Mould Loft first created 14/10/06 - last modified 15/5/08 Page Author: Ty Harness
News: I hope to release the MLoft software late 2008 and there will be a free version for educational and non commercial use and the full version will made available to existing full version users of STOR,SEGB,CONET and STOS.
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Mould Loft (MLoft) is a simple application that triangulates out a pattern between 2 curves. The 2 curves are described by n 3D vertices. The curves can be calculated independently with applications like spreadsheets or there are several well known curves 'built in' as standard like the helix. Once both curves are loaded then you can view a front elevation, plan elevation, pattern development and isometric views.

Triangulating out the 2 curves is very flexible algorithm because the 2 curves can describe most sheet metal transformers. The previous Ty Harness sheet metal applications allow the user to enter dimensions which the practical worker will fully understand where as functions and parametric equations are not really the domain of the sheet metal worker. There's no reason why plugin modules can't be developed independently which makes it easy to generate the curves for the non mathematician. Figure 1 shows helical curves where the 3D or isometric view becomes absolutely essential as a visual confirmation

Figure XX shows 2 helical curves with a different pitch but the same radius.

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Figure 1 - 2 helical curves separated with a different pitches


Helical work is quite common in metal working and is often used as signs, chutes, staircases or just as architectural features. All the previous sheet metal applications are based solely on orthographic projection to describe the 3D object. Sheet metal workers ,in general, require a 2D plan and elevations because you can easily determine the true length of any diagonals with a pair of dividers and hence mark out the pattern development but for the layman then the isometric representation is often easier to understand. Although MLoft stores the 3D vertices and you can export 3D vertices and faces (DXF) it's not a true 3D application in terms of the isometric view which when exported will be just be a projection on the z plane. This is useful if you wish to combine the DXF output with your favorite CAD package either 2D or 3D.

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Figure XX - Isometric view of the helical string.


The full versions allow you to export the 3D DXF or VRML where you can go on to incorporate the development into your 3D CAD world.

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Figure XX - DXF export rendered with Right Hemisphere's Deep Exploration [xx]


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Figure XX - Helicoid chutes xx a,b,c and finally assembling the 3D DXF models in TurboCAD[xx]


The advantage of being able to generate the pattern development is that more obscure work can be attempted like the Möbius strip. This is not a job that is going to pop up very often although the Liberty Science Center in New Jersey has a rather fine example[xx] of a Möbius strip used as a sign. The curves are generated from the parametric equations which fully explained at Mathworld [xx].
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Figure XX - a,b Möbius strip. C is the 3D DXF export rendered in Deep Exploration[xx]


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Figure XX - A family of quadratics separated with a constant z height

The future development of MLoft will be the segmentation between the 2 curves with a family of curves which will allow the creation of boat hulls and fuselages.

Some of the most difficult development to visualize are oblique cutting planes. I've designed MLoft on the basis of having 2 cutting planes. Figure XX below shows a Rectangular Hollow Section (RHS) sliced obliquely between parallel planes which is a common problem in construction. Note the oblique cut means the end views are rectangles and the amount of times I've cut square end caps before realizing my mistake.

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Figure XX - Simple oblique cut between planes


When the RHS is positioned oblique in 2 axes it becomes extremely difficult to visualize and extremely easy to cut the wrong angle even if you can orientate the vice or saw blade to the cutting plane angle it's difficult to get the length of the member correct.

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Figure XX - A more complex oblique cut between planes


Exotic material and uncommon sections are very expensive so it's important to get the cut right first time.

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Figure XX - A church steeple requiring several difficult cuts - D&D Engineering Ltd (Lincs)


Mitred joints for the sheet metal worker are one of the most difficult aspects of the trade. Joiners and stone masons can slice the moulding along the cutting plane with the aid of mitre boxes or compound angle chop saws. The sheet metal worker is starting from a flat sheet and needs to develop the oblique cutting line before the moulding is formed. All trades can benefit from a paper pattern. The paper template can aid in scribing an accurate cutting line on the front of the moulding which is useful for elaborate cornice work often seen on bay windows or the top of cabinets.

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Figure XX - Some simple quadrant moulding mitred at 22.5 degrees


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Figure XX - A regular octagon made up from the mitred moulding.


The same principle can be applied to create finials and ornamental products. It's very rare that ornamental sheet metal work is produced today. This type of work is still made by sheet metal workers who specialize in roofing.

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Figure XX - A selection of finials generated by the Mloft software


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Figure XX - 8 sided finial






References {Please note I have no affiliation with any of the references below}
http://www.righthemisphere.com/
http://www.turbocad.com
http://mathworld.wolfram.com/MoebiusStrip.html
http://www.narchitects.com/frameset-LSC.htm