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Silicon Bronze Screws Snapping

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Mark Christensen
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Silicon Bronze Screws Snapping

Post by Mark Christensen » Mon Feb 19, 2018 12:33 pm

I did a few test runs with my taper bit and some SB screws. In the pic you can see the depth I set the bit to. They seem to go in ok without snapping, but as soon as I try and back them out, they snap. This is going into white oak. I believe these are cut thread and not rolled. What am I doing wrong?
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1961 24' Chris Craft Sportsman - CUA-24-0007C
1940's Homebuilt 14' Racing Hydroplane
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KMuller
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Re: Silicon Bronze Screws Snapping

Post by KMuller » Mon Feb 19, 2018 1:37 pm

with a taper drill, the tip of the screw is doing the bulk of the pulling as well as absorbing the most torque. SB is not strong enough. bore the hole deeper or just use a straight drill. In fresh water use ss screws.

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mbigpops
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Re: Silicon Bronze Screws Snapping

Post by mbigpops » Mon Feb 19, 2018 7:14 pm

What number screw is that ?

You need to be using the recommended countersink for hardwood (not softwood) for your screw size.

I have a chart if you post the screw size.

Mark
1953 CC Rocket Runabout "Rocket Man"

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Mark Christensen
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Re: Silicon Bronze Screws Snapping

Post by Mark Christensen » Mon Feb 19, 2018 9:16 pm

#8 screw x 2”. I used the tapered bit per the supplier. I set the countersink a little deeper and that seems to have helped for now.
1961 24' Chris Craft Sportsman - CUA-24-0007C
1940's Homebuilt 14' Racing Hydroplane
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jfrprops
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Re: Silicon Bronze Screws Snapping

Post by jfrprops » Mon Feb 19, 2018 9:40 pm

I hope more folks will post on this....it seems odd to me?
John in Va
1980 Fairchild Scout 30
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1954 Whirlwind deluxe dual ckpt 16'
1921 Old Town Charles River 17' (founding Captain, James River Batteau Festival)

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Bilge Rat
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Re: Silicon Bronze Screws Snapping

Post by Bilge Rat » Tue Feb 20, 2018 7:21 am

When screwing into white oak, you may want to lubricate the screw threads to alleviate the torquing off the tapered point. I used to use a mainly beeswax compound by the name of Akempucky but it is no longer manufactured. There should be other lubricants still available. This helped greatly in preventing the dreaded snap-off.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

Denis D
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Re: Silicon Bronze Screws Snapping

Post by Denis D » Tue Feb 20, 2018 4:14 pm

I add almost a 1/8" additional depth when drilling white oak. Then I dip the threads of the screw in a small cup of dishwashing detergent as a lubricant. That eliminated the snapping problem both going in and coming out.

Denis D
Denis

1948 17' deluxe runabout

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