----- Original Message -----
From: "Al Williams" <alwilliams@olywa.net>
Thank you for the link to the photo of your "new" m2 2800 positioner. It
looks identical to my older one which is about 3 years old since purchase.
The mfr's spec is the same except that the starting torque has been
increased from 3500 to 4200 in lb and the rotating torque has been
increased
from 2800 in lb to 3200 in lb. I can visualize measuring the starting
torque with a simple heavy duty torque wrench. Maybe some mechanical
engineer will tell us how a small company can measure the rotating torque?
Steve (k7lxc) writes that "only 2-3 teeth per surface of clamp actually
contact the mast". Actually, for my 2" mast and older positioner (which
appears identical as far as the shape, clamping teeth, and bolts are
concerned), 12 teeth make contact with the mast. These 12 teeth consist of
3 teeth in each of the four rows. Because each half of clamp inside, where
the teeth are, is shaped more as a "v" than a "u" and the rigidity
("massive" of the clamp I suspect that the pressure supplied by the bolts to
each of the teeth is not distributed evenly. Steve probably meant that only
2-3 teeth per row for a total of 8-12 teeth...
Unless the "ductile iron" acutally ducts, it seems that the major holding
power is supplied by only 1 or 2 teeth per row and the other teeth in the
row may not be very effective. In the same way holding power of the teeth
in some of the other rows may be less effective.
It has been over 50 years since I learned about coefficient of friction in
college. I hope that some mechanical engineer will enlighten us on the
concept of using these narrow teeth as described.
k7puc
>
> ----- Original Message -----
> From: "Keith Dutson" <kdutson@sbcglobal.net>
> To: <K7LXC@aol.com>; <towertalk@contesting.com>; <alwilliams@olywa.net>
> Sent: Sunday, April 22, 2007 3:21 PM
> Subject: Re: [TowerTalk] Mast slipping
>
>
>> Ya'll have me wondering about my 40M tower plan. Last fall I took
>> delivery
>> of two M2 40M4LLDD Yagis. This antenna has 4 elements on a 42 foot boom,
>> but a surprisingly sparse 13 square feet windload rating. They will be
>> mounted at 100 and 200 feet on a 190 foot Rohn 55G tower. The top
>> antenna
>> will be rotated by an Orion 2800 that was purchased at the same time.
>> The
>> lower will be rotated by a TIC Ring.
>>
>> This tower was supposed to be going up this spring but unexpected surgery
>> has delayed the project for a year.
>>
>> After hearing about all of the mast slipping problems I decided to take
>> the
>> Orion out of its box and have a look. According to the instructions, the
>> "positioner" has been recently improved and strengthened. Since I do not
>> have an older unit, I have no way of knowing what is improved or how much
>> stronger it is. Here are some specs:
>>
>> wind area 35 sq ft
>> start torque 4200 in lb
>> rotating torque 3200 in lb
>> braking torque 17000 in lbs
>> vert load cap 1800 lbs
>>
>> I took a photo of the mast clamp halves (see below). Interestingly,
>> there
>> is a hole in each that is sized to take a 1/4 inch bolt. This could
>> certainly be used to pin the mast but leaves doubt about the strength to
>> hold it.
>>
>> http://www.dutson.net/Transfer/HamRadio/Orion2800Clampds.JPG
>>
>> 73, Keith NM5G
>>
>> -----Original Message-----
>> From: towertalk-bounces@contesting.com
>> [mailto:towertalk-bounces@contesting.com] On Behalf Of K7LXC@aol.com
>> Sent: Sunday, April 22, 2007 12:04 PM
>> To: towertalk@contesting.com; alwilliams@olywa.net
>> Subject: Re: [TowerTalk] Mast slipping
>>
>>
>> In a message dated 4/22/2007 8:43:23 A.M. Pacific Daylight Time,
>> towertalk-request@contesting.com writes:
>>
>>> About a year ago I had a conversation with the m2 people about their
>> rotator
>> clamp slipping on my Monstr's mast. What follows is my memory of the
>> conversation:
>>
>>> 1. It is better to have the clamp slip than to harm the rotator.
>>> (Note:
>>
>> the
>> wind banging repeatedly on the gearing can weaken the gears?)
>>
>>> 2. The specified braking torque has not been measured (or
>>> calculated?).
>>
>>> 3. Pinning voids the warranty. I would assume that using a
>>> different
>> mfrs
>> clamp would also void the warranty.
>>
>>> 4. They recommended a clamp bolt tightening sequence that should be
>> followed. Unfortunately I wasn't able to get a firm answer on what
>> torque
>> to tighten the nuts to. The sequence to follow is:
>>
>>> a) bolt the rotator to the mounting plate but leave the bolt/nuts
>>> not
>> tightened
>> b) with the bolts to holding the rotator to the mounting plate loose,
>> tighten the bolt/nut pair of the clamp that is nearest the bottom.
>> c) tighten the next (middle) bolt/nut pair of the clamp
>> d) tighten the top bolt/nut pair of the clamp
>> e) repeat steps b,c,d several times
>> f) now lastly, tighten the bolt/nuts of step a
>>
>>> I did get an answer of 40 ft/lbs from the m2 person but I think that
>>> was
>> just pulled out of the air.
>>
>> Very interesting but not useful. It doesn't do anything about the
>> significant design flaws of the Orion mast clamp that ARE the problems.
>> None of the above will keep the mast from slipping.
>>
>> Cheers,
>> Steve K7LXC
>> TOWER TECH
>>
>>
>>
>>
>>
>>
>>
>> ************************************** See what's free at
>> http://www.aol.com.
>> _______________________________________________
>>
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