Two thoughts: I can't find the reference just now, but I recall an awful
years-ago tower accident in which a ham was injured and trapped on his
tower when the thrust bearing bolts broke and the loaded mast fell onto
his hands. So I'd be concerned about any thrust bearing setup that
relied only on the clamping bolts.
I have had good luck with adding one or more clamps on the mast just
above the bearing, typically heavy U-bolts or machined bolted clamps.
There may be other more formal clamps that can perform this function.
Once I loaned my tower to some visiting hams to put a temporary contest
Yagi on my mast, and when they left they didn't know to replace the
clamps; the swooshing noise of the mast slipping down ended with the
boom of my own antenna hitting me in the head and shoulder. Luckily it
was cold and I had a thick hat on, or it could have been very much
worse. So if you use this approach, be sure to check that the clamping
is tight before you do anything else on the tower. I use two, just for
the extra redundant reliability.
Caution and plenty of your own research is strongly recommended.
Dave, W6NL/HC8L
On 6/22/25 5:00 AM, Tom Hellem wrote:
Looking for some input on the DX Engineering TB-400 thrust bearing.
Here is the scenario: Rohn 55 tower supporting a large 6 meter EME
array, in an "H" configuration. 4 yagis , each with 50' boom, and the
main boom is also 50 '. The total weight is approx. 700 lbs. The
rotor is one of Kurt's prop pitches, the small version (9,000:1). I
believe the max thrust that can be handled by this rotor is 500 lbs.
or so.
We have purchased the DXE-TB400 thrust bearing to be installed on the
BPL55G flat top. The hope is that this bearing can be used to support
the entire weight of the array, thereby eliminating any thrust load
on the rotor.
Problem is, the documentation that comes with the bearing does not
specify a max thrust load for it, nor does it give a torque
specification for the three set screws that tighten against the
mast. Furthermore, the upper half of the bearing is cast aluminum, so
the threads for the 3 3/8" stainless set screws are aluminum. My
gut feeling is that the aluminum threads are going to strip out
before we can get enough torque on them to prevent the mast from
slipping down and putting the entire weight of the array onto the
prop pitch rotor.
I am in no way suggesting that the bearing is not a good quality
part. But I am concerned that we are asking too much of it. Another
concern is that the bearing doesn't come with a grease fitting. This
setup is located near the coast of Oregon, they get a lot of rain
there.
Anybody have suggestions how we can improve this setup?
All input is appreciated.
Tom Hellem K0SN _______________________________________________
_______________________________________________ TowerTalk mailing
list TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|