Forums: Whisstock Designs: Full size plans New Topic Post Reply
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Posted: Jan 1st, 2009 at 17:59   |   Subject: Full size plans
I am sometimes asked why we do not supply full size plans (for items like frames for example). The answer is simple:

They are expensive.
They are inaccurate, unless they are on Mylar film, which is even more expensive.
They are ineffective.

Let me explain:

Expensive: This is quite straightforward. Whatever process is used to make large paper plans, it is expensive, both for the equipment required and the paper itself; and finally the cost of postage. The most common process nowadays is an ink-jet plotter, getting its information from a computer or a CD. An earlier process, called the Diazo process, reproduced the original drawing (drawn on transparent media – tracing paper or Mylar film) by shining an ultraviolet light on to the original laid on special coated paper.

Inaccurate: Ordinary paper shrinks, stretches and distorts mostly because of varying humidity. It also becomes creased and torn rather easily. Mylar film does remain true to size and will be accurate – but it is even more expensive than paper.

Ineffective: Even if you get over the inaccuracy and swallow the expense, a full-size plan is still not so very useful, partly because it is two-dimensional and you are making a three-dimensional object, and partly because you still have to lay it out and transfer the outlines and shapes to something (usually by pricking through).

To make a laminated frame for example the simplest method is to have a flat timber (or plywood or chipboard) setting-out floor, on to which the outline of the largest face of the frame can be marked out. Then screw blocks to the floor at fairly close intervals and just touching the frame outline. Then cramp the laminates up inside the blocks to laminate up the frame. Many of the Study Instructions describe this process in more detail.

To mark out the frame outline from a Mylar film requires a centreline and a dwl to be drawn on the setting out floor. The film is then placed accurately on the floor and the dwl and centreline aligned and the film secured in place. Then you can screw the blocks to the floor over the top of the film, as described above. An alternative with Mylar, and the only way with paper, is to prick through the film on to the floor and then join the prick-marks up with a batten to give the frame outline.

It is true that using our system of drawing a grid on the floor and then measuring the heights and offsets of the frame outline and fairing these with a batten is slightly more time consuming than using Mylar film directly - but only very slightly because the grid is used time and time again. It is about the same as pricking through from paper or Mylar, and accuracy is ensured without any trouble.

Once a frame is made, it has to be bevelled. Our Tables of Offsets on each drawing give you this information. And because the grid is already marked out, it is very easy to locate where the bevel is located and in which direction it should be measured. Paper and film plans should give you this information in digital form (numbers) or as a second outline. Transferring this information to the frame is certainly no easier, and often more difficult/time consuming, than working directly from Offsets.

And, finally, there really aren't many frames in a boat, as a proportion of all the parts and structures that have to be made. So spending a lot of time and money trying, without any real success, to speed up such a small part of the total job, just never seemms worthwhile. And the chances of inaccuracies creeping in are just so much greater.

So – as you might have guessed by now – I don't like full size paper or Mylar patterns! The only exception I would make is supplying outlines drawn on Mylar for aluminium alloy or steel components, if they are going to be laser cut.
Posted: Oct 19th, 2013 at 18:05   |   Subject: ...but maybe:
it could make sense to have the tedious work of measuring and marking the positions for the blocks done by a computer, with the result being printed on map paper or similar and laminated on the setting-out floor. With that vague thought I dedusted my PostScript programming skills and set up a virtual sheet of 2200x1700 mm, let a loop print a 20mm raster and gave the coordinates of a frame (-2600 of design 143, the one I'm seeking to build) to a small PostScript subroutine that printed register marks at the given positions. Coding the coordinates of all the other frames and laminated parts is now kind of cut'n'paste job and even if I don't know exactly, I do assume that printing the result on two 1000 mm wide web printing paper of a quality architects prefer shouldn't be too expensive.
If wanted I could send the PostScript source and the PDF conversion of the result. Do you (or anybody else reading this) has experiences with this approach?

Yours sincerly,