CNC Conversion

A forum for contacting other builders of Ken Hankinson designs. These designs are now a part of the Glen-L family.

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CNC Conversion

Post by meb46 » Wed Oct 17, 2018 5:52 am

Having spent the last couple of weeks making my eyes go square from looking at Solidworks hour upon hour, I have found the migration of the Barrelback 19 (stretched to a 20' version) plans into a digital format and enabling me to CNC cut the frames to be a pretty frustrating process. I'm fairly capable with Solidworks, but have found most methods of measuring off the plans and transferring into digital format to really lack the required accuracy, and then when in digital format really requiring extensive modifications to ensure stringers and chine logs actual correlate into the correct places.

Has anyone completed the task previously to a suitable level? At the moment, I am contemplating looking at alternative designs that are more focused on CNC approach, but wanted to check if anyone has had success on creating CNC files off the Barrelback 19' plans?

Excuse the heathen approach of CNC, its very non-wooden boat building process, but its a preference and capability I have that really enables accurate and precision manufacturing.

Keen to hear others experiences and how they made CNC Frames make sense.


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Re: CNC Conversion

Post by sproggy » Wed Oct 17, 2018 6:48 am

I know this isn't what you want to hear but these boats really don't need precision manufacturing. I started modelling one of the Glen-L designs (modified Overniter) in a ship design application but the measurements didn't come over well or fair correctly. So I gave up and did my modifications the old fashioned way.

Because pretty much everything (frames, chines, sheers, battens, keel) gets faired during the build they end up not the same size, at least on one face, as they are measured to on the plans. So transferring plan dimensions to CAD simply doesn't work unless you do a lot of work to account for the effects of fairing.

Think how far you'd have got actually making your boat if you'd spend your CAD time in the workshop :wink:

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Re: CNC Conversion

Post by NAMEngJS » Wed Oct 17, 2018 8:03 am

I will agree with sproggy on this one as well. CNC is a great tool to have but in the end the amount of work that will be done with the CNC where absolute precision is required is not there. In shipbuilding there is a term called mold lines. The mold line is the exact line of the ship at an infinitely thin sliver. since material has a thickness that has to be accounted for and this thickness is thrown to one side of the mold line or another. take the screen shot below:
If we look at the frame on the right of the screen and the purple line defining the batten line we can notice that the purple line intersects the frame outer edge on the aft side. Forward the curve of the batten takes it further inboard than the forward edge of this frame. the material on the frame will have to be faired away. The CNC my be able to get you started but the continuous bevel on the forward side of this frame would be difficult to reproduce and the chances of every single point of contact and/or every bit of fairing required cant be take out of play by the CNC.

Again, it can be useful if it helps you identify how the build will go together and/or eliminate errors that dont involve expensive lumber. However at some point you are going to have to attack the build with 80 grit paper to fair something.
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Re: CNC Conversion

Post by Roberta » Wed Oct 17, 2018 8:18 am

Since wood species and density plays such a big part on how the boats ultimately get finished, it is really difficult to predict how any given parts need to be cut in order to accurately cnc them. You could build the boat the old fashioned way and scan the parts as built into a cad program and still the parts may not accurately assemble in the same way. How the shears and chines bend is largely dependent on the wood used and it's similar properties and one piece may arc very differently than corresponding parts making frame width, height, and setpoints fit for a given arc, but not to another. The arcs drawn on plan sheets may or may not match actual arcs of the bend in the woods used, making it difficult to accurately predict frame dimensions and setpoints. That is why wood boats are as individual as the builders and so much of the wood ends up on the floor. A sharp eye for fairing and the expectation that in process adjustments is necessary. A cnc made part may or may not be the best approach. In many cases some cnc parts could be beneficial, but these wooden boats are unlikely to go together like a Revell Authentikit. Best to expect personal involvement and enjoy the experience of a wooden boat you hand crafted.

Roberta :D
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Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

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Re: CNC Conversion

Post by mrintense » Wed Oct 17, 2018 10:57 am

I agree with Roberta on this as well. I think that far too many of us are engineering types and it feels wrong to go into something with having everything to the umpteemth fraction of an inch. But the reality of boat building is that it is a hand crafted endeavor and like Roberta said, the wood may not cooperate regardless of how accurate you are .

