Threads on mast hardware

[Ian McColgin]

A pad is ertainly needed. WEST will work if you thicken it enough as will many other epoxies but a pad (it need not be teak) is nicer as it allows for change and choise.

Many do install with sheetmetal screws and things like fairleads are often low enough load that the distinctly inferior grip of a sheet metal screw will not be a problem. And it's certainly faster to drill one hole and force the screw in. For my own use and for any work I've done for customers, however, I always drill, tap and use a bolt on aluminum masts and booms.

G'luck

[Ian McColgin]

Reread and realize I very misinterpreted the post by not reading "machine screws (aka bolts) and instead thinking of sheet metal screws. My apologies.

I take it that you're planning on those fold-out steps. I'd be inclined to shape the inside surface of the step a little rather than adding a pad. Should be easy to just lay a bit of say 80# across the mast and rub till the step takes the shape. This makes a subtle error that will vanish in whatever you use for bedding.

G'luck

[seawolf]

Ian,
The sanding to form the shape of the mast onto the inside surface of the aluminum folding mast step is a clever idea. Now I know why I get on this forum occasionally.
Thanks for the input.

[Jim Fulton]

Originally Posted by Ian McColgin

Many do install with sheetmetal screws and things like fairleads are often low enough load that the distinctly inferior grip of a sheet metal screw will not be a problem. And it's certainly faster to drill one hole and force the screw in. For my own use and for any work I've done for customers, however, I always drill, tap and use a bolt on aluminum masts and booms.

I agree with what Ian says here. I also use appropriately-sized machine screws for mounting hardware on aluminum masts and booms. However, many people (including some of my friends) do not agree. In a separate thread, I asked about objective engineering data on the relative holding power of machine screws vs, sheet metal (self-tapping) screws in aluminum. I have seen no replies. Does anyone know of any such data? Or is it all just opinion?

Jim Fulton

[Brion Toss]

Hello,
I once conducted a come-along test with a padeye in a section of scrap spar, once with sheet metal screws, and once with machine screws. We tore the former out fairly easily, and couldn't budge the thing with the latter, even when we got down to just two screws.
Sheet metal screws have such big, deep threads because the threads are meant to act as backing -- there's enough space between threads so that they can sandwich the sheet metal. When dealing with thicker stuff, like, oh, a mast, one must drill a bigger hole, just to get the screw in. So rather than having the thread projecting beyond the hole, as with sheet metal, they merely scrape against the sides of the hole, with very little "bite". That's why they can pull out.
Now of course given enough screws and a light enough load, you can have hardware stay put. But with how much reserve strength? Clearly, the right tool for the job, for anything heavier than a winch handle pocket, is a tapped screw, with a good rivet a distant second.
Fair leads,
Brion Toss