Help for plug construction by CNC

[Malena]

Hi everybody!
First, I apologize if my english is not very good.
I´m writing from Spain where I´m working in a company dedicated to building boats in PRFV. Our boats have lengths between 6 and 20 meters.
We are thinking in buying a 5 axis machine to make all the plugs (hull,deck..)
I´ve been looking for information a about this subject ("5 axis milling for plugs, molds and tooling) was very useful....but I need more information about materials and more details about the process before and after the milling by CNC. We need to evaluate the costs of the proceess. We know the cost of the machine but we unknow the costs of materials.

Can anyone help me?

Thanks in advance

[Danielsan]

Hello,

Just some little ideas.

Is it necessary to have it 5 axes? The forms you need are not that complicated I think.

When you once have the machine, you will need the milling tools ranging from EUR100 to EUR1500 or more. These tools depend of the materials you will be working whit. Look at www.mazak.com or .be or equal companies.

The other thing is to find someone in Spain that can provide you de adequate materials, Stainless steel I316, Alu alloy, bronze, ... In tubes, bars, rectangular profiles etc. Try to find them over the internet I know to find them in Belgium.

Hope this helped you a bit further?


Maybe you could help me on this, I am designing my boat and willing to build it in GRP, do you have any hints? I would like to make hull and deck in one piece together.


Greetings,

Daniel Peeters
PS from which part of Spain are you

[War Whoop]

Most of the CNC’ed plugs we use are constructed from 2 Part foam The higher density stuff machines well and requires minimal finishing (spray filling/sanding) We also had some arrive poorly done on a wood armature with a lighter density Spray foam then Tooling putty and in the States we finish usaly with Duratec surfacing primer. The problem with this system is low profile webbing between frames...

I also have had them come in Styrene Foam Blocks glued together with Spray foam cut to say part one and an epoxy coating then ½ “ Tooling putty sprayed on then cut to part two or finished size this was built up on a steel reinforced plywood faced Pallet… You looking for a large Machine??

[Malena]

Hi War Whoop,
Thanks very much for your reply
We are looking for a large machine (X=8.5meters, Y=12meters, Z=4meters)
The new model of boat that we are developing is a 50ft. (17meters)
We are thinking in doing a wood structure and then cover it with a layer of expanded polyurethane. All this process would be manual. How to control the dimensions of these structure for the milling?
How is the best way to make this structure for a deck plug or a hull plug?
Which are the problems of using this method? After milling, the structure will be covered by any kind of material as epoxy and then we´ll mill it to get the finish surface.

If we constructe plugs from 2 part foam (how as you say), which kind of foam?

So, which are the best materials for the structure and which are the best materials for the coating? Which is the best way to build the initial structure?

Regards
Malena

[dereksireci]

I’m not a mill operator but this is the typical process I’ve observed while having 30 or so plugs milled for me by a half dozen different shops. Each shop uses their own techniques developed in house.

Briefly:

1. Build a very strong platform larger than the footprint of the part. This can be built from 16" wide 3/4" plywood in an egg crate pattern on 16" centers. Put a 3/4" face, top and bottom. Glass the joints. This base can not flex or move or else all is lost.

2.Build sections of the part every 16" which are smaller than the surface of the part by a specified distance. (See below) Line these sections up and again use the egg crate method to stabilize. This is called a buck.

3.Sheath the sections with thin plywood

4.Spray with a low density urethane foam.

[In place of steps 2-4 some use Styrofoam blocks glued together. There are also other types of foam you can use. To shape the blocks, make a “hot wire” connected to a wooden fixture. It looks sort of like a bow when finished. Get the shape close to the final one so you don’t try to mill off too much with the undermill pass.]

5. Mill the foam to a size smaller than the finished surface of the part. (Undermill)


6. Glass over the low density foam. This locks the foam in position and prevents the effects of thermal expansion or that of humidity variation. This is a vital step.

7. Spray the cured glass with a high density putty such as ITW Spraycore, HS product. Some prefer H2000.

8. Mill the putty to the final dimension.

9. Sand off the mill marks

10. Apply Duratec

11. Sand

12. Some apply gelcoat at this point and buff.

We could start a whole new thread on the proper method of going from plug to mold at this stage. Let’s not.

How much to undermill, how much glass is enough to lock the foam, which foam to use, which putty to use, all these things you’ll find out with experience. Better yet, hire someone with experience working a mill and adapt their methods to your shop.

As far as cost comparison. You'll need to mill a mess of parts to justify the cost of the machine. US Marine has a 60' Par mill and I think Sea Ray has two. If the machines are not running almost 24/7 they don't make sense.

In the States there are several companies that mill parts for builders who can not justify buying a machine but want the advantages of a CNC cut plug. In my opinion there is no cost or time savings over a hand built plug if you have a good crew. The advantage of CNC is that you get perfect symmetry and the plug in the shop matches my computer model. I can plan mechanical systems, generate patterns for flat parts and get really cool renderings among other things.

djs

[War Whoop]

On larger pieces use a Steel I Beam backed plywood faced pallet... The Frames can be CNC cut along with the keel.

I would loosely strip plank the plug with battens as wide as possible. I have seen other methods tried like draping a 1708 over the bare frames Bad idea. Then Spray with a Rigid foam after that machine 3/8 “ or so low then spray with a tooling putty ATC Chemical has one I have done business with Tom Johannsen for 20 Years T27 http://www.atc-chem.com/PGE/PR-PF-T27.html They also have a Surfacing primer http://www.atc-chem.com/PGE/PR-PF-P96.html we use the Duratec system also for finish sanding to around 1500 with dye coat then Molding..

