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Davit – Part 2 (Support Brackets Below Swim Platform)

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  • Davit – Part 2 (Support Brackets Below Swim Platform)

    A Davit is a small crane onboard a ship, especially one of a pair that are used for suspending or lowering a lifeboat. My friend and customer Ray has designed a Davit system to lift up his dinghy onto the swim platform of his boat. This post describes the brackets that will attach to the bottom of the inserts, which were previously glued into the swim platform. The purpose of the bracket assembly is to connect the bottom of the inserts to the Aluminum fabrication that supports and lifts the swim platform to take some of the load off the glue on the inserts.

    The first picture shows a Davit from another boat, to give you an idea of the typical design of the Davit. The support brackets described in this post would be located below the swim platform.

    1. Davit
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    The following picture shows the support bracket assembly for one side of the Davit. The two inserts on the top are 2” in diameter have a M10 x 1.5 thread and were previously glued into 2” holes that were drilled in the swim platform of the boat. (See Davit – Part 1 for information regarding gluing of the inserts).

    2. Davit support bracket asm
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    The pair of support brackets that I machined from angle Aluminum are shown below.

    3. Support brackets
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    I wanted to clamp the angle aluminum to a piece of plywood resting on the table of the milling machine. The plywood allowed me to drill and mill the angle Aluminum without cutting into the table of my milling machine. This configuration forced me to use an extra long center drill to reach past the leg of the angle Aluminum.

    4. Extra-long center drill
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    5. Plywood under angle
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    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Lincoln LE 31 MP
    Lincoln 210 MP
    Clausing/Colchester 15" Lathe
    16" DoAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Bridgeport

  • #2
    The plywood supported the Aluminum angle to prevent chattering when milling the slot in the angle.

    6. Milling slot
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    Below is a picture of all of the parts that I machined for the support bracket assembly except the compound angle spacer which will be discussed later.

    7. Machined details
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    I like to stack up details to save machining time. In this case the pieces were cut from two different pieces of stock so they were different widths and therefore wouldn’t clamp in the vise. The solution was to “C” clamp the pieces together as shown.

    8. Clamps to hold pieces together
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    Sometimes a piece is much larger than the vise. One solution is to support the cantilevered end with a shaper gage. The shaper gage has a shallow locking angle, so that it doesn’t typically slip for this application. Another solution would be to use a second vise that was machined to match the position of the first vise. Unfortunately, I don’t have a second vise.

    9. Shaper gage to support cantilevered piece
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    The two angle Aluminum pieces were cut from the same piece of stock so that the legs were the same thickness. This allowed me to clamp the two angle Aluminum pieces in the vise at the same time using two 1-2-3 blocks. This was done to save setup time.

    10. Clamping with 1-2-3 block
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    Smith Oxyacetylene Torch
    Miller Dynasty 200DX
    Lincoln SP-250 MIG Welder
    Lincoln LE 31 MP
    Lincoln 210 MP
    Clausing/Colchester 15" Lathe
    16" DoAll Saw
    15" Drill Press
    7" x 9" Swivel Head Horizontal Band Saw
    20 Ton Arbor Press
    Bridgeport

    Comment


    • #3
      One side of the swim platform fabrication was slightly bent in the area that the support brackets attached. Ray’s solution was to design a compound angle shim to fill the space between the support bracket and the swim platform fabrication. Ray’s philosophy was to fix what is wrong rather than to modify good parts, to work with bad parts. Also, in the final assembly the compound shim would be almost invisible. Below is a picture of the compound angle shim. The second picture shows the dimensions of the compound angle shim.

      11. Compound angle shim
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      12. Compound angle shim dimensions
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      To machine the shim, I used SolidWorks to calculate the angles to set on the compound angle vise. I used a sine bar to set the angles, because the graduations on vise were too course.

      13. Using sine bar to set angle
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      This vise can actually set three angles. I set the first angle to zero.

      14. Compound angle vise
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      This is what all of the pieces look like when bolted together.

      15. Parts bolted together
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      Smith Oxyacetylene Torch
      Miller Dynasty 200DX
      Lincoln SP-250 MIG Welder
      Lincoln LE 31 MP
      Lincoln 210 MP
      Clausing/Colchester 15" Lathe
      16" DoAll Saw
      15" Drill Press
      7" x 9" Swivel Head Horizontal Band Saw
      20 Ton Arbor Press
      Bridgeport

      Comment


      • #4
        Here are two pictures of the compound angle spacer in place

        16. Compound spacer in place
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        17. Compound spacer close up
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        Here is a picture of one side of the support bracket assembly temporarily installed.

        18. One of the installed support bracket assemblies
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        Ray is planning to remove the brackets and sent them out for powder coating. Before the final installation. The next phase in this project will be to design and fabricate the arms of the Davit, which will mount above the swim platform.

        -Don

        Smith Oxyacetylene Torch
        Miller Dynasty 200DX
        Lincoln SP-250 MIG Welder
        Lincoln LE 31 MP
        Lincoln 210 MP
        Clausing/Colchester 15" Lathe
        16" DoAll Saw
        15" Drill Press
        7" x 9" Swivel Head Horizontal Band Saw
        20 Ton Arbor Press
        Bridgeport

        Comment


        • #5
          Good show, as always.

          You need to make yourself some machinists jacks for that stuff that stick out of your vise. Very handy and a fun little project on the lathe.

          What speed, if you recall, do you like to run your Bridgeport at for chewing up aluminum? I don’t have the porta-cool, so I use a can of WD-40. I also prefer two or three flute end mills. I don’t have any good tin coated HSS ones.

          Comment


          • #6
            Originally posted by ryanjones2150 View Post
            What speed, if you recall, do you like to run your Bridgeport at for chewing up aluminum? I don’t have the porta-cool, so I use a can of WD-40. I also prefer two or three flute end mills. I don’t have any good tin coated HSS ones.
            The endmill that I used was HSS, four fluted with a 3/4” inch diameter. I ran the spindle at 1200 rpm with mist coolant. The coolant that I used is water based and is good for all materials. I do use WD-40 when I manually apply cutting fluid. I have never tried to mist apply WD-40.

            -Don
            Smith Oxyacetylene Torch
            Miller Dynasty 200DX
            Lincoln SP-250 MIG Welder
            Lincoln LE 31 MP
            Lincoln 210 MP
            Clausing/Colchester 15" Lathe
            16" DoAll Saw
            15" Drill Press
            7" x 9" Swivel Head Horizontal Band Saw
            20 Ton Arbor Press
            Bridgeport

            Comment

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