It was a bit tricky to get the mast hole right but in the end, here is what I did.
First, the profile of the mast is needed. The best way I think is to scan the mast with a light source above i order to get a clear contrast between the mast and the background. If you skip the light source, the background becomes black and it’s hard to see the profile.
I started out with taking a picture of the mast but I had problems getting the right profile due to perspective, camera angles or whatever. In the end, scanning worked perfect for me.
Next up is to get the profile into Fusion 360, creating a copy of the mast and cut the mast profile in the mast clamp. @pacificmeister has an excellent video of how to do this. https://youtu.be/HqTkrsiZBsw
This became an iterative process to make a perfect fit due to inaccuracy when copying the mast profile to a sketch, scanning vs image or printer calibration and so on. Instead of using the actual mast clamp I created a 30 x 130mm cylinder. That saved me a lot of time and filament.
Now I had the perfect profile, so on to the actual mast clamp. First I needed to create the elliptical body of the clamp. I found a tool for Fusion 360 on the web. A guy named Dave explains how to use it here https://www.davesrocketshop.com/?p=265 (sometimes a login popup appears, just press cancel and you are good to go). Mine is an elliptical cone 65.5 x 155mm.
Once the clamp is done, it’s just to make the cut for the mast as described above by pacificmeister, cut for the mounting holes, cut the body in half at the thickest part of the mast, make space for wires inside the body and then voila.
I don’t have much experience in 3D printing but I guess the weakest spots in a 3D printed part are between the layers (please correct me if I’m wrong). At least, the small number of tests I did, showed me that when a part snaps, it snaps almost clean of at one layer. In my design, the weakest spot would probably be where the mounting screws in the front part sits, and that got me thinking. What if I print the mast clamp as hollow as possible and then pour polyester resin inside?
Since I’m at the start of my build and winter is soon coming to Norway, I haven’t been able to test this in the water, but I have banged it with a hammer, jumped on it. The mast clamp is rock solid!
Has anyone else tried this technique? I’m so convinced of the strength that I have started to design a fuselage with a little twist but more on that in a later post.
Anyway, I exported the mast clamp as a solid body and had Cura doing the job of making it hollow with these settings.
Layer Height: 0.2mm
Wall Thickness: 1.2mm
Bottom Thickness: 0mm
Bottom Layers: 0
Infil Density: 7%
Infill Pattern: Line
Infill Layer Thickness: 0.4mm
This is (almost) how the print result looks like. These are with 15% infill but that was to much (forgot to take a picture with 7% infill). The polyester resin had problem float between the infill lines so I decreased the infill to 7% and the resin floats prefect all the way down to the bottom. One tip is to fill them with water first to get an idea of how much polyester resin is needed and you can also detect leaks.
It’s a good idea to mask the outlines and the holes. I used regular masking tape and some straws. Then it’s just to start pouring polyester resin into the parts.
Another thing I discovered is, when the polyester resin starts to cure and getting warm, the clamp gets a bit soft, mount the clamp to the mast and fasten it with tape or something and there will be an even better fit.
With a bit of sanding and perhaps some epoxy filler in the openings where the polyester resin went in, I have a perfect fit, rock solid mast clamp (I hope). Still waiting for my long stainless screws so a rapid action clamp has to be a stand in, just to show the result.
A few more things has to be tried out. I will spray some silicon on the mast, sand the surface on the clamp that goes against the mast and put a good layer of polyester resin on it and tighten everything together in order get an even more tight fit. The silicone spray will make sure that the clamp doesn’t get stuck to the mast.
Also a hole in the front clamp is needed for the cooling water.
Hope you find this useful and I’m looking forward to read your comments.
Next up is to drill the holes in the mast and plate box