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 Post subject: Re: Thermoformed Hulls
PostPosted: Sat Nov 09, 2013 5:56 pm 
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Joined: Fri Sep 23, 2011 8:37 am
Posts: 99
Hi guys,

Wow. Obviously there is considerable knowledge and expertise regarding plastics from you dudes in this thread. Which brings me to my question:

I hve been working on the design for a set of HAKAs for my TI. The image below shows one of the initial prototypes. The prototype has been machined out of 1/4 " plywood simply to test design. I've made a bunch of modifications based on this and soon would like to CNC out of plastic. I have a supplier, but am unsure specifically what type of plastic to machine it out of.

The design is based on a top panel that at this point is 1/2" with all of the spars being CNCd out of 1/4" stock. My supplier has a ron of different plastic stock in 48"x96" sheets. I'm trying to decided between PVC, ABS and polycarbonate, but have no real idea what the benefits and limitations of each material would be. As an aside, I plan to use some type of adhesive to glue up the HAKAs and I wanted them in black. I believe all three materials come in black. Any help figuring this out would be great.

img]http://postimg.org/image/53roq7p9p/[/img]

Image

[img][img]http://s22.postimg.org/53roq7p9p/image.jpg[/img][/img][/quote]


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 Post subject: Re: Thermoformed Hulls
PostPosted: Sat Nov 09, 2013 8:01 pm 
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Joined: Sun Apr 20, 2008 6:18 am
Posts: 1035
Location: sarasota,fl
If I were to select a plastic for those spars I think I would go with hdpe (high density polyethelylene). This material can't be molded ( it's not the same material the hulls are made of (but in the same family I guess). As long as your CNC machining it, it would be a very good choice. If you go to walmart and pick up one of the white kitchen cutting boards you can take some test cuts ( it machines really well with TN coated cutters with lots of coolant ( try to keep it cool)). It only comes in sheet form in pretty much any thickness you like. I would look at 3/16 and 1/4 inch , with 1/4 thick you can get by with less ribs.
Actually I have made several wood boats, you might try marine plywood vacuum impregnated with epoxy. Basically once machined you just impregnate with thinned epoxy in a vacuum bag, very strong and lightweight, and pretty impervious to rot. Plus it can be finished to look very nice. Just a thought.
Both HDPE and marine ply are very inexpensive. If your looking for strength glass filled nylon is very strong ( can be purchased in sheet form) but it's pretty pricy. Also look into composite board, since your machining anyway carbon fiber would be a really cool look. But I have no idea what a 1/8"x4x8 sheet of carbon fiber composite board would cost.
Good luck
Bob


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 Post subject: Re: Thermoformed Hulls
PostPosted: Sun Nov 10, 2013 5:45 am 
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Joined: Fri Sep 23, 2011 8:37 am
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Thanks fusioneng!

In your experience I will need to liquid cool it? Will slow enough spindle and feed speed accomplish this? I'm not in a position to liquid cool.


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 Post subject: Re: Thermoformed Hulls
PostPosted: Sun Nov 10, 2013 6:24 am 
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Location: sarasota,fl
Just use a spray bottle


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 Post subject: Re: Thermoformed Hulls
PostPosted: Sun Nov 10, 2013 11:13 pm 
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I'm not exactly sure what "haka" is... but it appears to be something used in place of a trampoline between the main hull and the pontoons.

If so, and it will see UV light, perhaps blue would be a better color. viewtopic.php?f=11&t=49782

From what I've seen.... black is the worst color you could choose. Color schemes and ability to store your kayak in a garage can make a huge difference on what you need/want to do, tho.


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 Post subject: Re: Thermoformed Hulls
PostPosted: Mon Nov 11, 2013 6:41 am 
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Location: sarasota,fl
Actually you might be able to vacuum impregnate (resin infuse) the plywood pieces you already made, even if it's not marine grade plywood, the vacuum impregnation process turns it into way better than marine ply or pressure treated anyway, and it will be much stronger and only slightly heavier.

