key to drilling is to go slow and let the tool do the work.  If you push too hard, you'll just generate a lot of heat and burn your paint up.  This holds true for the pilot hole too if you decide to use a punch instead.


Stephen
N5VTU
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W8JX
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« Reply #2 on: April 12, 2012, 11:46:09 AM »

I agree that a hole punch would be cleanest. Lacking that I would use a hole saw because it would create less metal shavings than a drill and make a fairly clean hole too vs a drill bit.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
K3GM
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« Reply #3 on: April 12, 2012, 02:34:17 PM »

Here's what a punch can do:
http://i9.photobucket.com/albums/a96/TwoSevenRight/nmo3.jpg
Very clean, extremely sharp edge.  By the way.... the car was several days old.
« Last Edit: April 12, 2012, 05:24:44 PM by K3GM » Logged
N6AJR
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« Reply #4 on: April 12, 2012, 03:04:38 PM »

I reccommend a Greenlee punch for the nicest hole, but a drill will work if you have no other choice. Good luck. enjoy,
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W8JX
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« Reply #5 on: April 12, 2012, 03:18:55 PM »

I reccommend a Greenlee punch for the nicest hole,

That's a name I have not heard for a while. They make nice chassis/hole punches.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
K3GM
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« Reply #6 on: April 12, 2012, 05:22:28 PM »

They are, and they're something that's a lifetime tool.  I got mine back in 1980, and have punched countless holes in my vehicles as well as friend's.  I'm sure my kid will rummage through my tool crap someday after I'm gone, and wonder what the heck that thing is.  Looks like the Greenlee part you're looking for is #730BB-3/4.  Amazon's selling them for $43 with free shipping.
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K5LXP
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« Reply #7 on: April 13, 2012, 02:56:49 PM »

There are downsides to using a punch, namely you need access to both sides of the panel, and a punch won't clean the paint away for the antenna ground to contact.

An antenna hole saw can cut a "clean enough" hole in seconds, takes the paint off for you and minimizes the chance of headliner damage because you won't need to touch it.

A punch will certainly work fine, but is a lot of messing around compared to a hole saw made for cutting antenna holes.


Mark K5LXP
Albuquerque, NM

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K0JEG
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« Reply #8 on: April 13, 2012, 06:01:22 PM »

Thanks guys. I'm still looking at the sharkfin and thinking that's the way to go, but this helps.
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K1CJS
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« Reply #9 on: April 14, 2012, 12:55:49 PM »

Either way you go, if you take your time, and as someone already said, don't force the tool and let it do the work, you're going to get good results.  One thing you do NOT want to do is drill that hole without looking at the underside of the roof.  You may end up drilling in an area that reinforcing ribs or something else is that you can't have in the way of an NMO installation.  You've either got to partially pull the headliner to eyeball--or have some sort of guide as to where the underside reinforcements and or the internal parts are on the underside of the roof.

Also, you really don't want to remove the paint around the hole on the outside of the car.  Bare metal like that should be on the inside.  That is where the contact (grounding) points are on most NMO mounts.  If you can pull the dome light (if its in the center of the car roof) you can probably avoid disturbing the headliner too much--but you've still got to pull it somewhat anyway to run the coax.

Good luck!
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K7RBW
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« Reply #10 on: April 15, 2012, 08:52:22 AM »

You can read about my recent experience at http://www.eham.net/ehamforum/smf/index.php/topic,81793.0.html.

If you have to buy a tool, i'd go for the NMO hole saw. It was incredibly easy and made as clean of a hole as I've seen from a punch (perhaps cleaner). Heed K1CJS' advice, however. There are a lot of ways to mess it up.

I was surprised by how shallow the result was. The hole saw doesn't penetrate more than about 1/2" and the finished NMO mount doesn't take up much more than that below the roof either.
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W8JX
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« Reply #11 on: April 15, 2012, 09:18:25 AM »

If you have to buy a tool, i'd go for the NMO hole saw. It was incredibly easy and made as clean of a hole as I've seen from a punch (perhaps cleaner).

Sounds like you never seen or used a Greenlee punch.
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K5LXP
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« Reply #12 on: April 15, 2012, 09:57:37 AM »

Also, you really don't want to remove the paint around the hole on the outside of the car.

It's a whole lot easier to do it from the outside than the inside, and NMO mounts mitigate corrosion risk though the use of an o-ring.  Countless commercial installations have been done this way for decades.


Mark K5LXP
Albuquerque, NM
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K7RBW
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« Reply #13 on: April 16, 2012, 06:30:49 AM »

If you have to buy a tool, i'd go for the NMO hole saw. It was incredibly easy and made as clean of a hole as I've seen from a punch (perhaps cleaner).

Sounds like you never seen or used a Greenlee punch.
I've done both (seen and used). That's why I was [pleasantly] surprised to see how clean the hole made by the saw was. On top of that, it was much easier to make the hole with the saw than with the punch because I couldn't easily get on the other side of the roof sheet metal to attach the other side of the punch die.

One area where the punch might have an advantage is in repeated use. I can see how the hole made by a hole saw could start to get uglier as the saw dulls, but that won't be a problem or me since I don't plan on drilling that many holes.
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K1CJS
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« Reply #14 on: April 18, 2012, 04:20:55 PM »

Also, you really don't want to remove the paint around the hole on the outside of the car.

It's a whole lot easier to do it from the outside than the inside, and NMO mounts mitigate corrosion risk though the use of an o-ring.  Countless commercial installations have been done this way for decades.

In a warm, dry climate such as yours, I don't doubt that you've seen minimal corrosion damage.  In other areas, however, the more protection that is given to metal improves the resistance of corrosion, especially in a cooler, more wet type climate area.  That is all that leaving the paint on the outside edge of the new hole does--gives more protection.  O-rings do 'seal' that mount, but you know as well as I do that moisture is going to get into the area--from condensation more than likely from the inside of the car.  Spend any length of time in New England, and you'll know what I mean.

Also, that o-ring insulated the mount from the roof metal--unless it is overtightened.  In any event, there really is no reason to remove the paint from the outside--and every reason to make sure the ground teeth on the NMO mount have good contact with the bare metal on the inside of the area where the mount is, because that is where those 'teeth' are.
« Last Edit: April 18, 2012, 04:33:33 PM by K1CJS » Logged
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