Silicone Bronze Screw Breakage

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Peter Jacobs
    Senior Member
    • Feb 2001
    • 123

    Silicone Bronze Screw Breakage

    WHile building the Acorn I've managed to break off a few silicone bronze screws. At the time, I put this down to maybe being a bit heavy handed with the screw driver. I noticed they all seem to break where the thread meets the shank.

    Low and behold, on page 24 of the latest issue of Wooden Boat, Rollin Thurlow is having the same problem.

    Is anyone else having this problem?

    -Peter-
    (BTW ... the floors are done
    Peter Jacobs
    Victoria BC Canada
  • Ed Harrow
    Retro Member #1235
    • Mar 2000
    • 7343

    #2
    It is, quite obviously, a conspiracy by the united forces of fiber, glass, and resin... Are you able to get them out? Have you tried? Left-handed drill bits might be an aid tho a bit hard to get. McMaster-Carr would be a source.

    You are, of course, lubing the screws...
    "Congress doesn't regulate Wall Street, Wall Street regulates Congress."

    MAKE WAY! MAKE WAY! "I have heard of some kind of men that put quarrels purposely on others."

    As a general rule, the better it felt when you said it, the more trouble it's going to get you into.

    International Financial Conspirator, Collaborator, Gun Runner, Ace Philosopher-King and all-around smartie pants

    Comment

    • johnwill
      Senior Member
      • May 2001
      • 257

      #3
      I had the same problem when I began to use the square drive screws in smaller sizes (#6 , #8). The square hole just leaves very little material at the top of the shank. I simply had to re-adjust my thinking on how much torque to apply in tightening the screw. Also, I never use a power driver for the final torqueing. Lubrication can help, but not prevent breakage. All kinds of screw extractors are available at machine supply houses.

      Comment

      • Cecil Borel
        Senior Member
        • Oct 1999
        • 205

        #4
        Peter: I had good luck installing silicon bronze screws if I prefitted a blue steel screw of the same size first. When I was worried about breakage, I would drill for the standard size steel screw, tighten it down, then remove it and install the silicon bronze screw. It was more trouble to install, but less trouble than removing broken silicon bronze screws, especially in critical locations.

        Comment

        • Alan Peck
          Senior Member
          • Nov 2000
          • 751

          #5
          I don't know if this is part of anyone's breakage problems, but I think it is best to use Bronze screws that have cut threads with a full-body shank. Many modern screws use rolled threads with a reduced shank.

          In addition, I have found that when using tapered drills, that the catalog listed size is not necessarily the best size. I experimented with various sizes until I found what I thought gave the best fit for various size screws.

          Comment

          • RGM
            Senior Member
            • May 2001
            • 1036

            #6
            Alan is 100% on the money, there are bogus screws out there. As he describes, you need to use the screws that have the deep cut threads and the large root diameter. When placed side by side the bogus screws are easy to identify, shallow threads with a tapering root diameter. As Alan mentioned, experiment with drill sizes, and shapes. For some applications you may want to use a straight drill with the preferred full root diameter screws.

            [This message has been edited by RGM (edited 07-03-2001).]

            Comment

            • Ed Harrow
              Retro Member #1235
              • Mar 2000
              • 7343

              #7
              There is so much crap hitting the shelves of our hardware suppliers these days, largely from the PRC. I bought a couple of shackles and the damn things close up when the pin is tightened! I wouldn't be surprised if these screws come from the same source.
              "Congress doesn't regulate Wall Street, Wall Street regulates Congress."

              MAKE WAY! MAKE WAY! "I have heard of some kind of men that put quarrels purposely on others."

              As a general rule, the better it felt when you said it, the more trouble it's going to get you into.

              International Financial Conspirator, Collaborator, Gun Runner, Ace Philosopher-King and all-around smartie pants

              Comment

              • Gary Kotara
                Member
                • Jul 2001
                • 32

                #8
                I was getting ready to order a batch of McFeely's "boatbuilding" screws, which are made in China. McFeely's says: "Designed specifically for boat building, these Silicon Bronze screws have cut threads and the full-body-diameter shank preferred by boat builders. Unlike our rolled thread steel screws with their reduced shank, the shank diameter below the head is the same diameter as the outside of the threads." Any experience with these?

                Comment

                • H Downey
                  Junior Member
                  • Dec 1999
                  • 3

                  #9
                  It just doesn't pay to be cheap on your screws. Jamestown Distributors has very good prices (and service) on high quality cut thread, full shank, square drive silicon bronze screws. Last time I looked, McFeely's wasn't even close on price!

                  I have used a few hundred #6 and #8 over the past year with no problems. I use the three-step drills, which have a straight drill for the root, a wider section for the shank, and a countersink/counterbore. I had two cordless drills, one to drill, one to drive. No breakage, no stripped holes, no sweat. Working against epoxy setup time, the last thing you want is a lot of fussing around.

