Javaprop to autocad 3d solid

Discussion in 'Propulsion' started by Edwinh, Apr 10, 2010.

  1. Edwinh
    Joined: Apr 2010
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    Location: NL

    Edwinh Junior Member

    Hello. I'm new to the forum,
    I looked over the forum a while ago, but could not find the solution to my problem.
    Now that I think I have the solution, I'll post it so maybe someone can benefit from it.

    I had been using Javaprop for some time, but struggled to create some nice 3d data which could be used for some CNC milling. The outputs form Javaprop seemed not abele to be transferred to solids, and using 3rd party tools I got a facetted file on which one could not create a fillet to smooth the transition form the blade to the hub.

    I managed to get a nice smooth 3d solid prop using the method described below.

    Regards,

    Edwin


    [​IMG]
     
  2. zeroname
    Joined: Oct 2008
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    zeroname Naval Architect

  3. Edwinh
    Joined: Apr 2010
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    Location: NL

    Edwinh Junior Member

    Hello All,

    Working on different props I ran into some problems using the solution posted above. Especially constand chord props gave an ugly edge. So this seems the best option until now.




    Creating a 3d solid model in Autocad using the data from Javaprop.

    I had quite a struggle to create a 3d model from the by Javaprop created data. I assumed the dxf output would be fine, but it seems this is not easy to work with. I have made several tries, and came up with these moves for the best result.
    The propeller model I created using Javaprop is a leave shaped blade with long chords nearing the center. I just use the longest chord in the design for all profiles nearing the center. I do not choose a spinner diameter, so the blade runs from tip to center.
    Using copy text, editing it in exel or an other spreadsheet, and selecting r,c and β to import one can easily create a constant chord length. I have no Idea if this is the best solution, but one neads some strength near the center. For the profiles I used E193 Re300.000 for the tree outer most sections, and MH126 Re500.00 for the profile in the center . This also to have a bit more body near at the hub.
    Now for the Autocad part.
    Open a exported DXF form Javaprop in Autocad. We see a nice mesh, we can not use this mesh directly, we can use it as a nice guide. First of all we explode the mesh, this allows us to remove parts of the mesh we have already traced.
    I remove the trailing edge, because this is so super thin and unmachinable.

    [​IMG]
    Erasing the trailing edge.

    Now we start to trace each rib with a spline (use spline CV and not knots to get a curve inside the rib) Make sure your osnap is set to END only to prevent selecting unwanted points. I like to start just before the end on the lower side of the foil, and end at the backside using the c (close) command to get a closed loft.

    [​IMG]
    Here I start the spline.

    [​IMG]
    This is the last point on my spline. After this use “c” command to close.

    We do not actually need all the splines, but we need to make twoo guide lines for creating the loft (surface) later, so we need to trace evey rib. Before we delete the old surfaces we do have to draw a helpline.
    The helpline runs from the lower back edge to the front edge.

    [​IMG]
    Draw helpline.

    Continue to draw the splines for all the ribs. After a spline and helpline is finished, it helps to erase the old surfaces, otherwise it gets quite complicated.
    Now we need to make two guide lines for to be able to make a nice loft. The first guide line connects the intersections of the helpline and the spline we drew. Make sure your osnap is set to intersection only so you do not accidently select an endpoint. Draw a spline knot. Be sure you do not use spline cv here because the guide spline needs to intersect the rib-splines.

    [​IMG]
    Knot-spline through intersections.

    Now we need a second guide spline, for this we draw a spline (knot) through the ends of the rib splines. Osnap had to be set to endpoints again, and it is wise to delete the help lines because they are not heeded, and can only confuse.
    Now we are ready to create a loft (surface) which we can use to create a solid later. We create a loft using not all of the ribs, if you do use all the ribs, you could get a slightly rippled surface. But it will work quite nice too. I prefer to use every fifth spline. (Javaprop also seems to interpolate from every fifth rib to the next).

    [​IMG]
    Every fifth spline rib is used making the loft.

