Davit – Part 2 (Support Brackets Below Swim Platform)

[Don52]

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


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


The pair of support brackets that I machined from angle Aluminum are shown below.

3. Support brackets


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


5. Plywood under angle

[Don52]

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

6. Milling slot


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


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


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


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

[Don52]

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


12. Compound angle shim dimensions


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


This vise can actually set three angles. I set the first angle to zero.

14. Compound angle vise


This is what all of the pieces look like when bolted together.

15. Parts bolted together

[Don52]

Here are two pictures of the compound angle spacer in place

16. Compound spacer in place


17. Compound spacer close up


Here is a picture of one side of the support bracket assembly temporarily installed.

18. One of the installed support bracket assemblies


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

[ryanjones2150]

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.

[Don52]

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