Strength of tapped bolts versus piloted sheet metal screws - SailNet Community
Reply
 
LinkBack Thread Tools
post #1 of 11 Old 01-30-2009 Thread Starter
Senior Member
 
Join Date: Jun 2007
Posts: 536
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 9
 
Strength of tapped bolts versus piloted sheet metal screws

OK for all you machinist/engineering types out there here is a question:
Is a drilled and tapped hole (bolt) into fiberglass more resistant to pullout than a correctly pilot drilled sheet metal screw of the same diameter?

Last edited by GBurton; 01-31-2009 at 10:45 AM. Reason: Clarify
GBurton is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 11 Old 01-31-2009
Senior Member
 
trantor12020's Avatar
 
Join Date: Mar 2006
Location: Singapore
Posts: 701
Thanks: 4
Thanked 10 Times in 10 Posts
Rep Power: 10
 
pilot drilled sheet metal screw has large & deeper thread to bite into the fiberglass so my money is on sheet metal screw.

Ken
2002 Hunter 326, SV Millennium 2
1999 Macgregor 26X, SV Millennium
trantor12020 is offline  
Quote Quick Reply Share with Facebook
post #3 of 11 Old 01-31-2009
Senior Member
 
kaluvic's Avatar
 
Join Date: Jan 2009
Location: Sana'a Yemen
Posts: 263
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 7
 
Me too...but the difference my be in the number of threads..the bolt may have more.
I still think the screew wins.

James S
S/V Arctic Lady
kaluvic is offline  
Quote Quick Reply Share with Facebook
post #4 of 11 Old 01-31-2009
Senior Member
 
tommays's Avatar
 
Join Date: Sep 2008
Posts: 4,296
Thanks: 1
Thanked 30 Times in 30 Posts
Rep Power: 7
 
Maybe

BUT NOTHING holds anything all that strong in glass which is why most stuff gets through bolted

1970 Cal 29 Sea Fever

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1981 J24 Tangent 2930
Tommays
Northport NY


If a dirty bottom slows you down what do you think it does to your boat
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
tommays is offline  
Quote Quick Reply Share with Facebook
post #5 of 11 Old 01-31-2009
Member
 
Join Date: Apr 2008
Posts: 70
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 8
 
The question does not seem to be worth a lot of thought, IMHO. If you are concerned about the holding power of a particular fastener use a backing plate and through bolt the assembly.

I would always choose a tapped hole in steel over a self threaded hole.

Paul
newpbs is offline  
Quote Quick Reply Share with Facebook
post #6 of 11 Old 01-31-2009
Telstar 28
 
sailingdog's Avatar
 
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 15 Times in 12 Posts
Rep Power: 14
         
Fiberglass is too brittle to take screws well. If the screws get highly loaded, the threads of the screw will just tear through the fiberglass.

Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
sailingdog is offline  
Quote Quick Reply Share with Facebook
post #7 of 11 Old 01-31-2009
midlife crisis member
 
AllThumbs's Avatar
 
Join Date: Jul 2008
Posts: 975
Thanks: 0
Thanked 10 Times in 8 Posts
Rep Power: 8
 
My thoughts is sheet metal screw unless the fiberglass is quite thick, If it's thicker than the diameter of the screw I might be inclined to vote for the tapped bolt.

Eric

I sail.
AllThumbs is offline  
Quote Quick Reply Share with Facebook
post #8 of 11 Old 01-31-2009
Senior Member
 
Omatako's Avatar
 
Join Date: Sep 2003
Location: Auckland New Zealand
Posts: 2,558
Thanks: 1
Thanked 33 Times in 30 Posts
Rep Power: 12
 
Glass fibre never holds a fastener tightly for long and will wear away with even minute movement and a fine thread will leave very little "meat" for it to be strong in GRP (OK in metal). So a fine thread on a bolt will let go first, a course thread on a bolt will let go next, a course self drilling screw will let go third and a through-bolt won't let go at all.

I know what my choice would be.

BTW, if it's a light-usage fitting in reasonably thin GRP, the better fastener IMO would be a pop rivet of suitable size, as long as the end of the rivet goes all the way out the other side of the skin.

But still, a doubler plate on the other side would be my choice.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

__________________

"Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying."

Arthur C. Clarke
Omatako is offline  
Quote Quick Reply Share with Facebook
post #9 of 11 Old 01-31-2009 Thread Starter
Senior Member
 
Join Date: Jun 2007
Posts: 536
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 9
 
Yes - of course a backing plate and through bolted is the way to go, but not possible in all applications. I'm leaning toward the pilot drilled SS sheet metal screw......thanks for the help.

P.S. Sailingdog - couldn't stay away could you
GBurton is offline  
Quote Quick Reply Share with Facebook
post #10 of 11 Old 01-31-2009
Senior Member
 
timebandit's Avatar
 
Join Date: Sep 2002
Posts: 928
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 13
 
Something I use--

After setting the screw remove it and put a drop of super glue in the hole and allow 24 hrs. before reinserting.

Quote:
Originally Posted by GBurton View Post
Yes - of course a backing plate and through bolted is the way to go, but not possible in all applications. I'm leaning toward the pilot drilled SS sheet metal screw......thanks for the help.

P.S. Sailingdog - couldn't stay away could you

Rick
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Mac 25
Copernicus
Southern California
I am not a prejudice racist sexist bigot. I just hate stupid people.
timebandit is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Keel Bolt Repairs Don Casey Gear and Maintenance Articles 0 11-10-2003 07:00 PM
Keel Bolt Concerns Don Casey Gear and Maintenance Articles 0 10-12-2003 08:00 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome