Accurate double curvature techniques

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Accurate double curvature techniques

Author	Message
Ian Mantula	Ian Mantula posted 8 Years Ago HOT Topic Details
Group: Forum Members Posts: 24, Visits: 668	Hello pattern making experts. I am trying to make a series of plugs for some new engine bay parts for my Marcos Mantula. I'm really hope to get some advice on the best techniques for creating complex shapes with some double curvature. While I'm getting close to the shapes that i want it's still not 100% perfect. I seem to be a perfectionist without the skill to achieve the results that I am looking for. Are there any special tools available from anywhere that make it easier to shape, for example, a concave curve with a varying radius? I am building the plug using an MDF structure with expanded 2 part foam for the curvy parts then covering that with polyester bodyfiller. After that Easy Composites Pattern coat primer and top coat. I'm using Permagrit tools to rough-out the shape, then various home made sanding blocks after that. In the photo below the box with the lid is for the air-conditioning system. In front of that there is the internal mud-guard. The double curvature is essential due to the shape of the Marcos bonnet. I'll be doing a mirror-image for the other side of the car. Perhaps the only answer is years of practice... Thanks for any suggestions. Ian Marcos Mantula blog
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*VVS*	*VVS* posted 8 Years Ago HOT Post Details
Group: Moderators Posts: 226, Visits: 334	Ive not used expanding foam, just recently been using the hd foam blocks to shape parts, should be similar and I'm using same kind of process to you. Id say 80% is technique and 20% in the foam, don't apply any filler unless the foam is spot on as you are only skinning this with a millimeter of top coat. you want to be putting the filler on super thin then sanding back very carefully.
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ChrisR	ChrisR posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 363, Visits: 3K	I prefer to draw everything out first rather than freehand a shape insitu, that way you can either make an inverse former fit to the profile when you are sanding or you can cut it out in coloured cardboard and stick foam blocks to it and shape down to the cardboard. But that's the engineer in me
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Ian Mantula	Ian Mantula posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 24, Visits: 668	ChrisR (28/04/2016) I prefer to draw everything out first rather than freehand a shape insitu, that way you can either make an inverse former fit to the profile when you are sanding or you can cut it out in coloured cardboard and stick foam blocks to it and shape down to the cardboard. But that's the engineer in me Yes that would be ideal, but in this case I am working in a predefined, tight space where the new plug has to fit under the existing bonnet. I found it easier to use expanding foam between the plug and the bonnet to take the basic shape. Then perfect it from there. Marcos Mantula blog
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Hanaldo	Hanaldo posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	It's better to make a profile, as Chris said. I realise that can be difficult when working in spaces like you are, but what I would do is use the expanding foam just to form your profiles. So cut cross-sections of the foam and transfer that shape to mdf to create a skeleton structure. Block fill with foam and shape to the profiles. Then it's a case of fitting and removing and perfecting the fit in your space. There really is no easy way of handcrafting patterns, anything hand made takes a degree of skill. Unfortunately it's virtually impossible to just shape a block of foam to what you want unless you are very very experienced or just born with outrageous natural talent, you need your 2D profiles to get that shape right. If you've got access to a CNC machine, well... That's why pattern making is a dying art.
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Ian Mantula	Ian Mantula posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 24, Visits: 668	I can see why this is a dying art, but I'm determined to master it! So far I have made some progress, but it's two steps forward, one step back. I'm getting a better feel for the shape of the surface and how to get better transitions between curves. However what I thought was a perfect shape by feel in raw body filler was not so good when I sprayed a gloss black guide coat over my hard work. The curves are smooth but the shine lines are all over the place! I won't give up! Marcos Mantula blog
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Hanaldo	Hanaldo posted 8 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Yeh panel beating is another skill of its own. You need to sand the panel as a whole, not concentrate on getting one area smooth before moving on to another area. And this definitely needs to be done with a block, there is absolutely 0 chance of getting a flat surface if you are sanding by hand. A trick the panel beater I work with taught me is to rub a piece of glass before you feel your part, and then close your eyes when you do. This really sensitises you to the ups and downs of your part. It also helps, once you think your surface is close, to spray a light coat of primer over the surface just so that the surface is all one colour. Varying shades of body filler etc can all mislead your eyes, so a uniform colour helps. Once you've done that, rub the primer off again using your sanding block. This will reveal any high/low spots etc.
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