What is a good drill bit for installing an NMO mount?

[GTR8000]

Cool. Except a decent quality and sharp 3/4" step bit will do a perfectly fine job drilling a clean hole through sheet metal. You absolutely do not need a $100+ specialty bit.

 

[prcguy]

But once you drill a bad or wrong hole in your car you are screwed

Whoever is drilling the hole is much more important than the tool. I’ve worked with so called techs that couldn’t drill a simple 1/4” hole in wood without ruining it. Anyone competent with hand tools should be fine with a hole punch, step drill, basic hole saw or the $100 NMO specific saw. If you’re not completely comfortable drilling the hole stop now and don’t bother with which method to use.

 

[AK9R]

Put a strip of painters tape where you think the hole should go. Then measure twice to make sure you're in the right spot. Light tap with a center punch to give the bit something to pilot on. Moderate pressure. Keep the drill straight. Don't get in a hurry. Let the drill do the work.

 

[mrweather]

I've done 13 NMO mounts across 5 vehicles in the last 20 years. The Antennex hole saw is the best money I spent.

 

[prcguy]

I've done 13 NMO mounts across 5 vehicles in the last 20 years. The Antennex hole saw is the best money I spent.

I’ve done well over 1,000 installs. Not all were NMO but many were and all done with a simple 3/4” hole saw that cost less than $14 today. There is nothing that a $100 specialized bit will do that I can’t do with my $14 saw and I can do it just as fast. If the headliner is 1/16” below the metal roof I will never snag it and never have.

 

[belvdr]

I’ve done well over 1,000 installs. Not all were NMO but many were and all done with a simple 3/4” hole saw that cost less than $14 today. There is nothing that a $100 specialized bit will do that I can’t do with my $14 saw and I can do it just as fast. If the headliner is 1/16” below the metal roof I will never snag it and never have.

Let me borrow that bit and I'll show you how to tear up a headliner in short order.

If I were to ever drill, I'd use a shop because I really don't want to carry that risk, but that's my preference. That said, I don't know of a quality radio shop here.

 

[Solidjake]

@JoshuaHufford If you pay for shipping both ways you can borrow my drill bit

I bought my bit by Laird I think years ago and it was not that much compared to what they are going for now.

 

[merlin]

Mine was like the Riply, and also had a Greenlee punch.

 

[GlobalNorth]

My concern is not the hole, but what lies underneath and around it. You may not electrocute yourself if you hit wiring, but you might disable the vehicle and heaven forbid you hit any part of the SRS system.

 

[prcguy]

My concern is not the hole, but what lies underneath and around it. You may not electrocute yourself if you hit wiring, but you might disable the vehicle and heaven forbid you hit any part of the SRS system.

For a roof mount you pull down the rubber upper door seal on one side (I prefer drivers side) which allows the edge of the headliner to drop a few inches at the door and you can see the under side of the roof with any bracing or wiring where the antenna will go, which takes less than 1 minute. Then find the spot for the hole and I place a small bolt on the roof and eyeball the spot from all four sides to choose the spot over measuring it. Turns out when people look at an antenna they see your rear view mirror or other things on/in the vehicle that are not exactly centered and if you measured perfectly the antenna usually looks off center. So choose the spot based on how a bolt on the roof looks from all four sides.

With the door seal pulled down a little slide something thin but strong up between the headliner and roof to catch debris and protect the headliner from the hole saw. I used to use a length of hard plastic about 1/8” thick and a foot wide by 3ft long for this. Drill a quick 1/8” pilot hole then use the hole saw with its 1/4” pilot drill.

I’m right handed so I place my left elbow on the roof and cup my right hand (which has the drill) with my left hand so I have complete control of the drill going up or down and drill away. My left hand with elbow on the roof can stop the turning hole saw right when it penetrates the roof so the bit will only go through less than 1/8” then I pull it out. That step takes less time to complete than it did for you to read it.

Then I tape the coax with mount on the far end to an old thin whip antenna I keep for installs and stick the whip down through the hole and out sideways between roof and headliner at the door pulling all the coax through until the mount is at the hole then I assemble the mount and tighten. From there you route the coax either down the front pillar for dash mount or down a door pillar for under seat or rear mount radios. Then stick the rubber door seal back on and the antenna part of the install is done.

Probably half the 1,000 installs I’ve done were roof mount so I‘ve simplified the process down to this over hundreds of actual installs.

 

[KevinC]

The OP said no headliner, but keep in mind side airbags have changed the roof mount antenna game. Just pulling down the headliner is no long a simple task and could be a disaster. Fortunately most of the over 10,000 installs I've done were pre side airbag days.

And no, it's not a competition.

 

[prcguy]

The OP said no headliner, but keep in mind side airbags have changed the roof mount antenna game. Just pulling down the headliner is no long a simple task and could be a disaster. Fortunately most of the over 10,000 installs I've done were pre side airbag days.

And no, it's not a competition.

Air bags are new to me and nearly all of my installs were done before they came along. It does add time to the install and causes you to rethink things.

In my heyday it was a competition between our installers to see both who could finish first and who had the best looking installs. I was the original installer at the place I worked and we had up to four installers when I left after six years. I trained many but also learned from some of the experts we hired over the years. Competition is good.

