Making a female mould directly??

I have searched the forum and the net.
It seems like everybody insist on making a (male) plug first, and then use this to make a (female) mould.

However, if the shape is quite simple, like hard chines with filleted (rounded) corners, would it be possible to make the mould directly? I think we can make a stable sceleton of transverse and longitudinal frames with cnc cut plywood that fit into each other with slots, then build the surface of plywood and then fillet the corners and sand..

This is how a typical section may look, it's a cross cart body 2 x 1.5 meter approx..

 

Hi Ragnar, its possible & commonly done on simple shapes & boxes with melamine sheet or similar with plasticine or poly filler in the corner fillets, on boat molds/plugs its much easier to fair & smooth the convex surface of the boat hull or plug than the convex surface of the mold although its very possible to get a good result with effort. http://www.sayerdesign.com/
Chek the sayer design link for some sweet examples featured such as Wasabi. All the best from Jeff.

 

Thanks. INteresting link.

I also found this,
http://www.homebuiltairplanes.com/forums/composites/2436-female-plug-mold.html

 

I have seen this in various formats many times.

usually it is used for low-volume production runs (1-10 pulls). For production boatbuilding, a polyester tooling resin mould made on a male plug (master) is more suitable.

Materials i have seen used: MDF for small parts, melamine sheet, PE or PVC sheet, but also an interesting one:

Cheap EPS foam (slightly higher density) covered with stretchable vacuum film (SL200 from Airtech as an example). A vacuum is pulled, and in the "mould" one can produce one or 2 products, even without using mould release. This way I have seen one-offs made quite cheaply.

I also recall that ATC Polyesters claim to have clients that have female moulds CNC cut from their polyester paste directly, and that longevity of the moulds is really good.

 

Thanks Herman, thats a lot of interesting info!

btw, here you se my son, named Herman

http://www.youtube.com/watch?v=EOT15enr4bE&feature=channel_page

 

i used to work in aviation development and we made plugs with sheet metel forms every few inches interconected by all thread and nuts so they were on station, fill in the gaps with waddling then plaster to the surface then fair it in

after making one half it was taken apart and the sections flipped around to make the other half assuming they were symmetrical

care had to be taken that the forms were in alignment

another advantage of this method is it can be taken apart and stacked in very little space in case you need it in the future

 

He is definately better on skis than I am....

On the sheetmetal stuff: Sounds like a good idea. Lot of work, but still a good idea.

For cored boats a similar system is used: Framing, held apart with pre-cut slot-in spacers. After releasing the boat, the frames can easily be taken apart, and stored without taking too much space.

 

Hi wardd,

How can I learn more about this process?

thanks!
Tarek

 

molds

in theory its simple

just for simple numbers the forms are 1 foot apart use the all thread to adjust them to that

tilt it back 45 deg and fill most of the space between the forms with anything that will work then glop in the plaster above the form edges and using a spline work it back and fair put on a parting coat and your ready to make half the mold

take the templates and reverse them for the other half

one advantage of this system is mods are easy to make

you can stiffen up the paper by dipping it in a mix of water and cheap wood glue

 

Another usefull site detailing temporary female moulds

http://www.bruceroberts.com/public/HTML/boat_building.htm

 

Thank you very much for the explanations Wardd, Herman, and Rwatson. You guys are great !!! Sorry I was being thick

Tarek

 

dont know about great, but im ok