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Sonrisa · 26-01-2010, 20:01

Hi All,

I'm mounting a rope clutch on my mast. Rivets aren't an option so I'll need to drill/tap some holes and use machine screws. I'm wondering if I should use a finer thread in order to have more turns or just stick with the standard for a strong thread?

It's a 30 year old lafiel aluminum mast, there is a reasonable amount of material to bite into. Thoughts?

johnar · 26-01-2010, 20:09

I can tell you the bolts/screws for my cleats on my mast are standard thread, but remember when you go to drill you have wires for masthead/spreader lights.

Dutch

cantxsailor · 26-01-2010, 21:47

In soft material like aluminum I would suggest standard thread as they are a bit deeper and are less likely to strip. Like johnar said be careful of going into the inside of the mast with the drill bit. Those wires wont like it.........m

Weyalan · 26-01-2010, 21:57

I recently had to add a couple of cam-cleats on the mast. I just went with standard old "UNC" thread type. When we repainted the mast last winter we had to take all the threaded and riveted fittings out. All the threaded fittings were UNC threads. I did have to put helicoil inserts in a few though.

I'd recommend helicoils for any high-load applications.

Grasshopper · 26-01-2010, 22:02

I believe fine threads would be easier to cross-thread, that would be unfortunate. A big challenge will be tapping the hole through the same axis that you drilled the whole. In a thin walled material having these two activities out of alignment means you won't get as tight a fit as you want. Use a generous amount of cutting fluid and don't forget that the tap is stronger than the aluminum so you don't get the typical feedback from the tap, like feeling the tap itself twist. While the thin wall of the mast won't likely cause too much buildup on the tap, it is always a good idea to back it out half way through to clean it off. Forcing through any build up can cause the soft aluminum to smear and damage the threads compromising the fit. There are a number of "strengths" of threadlock, a low strength is probably appropriate mostly to fill the space between the mast threads and screw threads. Sometimes you have to put your beer down and use both hands but this is alright, you can generally pick it back up in a second or two. Hope you're in a warm and sunny place.

Sonrisa · 26-01-2010, 22:47

Thanks for the advice, I'll stick with the standard thread. And thanks for mentioning the internal wires, I hadn't considered them, might have made for an unpleasant surprise.

Drilling the holes straight is a problem I always seem to run into. I just searched online and found a guide, I might pick one up and give it a try.

Versatile Drill Guide - Lee Valley Tools

johnar · 26-01-2010, 23:23

another thing you may like is, they make a drill bit tap , it will drill and then tap the hole in one step but go very slow, no matter what type of metal drilling or taping the slower you go the better your work comes out.

I also agree with the post above when taping you work the tap in alittle then back out clean and tap again. I also agree helicoils are very nice but I have never used them on thin metal.

Depending on the type of Alum. your mast is made of you can also flame harden but to be honest its been so many years that I have done it I can not give anymore advice. Just remember I have done it years ago.

Dutch

**James S** · 27-01-2010, 01:10

A trick to stay straight is to first put a piece of shinny metal tape (like you use on insulating duct work) on the place you want to drill...then you can see the reflection of the bit and line it up with the actual bit.... its a lot easier to keep straight.

When I installed my boomvang attachments I drilled and taped many holes....after drilling I put the tap in the drill ...one shot in...no back and forth and cleaning out, and didn’t use any cutting oil.
Standard thread.

**s/v Jedi** · 27-01-2010, 09:49

There's another way that you Yanks not think of: use standard thread METRIC. This thread is a little finer than US course threads. Also, when you buy A4 quality fasteners, they should be equal to 316 but in real life, hold up much better so steel quality must be higher.
(A2 equals 304)

I agree with James that on a mast there's no need for reversing halfway the tapping process. I do use a little cutting oil, mostly because it contains the mess a bit.

I hand tap but now that I think about it, if you use a machine tap (one bit instead of a set of three), putting it in your low-gear drill might give better results if you have little experience tapping by hand as it's easier to go straight.

ciao!
Nick.

**s/v Jedi** · 27-01-2010, 09:54

James: your boom vang mast attachment looks exactly like mine... you copied Sundeer there or is it by coincidence? ;-)

But the boom attachment.... the reinforcement should have been inside the boom. which would also have allowed you to use just blind rivets instead of screws and tapping! Nice job though!

cheers,
Nick.

**James S** · 27-01-2010, 10:06

Thanks Nick....I would love to have copied yours but you don’t post any pictures!
Why inside?
Is the skin if the boom better under tensile?
I envisioned it as a saddle.
Since I did this in Leb. My fasteners are metric and your right about the thread size.

**James S** · 27-01-2010, 10:12

I was just thinking that the fitting should have been on the inside because the load is to pull down on the boom...but the same would then be true for the mast fitting as well.

delmarrey · 27-01-2010, 11:06

Use a smaller tap drill then what the charts say. The tap drill sizes on the charts are for 75% thread, which is fine for a long threads but for thin metal you'll want as much metal as you can get. On aluminum, as long as you can get the tap started then it's big enough hole.

And use a grease for tapping. The chips will collect on the tap instead of falling to the bottom of the mast.

Yes on the course thread. Fine threads are for torque and if tighten too tight it could just strip them out, in thin aluminum.