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Re: [TowerTalk] Sprockets with 2" bore needed

Subject: Re: [TowerTalk] Sprockets with 2" bore needed
From: K8RI <>
Date: Sat, 28 Apr 2012 01:03:26 -0400
List-post: <">>
On 4/27/2012 7:18 PM, Jim Lux wrote:
> On 4/27/12 8:59 AM, K8RI wrote:
>> As the subject line says, I need a source for some relatively heavy duty
>> sprockets with a 2" bore.  I spent over an hour and a half stepping
>> through Granger's web page but found nothing with a 2" bore.
>> Outer diameter may be anything larger than the 2" bore up to 4 or 5
>> inches, but I'd rather not pay a fortune for them as I need 4.  Granger
>> had some in that size range with a 2 3/8" bore for $32 or $35 each. I
>> just couldn't find a 2" bore listed.
> how heavy duty? what pitch chain?  Would bicycle or motorcycle sprockets
> work?  (because they're readily available)..
Going back to an earlier reply:

"I had e-mailed them earlier.  I just received a reply back stating they
could not make a recommendation for my application which was:
2" ID/Bore, finished or machinable, OD of roughly 4" and a linear force
on the chain of 500# which includes a safety factor.
I know I've seen systems that ran far more force than this.

Torque on the 2" shaft is roughly 1000 inch # at maximum wind gust. With
an OD of 4" this is reduced to 500# which would translate to 500 linear
#  on the chain.
OTOH the small rotator can go to about 1500 in # so that would translate
to  750 # of linear force on the chain.  As the mounts depend on thrust 
bearings on both inside and out side masts, the torque would not 
translate to pull on the tower. Where as if I used the standard 
accessory shelf inside with a separate mount outside it would create a 
Push-pull action on the tower legs.

With bicycle chain I have 4 sprockets that are roughly 5" in diameter. A 
double sprocket system with 5" OD would drop for tension on the chain to 
2/5 or 400# linear pull at 1000 in/# of torque or 600# linear pull with 
1500 inch/# of torque..  I have 2 SS chains and the sprockets are 
Aluminum racing sprockets. Using a double sprocket arrangement would 
drop the tension to 200 to 300# per chain.  It would take some machining 
to make the mounts but they should be more than sufficient and stand up 
to the weather quite well.

Actually I could do most of the work on the mill, but I'd prefer to do 
the mounts on a lathe which I don't have yet, or a place to put it.  I 
still have to finish hooking up the 3 phase rotary converter for the 
mill.  This is one of the reasons I wanted to find sprockets I could 
just bolt in place.


Roger (K8RI)
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