Forums: Whisstock Designs: alternative method to make plywood frames New Topic Post Reply
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sante
Posted: Apr 26th, 2013 at 09:37   |   Subject: alternative method to make plywood frames
Hi,
I am interested in building the 15' Half Deck Yawl, which is a great design. The plans are really very good.
I want to make the frames from plywood instead of laminating them.
Somewhere here it is described to put the frames together from 3 layers of thinner plywood, where the outside shape of the fwd and aft layer can be derived directly from the Table of Offsets on each frame drawing and the middle layer, data can be interpolated between the fwd and aft data. In my eyes, this means many plywood cutting work.
Is it also possible to make the frames from one thicker single layer plywood and bevel the edge?
What advantage and disadvantage would this method have?

Regards
Sante
debenriver
Posted: Apr 26th, 2013 at 23:00   |   Subject: alternative method to make plywood
Hi

There are a few reasons we use three layers of plywood, rather than one.

Firstly it is stronger. We get much better grain variation. And the bonding layers of epoxy add strength and rigidity.

Secondly it is much easier the fasten the skin to a thicker frame than a thinner one. With just a single thickness of, say, 12mm ply, you have to be very careful how you drive fastenings so they don't come out the sides of the ply frame.

Thirdly, a thicker, less deep frame is more stable than a single layer of deeper ply. So it is easier to set up and keep to shape in a jig before the skin is put on. Thin frames tend to distort more when you bend the hull skin around them.

Fourthly, because you can use shorter sections of ply (because the join in one layer will be covered by the next layer), it is generally much more economical of plywood, than using a single layer where you really can't have any joins.

And I suppose, finally, bevelling the edge of a thick ply frame is not that easy. Ply doesn't plane or spokeshave too well. So the stepped bevel system gets over that problem.

I know it looks like more work, but in the end it is less work. Sometimes it pays to invest in more work in the early stages of building a boat so that the foundation is good and accurate – then in fact the boat as a whole goes together more quickly.

We are making CNC cutting files for this design at the moment. They should be ready in about a couple of weeks. These will include sandwich-style ply frames. You will be able to send the files to a local CNC cutting facility (e.g a local kitchen cabinet maker) and get back all the parts pre-cut. The CNC files will also include all the lapstrake planking and all other ply parts. This will of course add some expense to the total job, but it will speed up the build very substantially indeed.

We will be making drawings of the ply frame layers and planking as well, with all the data so they can be cut by hand. But this will take us a little while to complete as there is quite a lot of drawing work involved.

Having said all of this, you can use a single layer of ply (I would use 12mm) and I can provide you with details of the depth I think you should make them.

Hope this helps

George
sante
Posted: Apr 27th, 2013 at 06:48   |   Subject: 3 layers
Hi George,

thank you for your reply. Now I am convinced that it is the better way to use 3 layers. If I do so, I think there will be little "stairs" at the edge of the frames. Do I have to adjust them, for example by filling them with epoxy?
And what thickness to you suggest for the layers?

It is great that you will provide CNC cutting files! But to be honest it is not easy for me to wait for them. I am straining at the leash to start building as soon as possible.
What format will the cutting files be? I think there must be any software which is able to convert these files to pdf format.

Sante
debenriver
Posted: Apr 27th, 2013 at 21:34   |   Subject: 3 layers
I think we will make the ply frames from 3 layers of 6mm ply. We could do 2 layers of 6mm with a centre layer of 9mm – but that is less economical ply usage.

There will be a "stepped" bevel on the outside edge, but the "steps" or "stairs" will easily fill with the thickened epoxy as the hull skin (lapstrake or cold moulded) is bonded on. So no special treatment is necessary.

The new drawings will be available in a couple of weeks I would think. I am about halfway through the lapstrake planking at the moment.

The format is DXF for the new files, which the CNC facility computer will read and cut to shape. As well as the DXF files we include a PDF file for each DXF file so that you (the builder) and the CNC people can see what it should look like.

However I must stress that these PDF's are not dimensioned – they are simply an image of what the DXF files look like. They are of course accurate to scale (usually 1/10 - the DXF's are full size). As the DXF's are full size, if you have a program that can read these back into a CAD program, you can of course extract the size data from them, and so transfer this directly to the plywood and mark out for cutting by hand.

