Our old mailbox was hit by cars, snowplows etc, too many times. It is falling apart. (no foul play involved, just a lot of idiot drivers and snowplow operators)
I made a swinging arm for a mailbox, so that when the mailbox is hit, it swings away and then back.
So, now is the time for installing a new mailbox post. I bought a 30" post support that is made to be beaten into the ground with a sledgehammer. It is like an arrow with four fins.
I am now having second thoughts and am not sure if this is a good long term solution. One of the reasons is that there is going to be quite a bit of tipping moment due to a little longer swinging arm. (my guess about 40-60 extra foot pounds of moment of force).
I want this mailbox to stay vertical and not "tip".
I live in Northern Illinois, so we have frequent freeze/unfreeze cycles of soil.
So... What's a good way of mounting a mailbox post? Maybe I should set that mailbox post support at least partially into concrete? (ie, digh a shallow hole, beat it into the hole level with ground, and fill the hole with concrete?
You have a classic problem with off center load on a post: fence gate posts, fence corner posts, and side loaded power poles have the same issues. Your problem will be ground creep if the load gets too high.
You post will want to pivot around the center of what is underground. The lowest part goes one way, the top goes the other. Underground resistance is more substantial than the top but still can move.
A bare post will really move quickly, just not enough surface area. Encasing it in concrete helps by increasing the surface area exposed to the dirt. Tamping gravel in around the post helps by increasing the load bearing capacity of the dirt around the post.
I'd suggest 2 plates about 8"x16" m> Our old mailbox was hit by cars, snowplows etc, too many times. It is
There are lots of those in MN. You just need a longer post. Buy, borrow or rent a manual post hole digger, like this:
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you lived nearby I'd loan you mine.
Dig a hole a bit over a foot in diameter and 4 feet deep. Put in one of those 12" dia fiber tubes, Sonotube I think it's called. Home Depot. Plant post in center, supported plumb with temporary supports if necessary. Fill tube with concrete, backfill and tamp around the result.
It doesn't really take very long to do it right, and you'll only have to do it once.
Thing is, you want some of the concrete well below the frostine, not just a cap sitting on top. You can stop pouring 6" or so below ground level and backfill with soil so grass will grow there and it's easy to mow.
My own plan for now is as follows. I have this giant 40" or so stake for posts that I bought at Menards. I dug a hole for 2 bags of concrete. About 16 by 16 wide by 10 inches deep. I will pound the stake into the ground in the middle of the hole, so that after pounding, it should be level with ground on the same level as if I never dug a hole. Then I will fill the hole with concrete. This way, the concrete will support the stake in a vertical position.
That, I think, will be good enough -- about 170 lbs of concrete and a stake going even deeper.
The nice thing about this is that later, I could remove the actual post.
I will also add "eyes" so that later, I could lift the concrete out of the ground with a "shop crane".
This is my basic design, just have to get a Round Tuit to do it:
About a four-foot length of Well Casing or 4" square extra-heavy tubing for the mailbox post, with a 12" square of 1/2" HRS welded to the bottom. Four 3/8" holes in the corners for the shear bolts, and eight gusset plates pocketing each corner shear bolt so the plate doesn't bend (much) while the bolts are shearing. And a hole through the middle of the plate into the tubing for the restricting device.
For the base, a concrete footer around 24" diameter by 3' or so deep
- you may need to go deeper to get below the frost line, so it stays put from frost heaves. (Concrete is cheap.) A simple rebar cage, and
8 or so heavy foundation J-bolts with double nuts for leveling. Set the bolts up high enough so you have a 1" gap to get a stick with a nut underneath.
And in snow country don't put the top of the J-bolts above average ground level, so the plow blade can't hit them easily - better it should be a bit low. (I thankfully don't have to worry about that.)
The bottom plate for the footer is 16" square by 1/2" HRS with holes for the foundation bolts around the edge, and four holes in the corners of a 11" square to mate with the post baseplate.
And some sort of a restrictor to try and keep the sheared off post in the same county - a piece of slack chain or aircraft cable coiled up inside the post, hooked to both halves with shackles, and anchored to the top cap of the post that is removable for servicing. Perhaps a garage door tension spring at the post top cap end to slow it down gradually at the end of the flight path.
If someone hits the post dead-on and hard, they just shear off the
3/8" bolts holding the baseplates together, and it gives way just like a fire hydrant - but without the instant fountain... Put it back upright, and bolt it back together. To apply the nut under the plate, you hold it on a paint stir-stick with some double-stick tape and slide it under, followed by an open-end wrench to tighten once it's threaded. Simple and slick.
The chain or cable keeps the flying box and post from going into LEO or through the neighbor's window. And if they REALLY do a good job and screw up the baseplate, you can unbolt the bottom plate from the concrete footing and devise a Plan B.
I will also have a PVC conduit through the footer stub up at the baseplate center hole for future low voltage wiring. One circuit for a "Mail Here" chime connected to the box door, another for a decorative 12V light on the top of the post and/or a lit address number sign, and a normally-closed circuit for an alarm - "Gee, the mailbox isn't there anymore."
