Well, will I be screwed if I touch these screws on the mast?

Discussion in 'Multihulls' started by pbmaise, Aug 8, 2013.

  1. pbmaise
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    pbmaise Senior Member

    My mast has several very thick stainless steel bars that run through the entire mast. The hole sizes are 5/8th inch and I want to have them drilled larger. The problem is this bar is 1 inch thick stainless steel and should only be drilled at a machine shop.

    In the photo you can see 4 screws. I suspect the screws just tap into the mast and that there are no nuts on the back of these screws.

    Has anyone ever seen something like this and taken it apart. I don't want to turn that screw and then hear a nut on the other side fall. Then I would really be screwed.
     

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    Last edited: Aug 9, 2013
  2. Richard Woods
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    Richard Woods Woods Designs

    I think it is extremely unlikely that there are nuts on the inside (if so, how did the rigger fit them?). Probably they are just tapped in as the plates just spread the load. But what is stopping the bar from falling out? presumably it is welded to one plate

    It might be an idea to blowtorch the bolts before unscrewing them to burn off any corrosion

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. John Perry
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    John Perry Senior Member

    I think it is fairly unlikely that those screws have nuts on them, but it is possible that they go into tapped holes in internal stainless steel or aluminium backing plates. At one stage during my rather varied career I worked at a mast making factory and we fitted tapped backing plates behind all heavily loaded threaded fasteners. If significant loads were anticipated we would never rely on a tapped hole in an aluminium extrusion, or into a carbon fibre spar. The backing plates were fitted using two thin messenger lines threaded through the screw holes in the mast, down the length of the mast then stopper knots through two of the corresponding tapped holes in the backing plate. Once you have two screws in place the rest is easy. A bit of a fiddle but not too bad with practice and using modified drain rods to catch the end of the messenger lines and pull them through. Well trained ferrets could be an alternative.

    If you can remove one of the four screws you will easily see whether or not there is a backing plate behind.

    Just a thought - if you only need a small increase in the diameter of the holes I wonder about an expanding reamer, or set of expanding reamers?
     
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  4. catsketcher
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    catsketcher Senior Member

    If there is a backing plate there - (to me they look like pan headed self tapper screws) you need to hold it there when you take the plate off.

    I would take off TWO screws. Find out what gauge (thickness the screws are and then buy the longest screws of this type you can. Then screw them just back in enough to hold the backing plate onto the inside of the mast, Then unscrew the other screws. When you try to wiggle the plate off past the two long screws you may have to use two more SHORT screws to hold the backing plate on (put them underneath the plate - you may need a few swear words to get this done) once you take the long screws out. So you will need two long screws of the same gauge and two short to ensure the plate stays there.

    cheers

    Phil
     
  5. PAR
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    PAR Yacht Designer/Builder

    I doubt there's a backing plate, the flange appears to be just screwed to the mast. remove three screws and loosen the 4th, so you can have a look inside, but I'd be very surprised to see a nutsert or backing plate.
     
  6. pbmaise
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    pbmaise Senior Member

    Thank you guys. This really helped

    Yes this really sounds to me like a backer plate is in there. There is no way I would depend on the thickness of the mast to hold a 1" thick stainless steel bar. I can feel that this bar is very solid in this mast.



    There really is some magic in these big masts. Just above this point I have two sheave blocks. The only thing you see is the edge of the block and there is no way to get to the shaft withing the sheave block. That is a bit of a worry since I have been on two big sailboats now where enough tension on that shaft bent it and the sheave block jammed. There is zero access into the mast to get to that shaft.

    For this reason I suspect there isn't just a backing plate, there is a complete assembly with a whole lot of stuff on it.

    Down lower in the mast, there are similar stainless steel bars, however, they are too far apart to be assemblies. Therefore, there it is likely it is just a backer plate. Phil, thanks so much for the idea about putting in a screw to hold any backer plate in place.

    A reamer was a good suggestion too, however, finding one here in the Philippines may be a challenge. I have already badly bruised myself by trying to drill the hole larger with progressive drill bits. All I did was destroy my drill bits. At least I am experienced enough trying to drill bigger sizes to have had the drill secure between my legs so I just bruised my leg instead of breaking a rib or wrist.

    Philip
     
  7. PAR
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    PAR Yacht Designer/Builder

    The big piece of 1" stock is a compression/tension bar and absorbs the loads imposed on it handily, the flange just keeps it in position and doesn't transmit any loading to the mast walls (okay, very little relatively). I've removed these many times, it's a two piece assembly - one is just a flange, the other is a flange welded to the bar, which passes all the way through. Sometimes they are sheet metal screwed, but also they can be tapped and machine screwed to the mast walls, which is especially common of bigger mast section, where wall thickness can support threads. You can guess and make up ways to fix imaginary things, or look up the replacement part and have a look for yourself. It looks like a Kenyon piece. Web sites just carry the most common items, so it's not likely you'll find this particular piece. A phone call to them with the appropriate information in hand (year, make, model, mast section, etc.) will get you the information you need. The simple thing to do is just back out one screw a little. It'll be sheet metal or machine threads, which will quickly offer suggestions to your next steps. Why do you want to remove this piece?
     
  8. Petros
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    Petros Senior Member

    I agree that there is not likely any nuts on the back. I recommend soaking the fasteners in automatic transmission fluid (ATF) over night. It is one of the best penetrating oils ever discovered (better in fact that the oils made for it). If there is any corrosion it will soften it before you attempt tpo remove them, prevent galling and damage to the threaded hole in the mast. A little heat on the area would also likely help, but do not get it too hot, you could damage the heat treat on the aluminum mast.

    Aslo try using some ATF on the drills and you will find it goes a lot easier on you.

    good luck.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Given that the stainless screws are in an aluminum mast, you can pretty much guarantee some galling is going to happen. Drill and tap to the next size if necessary.
     

  10. pbmaise
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    pbmaise Senior Member

    Job competed today

    Thank you all. Job completed today.

    The screws came out almost 100% fine. After doing most of the screws I had my helper try. He is a big gym guy. Even though he just watched me do 7 screws by carefully positioning the screw driver and holding it very tight with my chest, he was determined to show me how strong he was.

    Bad idea. Fortunately, he only slightly damaged the head. Putting his heavy weight to better use, I had him push against my back while I carefully turned the damaged one out. Skinny guy wins.

    I attached a drawing of the complete bar after removal. I show in gray double mast walls. The bar rests directly on the aluminum mast wall, however at this point it is double thick. When the stainless steel cover plate was removed, it exposed a slot so the bar could be lifted and then slid out.

    All told, I removed 3 bars and took them to the machine shop. They charged about $25 USD to make 6 larger holes. Since one big drill bit for stainless is almost $100 USD at the hardware store, it was well worth it.
     

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