: OTA Mounts, Towers, Rigging Hardware

2009-11-24, 07:46 PM

The tripod has 3 holes per foot.

1. do I fill each hole (total 9 holes) with a lag bolt, or can I use fewer bolts.
The reason I ask, is, it seems to me if each hole is used on the foot, the support bracing I added under the roof, and the existing roof joist will simply split up, at least at the top edge, even if predrilled?

2. what size/length lag bolts or combination of bolts should be used. My joisting is 1 1/2" (thickness) x 4 1/2" (depth), and 3 1/2" x 3 1/2"?

thank you

Dead Short
2009-11-25, 05:04 AM
Hey Balm - Hope you don't mind that I jump in here.

Those holes aren't there just for looks. Use them.

Unless the bolt holes are incredibly large (I'm guessing they're 1/4" or 5/16". 3/8" max.) you shouldn't have to worry about splitting anything, especially if you pre-drill. If you are concerned about any bracing you may have put below your roof decking, consider using bolts and large washers to spread the load rather than lag bolts if you are concerned about strength. In the case of anything that you are bolting to existing roof trusses, going with longer lag bolts certainly won't hurt. Bolting into a typical 2"x4" you can easilly use a 3/8" x 3" lag bolt without any worries.

Playing devil's advocate for a minute, I'll offer a couple of things to consider if you haven't already. What are you putting on top of the tripod? What's it's surface area? Have you done wind load calculations? Did you account for icing too? Give yourself a good margin for error. When it comes to antennas and wind loads, never underestimate the power of nature. Unfortunately, if you do you won't know it until it's too late.

Dead Short
2009-11-25, 05:13 AM
Please take care about the masting material.
An old trick we used to use was to "double mast" by putting a chunk of pipe up inside the mast as a reinforcement.

2009-11-25, 08:40 AM
You need to calculate the bending moment acting on the antenna and mast, and compare this with the tensile and compression strength of the antenna support structure, and shear strength of the bolt system. The weight of the antenna in and of itself is not generally a determining factor (unless its something huge of course).

To do this you need specific properties of each material involved, but an approximation can be done, and probably has been done. That is why I asked what is standard (for a 4 bay).


2009-11-25, 10:06 AM
you shouldn't have to worry about splitting anything, especially if you pre-drill.

You should definitely drill a pilot hole to prevent splitting. You can find a chart with the correct sized hole to drill for the size of lag bolt you are using here (http://www.portlandbolt.com/technicalinformation/lead-hole-diameter-lag-bolt-chart.html).

2009-11-28, 08:02 AM
i dont think ive seen the answer to this yet, but is it better to seal, cap, or otherwise cover up the top (inside) of the antenna's mast, and the antenna spine...or is it better to let precipitation go in the top and run out the bottom...

I was thinking more about the amount of ice build-up inside the mast tubing...????


2009-11-28, 06:34 PM
I've never sealed up a mast. Best to let it remain exposed to air, where condensation can evaporate out, IMO.

2009-12-07, 01:02 PM

thanks for your help.

I have another question, im close to mounting my tripod on the ridge.

Im using 4" long, 1/4" galvanized lag bolts (3 bolts per foot).

Now, im not sure I should use the galvanized bolts, as I seem to recall reading that these are actually weaker than standard zinc plated alloyed steel due to the effect of the galvanization...

Is this correct, if so what grade bolt should I look for?


2009-12-07, 01:27 PM
Regardless of the coating, check the bolt head markings for its class of hardness and strength. SAE Grade 8 would be excellent, but if I was going all out I'd use ASTM A490 - Type 3 (http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx), although Jase88 has raised the point that there may be counterfeits on the market of such harder bolts so choose your supplier wisely.

2009-12-07, 01:37 PM
Thank you Stampeder,

The highest strength bolts cannot be had in 1/4" though.

whats worse, is the bolts I bought do not match any grade markings as per the various websites!

Now ill have to go to a bolt specialty supplier here and ask.

thanks again

2009-12-07, 08:11 PM
Grade 5 bolts should be enough to do the trick--especially for a tripod mount. You can get zinc coated grade 5 at most reputable hardware stores.