Far better to simply take Glen L's plans for what they are and get started building. I can't begin to tell you the number of people who have come on to this forum and wanted to do the CAD / CNC thing and then you never hear from them again. I think it's precisely for the reasons you mentioned, it can be a frustrating experience. On the other hand if you dive in head first, you'll make some mistakes for sure, but usually they are recoverable and you will have far more fun.

Come on in, the water's fine. No toe dipping necessary!! :D :D
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Re: CNC Conversion

Post by Hercdrvr » Wed Oct 17, 2018 11:24 am

Well said Roberta,
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Re: CNC Conversion

Post by TomB » Wed Oct 17, 2018 3:27 pm

The guys that built Saetta Classic Boats, barrelback transom and Tahoe stem, used CNC for their frames. They imagined selling a kit for home assembly. If they had received orders CNC would have been great.

I have the barrelback plans and studied them extensively while wishing I had room for a build. There are many curved frame parts and making right and left hand duplicates concerned me. CNC would make the pieces quickly and accurately if you have the data to feed the machine. As an alternative, I made templates. A 1/4" of plywood or fiberboard, tracing from the plans, rough cutting and sanding to make the templates look like the drawing got me templates in a couple of days. Then use the templates to make frames, another couple of days at most (I'm now building a bigger boat and saving the barrelback templates for the next build :D ).


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Re: CNC Conversion

Post by kens » Wed Oct 17, 2018 6:11 pm

Maybe I'm old-school, maybe I'm expecting immediate results,
But I have to ask why do guys take a set of plans, and then, try to interject them onto CNC, CAD, or any numerous computer program???
My gosh, the time it takes you to input all the info, then twiddle with it, then fret about it, then cut the parts, then start the build, then put a shim in it SOMEWHERE and to think that you started off with a full set of plans that are already known to work.
I must ask why?
My perspective is to take all the time involved for inputting the CAD/CAM/CNC ,,,,,,,and just build the damn boat!!!!

I apologise for my rant.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Re: CNC Conversion

Post by Hercdrvr » Wed Oct 17, 2018 8:36 pm

Amen to that!

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Re: CNC Conversion

Post by PeterG » Wed Oct 17, 2018 9:16 pm

So I think if one wants to work in a CAD or 3D design program that's OK, especially if it's a learning experience and helps one understand the complex shapes and curves with a boat hull. It's a good tool for design and visualization as well as repetitive production. Done well it will get you really close to what you want to produce. It's all in the effort you're willing to put into it. The vast majority of us don't find it very helpful and don't have the skills for it on our projects which are usually one-offs. I have even seen it done badly on some boat designs where the structure wasn't faired properly. I was taught old school lofting on hands and knees in a shipyard mold loft (they are strictly CAD now) that's a lot of fun on a 425 foot ship drawn in full size profile and plan. Those skills helped me tremendously with my boat project but weren't really necessary. That's my position on CAD efforts. Bravo for trying CAD, just understand it's not the end all be all for boat design or construction, just another tool. This is from someonene who is more likely to grab a sharp hand tool than a power tool...
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Re: CNC Conversion

Post by meb46 » Wed Oct 17, 2018 9:30 pm

Team - Many thanks for your valued input, and to be honest, very much the response that I expected given the nature of the builds. As what was touched on briefly, I do use the Modelling process as part of my visualization process and to work through the understanding of the structure, and helps me work out my build process and technique, not to mention modelling out some modifications.

I run a couple of shipyards in Asia, and have a pretty sound understanding of building boats in Aluminium and Steel, but the classic wooden boat build process is new. Typically my vessels are 100% modelled before any metal is cut, so the CNC/3D CAD habits are hard to break :)

Thanks again for the input, much valued!

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CNC Conversion

Post by Imanny » Mon Feb 04, 2019 9:41 am

When do you think youll start working on a SX3 type conversion?
I have a G0619 and the CNCFusion Conversion kit already assuming thats the route you will take I would definitely want to be part of that one when and if you do

Have you thought about CNC Lathe Conversions
Theres even less out there on those than on the MILL conversions

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