Software to convert lofting offsets to CNC?

[jakmang]

Hello,

I am a newbie. I have done some searches and have not found much. What I would like to do is automate the lofting and cutting of molds and bulkheads for a strip planked boat. Ideally, I would be able to enter offsets off of the plans and receive CNC instructions that would allow full size cutting of molds and bulkheads in plywood. Does software exist to do this?

Thanks.
-jak

[Lurvio]

I think the easiest way would be to just use the software connected to the cnc-machine you'll be using. In a program I've used (a version of AlphaCAD/CAM) you draw lines using the offset-points, then add tooling commands (cnc-machine specific) and export the NC-code to the machine.

You can also write straight NC-code on the machine, but that takes time to learn.

Lurvio

[duluthboats]

You can loft the stations in 2D CAD, or draw a 3D model from the offsets. Once you have the stations in digital form they can be exported in .dxf format to most any CNC control. Sometimes there may be some intermediate steps but it is a simple process. The hard part is to get the these files fair and true to the offsets before they go to the CNC. If you are not familiar with CAD and are only doing one simple hull it would be much easier to loft on the floor. If it is a bigger project you might look at some help for the CAD work.

You can download Rhino 3D for free which will give you 25 saves, that may be enough to do a simple hull if you are careful. There are packages from totally free to many thousands.

If you read through this section of the forum you will find endless info on this subject.

Gary

[Tim B]

Import it into 3D CAD, produce a fair smooth hull surface, then extract what you want CNC cut. Due to the fairing process you need some manual intervention. You will also need to design bulkheads, with appropriate cutouts for stringers, keels, deck edges, access holes, cockpits etc. 3D CAD packages with CNC capability and/or export is not hard, doing a good job of the CAD work can be very hard.

Tim B.

[jakmang]

Thanks for the responses. I guess that I would like to avoid the drawing step because it looks like a potential source of errors. One of the respondents mentioned that quality CAD work is hard.

I am hoping that I might enter the offsets and generate the drawing through RhinoOffsets or another plug in. It is true that I need to make automated adjustments to the basic plan. I would like to uniformly shrink the mold layouts to adjust for skin thickness. I would also like to automate the addition of notches for stringers. The bottom of the molds may need some dressing for legs to fit in a strongback.

Conceptually these modifications look like they are doable given a set of fairly standard inputs such as skin thickness, stringer dimension, stringer spacing, etc. Since I am not a lofting expert, there maybe problems that I do not yet understand.

-jak

[DCockey]

RhinOffsets from BaseLine Technology is a plug-in for Rhino which generates a table of offsets from a set of lines in Rhino. It's not for inputting a table of offsets and geting a surface.

[duluthboats]

The addition of notches for stringers and cut outs for beds, plus allowances the strongback is not automated. It can be time consuming to get right. Here is a boat designed for CNC cut parts in your area. A look at their site can give you an idea of how much is involved.
http://www.ptwatercraft.com/ptwatercraft/Welcome.html

Here is a building jig designed to be cut with CNC. It was not a simple job. There is no software that I know of that will automate is process.


Gary

[jakmang]

The URL seems to be for the jpg rather than a website.

Thanks,
-jak

[DCockey]

One procedure to go from a table of offsets to DXF files using Rhino. Presumably other 3D modeling software can be used in a similar manner.

1) Type the offsets into an Excel spreadsheet. In addition to the table of offsets there are dimensions from the lines drawing or construction plan are sometimes required. The Excel spreadsheet can be used to transform the offsets into a set of points in the form of coordinate triplets. Save the points as a CSV file or text file. I have an Excel template I use for this. It typically takes me 30 minutes to an hour.

2) Import the point file into Rhino. Sort the points and create sections, waterlines, buttocks, diagonals, sheer, keel/rabbet/centerline, etc from the points using the curve interpolate command. This typically takes me under an hour.

Fairing is next and I've used two alternative approaches, depending on how good the offsets are and how close the final result needs to be to the original lines. Time required depends on how fair the original lines and corresponding offsets are, and the degree of fairness required of the final result. For example a surface which will be used to cut Class A surface from needs higher precision than a surface used to derive mold geometry for a strip built boat from. The actually strip built boat will ultimately be faired by hand sanding.

3A) Fair the curves. Modify the curves so that they intersect and adjust them so they are suitably fair. Practice helps. Once the curves are suitably fair generate a surface from the curves. Several different ways to do this dependent in part on the hull shape. Then tweak the surface for final fairness.

3B) Modify the curves to close any significant gaps and adjust them to eliminate any obvious un-fairness. Create a preliminary surface based on the curves. Simplify the surface where possible. Fair the surface until it is satisfactory. Practice is helpful.

4) Assuming the lines and offsets and resulting surface were the outside of the hull, create an inner hull surface as an offset surface from the outer surface. This is simple to do for most shapes but some cleanup is usually needed.

5) Create curves on the inside of the hull representing the desired stringer location. Then create the stringers along the inside of the hull. InterpcrvOnSrf, OffsetCrvOnSrf and Sweep2 can be used for this.

6) Create planes at the desired mold and bulkhead locations. One alternative is to create planes at the for one side of each mold and bulkhead. In this case they should be the sides which will be larger to allow for beveling; generally these are the sides closest to amidships. The other alternative is to create planes for both sides of the molds and bulkheads.

7) Trim the planes with the inner hull surface and stringers. Either a deck surface or other surfaces from the sheer will be needed to close the trim.

8) Extract the needed surfaces and save the geometry as .dxf files.

This is just one way. Other folks may have other methods.

[duluthboats]

Sorry fixed the link.