Machine Screw vs Tapping Screw

Len · Post by **Len** » Apr 30th, '10, 09:44

Machine Screw vs Tapping Screw--
Which holds stronger in an aluminum mast- a machine screw drilled and tapped into the mast or a tapping screw screwed into a drilled hole ?

Andy Denmark · Post by **Andy Denmark** » Apr 30th, '10, 10:08

Use TefGel to hold down corrosion and help with removal at a later date. To get the best strength use the correct number sized drill as opposed to fractional sized.

Hope this helps
________
M112 Engine

Ray Garcia · Post by **Ray Garcia** » Apr 30th, '10, 10:29

For a vertical load I would imagine either screw would do. When you think about it, there are not many fittings on a mast that experience a horizontal pull to the fitting. The fitting is either pulled up, down or at an angle to the mount. There are not many backing plates used on a mast. Other than the boom vang, and bale, which require heavy fasteners, either screw should work for anything else. I have used aluminum pop rivets in places, they are holding up just as well as screws.

I second Andy's reply. A definite if you ever want to remove or replace the item. Our halyard cleats on the mast are stainless and frozen to the mast, permanently. I have not gotten around to removing them because I will have to drill them out.

-R

Daniel Owen · Post by **Daniel Owen** » Apr 30th, '10, 10:29

Me thinks a properly tapped machine screw holds better than a self tapper. Also the finer threaded machine screws hold better than the coarser version. for example a #10-32 is better than a #10-24. Always use tefgel or equivalent when placing s/s into aluminum.

Cheers Dan O.......

mgphl52 · Post by **mgphl52** » Apr 30th, '10, 10:55

You can also use "blind-rivet-nuts" to insure even better remove-ability...

-michael

Russell · Post by **Russell** » Apr 30th, '10, 11:44

Never heard of someone using a self tapping screw into the mast, definately drill, tap and use a machine screw, or use a rivet.

jim trandel · Post by **jim trandel** » Apr 30th, '10, 16:15

As I am adding a dedicated aspin halyard to my Typhoon mast, I need to add a two- screw pad eye mounted above the jib sheave. I continue to be hesitant in doing the addition since I have the same concern with installing self threading SS screws and its ability to withstand the forces. Although the force vector on the pad eye is at eight o'clock, it is pivoted by the lower screw resulting in a direct horizontal force vector on the top screw.

My launch date is 5/10, so I'd like to see other thoughts on the subject before I'm forced to make a discision. Currently, the rivet plus compound is looking good! I only wish there were supporting data.

Jim
Ty#1907

mgphl52 · Post by **mgphl52** » May 1st, '10, 00:50

jim trandel wrote:As I am adding a dedicated aspin halyard to my Typhoon mast, I need to add a two- screw pad eye mounted above the jib sheave. I continue to be hesitant in doing the addition since I have the same concern with installing self threading SS screws and its ability to withstand the forces. Although the force vector on the pad eye is at eight o'clock, it is pivoted by the lower screw resulting in a direct horizontal force vector on the top screw.

My launch date is 5/10, so I'd like to see other thoughts on the subject before I'm forced to make a discision. Currently, the rivet plus compound is looking good! I only wish there were supporting data.

Jim
Ty#1907

Hi Jim, I cannot remember for sure, but I think the bail for the spinnaker halyard block was simply rivets on my last Ty. For the load and force exerted, I would not rely on just tapping the mast! Blind rivet nuts would be best, but your basic "pop-rivet" would probably be strong enough and I believe that's all that Babette had for the fractional spinnaker. I later added a bail to the mast head for a custom designed drifter that worked quite well. It really was a cross between a big-ass-light-weight drifter and an asymmetric spinnaker. If you search the archives for "Babette" you should find a picture of her flying the drifter and a 155% plus main...

-michael

Russell · Post by **Russell** » May 1st, '10, 01:03

mgphl52 wrote: For the load and force exerted, I would not rely on just tapping the mast!

My boom, my rigid vang, all my winches, mainsheet, are tapped into the mast or boom and using machine screws, on a CD36. Trust me, its absolutely more then enough on a Ty, if not serious overkill and certainly more then enough for this application. If worried, go up a size in screw.

SS rivets are great, but you need a very good rivet gun to install them, and it wont be cheap.

Steve Laume · Post by **Steve Laume** » May 1st, '10, 07:43

The two TY's I have had both had the spinnaker attachment pop riveted in place. It seems like a lot of load but they seem to have held up well. If it ever were to fail it would be exciting but not catastrophic.

I wold pop rivet it and go sailing, Steve.

Rollergirl · Post by **Rollergirl** » May 1st, '10, 08:48

The self tapping screw leaves a sharp end sticking into your halyard/wiring space. Can't help anything.

Bill

Maine Sail · Post by **Maine Sail** » May 1st, '10, 10:58

Pleas do not use self tappers..

I quote from the best below.. Brion Toss..

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

P.S. Fine threads are preferred over coarse. = more TPI in contact with the aluminum. Use Blue Loctite or Tef-Gel...

Len · Post by **Len** » May 1st, '10, 17:02

First off: I believe there is a difference between self tapping machine screws and self tapping sheet metal screws. I was referring to the former.
I installed my boom vang with tapped fine machine screws. I am confident it would take a tremendous force to dislodge it.
This season project is a hailer. I didn't want to tap the mast. I came up with another solution. I built a bracket of marine lumber which sandwiches the radar bracket. So now the hailer and the radar are bolted to the bracket.
The bracket holding the radar and hailer is itself riveted (8) to the mast

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