2009-12-07, 08:16 PM
the guy at HD told me I will never find any grade markings on any of their bolts, or anyone elses which are assigned for the construction industry. And he was correct, neither the HD, RD, RE, or CT stores bolts had any markings!

He was a machinist at Bombardier, and told me only industrial quality bolts will be marked.

he had no clue how strong the HD lag bolts were, but said they were WAY stronger than I need to worry about! He basically was saying the roof or tripod would tear apart before the bolts would fail...

The no marking on bolts mean no strength data given, the next grade up, indicated by markings, provide over 50000 psi strength, which I should think is more than enough

but I seriously wonder how many people actually ordered specifically graded bolts for their antenna installation :eek:

2009-12-07, 10:30 PM
The lag and carriage bolts are unmarked, other bolt types are marked Grade 5 at RD.

2009-12-07, 11:16 PM
Obviously the risks of using inferior fasteners on a tripod mount are less than say a 60' tower installation. And your adviser could be right: Using standard bolts on a tripod will likely give you years of trouble-free service. It's up to you to weigh the risk vs. cost.

Higher grade bolts really aren't that much more expensive. Therefore, IMO, they are worth the expense. Especially in climates such as Montreal's (or QC in general), where there is significant snow/freezing rain precipitation throughout the winter. Even if the tripod fails before the bolts do, you at least know that your equipment won't tumble to the ground; or that your roof won't spring a leak come spring. ;)

2009-12-08, 08:25 AM
I learned the ONLY GRADED fastners are OTHER than LAG BOLTS (screws).

ALL lag bolts (screws) are GRADE 2 or less.

To get more than GRADE 2, say GRADE 5 which is next most common, you must use a regular BOLT & NUT type fastener assembly. This implies drilling right thru your structure and threading a nut on the inside (in attic) of the joist. I know of NO ONE who does this for this type of installation.

This means EVERYONE using lag bolts (screws) on the tripods are actually using GRADE 2 or less- no doubt about it.

2009-12-08, 01:33 PM
Ahhh. Gotcha. Well, unless you live in a hurricane prone area, you should be okay. ;)

2009-12-08, 02:20 PM
ALL lag bolts (screws) are GRADE 2 or less.

That makes total sense since the wood the lag bolt is threaded into would give way well before the metal in the bolt would.

To get more than GRADE 2, say GRADE 5 which is next most common, you must use a regular BOLT & NUT type fastener assembly. This implies drilling right thru your structure and threading a nut on the inside (in attic) of the joist. I know of NO ONE who does this for this type of installation.

For this to be effective, you would need a very large washer or better yet metal bar on the inside to distribute the over a large area, otherwise, once again the nut would just pull through the wood before the bolt would break.

2009-12-09, 11:37 PM
hookay i wanted to post this concering my recent (like recent as in just bloody right now) issues with all my channels! No dropouts yet, but signal bouncing heavily between 40-80%.

I heard a terrible creaky noise coming from my back yard.

Lo and behold. My beautiful 30ft tower is swaying around 20-30 degrees back/forth.

My dad and I cemented that thing in 3 bags of concrete 3 months ago and buried it under rocks and another 5 feet of dirt.

Now it looks like the only thing keeping it in place is the coaxial cable and a rope tied to a pole on my house.

it's happening right now! what do I do?

2009-12-10, 12:17 AM
Don't try to stabilize it yourself if its wagging around like that - get some help!

I helped stabilize a 40' antenna tower once before and the guy in charge was brilliant so here's what he had us do: 3 of us young guys were each given a nylon rope, then one of us climbed up only about 15 feet where he was told to tie all the rope ends. Once they were on there each of the 3 guys pulled on his rope outward from the tower, and within less than a minute most of the swaying was gone. Then the climber went up again, untied the ropes, went up to about 25' and tied them, then we repeated the whole thing. This time the tower was totally still. :)

It was only a temporary fix because the next day the owner signed on for guy wires.

2009-12-10, 12:23 AM
By the way, is it a self-supporting tower like a Delhi DMX?