Trouble with Splines whilst drawing a boat from plans

[Anonymous]

I am relatively new to Fusion 360 and have no CAD background - so I have been muddling my way along in a fairly haphazard manner.

I feel that I have gotten to the stage where I can get my brain around "how to do stuff" - but I am struggling with splines.

So I have spaced a series of frames (drawn from plan dimensions) the appropriate distance apart.  I wish to join the frames to each other, but cant manage to get the splines to "lock" to the corners of the frames, without having to pull them around in a very awkward manner.

This then means that the lines then don't quite touch - which becomes a problem when trying to loft the whole thing together.

[davebYYPCU]

Loft is so Finicky! There are a few workflows that do work for your case.

2d Splines, eg, keel spline rail, when sketch is created, you Project > Intersect, the points in the frames that pierce the rail sketch.  Turn off all sketches of the frames, you should only see purple dots in your current sketch, create the spline, snapping to each purple dot.  loft with that rail will work.

3d splines, top of the hull edges, if not 2d.  In this case you create a 3D sketch, use Project > Include 3D geometry, and select the point at the top of each frame.  Turn off all frame sketches, (Fusion just loves to snap to anything but the right point)

you should only see purple dots, create the spline, snapping to each dot.  Loft will work on that rail.

Create half the model and mirror the other side when the first half is complete.

I prefer to do the rails first, but use the same purple dot routine for the frames.  

Another tip, you don't need all the frames to make a smooth hull, you can develope frames from the hull.

A lot of plans have errors, you have to sort those as you find them.

[Anonymous]

Dave thank you for your reply; I can manage to do splines like you said in 2D - if for example I have made a workplane to go off and the spline "sticks" to this. My trouble some - exactly as you said with 3D splines where I am trying to get a spline to move in several directions - again exactly like you said - for example the sheer line, or the chine, where I am trying to make a rail from a spline that cannot be achieved in one plane only.

Could you elaborate on how to do these so called "3D" splines and also how to get them to "snap" to a point. I have tried to find tutorials, but this is one I havent found a clear explanation of that I could get to work for me.

Also would using a mouse on my mac make things easier?

[davebYYPCU]

Hulls are not so simple to give examples with, after referring to your screen shot,

The rail for the chine, will be a 3d Sketch.  To make a sketch 3d, tick the box in the top section of the sketch pallete, just above the coincident constraint button.

For your model, I would use the Keel, frame 1, 2, 4, and the last as you progress back, turn all the others off, so now you have 5 sketch light bulbs on, the rest turned off.

Then you open Project > Include 3d Geometry command.  Clicking on points not the lines, select all five chine points from the keel and the four frames I nominated.

Turn those five sketches off, to check that you now have 5 purple dots.  OK?

Draw a spline, from first to last purple dot, making sure the small blue square snap curser is visible when you click on the purple points, Important.

After the last dot, finish the spline.  Now you can turn on the reference material, canvass, side views etc, and see how close this rail is to scale position.  It should be OK as it is, but if not happy, the trick is with the 3d spline handles.  They can only be moved with the Move Command, with all it's options.

So it's click the spline fit point to activate the green handles, open the Move command and the triad appears, reset the triad to the handle end point you are moving, and confirm the pivot point with green tick box, now with the triad attached to the handle, (doesn't always work first time), you can lift, slide, push the handle point to make the spline adjustments.  For me it is usually only the two ends of the spline that needs tweaking.

Now you can turn on the frame/s sketch you didn't use, and see how close the spline is.  This method usually shows up the data errors from the spline or the frames or both.

I would need access to your file to help further, Export a copy and attach to a post if required.  Easier to explain with your data, than an example.

Couple of things, Use the Patch loft command, and a half hull, doing the bottom of the hull below the chine as one loft, above the chine as a second loft, if all works ok, great, if errors, work on them until these two do work, when they do you can close the frame profiles and use solid lofts.  Lot less greif this way.

Happy to help if you get stuck....

[Anonymous]

I am really struggling to get a loft to work on this sketch - I believe that I have all the rails and corners touching and it keeps telling me they intersect .... and it refuses to take the loft to the bow no matter how hard I try! Very frustrated, but I am sure I am doing something stupid

[davebYYPCU]

Well, not really, 

some work to do yet, 

Transom is not connected to the keel.  Pic, shows its connected to a line, wasn't sure which one to adjust.....

Sketch 18 had a copy of the top rail projected in so deleted that.

From sketch 18 to Frame G, Loft work with all your drawn rails, but you need a top centre line rail, to assist the shape, 

The loft in front of sketch 18 has to be a second loft, because of the rail terminating on the bow at it's low point.

Once those are done, should be right, but the keel spline is not as smooth as it could be.

Last yellow icon is a solid mirror command, but there were no bodies in the file when opened.  Maybe sketch mirror was required

Might help.....