[ML-Hams] new mast

[Kris Kirby]

On Mon, 22 Aug 2016, Jeff Cotten wrote:
> The one thing we might want to weld is a base plate.  They were 
> ungodly expensive at hamfest, for what amounted to a cafeteria serving 
> tray sized plate of steel with a 1 ft steel pole welded to its 
> surface.

Check the plates with a micrometer before you assume that it's a 
cafeteria tray. You can buy cafeteria trays from eBay however, should 
you need them. 

A lot of tower and tower-related stuff has to be built in such a way to 
prevent lawsuits due to people falling, dying, property damage from 
things being dropped, etc. As a result, all the designs are signed off 
by a professional engineer (PE), and safety factors are included, from 
2:1, 5:1, and sometimes up to 10:1. So if it looks expensive, that is 
probably still cheaper than doing the math yourself and trying to figure 
out wind speed survivability, and prevalent wind speeds in your area, 
etc. 

http://training.bnl.gov/demo/BasicRiggingWorkbook.pdf
http://energy.gov/sites/prod/files/2014/01/f6/HoistingRigging_Fundamentals.pdf

Lines and gear used to transport men have to have a 10:1 safety factor 
(~5,000 lbs), lines and gear used to transport equipment have to have a 
5:1 and it's stamped on the equipment. 

http://www.acmerigging.com/index.php/hardware

Remember, you can get yourself hurt or killed doing this stuff, or when 
stuff fails. But also remember that part of it isn't (just) 
over-engineering but putting in the weakest point at a place that is 
easy to replace (i.e.: at the hook, not in the middle of the wire). 

Also pay special attention to lifting, chokers, and the angles of the 
lift (i.e.: 45-degrees, 30-degrees, and less). 

There is crossover between this stuff and ship rigging / cranes / jibs / 
gin poles / derricks / loading and unloading.

> Any tips on where to get scrap steel plates? :)

Good luck on that. 1" thick "street plates" are commonly used by ALDOT 
for covering holes in the ground temporarily. They rust however. Steel 
and iron are very heavy, so 1" thick steel plates require heavy 
equipment to move. Unfortunately, they also make great rifle targets, so 
anything that might be acquireable may have costs associated due to 
demand. Steel and iron have a terrible scrap value compared to aluminum, 
so they will be easy to locate, provided you have manpower enough to 
move what you find. It will stay put, generally speaking.

You might even reach out to the railroads and see if you can locate a 
piece of iron rail and use it for a base. 

Also remember that dissimilar metal create a battery, and a battery 
means corrosion. Always sandwich stainless steel between copper and 
aluminum. Remember that stainless steel can gall, and after that it's 
time for the bolt cutters. T6061 Aluminum is a good thing, but make sure 
that it's thick enough for the application. The venerable DB-224 is 
actually three sizes of heavy-gauge T6061 structural aluminum pipe stuck 
inside of each other, with an outside diameter (OD) of about 2". 

--
Kris Kirby, KE4AHR
Disinformation Architect, Systems Mangler, & Network Mismanager