Monday, 26 September 2011

Gipsani otisak - Plaster mold

Dugo vremena sam razmisljao kako dobiti potrebnu zakrivljenost daske za kite boarding/surfing iliti kajtanje. Ima nekoliko "skola ucenja" izrade zakrivljenosti daske.
Naprimjer, jedan od nacina za dobiti zakrivljenost je izrada tzv. "stola" od deblje ili tanje sperploce koju unaprijed zakrivimo stegama. Ili masivnim sarafima. Na taj stol polazemo novu dasku.
Drugi je nacin izrada zakrivljenosti od drvenih letvi koje ispilimo u odgovarajuci oblik, poredamo jednu do druge i time dobijemo potrebnu sablonu. Takodjer na tu sablonu stavljamo novu dasku.
Za vecinu slicnih stvari postoje programi na Netu koji vam mogu pomoci kod izrade.

Zatim ljepimo slojeve daske jedan na drugi na ovakvom "stolu" ili sabloni. Kad se ljepilo stegne, daska ostaje u obliku stola.
Ja sam odlucio pokusati najbrzi i najjednostavniji nacin za izradu zakrivljenosti. Jednostavno sam stavio par letvi, pleksiglas ispod i deblji najlon preko svega te nasuo dovoljno gipsa da mogu "otisnuti" svoju komercijalnu dasku. 5kg gipsa je skoro pa dovoljno. 7 kg bi bilo taman.
Time cu dobiti potrebnu zakrivljenost! Sve gotovo u 30 minuta. Primjetite fibreglass pojacanja na najlonu. Ista pojacanja su na doljnjem dijelu daske prije nego sto ju stavim na gips.

Nakon toga obradim rubove gipsanog otiska, stavim slojeve sperploce koje lijepim, vakumiram kompletno sve i nadam se najboljem!


For a quite some time I was thinking how get a rocker and concave for my kite board. There are a few "schools of thoughts" how to do this.
For example, a lot can be done by making a "jig table" of thin or thicker ply wood. With or without a massive bolts/nuts. Than we put a new board on a jig table.
The other way for doing it might be to cut a number of wood pieces with a router or similar and than placing all this pieces together into one shape. The new board goes on top of it as well.
For all of this there are a number of different software on the Net.

I've decided to go with a fastest and much easier "jig". Simply placed  some perspex under the PCV foil, put some wood leftovers around and poured 5kg of casting plaster on top. Than, my commercial board goes on top to get the exact shape. 7kg of plaster would be better to work with.
All together, 30 minutes of work. Note, a fiberglass reinforcements on the foil. Same applied at the bottom of my board before placing at the mold.

Latter on, a board goes out, final touches around the edges of my plaster mold, the ply wood goes on it, vacuum applied on everything and hoping for the best!



  1. Hey Dean. Nice work! I like the idea of the plaster. I have been thinking about something similar as I want to be able to put the entire rocker table in the vacuum bag rather than use tacky tape on the mold surface (which each time has meant I have spent a long time trying to find air leaks). Having a solid rocker table (without bolts sticking out) seems like the best way. It might also make it easier to apply positive pressure on top of the board without distorting the mold surface.

    Great work! BTW I just got the wood from Paulonia Paradise in Melbourne to try some wood cores this summer!!


  2. A little update on this: a blue tape in the middle white area is holding two perspex sheets in place. Under both end of perspex I've placed some 5cm thick wood offcuts to get a curved shape when a plaster went on top. The above photo is just before placing my factory made board (wrapped in some foil) on top of the plaster. With a bit of compression this board made a fine imprint after 24hrs. The board was completely in the plaster and this was important!
    It means the imprint was almost carved in the plaster, rails too.
    After lifting the board up, there were some dry spots under.
    I didn't care about this since the next layer of plaster (and fiberglass) was poured on top to cover the complete imprint which was 6 to 3 millimeters deep (as per factory board rail thickness).
    Surface finished by hand and nice curved shape in place. Almost perfect. A bit of sand paper after a few days and template ready for vacuuming.