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Hanaldo
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Hey all, I know a few guys on here have experience with building kit cars and the likes, and was hoping for some advice on building larger plugs from scratch. So far all the patterns I have created have been relatively small and I've built them using 2D cross-sections and polyurethane foam. However I have been asked to design and build a carbon fibre roof for this:  Now the original never had a roof panel, so this is something that I will need to design and build totally from scratch. The design aspect I'm fine with, and I'm sure I could find a creative solution for creating a 2D cross-section and polurethane foam plug, but I wanted to find out if there is a better way to go about it? I realise MDF etc. are good options for flat areas, but are there any other good methods for building something like this? Also, on an unrelated note, I could do with some business advice. I haven't been operating as a business for very long, and having never taken on a project like this before, I'm a little bit unsure on how to quote for it... Normally I work out material costs and try to estimate labour time and come up with a number from there, however I have no idea how much either of those things will end up with this project. It's a large project and will involve a lot of time I'm sure, so for those of you in the industry: how do you quote or charge for a project where you are unsure on how much you need to charge to be profitable? Last thing I want to do is underquote and end up having to pay for this thing out of my own pocket, I need to make sure I make a good profit on the job. Thanks for any help, always much appreciated.
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Dravis
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hi, for the business aspect of a large project like this, you really need to split it up into two parts and agree that with your customer.. Since I do not know if this is a one off project, I will assume it is not, but that you may be able to sell further copies of the roof. That makes the initial design a "prototype" work, which you should take into consideration when making a quote. part one is the design work, plug manufacture and mechanical engineering that goes int it ( how is the roof fastened to the car, what sort of properties are wanted by the customer. this is mainly Time.. hours spent... probably the bulk hours of the project :-) second is mold manufacture, and making and finishing the part, adapting it, gluing in/mounting fasteners e.tc. here you can cost materials,based on the result of the design work, and also hours for the work. Assuming the part can be sold in multiple copies, try to estimate how many, be conservative and realistic! :-) then divide the cost of the "common work" ( design, plug and mold ) out on the number of copies realistically sold.
"Sapere Aude"... Dare to KNOW!
The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...
103% of all people do not understand statistics...
Do not adjust our mind, theres a fault in reality :-)
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Hanaldo
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Thanks mate. At the moment I'm treating this as a one off, realistically I can't see there being a big market for these things. What you've described is basically what I normally do, my issue with this one is not knowing how much labour time to quote. I need to be sure that I don't sell myself short.
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brainfart
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> I need to be sure that I don't sell myself short.
You probably will. Such projects tend to take longer than anticipated.
I'd split it up in more than two parts, like design, plug, mold and final part each.
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Dravis
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If this is realistically a one-off, then you need to make that clear to the customer! It will make the part quite expensive for him!
I have done a couple of mid - size projects for a "friend of a friend" I made it very clear from the start that a large part of the work woould be done on a "consultancy basis" i.e. I would charge him by the hours spent on the whole design phase, then quote him for the manufacture of the actual part(s)
He is a consultant himself, so agreeing on a reasonable hourly fee was not difficult.
I normally quote a "materials draft" using slightly higher prices for the materials needed, right at the start, then tell the customer that that just covers the materials, not the work.
I agree with "brainfart" in that you should probably divide this project up into more than just two parts.
"Sapere Aude"... Dare to KNOW!
The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...
103% of all people do not understand statistics...
Do not adjust our mind, theres a fault in reality :-)
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brainfart
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> The design aspect I'm fine with, and I'm sure I could find a creative solution for creating a 2D cross-section and polurethane
> foam plug, but I wanted to find out if there is a better way to go about it? I realise MDF etc. are good options for flat areas,
> but are there any other good methods for building something like this?
Will you have to build a windscreen, too?
In general, when you want to build round, symmetrical objects which have compound curves (curved in more than one direction) you are actually entering boatbuilding and aircraft/automobile design territory. The still most important tool in those trades is called a batten, a thin, long, perfectly straight piece of wood which can be bent. This allows to produce visually pleasing, continuous lines by aligning it with existing surfaces, and checking for positions where material is missing or needs to be removed.
Position the car perfectly level, or establish a level plane like the edge of the cockpit. Determine the middle of the car with a piece of string weighted on the ends and a plumb bob. This establishes your absolute zero, "waterline" and stations from which all measurements are taken. Build a platform made from plywood or similar material approximately on the lower height of the planned roof. On this platform you will build the roof structure.
Get many thin long strips of wood and start building the general outline of your roof. The battens can be bent to produce compound curvatures. Generously overlap the battens onto existing car structures for continuous lines. Take measurements from the middle line, stations and height above the platform to ascertain the structure you are building is absolutely symmetric. Support the battens with lots of pieces of wood or even properly shaped thin plywood glued into place. This is the actual design process, but you are also building the plug. When you're finished building a lattice structure of your roof you can fill the empty space between and under the battens and support structure with foam and then pour a layer of 2 component pour foam on top. This is then sanded into the desired shape.
I don't have pictures showing this process and I'm lacking the proper vocabulary in English, but I hope this description made sense.
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ChrisR
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errr.... I think that's a pretty succinct description!!! brainfart (01/09/2014)
>
I don't have pictures showing this process and I'm lacking the proper vocabulary in English, but I hope this description made sense.
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brainfart
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kidpaint
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Look into buck building for automotive use. This was once used widely when cars where hand produced before modern assembly lines where used and computers. Today coach builders, and true metal shapers still use this form of design to make new or replacement panels. It goes along the lines of what was mentioned above about finding center lines and going off there.
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