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Old 12-05-2012, 12:10   #1
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Mounting a Winch to the Mast

I am mounting a halyard winch onto a prexisting base plate that is welded to the mast. The previous installation skipped a bolt and the winch cracked. Now I am faced with retapping holes into a base plate that is, in places, one inch thick and in others 1/2 inch thick.

I am mounting a used Barlow 20 and am wondering about the methods and pitfalls of drilling and tapping a thick piece of aluminum with stainless bolts. I have never tapped a piece of metal before. I also am curious about what length of bolt I should be using. I can't find any info about that in any of the online barlow manuals.
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Old 12-05-2012, 13:06   #2
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Re: Mounting a winch to the mast

alloy taps very well you need to drill the pilot hole 1-2 mm smaller than the bolt ie m8 thread you would use a 6.5 mm pilot hole.

a bit of wd40 stops the tap sticking.

use a plastic gasket between the alloy and the winch base,loctite or coppercote,stops the bolts getting siezed if you need to remove them again.

1/2 inch of bolt x 5 is plenty of depth to hold a winch under load.

comperessed air and a vacume are good for cleaning out the tapped holes
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Old 12-05-2012, 13:14   #3
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Re: Mounting a winch to the mast

When you tap aluminum, make sure to apply cutting oil, go slowly, and every few turns back out the tap to clean out the shavings.
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Old 12-05-2012, 15:21   #4
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Re: Mounting a winch to the mast

I am using 5/16" X 1" Phillips head bolts. By the time the bolt gets through the winch base and the plastic gasket I am using it will probably be about 1/2" if thread. What drill bit size should I use?
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Old 12-05-2012, 15:33   #5
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Re: Mounting a winch to the mast

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Originally Posted by unbusted67 View Post
I am using 5/16" X 1" Phillips head bolts. By the time the bolt gets through the winch base and the plastic gasket I am using it will probably be about 1/2" if thread. What drill bit size should I use?
i would think a 1/4'' or slightly smaller bit,maybe do a test hole first.
1/2" should be fine in solid ally
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Old 12-05-2012, 15:45   #6
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Re: Mounting a winch to the mast

The recommended tap drill for 5/16-18 in Aluminium is an "F" drill, diameter = .257 inch.

Most folks don't have letter size drills in their kits, so using a 1/4 inch drill would be ok.

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Old 12-05-2012, 16:08   #7
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Re: Mounting a winch to the mast

As said, lubricate well and tap slow, at least backing the tap a little to "break the chip", if not back it out a time or two. Two flute taps are normally used in aluminum. Beware, hand drilling into aluminum.... often the drill goes sidways/off track. Drill a pilot hole first or buy a 1/4 "center drill". Some winch base/supports are hollow at the thick part... are you sure yours arent? I guess you probably are by now. In a perfect world, alum threads should be 3 x the diameter of the bolt. that would be almost an inch of thread in your case.... then again... it'sx not a perfect world! >
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Old 12-05-2012, 16:39   #8
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Re: Mounting a winch to the mast

If you want to save some measuring and make sure that your bolt is centered get a cheapo set of transfer punches. If the bolt is 5/16ths then use the 5/16th transfer punch It will put an indentation right smack dab in the center. Saves a lot of measuring and mistakes. Kinda like this set for about $15.00 from Amazon.

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Old 12-05-2012, 16:46   #9
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Re: Mounting a winch to the mast

Mo Debbley!
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Old 09-06-2012, 08:19   #10
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Re: Mounting a Winch to the Mast

Lewmar also recommends an insulating gasket between the base of the winch and a dissimilar metal mounting plate... assuming aluminum mounting plate and chrome plated\bronze winch.

Are there any recommendations for material type for the insulating gasket. Polypropylene or starboard ( as a winch foundation ) has been suggested by some, but also dissed by others due to water absorbtion.

I'm wondering if a thin plate .06 or .13" of the starboard would be ok for a mast installation on an aluminum plate. My configuration is thru-bolts.

polyethylenes are generally lower water absorption then nylons, delrin.

starboard is a polyethylene, so maybe not a bad choice. Lexan as a thin gasket might be okay.
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Old 09-06-2012, 08:52   #11
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Re: Mounting a Winch to the Mast

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Originally Posted by Anduril View Post
Lewmar also recommends an insulating gasket between the base of the winch and a dissimilar metal mounting plate... assuming aluminum mounting plate and chrome plated\bronze winch.

Are there any recommendations for material type for the insulating gasket.
See if you can get your hands on an old inner tube. You can make a gasket out of that.

I would use Lanocote on the bolts NOT Coppercoat or any other Anti-Seize compound with Dissimilar metals in it.
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Old 09-06-2012, 08:56   #12
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Re: Mounting a Winch to the Mast

I would think that starboard is fine. I don't think that it absorbs water at all.

I am not an expert on tapping but aluminum is an easy place to start. Remember to go slow and back it down regularly.

http://www.permatex.com/products/Aut..._Sealant_a.htm

This is a great product for dissimilar metals. It forms a gasket between the SS and the Aluminum and acts as a loctite. IT is also pretty inexpensive. I have taken to putting it on most of my threads.
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Old 09-06-2012, 11:14   #13
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Re: Mounting a Winch to the Mast

I would avoid lexan etc, crack prone I would think. Heck, swim steps are often made of starboard.... Your winch base isnt going to soak up much water I wouldnt think. Use lanolin or lanocote on the screws..... seems to last forever...
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Old 09-06-2012, 11:40   #14
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Re: Mounting a Winch to the Mast

Vinyl window material makes a good insulator but you have to punch the holes for the fasteners or otherwise cut them out or it bunches. I've also used electricians tape. The insulator doesn't have to be thick, just not absorb water and keep the bronze off the aluminum.

If you haven't already bought the tap, Lowes has tapping kits for all common thread sizes. The kit is the proper drill, believe they are titanium coated, and the tap. If you are anal about using the proper tap drill, an industrial supply place will have the letter size drills.
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Old 09-06-2012, 11:52   #15
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Re: Mounting a Winch to the Mast

For aluminum use a two flute tap.
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