Basically all you would need is some West epoxy (something that sets up kind of slowly) I used West systems 105 epoxy on a recent project and had very good luck. What I did was mix the epoxy like normal, then thinned with de-natured alcohol till it's a little thicker than water consistency. I then liberally swabbed it all over the wood, I then laid it into a polyethylene bag (basically two pieces of fairly heavy polyethylene sheet sandwiched ( I used double sided tape to form the outside seal). You then just apply a strong vacuum to get the epoxy to soak into the wood. It's much easier if you have a storage tank for the vacuum, this way you can use a small vacuum pump, and when you open the valve, it sucks out all the air immediately (you need pretty good vacuum ( max for most small vacuum pumps ). While your setting up for your next load, the vacuum pump chugs away at emptying the vacuum tank for the next load (it takes a long while with a small pump). I just used patio screen above and below each piece (which I re-used over and over again) to keep it from sealing against the wood.
Let it sit in the vacuum for about 5 minutes, then cut the bag pull the wood out and brush on another coat of resin (this can be a little thicker). then let it stand and setup. Remember you are under a time constraint before the resin sets up (usually about 30 minutes). If you melt some boric acid crystals into the alcohol and mix in a tiny bit of automotive anti-freeze into the alcohol it also helps with rot prevention (not needed if your using in salt water).
I have no idea whatsoever if this is the best way to do this or have I looked into any better (more modern) way. This is the way my father instructed me to design and build when I asked him to help me design and build a some wooden boats by hand (this was 40 yrs ago). It was a pain in the butt but they were very strong and durable racing hydroplanes. I built several boats using that same method and it seems to work.
It's likely one of those old world techniques that's been lost in time and not used anymore by anyone, with all the fiberglass, foam core and carbon fiber stuff available now days. But in my opinion wood still has it's place in some things. I doubt anyone else even does anything like this on boats in real life, I suspect my dad had me do everything the hardest way possible just for his own enjoyment. As an example, he was a master Craftsman, and had a cherished wooden tool box that he had earned from his father. He told me when I became a master craftsman I could have the tool box and his cherished tools. He said the only requirement was I had to take a set of 1-2-3 hardened steel blocks and finish them parallel/square and equal to each other within a tolerance of fifty millionths ( half a tenth), and also a 6 inch hardened angle block. I could do it any way I liked but was not allowed to use any machines of any kind to do it. It all had to be done by hand ( ie.. scraping and hand lapping). I got the box from him 3 yrs later. (true story). I still have that box, but none of my 4 boys would accept the challenge (thinking it was a little nuts just for a stupid old tool box full of really old junk LOL).

If you find someone in your area who builds wooden boats by hand in their garage using the old ways (some people like to do that stuff), they likely have all this stuff in their garage and the knowhow to do it, guys like this are usually willing to help and advise or even do the resin infusion part for you.
I'm sure there are newer and way easier ways to do all this stuff (like CNC cutting plastic sheet LOL)


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 Post subject: Re: Thermoformed Hulls
PostPosted: Tue Nov 19, 2013 11:42 am 
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A couple thoughts on HDPE. I've worked a little with it using handtools & powertools (no CNC though) to make sideboards for my i12s.

First, and not sure if Bob covered this, there's NO reliable way to glue it. Some claims that certain 3M adhesives will work, but I'd bank on using traditional joinery and/or mechanical fasteners.

Second, I've found the "marine" formulated products like "Starboard" are flatter, stiffer & easier to machine than generic "cutting board" HDPE. They also are, theoretically, UV stable.

It's easier to work with than wood in most ways as it's not prone to spltting/chipping/cracking. Routs easily, so I'd imagine would work well with CNC if you follow mfrs. guidelines.


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 Post subject: Re: Thermoformed Hulls
PostPosted: Tue Nov 19, 2013 12:03 pm 
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Joined: Fri Sep 23, 2011 8:37 am
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Gas Yakker Can ya glue "Starboard"?


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 Post subject: Re: Thermoformed Hulls
PostPosted: Tue Nov 19, 2013 1:42 pm 
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Joined: Mon Jul 04, 2011 7:12 pm
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Location: Columbia, MD
Starboard is HDPE, so no reliable gluing AFAIK. Forgot that you CAN weld the stuff with a PE/HDPE rod.

Everything you ever wanted to know here: http://www.kingplastic.com/products/all-products/king-starboard-family/king-starboard/


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