OT: DIY Tilt-base for Loop Support or Antenna Mast

[Clay Autery]

Putting up a multi-band, horizontally oriented loop and I have ZERO
trees in my yard.  I am borrowing trees from my two next door neighbors,
but I needed to supply one support for a delta config (yes, I'd prefer a
square).

Didn't like the commercial telescoping masts available, so I designed my
own (another thread if anyone is interested...  it's pretty cool and
well within average DIY skills).
Then I decided that I would like to bring the mast/support down for
maintenance WITHOUT having to collapse it, so I decided to use a
tilt-base.  Those available for a mast lower section diameter like mine
were either wayyyy too expensive, too flimsy, or just plain cumbersome.
So I decided to design and build my own.

Here is an ISO picture of the completed base with the 2" RMC
nipple/coupler installed in the upright position:

*http://montac.com/images/antenna/tilt_base_iso.jpg*

Here is an elevated front view:

*http://montac.com/images/antenna/tilt_base_front.jpg*

Here is a view with the top rear bolt and safety pin nut/washers removed
simulating prep for lowering:

*http://montac.com/images/antenna/tilt_base_top_pin_pulled.jpg
*
And finally, here is a view with the "mast" in the horizontal position:

*http://montac.com/images/antenna/tilt_base_horiz.jpg
*
The base plate is 12" x 12" x 3/8" hot-rolled steel.  It will be mounted
on a 10' x 20' x 6" concrete slab ("patio") directly behind my house
adjacent to my "shack" window, using 1/2" concrete anchors set full
depth in the slab.  The holes for the anchors are located inboard of the
edges by 1/2" to leave plenty of material to support them while
spreading the load.  The base plate will be leveled on the slab to
compensate for the slab drainage pitch and isolated from the concrete
using a concrete patch material to avoid corrosion on the bottom surface
over time.

The upright "c-channel" was constructed of 3 pieces of 3.5" x 5.5" (nom.
cut to fit under coupler on nipple as installed) x 3/8" hot-rolled
steel.  The back was specifically left full size to minimize cutting,
provide more strength and surface area to weld (welding later). The
assembly is located on the base plate to center the mast center
coincident with the plate center for load distribution.

* The plan called for a radius cut on the "ears" to clear the coupler on
tilt down, but I simplified it to a simple straight cut from the
nipple/coupler mid-line to the front edge to provide sufficient clearance.

* The plan called for a machined relief cut in the inside surface of the
back plate to clear the rear arc of the swinging nipple, but I
simplified that by simply removing minimally required material from the
nipple in a small arc/radius to clear the un-machined back plate.

* All three fasteners are 1/2' x 4" 316 SS with top-locking eccentric
nuts and 316SS washers.  The washers are technically unnecessary because
the through holes in the "ears" are only +0.004" over the bolt size, but
I am using them for "good measure"  There will only be 1 or 2 per side.
The extras in these images are to allow me to tighten the nuts without
engaging the lock for repeated fitment (nuts are rated for 5
installations).  The 2 through nipple holes are on the exact nipple
mid-line and result in the nipple being flush with the back plate within
0.003".  This took a lot of math, close measurement with calipers, etc.
and VERY careful setup on the drill press with good quality drills.

* The third fastener is through the ears alone and flush with the front
edge of the nipple as a "safety" pin for tilt-down ops.  The bolt will
be replaced at some point with a pull-pin that will be dummy-corded to
the left base ear with SS aircraft cable to keep it from being
misplaced.  The idea is that the top rear fastener might need to be
tapped out of its seat to remove, and the safety pin will keep the mast
upright. When the rigging for lowering the mast is set, I can rig a
remote pull cord for the safety pin and lower the mast in a 1-man
operation while remaining clear of the drop area and the base itself,
reducing chance of injury (the mast is HEAVY!!!).

* Currently, the entire base is cold galvanized to protect the bare
steel underneath (as all scale/oxidation was removed for machining and
welding).  I will likely take it to my local coating shop and have it
sand-blasted and either hot galvanized, zinc chromated, or powder-coated
to protect against corrosion.  Cold galvanizing is NOT for moving parts
or parts on the ground.

Note:  IF this base is used for an antenna mast, I would personally add
an adjustable mast rotation stop to the base plate under the coupler
drop zone to "catch" the mast to prevent the antenna from touching the
ground and/or to stop it at a convenient work height.

WELDING:  Yes, my welds aren't particularly pretty.  I am NOT a welder
and haven't done ANY welding in over 10 years.... so cut me some slack.
This is probably a lot of gobbledygook to most of you, but is included
to show that a small welder CAN do this job successfully.

This is THICK steel.  I do NOT recommend welding this up yourself... but
I did.  And I did it with a Millermatic 135 (115VAC) MIG machine using
0.023 ER70S-6 wire (old wire that was somewhat oxidized).  Needless to
say, it took some finagling to get good penetration.  here is how "I"
chose to do it:

I beveled BOTH sides of the two ears on bottom and on the back edge.  I
beveled the back-plate on both sides on the bottom edge.  I left
approximately a 1/8" flat "land" to allow for a 0.0625" thickness to
from each side to theoretically JUST allow for touching penetration when
welded as setup for 1/8" steel using 0.023" wire.  The bevel angle was
set at MORE than 45 degrees (about 52 degrees plus/minus) to allow for
better access considering the bevel was meeting to a vertical flat...
bevel to butt joint.

The machine was set to 7 on the voltage knob and 70 on the wire feed
knob...  basically yielding around 90 amps using the 0.023" wire and a
wire feed rate just barely adequate to keep up.  It would have been
better to use 0.030" wire and FRESH, unoxidized wire.  This would have
netted a higher realized amperage (need about 125) due to the wire
supporting a higher voltage before melting, and allowed for a higher
feed rate.

As I didn't have those options on a SUNDAY (no welding supply places
open), I worked with what I had.  I used a dedicated 20 AMP circuit from
my sub-panel and made sure I had a super good ground (put a wad of
welding wire core between the clamp and the cleaned metal base.

Procedure:

1) Tack together and refit the nipple/coupler/fasteners to make sure
nothing moved.
2) Make first pass with a stringer to connect tacks.
3) Grind stringer weld clean and smooth (a la pipe welding)
4) Make multiple fill passes (I only needed 2) cleaning WELL with a wire
brush between passes.
5) Make a final cap weld pass.

I also pre-heated the assembly with my torch to reduce the massive
heat-sinking ability of that much metal compared to the welder's ability
to supply current.

Result was not perfect, but sufficient penetration to make the welds
plenty strong for the purpose.  The base will rip up the slab before it
fails at a weld.

That's about it...  heavy-duty, can be adapted to any mast size,
customizable to mount in various locations, etc.

Have a great evening!

--
______________________
Clay Autery, KG5LKV
[phone]

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[Clay Autery]

Dang it... don't know why my setup is adding those asterisks and screwing up the links... Here they are again:

http://montac.com/images/antenna/tilt_base_iso.jpg

http://montac.com/images/antenna/tilt_base_front.jpg

http://montac.com/images/antenna/tilt_base_top_pin_pulled.jpg

http://montac.com/images/antenna/tilt_base_horiz.jpg

______________________
Clay Autery, KG5LKV
MONTAC Enterprises
[phone]

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