[TowerTalk] Mast slippage

[john at kk9a.com]

WE3NNT is not pinning the mast with the grade 8 bolts, I think some towertalk posts scared him away from drilling though 4130 tubing.  He is just replacing the M8 stainless steel clamp bolts.  

John KK9A


-----Original Message-----
From: Charles Gallo [mailto:charlie at thegallos.com] 
Sent: Friday, July 31, 2020 5:54 PM
To: john at kk9a.com
Cc: TowerTalk at contesting.com
Subject: Re: [TowerTalk] Mast slippage

Indeed, 304 stainless bolts are roughly the same shear strength as grade 2. That said, through shoulder, single sliding shear is about 4900 lbs. Do you really need more than that?
Sometimes as hams, we get so hung up on the theory, we don’t think about the practical. 4900 lbs exceeds the brake torque of the PST71. Grade 3 exceeds the brake torque of the PST110
I’d say while I’d want to pin my mast, I’d probably want my yield to be lower than brake hold values

--  
73 de KG2V
Charlie

> On Jul 31, 2020, at 12:37 PM, john at kk9a.com wrote:
> 
> Will 3/8 bolts fit into a plate designed for M8?  I believe that stainless steel bolts are typically not much stronger than grade 2. Grade 8 bolts are available with Armor Coat which has great corrosion protection.
> 
> John KK9A
> 
> 
> Les Brown VE3NNT wrote:
> 
> Thanks for all the advice guys. I think I'll start with replacing the SS M8 bolts with 3/8 inch grade 8 bolts (or grade 9 or 10?) to see if that solves the problem. If it doesn't, I'll have to try the K7NV clamp, but that will require me to remove the rotor to slip the clamp on to the bottom of the mast, which won't be so easy. Given that half the mast is sticking out of the top of the tower, I'll have to rig up some pipes to hold the bottom of the mast in place for the operation.
>   It sounds like drilling and pinning isn't a good solution, and not so easy to do.
> 73, Les VE3NNT
> 
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