[TowerTalk] To pin or not to pin

[Floyd Rodgers]

May I suggest you do not use a high strength heat treated bolt as a pin, you would be much better off using 1 or two roll pins. The most important part is to line drill a close tolerance hole through both clamps so torque is evenly distributed between the two shear zones. Start with one pin and the if that also fails you can go to two pins. The holes should be a no slop metal to metal fit with the mast and clamps. Make certain the place you choose to drill hole has no air gap between the mast and clamps. Your goal is ZERO rotation slop of the assembly when you are done.


Floyd KC5QBC

> On Aug 28, 2016, at 1:39 PM, Kevin <kstover at ac0h.net> wrote:
> 
> Rudy,
> 
> I would consider changing the mast clamp to something like what K7NV or K7LXC produce, assuming they will fit the Prosistel rotor.
> 
> As to question 1 below I'd use a bolt slightly softer that the mast. The bolt is a less expensive replacement if it shears.
> 
> 
>> On 8/28/2016 11:47 AM, Rudy Bakalov via TowerTalk wrote:
>> I am getting really tired of my mast slipping during major wind gusts. The mast is supporting a 4 el 40m M2 yagi and a 6 el M2 KT36XA. The clamp is the standard clamp that comes with the ProSisTel PS61D rotator.
>> So the question is if I should pin the mast to the rotator clamp using a M8 bolt. The clamp has 8 bolts, but clearly the friction between the clamp and the mast is not sufficient under extreme conditions. My one and only concern about pinning is that the hole in the mast may weaken the mast. The PST61D is rated for 36 sq.ft so, right or wrong, I am not concerned about the wind damaging the rotator.
>> If you suggest I pin the mast, there are two follow up questions:
>> 1) What grade bolt should I use for the pin? The mast is 120K psi. Should the bolt be rated for less (e.g., Grade 5) or more (e.g., Grade 8 or 10.9) psi? That is, do I want the bolt to break before the mast does under extreme conditions?
>> 2) Further, is it OK if the bolt is zinc plated? I could not find stainless steel Grade 8/10.9 M8 bolts. Is the contact between zinc and the mast going to lead to corrosion?
>> Rudy N2WQ
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> 
> -- 
> R. Kevin Stover
> AC0H
> ARRL
> FISTS #11993
> SKCC #215
> NAQCC #3441
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