>>>This may not be what you wanted to hear......but you were lucky. Those
>>>thrust bearing centering bolts were not intended to hold the vertical
>>>weight
>>>of a steel mast and maybe some beams mounted on the mast. They are
>>>simply meant to center the mast inside the "hole" of the thrust bearing.
>>>
>>>I have stacks of monobanders mounted on a 24' mast (14' above the tower)
>>>I use two muffler clamps above each of the two thrust bearings. I mount
>>>them
>>>one on top of the other facing opposite directions. The bottom muffler
>>>clamp then puts the weight of the system onto the thrust bearing. My
>>>guess
>>>is that the weight of the mast and etc could have been ""released"" at
>>>any
>>>time and you could have had major damage or injury. I 'm glad that did
>>>not
>>>happen to you.
>>>
>>>73, Jerry Liley, K0GUG, Holts Summit, Missouri
>
>>This is an interesting observation. As a Rohn Dealer, I have noticed that
>>those bolts do not seem to be the right type to "bite" into mast and still
>>keep the threads in good shape. They are defineitely not "set screw" type
>>bolts. I have never seen any mention of any of this in any Rohn literature,
>>however. So, I was wondering how you came to the conclusion that the Rohn
>>TB3 bolts should not be relied upon to support the mast and antenna weight?
>>Just your own observation or did you read something from Rohn about this? I
>>don't disagree with your conclusion, I just wonder if Rohn ever said
>>anything about using other clamps above and below the bearings to support
>>the weight.
>>
>>Stan w7ni@teleport.com
>_____________________________________________________________________________
>I guess ignorance is bliss and I've been most blissful in not realizing that
>one shouldn't use a thrust bearing to bear thrust! I thought that was what
>it was made for and so when I put up my 20 foot Texas Towers 3/16" galvanized
>mast on my 130 foot tower, I first drilled into the mast 120 degrees apart
>3 indentations that would allow the bolts to "bite" into the mast and support
>the weight of the mast and the TH7DX and 40-2CD that was installed thereon.
>
>I was concerned that the bolts might back out and so put nuts and jam-nuts
>on the bolts, screwed them into the indentations (not holes all the way
>through the mast) tightly, and then tightened the nuts and jam-nuts up so that
>they would not back out. The indentations were made at some considerable
>effort because the steel was so tough that I had to use a number of high
>quality steel bits in order to get the indentations deep enough for the bolts
>to "bite". The indentations were also made such that the bottom of the mast
>is held about 3/4" to 1" above the "resting spot" on the TT2 rotor.
>
>I also worked wheel bearing grease into the indentations well so that time,
>moisture, and oxygen would not be able to rust them. I've been up on the
>130 tower a number of times and have observed that there is no apparent rust
>at those indentations that have been up there for 5 years now. The TT2
>rotor has had to be changed out 3 times, now, due to lightning. It is a
>pleasure to be able to change out the rotor and not have to worry about the
>weight of the mast/antennas.
>
>Am I dumb, lucky, ignorant, or correct in my approach? Direct comments
>welcome.
>
>Regards,
>
>Rod, N5HV
>w5hvv@aeneas.net
Hi Rod,
The only comment I would have is that the indentions you put in the mast are
EXACTLY at the point of maximum stress and have weakened the mast
considerably at that point. I have no idea how to calculate how much but I
believe discontinuities in the steel like partially drilled holes act as
"stress risers" and the weakening effect is more that just a small amount of
steel that is missing. How about one of you learned types who know about
this stuff educating us?
Stan w7ni@teleport.com
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