 

[AK9R]

Probably half the 1,000 installs I’ve done were roof mount so I‘ve simplified the process down to this over hundreds of actual installs.

Fortunately most of the over 10,000 installs I've done were pre side airbag days.

OK, who's going to be the guy who steps up with 100,000 installs?

 

[JoshuaHufford]

@JoshuaHufford If you pay for shipping both ways you can borrow my drill bit

I bought my bit by Laird I think years ago and it was not that much compared to what they are going for now.

Thank you very much, I really appreciate the offer.

Sometime this week I'm going to check with the radio shop and see if they will give me a discount to just drill the 3 holes and I can do the rest.

 

[buddrousa]

When we did Vehicle Extrication Classes we had GM Ford Guys come in and give us tips on dealing with airbags and with the addition of side airbags there are so many triggers you can hit.

 

[prcguy]

When we did Vehicle Extrication Classes we had GM Ford Guys come in and give us tips on dealing with airbags and with the addition of side airbags there are so many triggers you can hit.

It is a bit scary working in a headliner and trying to route antenna cables behind and well away from airbags. But I can’t say I’ve ever ever heard about an installer setting one off or having a radio/antenna install affect airbag deployment.

 

[Ubbe]

In the older days the headliner where a thin plastic sheet that where suspended over a metal frame. If the drillbit or holesaw where dull it became more of a grinding function that heated up the metal and if any shavings dropped down on the headliner it could make burn marks. Any metal shavings needed to be vacuumed and/or use a magnet to remove all of it or it would rust in no time.

I've heard of people who used both hands to drill the hole and didn't use that important elbow support that prcguy talks about and forced the drill too far and wrapped the headliner around it. Probably no risk today with the thick hard plastic headliners that are used for sound proofing.

It was important to check where the supporting beams where that run across the roof that you didn't drill into one of those, or too close to one that would make it more difficult to do the installation. We had a tool that inserted into the hole to scrape the inside of the roof free from any paint to make a good grounding for the antenna foot. We would always resistance check the antenna connector at the radio to chassi ground to see that it was just some tenths of an ohm. If we had a customer with a problem with generator whine or ignition noise and had installed the antenna themselves, then when we checked the resistance to ground it was usually several ohms and not a good ground. But it could also be a need to ground things properly in the chassi using copper braids.

So there are several things that probably makes it more suitable to leave antenna installations, or any radio related installations, to the experts.

/Ubbe

 

[KR4NIV]

I like Uni-bits because you can stop at the desired diameter and you don't have to worry about punching through a headliner. As prcguy said, gain access to the void above the headliner first.

 

[ramal121]

For a roof mount you pull down the rubber upper door seal on one side (I prefer drivers side) which allows the edge of the headliner to drop a few inches at the door and you can see the under side of the roof with any bracing or wiring where the antenna will go, which takes less than 1 minute. Then find the spot for the hole and I place a small bolt on the roof and eyeball the spot from all four sides to choose the spot over measuring it. Turns out when people look at an antenna they see your rear view mirror or other things on/in the vehicle that are not exactly centered and if you measured perfectly the antenna usually looks off center. So choose the spot based on how a bolt on the roof looks from all four sides.

With the door seal pulled down a little slide something thin but strong up between the headliner and roof to catch debris and protect the headliner from the hole saw. I used to use a length of hard plastic about 1/8” thick and a foot wide by 3ft long for this. Drill a quick 1/8” pilot hole then use the hole saw with its 1/4” pilot drill.

I’m right handed so I place my left elbow on the roof and cup my right hand (which has the drill) with my left hand so I have complete control of the drill going up or down and drill away. My left hand with elbow on the roof can stop the turning hole saw right when it penetrates the roof so the bit will only go through less than 1/8” then I pull it out. That step takes less time to complete than it did for you to read it.

Then I tape the coax with mount on the far end to an old thin whip antenna I keep for installs and stick the whip down through the hole and out sideways between roof and headliner at the door pulling all the coax through until the mount is at the hole then I assemble the mount and tighten. From there you route the coax either down the front pillar for dash mount or down a door pillar for under seat or rear mount radios. Then stick the rubber door seal back on and the antenna part of the install is done.

Probably half the 1,000 installs I’ve done were roof mount so I‘ve simplified the process down to this over hundreds of actual installs.

All good advice. I have used the bolt trick and eyeballs since day one. My installs are centered perfectly.

I will say if you forego a real antenna hole saw for cheaper jobber one from the hardware store you can prevent the deep dive after punch through with some electrical tape. Just use a thick multi-layer wrap just above the teeth. Also with a more aggressive tooth pitch you will leave a burr on the underside of the hole and this makes it harder to center the mount or it will spin easier. Use a rat tail file to remove that burr.

As for air bags, the safest route for the coax is forward to the windshield then over to the A post and down. If you need to cross an air bag then obviously go over the top of it and never under.

 

[SurgePGH]

Uni-Bits / Step Bits are OK until they aren't.
3/4" Hole Saws MAY make the hole too large.
Theres a right tool for every job.