Perhaps you could cut one out of wood (or something else), sand & plane it to get your desired shape then and use epoxy & fiberglass to get the curves towards the ends of the rudder to your liking.
This approach gets my voteā¦although Iāve never built a rudder. My main concern would be that it might be weak in the direction that the rudder most needs to be strong in. Maybe each layer could have some holes cut in it and carbon fiber or fiberglass rods could be run vertically to help the layers stay attached?
You can also epoxy a layer of glass cloth betwwen each of the layers of foam, so they will act as a section frame.
But I guess you will still need some higher density parts in the rudder where you attach the rudder stock or shaft to. Those higher density parts could be plywood.
Is weight really that important? A full ply and epoxy rudder will still float.
I once made a rudder for a 31ft sailingyacht, of 4 layers of 18mm marineply glued around the stainless steel rudderstock. Afterwards shaped into a nice aerofoil shape and covered in glasscloth. This makes a very strong rudder.
And you could still use the Maslow to shape the aerofoil shape, even without a gantry.
The way to do that, I tkink, is to machine 3D adaptive pockets of about 10x10cm, leaving a centimeter between the pockets that will form a kind of grid for the sled to slide upon (the bottoms of the pockets are the desired aerofoil shape). Once one side is shaped, turn the rudder and do the same with the other side. That grid will eventually have to be removed ofcourse, but that is a lot less work than shaping the whole rudder by hand. And youāll get a more accurate shape.
Good luck,
Arjen
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Just spitballing here but another option might be to create the shape in Fusion360 then use the Slicer function to create interlocking slices of plywood (like āparametricā furniture) that could then be filled with expanding foam and wrapped with fiberglass. Iāve never used F360 but Iāve done this pretty successfully using Sketchup. You could just use 1/4 ply to get the shape or up to 1/2 or 3/4 for a pretty strong part. Gap size can be adjusted to in order to minimize wood content or weight.
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This is an intriguing idea.
Since most of the strength in compression and tension comes from the skins, the āskeletonā in the middle wouldnāt make much difference.
-m
That last idea about milling pockets and leaving a grid is also intriguing.
Iāve built a rudder as you describe with plywood before. it was for a much smaller boat, and it was super heavy. Given my need to manhandle this into position in the boat, if itās too heavy it will be impossible.
-m
If you built the skeleton, filled it with expanding polyurethane foam and then trimmed it back it would be extraordinarily strong and provide a pretty smooth base for the fiberglass.
First I will say that I am in no way a boat builder so I could be completely out of my league here, but going off of what @COlden and some of what you were saying as option #4, you can take an approach similar to this project, and using 1/4" ply or even 1/8" hardboard, you can get design the shape you want, slice it up like the project I mentioned, and just figure out your spacers for in between to create your āskeleton,ā then use the expanding foam to fill the spaces. The hardboard can then be your guide as you sand down the foam to the proper shape, then fiberglass the outer shell of it. That should give you the lighter weight you were looking for, as well as some structural support. this way, all you are doing is cutting flat surfaces and donāt have to worry about the 3D contour milling. Just a thought (please, if I am wrong about this, someone tell me)!
Good luck either way!!
This is a pretty neat thought!
and for areas with minimal curvature, I could have fewer āspinesā but in areas with a lot of curvature, I could have more to refine the shapeā¦
-M
That would be my thoughts as well!
I think a simple approach would be to slice it in horizontal planes, and cut that from a relatively thick piece of foam (think 2-3 inches). Stack them up vertically, sand / fair the steps and cover with fiberglass cloth.
The shape youād be cutting is essentially a bunch of NACA foils, the same length / width as your rudder at each āstationā but a smaller height.
To simplify the fairing step, cut a copy of the top & bottom profiles in plywood, and use that as a guide for hot wire cutting on your foam āstackā.
Going with thinner foam will also make for less sanding / fairing, but itāll make more cuts, more CAD work, and will give a heavier result (more glue layers).
I had thought of that technique.
The one thing I worry about this method is how to keep the center in line.
The top-to-bottom dimension is something like ~40-inches. With even 3inch-thick NACA profiles, thatās 13 or 14 layers to keep in perfect vertical alignment, otherwise my rudder would have a twist, and make the boat want to constantly turn one way or the other under motion.
Perhaps if there were a few alignment plates or rods, that might help.
also, 3-inches is a very thick cut for my setup. not sure if there is even a router bit big/long enough to do that, or if my Z-axis has that much plunge depth.
but this is an interesting idea. Itās the ātopographic mapā technique along a different axis, one that I hadnāt considered before.
Thanks!
-M
Yeah, including 2 alignment holes in each layer would probably solve that, assembly would simply involve sliding the profiles on 2 rods.
Even better you could model your rudder stock in there. From what Iāve seen, most rudder stocks are a stainless rod with a stainless plate welded to the side. If you cut a hole in that shape in the center of your foam layers, youād just have to slide them on the rudder stock directly.
3 inches was just a suggestion to keep the number of layers reasonable; you could use the thickness you can actually cut.
Is the current rudder structurally sound? If its ābumpyā that could indicate internal problems, osmotic blisters, or just the need for fairing. If osmotic blisters or just needs fairing then either of those issues can be addressed with a lot less pain and suffering than fabricating a whole new rudder.
Note that most rudders are made with a stainless steel frame attached to the rudder post, foam over the frame, then glassed. If the older rudder frame/post are good them reusing them might be worthwhileā¦of course getting at them will require destroying the old rudderā¦then you are really committed to building anew one!
Would you be willing to share the dxf, scg and gcode files?
This is an old topic, and the member youāre replying to hasnāt logged into the forum in over a year. Good luck, but it would not be surprising if you donāt get a reply
As a general rule gcode files arenāt worth sharing. Different spindles, different bits, different machine construction even within the Maslow family (I see youāre a new poster. Do you have a Maslow?), different workpiece material means that somebody elseās generated gcode often will not produce good results on your particular machine. With the vector files you can create gcode for your particular machine and environment, rather than trying to use somebody elseās. While it might seem difficult the first few times with a little practice you can get it sorted out, and if you have difficulties you can ask here for help if itās a Maslow
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