NMO mount help

[CCPD213]

Ok so I drilled a hole in the roof of my new truck for my nmo coax base. Use a 3/4 still they said, now the hole is to big for the nmo mount. It ended being an 1" size hole. Don't ask me how because the bit was 3/4". My question is how do I fill the gap and make this nmo coax base work?

Thank,
John

 

[rescue161]

Don't use normal hole-saws for drilling antenna holes! If you aren't going to buy an antenna hole-saw, then at least use a step-bit and mark it at the 3/4" step with tape to ensure that you don't go bigger than 3/4". Or just use 3/8" NMO mounts and push the NMO from the underside.

You can use a rubber 1" hole-plug to seal up the hole and drill another 3/4" hole. When using the new 3/4" bit that you get, drill into a scrap sheet to make sure it isn't going to be too big. Remember that the NMO 3/4" is fished from the outside of the vehicle to the inside. You push the coax into the hole first and then angle the NMO into position. The NMO will not fit from the inside-out, i.e., you cannot install the mount by pushing the NMO into the hole threads-first.

Some people will drill the 3/4" hole and think that it's too small as the NMO won't fit (threads-first), so they drill the hole bigger and then it becomes too big of a hole for the mount to hold. Don't do that.

Short of doing the above, you'd have to take it to a body shop to fill/paint the roof. Even then, you'd still have to pick another place to mount the antenna.

When you go to sell the vehicle, if you don't like the idea of having two rubber plugs on the roof, buy two cheap GPS pucks and install them. They look like satellite radio/GPS antennas that most cars have these days, so it shouldn't harm your value.

 

[jim202]

I have never had a problem trading in a vehicle with multiple rubber plugs covering the holes drilled for NMO mounts. All the dealership cares is that the holes are sealed and water doesn't leak into the headliner.

The problem with trying to buy a normal hole saw drill from the hardware store, is that they are made for electrical conduit. The 3/4 hole saw is not 3/4 inch in size, but larger. As was mentioned by one post here, if you don't have a regular "ANTENNA HOLE SAW" that is a true 3/4 inch in size, you can use a step drill. Only problem in using a step drill is that you can destroy the head liner if you don't drop it down to provide the space needed by the step drill.

Those of you that are new to installing the NMO mounts to the roof of a vehicle, you have been warned many times on the site here. Maybe it is worth doing a search on here to find the comments that have been posted for many years on just this subject. You would be surprised just how much information can be found by a simple search. You might just try to use the term "how to install an NMO antenna mount" and see all the good information that shows up.

Even searching the Internet can provide a wealth of information.

 

[Project25_MASTR]

Filling the hole isn't trivial and is actually simple in theory. Cut a blank (7/8") the same gauge as the roof, support with copper from underneath, weld it up, grind it all flush and repaint. The hard part is the paint (generally because you are repainting the entire roof at a minimum).

Best way to move forward is to either plug it or choose a different antenna (like a Panorama Sharkee).


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[SteveC0625]

Ok so I drilled a hole in the roof of my new truck for my nmo coax base. Use a 3/4 still they said, now the hole is to big for the nmo mount. It ended being an 1" size hole. Don't ask me how because the bit was 3/4". My question is how do I fill the gap and make this nmo coax base work?

Thank,
John

As already pointed out, plug the hole with a rubber plug and drill another.

Your 3/4" bit is useless for antenna installs. Get a bit that measures 3/4" Outside Diameter with straight teeth. Your typical Milwaukee (or other brand) wood hole saw has very coarse teeth. Get one with smaller, finer teeth. If you can swing it, get one made specifically for installing 3/4" NMO's. You won't regret it.

As Jim202 stated, this whole thing has been discussed here over and over again. The correct advice has not changed. For others who may read this some day, don't think you know better! This advice comes from experts who have done hundreds, if not thousands, of these installs. Don't believe us? No problem, search back and find out how many others have made the same mistake. Search and read before you start a project. Measure twice and cut once. Read the instructions FIRST!

 

[mrweather]

Maybe this needs to be a sticky?

When drilling for 3/4" NMO mounts use the proper bit!

 

[phask]

Measure twice, drill once.

No reason a PROPER 3/4" steal hole saw will not work. We already beat that discussion to death previously. Problem in this case could be multiple, but probably was a 3/4" conduit bit which is a little over 1".

Fix - as others said , find a plug, which might not be as easy as it sounds since a normal NMO cap won't fit - or spend severaa; hundred$$$ to fix it properly.

 

[AI7PM]

Plug it and start over. My NMO saw bit has paid for itself many times over.
If you can't find a big enough plug, a large enough piece of metal and some JB Weld will close it up forever.

 

[FFPM571]

Use the right tool for the job....

 

[cmdrwill]

One can... use a 'fender washer' on the under side and a thin pattern washer on the outside.

 

[mmckenna]

Ok so I drilled a hole in the roof of my new truck for my nmo coax base. Use a 3/4 still they said, now the hole is to big for the nmo mount. It ended being an 1" size hole. Don't ask me how because the bit was 3/4". My question is how do I fill the gap and make this nmo coax base work?

Thank,
John

Yeah, this happens.
There's a thing called "Trade Size" hole saws. These are designed often for electricians and are designed for drilling holes for conduit fittings.
1/2" trade size is actually 7/8" diameter
3/4" trade size is actually 1 1/8" diameter.

It's critical to understand this when choosing hole saws or chassis punches. It's important, as you've discovered, to know if you are getting a "trade size" or a normal hole saw.

A true 3/4" hole saw will work just fine, same with a true 3/4" chassis punch. The "official" NMO hole saws do work well, and are a good choice.