The switch and light wiring is sacrificial, the restrictor chain going through the same hole will snap it and chew it up if the mailbox ever takes wing. So be sure to place a buried splice handhole in the lawn near the footer so you can repair it easily.
Thank you Don, Roy and Bruce. I have never seen 12" by 4' deel concrete bases for mailboxes, myself. Unfortunately, by the time I read your messages, I already advanced along the line of not very deep concrete and a big stake held by the concrete and pounded a foot or so below it.. I made sure that the concrete pad would be extended beyond the center of gravity of this mailbox post.
I am off to buy concrete, but will read messages before pouring it.
Some pictures are here:
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Regarding Bruce's point about shear bolts: I set the post back by quite a bit compared to where it was. I hope that it does not get hit by cars, and snowplows, now that it is farther. The mailbox will be mounted on a hinged arm (see pictures), and will simply swing away when hit, at least that is my hope.
i
Google search for "mailbox post" on this newsgroup and you'll find that it's all been discussed here before.
My personal favorite post on the subject of posts was the one where the grader operator blew the mount bolts off the blade of his machine when the "poster" got tired of redoing his post and planted a really solid concrete mount into the ground. It seems there was some discussion about how close to the road such an installation can be put in, so it may be worth checking on that.
There have been some discussions about indestructable mailboxes as well, like taking the small size tin mailbox, placing it inside the large size tin mailbox, and filling the space between with concrete as a solution to the "mailbox baseball" players.
I would look to put in a solid mount, well back from the road, with a swingable extension holding the box itself.
If you are at all concerned about liability issues from it being hit, plant a really good solid base into the ground and mount the post onto the base at ground level with fairly light duty bolts so it can shear off, but be reinstalled easilly.
"Trevor Jones" wrote: (clip) If you are at all concerned about liability issues from it being hit, plant a really good solid base into the ground and mount the post onto the base at ground level with fairly light duty bolts so it can shear off, but be reinstalled easilly. ^^^^^^^^^^^^^^^^^ How about incorporating a coil spring (like from a car front suspension) at the foot of the post, so instead of bending or breaking, the post springs back?
You're setting yourself up for heartache. Even the pros make this mistake, I was driving along I-80 in PA a couple years ago, after they'd had a really cold spell that winter.
Every end of every guardrail, where it had been stuck in the gound, had been encased in concrete. And every one had been pushed back out by 6" to a foot.
I think a shallow pad would be your absolute worst option for frost. Either dig it deep and fill with concrete, or dig it and fill with gravel. Anything else will just p*ss you off after
2 or 3 hard winters, when the water gets under it and expands and tilts your spiffy new post.
Deep hole. Concrete. Below frost line. Or a largish (4 inch, 6 inch dia.)chunk of steel pipe set in at least as deep. Rent or borrow a gas post auger with an extension. Don't bother trying to dig one of these in by hand unless you are really cheap or feel the need to exercise.
I had a swingset in my yard at the last place I lived. About 50 feet up to the crossbar at the top, 4 inch diameter drill stem for the frame. The mounts in the yard were augered holes about 8 feet deep, 12 or 14 inches diameter, and none too smooth sided. I pulled one, the rest are the new owners problem. I can say with authority that they were solid, and frostproof. Those were north of Edmonton Alberta, Canada. I doubt that you will face winter temperatures in the same range.
Got big rocks in your area? How do you feel about them as landscaping?
A couple boulders on either side of the entry, a nice set of cast bronze numbers and a nameplate, and mount the box to one of them. Just a thought.
My new mailbox setup is really two things: the foundation and the swingable mailbox. I made sure of two things:
1) that the post with mailbox can be easily removed from the foundation when I need to do it
2) that if something goes wrong with the foundation, I can fix it.
I ended up making a large, but relatively shallow pad. About 4" of gravel underneath. Two cf of concrete. About 16" by 24" or so. About
6" deep. There is rebar reinforcement made of welded rebar, with an integral "lifting eye". That means that the pad could be pulled out of the ground with my "shop crane" if/when I do not like it. The lifting eye is actually flush with the surface of concrete.
The pad is meant to be covered by a couple of inches of soil.
See pictures
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It is similar to a pad that I made for my grill, only a little smaller, and the one under the grill does not seem to move much, if at all.
So, worst case, if this pad heaves too much, I simply pull it out in
15 minutes and drill a very deep hole with a rented posthole digger. (I do not like them, I hurt my arm with one 3 years ago, when I built my shed).
The story is still ongoing, now I need to mount the mailbox on the post for installation tomorrow. I do not want to install it before the concrete hardens a little bit.
Those things are for lazy homeowners or temporary use. Auger a hole about
36" deep (after getting utility/private markouts) then pound a galvanized pipe in with a pipe driver, as far as you can. Cut off the pipe at the desired height with a pipe cutter. Pour concrete around (best) or tamp around the pipe as you fill with a small headed tamper.
When I used to live in AZ a co-worker had the same problem (minus the snowplows). He solved it by burying a railroad rail in 6' of concrete. Combined with the hard soil composed of several layers of caliche he had the proverbial immovable object. The last I heard the score was: mailbox 2; drunks 0. YMMV subject to local soil conditions, laws, etc.
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