    After selecting the five cross sections and pressing enter one sees some twisted lines representing the loft. Now press “g” to select the two guide lines (splines) we created at the leading and trailing edge. And pess enter to finish the loft. It is nice to switch to a shaded view to see the results.
    Now we have the main surface, in order to create a solid we need a watertight surface. The both ends are open. First off all we apply a surface patch to the tip.
    If we have a prop using constant chord, it is wise to trim the end to a circular form in the same way we trim the end facing the hub.
    The surface now extends to the center of the hub. To prevent having obstructions in our hub we need to trim the surface. For this we set the view to left, and draw the outline of the hub exactly. Using revolve we make a surface. This surface intersects the wing surface. Trimming these surfaces to each other will make a nice watertight set of surfaces.

    [​IMG]
    Drawing the outline of the (conical) hub, just a single slanted line.

    [​IMG]
    Trimming both surfaces on each other to create a nice watertight surface.

    After the trimming one can sculpt the surface into a solid. Use sculpt and just draw a big box around all surfaces, all other parts will be filtered out leaving only tree surfaces. These become one solid. Move the cursor over it to see the part is no longer a surface but now a solid.

    [​IMG]
    Sculpted into a 3d solid.

    Now that we have a nice solid, all help lines and splines are no longer needed, you can remove them. We continue drawing the hub. We switch again to the left view. To create the hub we draw a pline representing half the cross-section. With the revolve (solid) command we can create a nice hub exactly fitting the propeller blade.
    Now we need to create a second blade to our prop. We can do this using a circular array. Make sure you set the coordinate system to WCS, otherwise the array will be round the wrong axle.

    [​IMG]
    Hub with one blade, set to WCS before circular array.

    After doing the array we have tree solids in our part. We can join these using the union command. This makes them all into one piece. Now that it is one piece we can apply a nice fillet between the blade and the hub this gives a nice view, and some additional strength.
    [​IMG]
    Finished prop.

    Now we have a nice solid 3d model which can be machined, or maybe even made using rapid prototyping. FDM is a nice technique to create it in polycarbonate. This might give a usable prototype if not too much power is applied.

    I have no idea if this is the best way, but it works for me.
    Let's hope someone can benefit from my struggles with javaprop and Autocad.

    Have fun!

    Edwin Houwertjes
    Created May 9, 2010
     
  4. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    That is pretty much how I did SubHuman III's prop in Acad back in '92 to develop a file for CNC milling. One thing though, becuase you used sections that were not developed to radial cylinders, the effective blade section will not be the shape you think it is, it will have a longer cord and be proportionaly thinner (i.e. the true shape of the blade section should be on a cylinderical surface co-axial to the shaft, not a plane surface perpendicular to the radial cord line). If I had to do it today, I would use Rhino because Acad's 3d surfaces are really not that fair. If you do have it CNC'd, hog it out first leaving it fat to allow the billet to releive itself, then go in a make the final cuts.

    FWIW, your blade also looks a lot like SH III's blade without the forward sweep. Did you use the tip advice from the other thread? http://www.boatdesign.net/forums/props/prop-constant-chord-length-32527.html#post361196
     

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  5. Edwinh
    Joined: Apr 2010
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    Location: NL

    Edwinh Junior Member

    Hi Jehardiman,

    Thank you for the reply.
    I had to read it a few times before I onderstood about the chord length. The actual chord length is a curve. The closer one gets to the center the more curved it is, so the longer it gets.

    I have no idea if I should have compensated for this, now that I increased the chords near the center of the prop.


    I actually made a few props. I have a low rpm prop, leave shaped blades, with the biggest diameter.
    For higer rpm a smaller cosntant chord prop, a constant chord prop with "wingtips", no idea how this compares, an other constant chord prop with larger diameter and a prop with leaveshaped blades.
    These four I can compare to eachother because they use same rpm.
    The sixth prop is for our spare electric outboard motor.

    [​IMG]

    It is quite hard to use the dxf data from javaprop to make a good looking prop.
    I have some acad experience, and some rusty Pro-e skills. Unfortunately Pro-e has changed so much it takes a long time to get to work with it. I also tried Solidworks, but I could not import the curves. Also Inventor, whis I am new too, did not do a great job so far. I might have to study on this. Rhino is something I have only heared about. Maybe this was better for making a prop, but with the way I worked in Autocad I get a great looking profile.

    I'll get these props produced in Polycarbonate, this should bend a little, but since I have only a little power to use they should be fine. "printing" this with FDM fused deposition modeling I can get these props made for about Euro 160,- a prop. (a single one will cost me over Euro 200,-)

    I hope to be able to vind the best prop for our boat.
     
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