My own view is that it is probably worth the extra expense to get the frame components and planking components CNC cut, because that gives you such a head start timewise.

We will be making dimensioned PDF's so that the ply layers (and all the other ply parts) can be marked out and cut by hand – but this will take us a little longer to get done because there is a lot of work involved for me!

Best

George
sante
Posted: Jun 8th, 2013 at 12:05   |   Subject: DXF Files
Hi George,

any progress concernig the DXF Files for Design 055?

Regards
Sante
debenriver
Posted: Jun 8th, 2013 at 22:49   |   Subject: DXF Files
Hi Santé

I'm more that half-way through. All the lapstrake planking is done and I'm working on the new frames now. I would think about another week and they will be available.

George
sante
Posted: Jun 9th, 2013 at 05:36   |   Subject: :-)
Hi George,

that sounds fine,
I am curious about it!
Thank you for your answer.

Sante
sante
Posted: Jun 20th, 2013 at 05:31   |   Subject: cnc cutting
Hello George,

do you know a proper CNC cutting company here in Germany?
I can not find one.
So I wrote an email to Alec Jordan (Jordan Boats). He would cut the plywood parts for me. For that, of course, I want to ask if you agree with it?
And by the way, how do you get ahead with the files?

Regards
Sante
debenriver
Posted: Jun 20th, 2013 at 16:01   |   Subject: cnc cutting
Hi Sante

You are free to get the parts cut anywhere. I don't know a CNC cutting company in Germany, but there must be plenty of them. Companies that make kitchens for example, or steel items. They don't have to be specialist boat companies.

Having said that, Jordan Boats are very good and you know that you will get a really good job from them. I have been in touch with Alec Jordan and I will send him the full set of files as soon as they are ready – I just going through the final checking process now. He will then be able to give you a price.

Best regards

George
debenriver
Posted: Jun 22nd, 2013 at 12:19   |   Subject: cnc cutting
Hi Sante

Just a note to say that the CNC files are now available on the website.

George
sante
Posted: Jun 22nd, 2013 at 13:37   |   Subject: Good Job!
Hi George,

thank you for informing me!
I have purchased the files and studied them.
They look very satisfiing to me.

I noted the finger-joint system for the planks and I have a question about it.
Do I have to reinforce the planks in the area of the joints?
Another question is related to a clear finish.
Will these joints be visible when glued?
I don't know by now if I will choose a clear finish, but visibility of the joints could have an influence on my decision.

Regards
Sante
debenriver
Posted: Jun 22nd, 2013 at 21:56   |   Subject: Good Job!
Thank you. I am glad the parts are done!

I also made some brief notes on the George Blog today about minor changes to the building jig.

And I realized that, with the outboard well, there needs to be a little beam (because the aft deck is cut back). I did mention that to Alec Jordan. I will draw it and post the modified files shortly.

Provided you bond the planking finger joints with epoxy thickened with microfibres and/or colloidal silica (I'm talking WEST system products here – other epoxy systems should have similar additives), and wet out the bonding area very well before applying the thickened resin, there should be no need for any further strengthening of the join – it should be as strong as a scarph.

You need to bond the pieces together on something nice and flat – like a sheet of ply or particle board or MDF. And cover the board with shiny brown parcel tape in way of the join so that the planks don't get bonded to the board.

The finger joint will show very faintly – depends somewhat on how well the CNC cutting is done. And it also depends on how well the two sections of ply are matched (colour and grain). Generally, if the two ply sections are similar in grain and colour, I think you could clear finish perfectly well.

In this respect you need to be sure to talk with your CNC cutters – if they are used to boats they will know that the surface grain on the planking should be lengthways – but you need to discuss this with them. Same for all the parts, depending on the finish (clear or painted). Surface grain on the frame parts is not so important – best if it is different on different layers, but not really vital. Anyway – you need to just talk with them to decide how you want the pieces cut for everything – which may not always be the most economical nesting (nesting is the arrangement of all the pieces on a sheet of ply to use the ply most economically).

I'm looking forward to knowing how it all goes. I hope you will be able to send me some photos.

Best regards

George