So, what do you do?
There's a number of options:
Plug the hole with a plastic plug. Done right these work well.
Go to a body shop and have them weld in a plug, as MCore25 suggested. It'll cost, but it'll be done right.
You can get a "thick" NMO mount and a big fender washer and see if you can make it fit.
You can try some of the various ways of patching it, bondo, a JB Weld patch, etc.
If you can get to the underside, you may be able to get a proper 3/4 punch or hole saw and drill a sheet of steel to go on the underside. A similar patch/fender washer, or similar, might work on the outside

It all depends on how good you want it to look.

As they say, lesson learned. Not impossible to fix, but not easy.

Since the top of the NMO mount is standardized, there isn't a different type of NMO mount that's going to make this work.

Good luck, and let us know how it turns out.

 

[Aquamed]

We all have made similar "learning experiences." I was able to repair mine with a couple of oversized fender washers. Using one washer only the regular NMO mount will still work. I mounted the washer on the underside and put a ring of sealant around the inner ring of the washer. For what it was worth I filled the extra space with dialectic grease. Using dual washers , with a think mount NMO, I put one washer under the roof and a fender washer on top of the hole. I used dialectic grease on the contact surfaces. Prior to installing the top washer one could paint it black or the color of the car or of the antenna mount. The ones I repaired that way looked fine after and EVEN better from a distance!


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[lifeisgoodoneasystreet]

We all have made similar "learning experiences." I was able to repair mine with a couple of oversized fender washers. Using one washer only the regular NMO mount will still work. I mounted the washer on the underside and put a ring of sealant around the inner ring of the washer. For what it was worth I filled the extra space with dialectic grease. Using dual washers , with a think mount NMO, I put one washer under the roof and a fender washer on top of the hole. I used dialectic grease on the contact surfaces. Prior to installing the top washer one could paint it black or the color of the car or of the antenna mount. The ones I repaired that way looked fine after and EVEN better from a distance!


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I have used this washer application before. It works like Aquamed says.. but gives you little room to spare. The 3/8 hole mount is better than the 3/4, you come up from the bottom, the brass ring on top discard the nylon washer and use just the rubber O ring. It will just cover the 1 inch opening will no room to spare. If using 2 fender style washers, this same 3/8 mount is available in thick surface apps, fire trucks for one.
I believe you won't make the mistake again.
A little patience is your best tool....

 

[lu81fitter]

This may sound crazy, but it worked. I was visiting a friend when his neighbor came over asking for a hole saw to install an antenna. We both went to check out his project. It was an NMO mount on his truck. No one had a hole saw that was suitable. We found an old 3/4" spade wood bit that still had the sharp points on the sides. It worked really well. Just had to drill really slow and not press too hard. We just let it "scrape" the metal off. The points on the edge of the bit were long enough to cut through the metal before it actually got to the spade part of the bit.

 

[jhooten]

1 to 3/4 reducing washer X 2. One inside, one outside.

Like this:
https://www.lowes.com/search?searchTerm=1+to+3/4+reducing+washer

https://www.grainger.com/product/GRAINGER-APPROVED-Reducing-Washer-3LV42

 

[EZlistener]

Tessco Technologies (Hunt Valley, MD) sells an hole saw bit that correctly makes the hole needed. A very minimal and good investment.

 

[cmdrwill]

Reducing washer. Gampak 2-Pack 3/4-in Metal Reducing Washer $0.48 at Lowes. Great Idea...

 

[RFI-EMI-GUY]

Yeah, this happens.
There's a thing called "Trade Size" hole saws. These are designed often for electricians and are designed for drilling holes for conduit fittings.
1/2" trade size is actually 7/8" diameter
3/4" trade size is actually 1 1/8" diameter.

It's critical to understand this when choosing hole saws or chassis punches. It's important, as you've discovered, to know if you are getting a "trade size" or a normal hole saw.

snip.

It is insane that here in the US we deal with such an archaic measurement system and then apply all kinds of variations like "trade size" , "Troy ounce" and such. Then we have 5/8" and 7/16" quick, which is bigger?

Just the other day I was researching something that required inches to metric conversion, a weak spot in my little head. I know it is 25.4 of one thing and 2.54 of another.

Anyway I grabbed my 12 inch steel rule from Staples (item number 103960) and noted that it had a 30.4 mm scale. What! It came from the factory marked in mm not cm. No kidding. I should return it. Somewhere someone made a very expensive mistake using one of those rulers.

No wonder we don't make anything in the US any longer.

 

[mmckenna]

It's certainly a lot easier to teach kids metric. My 12 year old son can easily process base 10 stuff. Trying to remember how many pints in a quart, how many quarts in a gallon, how many ounces in a pound, is just silly.
Nothing like keeping our kids in the dark ages.

 

[RFI-EMI-GUY]

It's certainly a lot easier to teach kids metric. My 12 year old son can easily process base 10 stuff. Trying to remember how many pints in a quart, how many quarts in a gallon, how many ounces in a pound, is just silly.
Nothing like keeping our kids in the dark ages.

It is insane how many different sized fasteners and screws exist, none of which ever quite fit. The plumbing section at the hardware store drives me bonkers trying to mate different threaded pipe and tubing solutions, all of which weep and leak no matter how carefully you assemble them.

I bought some expensive German faucets for the master bathroom remodel. The contractor hired a plumber (low bid, no kidding) who proceeded to ignore that in Europe the supply lines on the faucet are fitted with nice "O" rings, precision threads and simply thread together where they meet the faucet. He wrapped them with several sloppy layers of Teflon tape, twisted them in, turned on the stop valves and was no sooner out the driveway while I am checking his work and as I turn the valves on and off I hear the supply lines banging around inside my new custom made cabinets. One of them immediately shot off filling the base of the cabinet. I had to redo his work myself, didn't need him fouling up more stuff.