Every tool box should have a set of screw extractors:
Get some real "penetrating oil" not WD40 in there first.
[mailto:firstname.lastname@example.org] On Behalf Of Jim Thomson
Sent: Friday, July 02, 2010 2:16 AM
Subject: [TowerTalk] Rohn TB-4 bearings, sheared off transverse bolts !!
OK... the 3 x 3/8" G-5 bolts [ that appear to be cold galvanized] on
BOTH my Rohn TB-4 bearings
are rusted really badly. I soaked all 6 of em with WD-40.. from both
sides. I got 4 of em out with no problems
and of course 2 x of em sheared right off flush to the aprx 3/4" thick AL
collar! [ one sheared on each bearing]
Of the 4 that came out ok.... a new 3/8" SS bolt fits like a glove.
There is NO way the original rohn bolts were
ever hot dipped galvanized. If they were, the tapped threads in the solid
AL collar would be tapped slightly oversized.
[and a 3/8" SS bolt would then make a sloopy fit.. and they don't] I
suspect the stock bolts were just cold galvanized.
Cold galvanizing adds just .001" or less..zinc. Hot dipped [per the
ASTM spec] adds .0025" of zinc on all sides... IE; bolt diam
then increases by .005".... therefore the mating female nuts /threads are
always slightly oversized to compensate.
My game plan was to replace the rusted bolts with SS bolts and SS nuts. I
can't use real, hot diped galvanized bolts.. since the
threads in the solid AL collar's are not big enough in diam. I also don't
have a slightly oversized tap either. We are not using the
top bearing to take any weight at all [ the rotor takes all the weight] .
The lower bearing doesn't require the 3 x transverse bolts
anyway. it's virtually impossible to align two bearings + a rotor. So
just the top bearing + rotor are aligned. The lower bearing
just provides some lateral support in high winds. This is on my Trylon
T-500 tower. I custom made my own bearing and rotor
plates with 3/8' thick 6061-T6 AL plate.
Funny thing is... the 4 x 1/2" bolts that hold each bearing to the AL
plate came out very easily. They are real G-5 bolts that are
hot dipped galvanized.. and ditto with the mating nuts. One would think
that Rohn would have figured out this problem
with the transverse junk bolt/nuts on their TB-3/4 bearings..after 50
years in production.
OK.. what's the... 'easy' way to get the 2 x sheared off bolts out..
without destroying the AL threads ?? I was thinking of drilling em
out, starting with a small drill bit, and progressively using bigger bits.
Even then, that all hinges on initially drilling, dead center
in the sheared off bolt. In retrospect, I shoulda inverted the bearings
into a dish.. full of wd-40.. and soaked em for 2 x days.
Just high enough level of WD-40.. to encompass the 3 x bolts.. and not get
into the main bearing assy.
Plan B was to just drill, and tap a new 3/8" hole.. adjacent to the
sheared off bolt.
Fit to be tied.. and just pissed.
later......... Jim VE7RF
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