                  Comment

                  • Eb
                    Senior Member
                    • Jan 2000
                    • 159

                    #10
                    Last fall I bought a box of McFeely's "Made in China, Boatbuilding, Flat Head, Square Drive, Silicon Bronze"... #8 x 1". Paid $71.57 for a thousand, have used over half and have had no problem. I do predrill, but use a power driver and can't recall busting more than two or three, and that was into locust.

                    Eb

                    Comment

                    • pwilling
                      Senior Member
                      • Jan 2000
                      • 236

                      #11
                      Anybody good enough with computer pix to draw what you mean by root diameter, all that? Diagrams of the good the bad and the ooogly? I have run into what look like cheapo SB square drive #6 -- the threads go right up to the head, and they look kind of like sheet metal screws -- not like the old stuff.

                      Comment

                      • Ken Liden
                        Senior Member
                        • Sep 1999
                        • 178

                        #12
                        Look in the archives. We have had this discussion before. There is no doubt that cut threads are much better than rolled threads. I use bees wax to lube the threads and always use a tapered bit.

                        There are plenty of screw manufacturers here in the US. You don't need mail order folks like Jamestown or Hamilton. Simply call your nearest fastener distributer listed in most yellow pages. You will be amazed at the stuff that is available and in sizes you only dreamed of.

                        Comment

                        • Ed Harrow
                          Retro Member #1235
                          • Mar 2000
                          • 7343

                          #13
                          WoodenBoat's book, Planking and Fastening has an excellent chapter on screws. Well worth reading, probably more information than one really wants to know (sure was for me!).
                          "Congress doesn't regulate Wall Street, Wall Street regulates Congress."

                          MAKE WAY! MAKE WAY! "I have heard of some kind of men that put quarrels purposely on others."

                          As a general rule, the better it felt when you said it, the more trouble it's going to get you into.

                          International Financial Conspirator, Collaborator, Gun Runner, Ace Philosopher-King and all-around smartie pants

                          Comment

                          • George Roberts
                            Banned
                            • Nov 1999
                            • 6617

                            #14
                            I don't know what the design strength standards of the silicone bronze screws are but ...

                            Let's assume that in times past the strength exceded the design standards by 15% and you torqued them 10% above the design standards. No screws failed.

                            Let's assume that in times current the strength exceded the design standards by 5% and you torqued them 10% above the design standards. All screws fail.

                            If this is true, you are at fault not the screws. I don't intend to place blame.

                            The proper way to use screws (or any materials) is to test each batch that comes in to determine the breaking strength (you can use the design strength if that is easier) and then limit your torque to some fraction of the actual breaking strength.

                            I understand that is a bit hard to do for the home builder but it is necessary. Several people told you how to do that. I think one way was to prethread the hole with a steel screw (you can purchase actual tools shaped like screw threads) and then set the clutch on your screw gun to a light setting.

                            A second method is simply to use screws that meet your strength needs. Most screw machine companies will run a batch of 50,000 for you. If you give them the strength requirements, you will be happy with the results. If the size is standard, the cost should be reasonable.

                            Comment

                            • Ross Faneuf
                              Senior Member
                              • Dec 1999
                              • 598

                              #15
                              One thing to look at carefully is the way you're drilling for the screws. I got a great bit of advice from a builder years ago: if you're breaking screws (bronze), you're not drilling your pilot hole deep enough. Actually, he was more emphatic - you shouldn't have to lubricate, and if anything breaks you're not drilling deep enough. I always use a setup which drills as deep as the length of the screw (I use tapered drills, except for 3/4" and under), or a dight further. I can't remember when I last broke a screw, and they certainly hold well.

                              The point here is that force you're puttting into the screw is driving the threads into the wood, which is where you get your holding power - not into forcing apart the fibers at the tip of the screw. If you want to do that, use a screw that was designed for it - like a drywall screw. But now we're not talking bronze any more. A conventional wood screw, particularly in hardwood, should have a pilot hole which relieves the tip of forcing itself through the wood.

                              I would like to make a bit of a point of this: I don't lubricate screws, and think it's bad practice - at least in the woods I usually use. I don't use oak, so I can't comment on that. But mahogany, cherry, teak, tulip poplar, white pine, and both fir and okume plywood need no lubrication.

                              Any time you can drive a screw hard enough to begin to crush the wood under the head you've driven hard enough. I try to stop at just that point, but I probably overdrive more often than underdrive.

                              I'm working mostly in SA mahogany, and driving with either a screwdriver bit in a brace, or (preferably) cordless driver with Frearson bit. Lengths 3/4 to 4", #6 to #16. I actually prefer Frearson to square drive; it's only me, but I can't get along with square drive, and strip them all the time.

                              [This message has been edited by Ross Faneuf (edited 07-03-2001).]

                              Comment

                              Working...