Smaller stuff can be done on wood or metal platforms straight up using a much higher density foam; Marine Concepts in Cape Coral Fla has done this for us in the past and it is a good system fairs out quick and leaves minimal work for the Proto type guys..

I got a 41 foot CNC Hull plug from a well known outfit up north and it was nothing but trouble, .

An in house system would be hard to beat. I am looking at a 12 x 6 Meter unit now for some people in Kuwait.

[RyanSmith]

CNC machining components using large mills is a complex process, worthy of a stand-alone business. For large, multi-product companies it makes a lot of sense since the mill can be kept busy. Many of our clients considered purchasing a mill for in-house work, and after visiting our facility determined that the learning curve was too steep, and the process required specialized capability.

Unless you have a large budget and extra people to use, then I would suggest concentrating on building product. Seek out a close alliance with a CNC tooling supplier and let them worry about how to produce the complex shapes you design.

-- Ryan
www.cadence.biz
Cadence CNC Manufacturing

[Speedwagon]

Hello glass folks
The CNC milling machine you are thinking of would be rather expensive to purchase. In addition floor space, tooling, programmer, mill operator, unless you are using it all the time, it is a lot of expense to have a big CNC mill hanging around.
Have you given much thought to using a smaller CNC mill and machine the hull shape in smaller components, and assemble to create the completed hull. Not as a split mould, but assemble the mould parts permanently.
I am working on much smaller fiberglass projects, I don’t know if this is an idea worth looking at.
Dave

[RyanSmith]

SpeedWagon:

We split our components up as necessary and reassemble depending on size and complexity. It is a valid way of doing things.

hola Malena

yo tambien trabajo en una empresa parecida a a tuya, y esamos interesados en construir algunos botes con nuevas fibras, tal vez alguan ceramida, por lo tanto me gustaría seguir en contacto y si es posible intercambiar experiencias en el diseño y construcción.
e-mail: est-mat1@cotecmar.com

[Malena]

Thanks for your reply Ryan
I´m agree with you. We have been looking for someone who could make the plugs by CNC machine, but the problem is we haven´t found any company in Europe. I know some companies in USA, but not here.

Do you know any company like Mollicam but in Europe????


Thank you
Malena

[Dutch Peter]

Originally Posted by Malena

Thanks for your reply Ryan
I´m agree with you. We have been looking for someone who could make the plugs by CNC machine, but the problem is we haven´t found any company in Europe. I know some companies in USA, but not here.

Do you know any company like Mollicam but in Europe????


Thank you
Malena

Malena,

Try this company:

Koch Houtkonstrukties
Tel: +31 (0)55 522 1775
Fax: +31 (0)55 522 6543
Apeldoorn
The Netherlands
www.kochhoutkonstrukties.nl

I hope they can help you!

Good luck

[sorenfdk]

You could also try Tuco in Denmark: http://www.tuco.dk. There is also a company in Spain, but I don't remember their name. They built the Shipman 50, designed by J+J - use these words to do a search on the internet.

[lucas adriaanse]

Malena,

Why spend so much money on a machine that needs 24/7 orders to be economically viable ? I believe Port Pendennis in Falmouth (UK) tried it.
I am following a different path that takes a little more time, but is so much more cost-efficient: use specialised companies in Poland and Latvia. At € 650-700 per sqm for fully finished tooling (plug + mould) they compete strongly with your CNC proposition.

I am setting up a 'European Composite Co-maker Group', set up as a joint venture between several parties like yourself and us. Whereby we would do all the quality control and overall management of the local company ( in other words take care of the worrying ). ECCG will only produce for its partners. We are talking about this with parties in Holland, England and Germany.
If you would like to know more, mail me: fasttrackyachts@corby347.nl

Lucas

[Ilan Voyager]

It seems that a salesman is trying to sell a very big CNC in Spain...

RyanSmith is right. A big CNC machine (5 axes or other) is too costly for a single shipyard which will use very little time. These machines must work 24/7 to be amortized. You'll have to add the price of the guys able to use it and you'll get probably the most expensive molds of the last 50 years. I would give the job to a specialised company.

A solution is to make the "general" plug of the hull where the curves are soft and easily controlled and use the CNC for the "fine" details as bow or skeg which will included in this "general" mold Also for the deck plug where you can find a lot of details. Make the big and heavy, saving a lot in transportation and give all the details to the CNC company. That would save a lot.

You can find at La Trinité in France a lot of very capable "mercenaries" to make fastly your plugs and molds. These guys are used to go from shipyard to shipyard and Spain is just a bit south of France. Some are specialised in finishing the plugs and are able to do miracles.

I affirm that nobody will see a 1.5 mm difference of symmetry at the bottom of a 50 feet hull; we have all that I call the "builder's syndrom" and we worry about all the small defects that NOBODY will see it on the finished product, a part an alien diver with doppler laser eyes, a very unlikely customer... But everybody will see the defects of the details on the deck, where CNC is useful to have the best results.

I'll add that the CNC plugs I've used were fragile and needed great care. In big sizes that may be a concern. I hope that had changed.

Lucas' idea is very good: a groupment of builders using the services of a specialised company will permit a drastic reduction of cost of molds. The molds are the major investment in composite fabrication.