Ski Builders Forum

I dont understand why MDF has to be used for the mold... it is going to be covered up by layers of masonite, so why cant the mold be made out of 2x4's cut to shape and sanded smooth and uniform? If anyone can shed light on this for me please do.

It doesn't have to be made with MDF. MDF just works well because it is easy to route out to the correct shape, it is ready available, and is very strong.

2x4 would work as well.

I have used 2x4's and they worked great.

My next one is going to be done with plywood or masonite, and made extra fancy.

The one time I used MDF, the MDF collapsed under the load of the fire hose, so I have been trying to stay away from materials that consist mostly of glue.

just use any wood! i took fir for my last mold because it was the cheapest wood available, and it worked perfectly well. maybe even better than mdf - normal wood is way better in terms of sawdust. mdf leads to really really nasty sawdust when you machine it... so be careful with mdf and use a respirator at any cost.

edit: i made a pic once, it also can be seen in the skibuilders-gallery. so for one more time: wear a respirator when working with mdf. actually this picture scared the shit out of me. this was the amount of dust it collected after 2h of work. as i built my first mold i worked with crappy facemasks form my local store. this is a P2 filter which should take out about 96% of the particles in the air... so i really don`t want to know how much of this nasty dust came in my lungs the first time.

sometime soon I will be making my first mold and would like continue discussion on same question asked in this old thread. Why MDF used to make mold? Why not plywood, regular wood? is it the best material for the job?

It's easy to cut, route, and sand, it takes compression loads very well without deformation, and it has a completely homogeneous structure. With no grain there are no weird load paths. You can really use anything you want as long as it can take the forces, I just think the fact that MDF has no grain is the biggest benefit. It will also expand/contract uniformly with heat, where as wood with grain may not.

Hi. MDF is toxic, heavy and expensive. I only used it first time and for all the others (20 ish) molds I used Radiata Pine 90x45mm. (2x4 inch in metric) No worries at all.

my cnc-girl (!) told me that she would recommend using something like ureol / renshape (polyurethane rigid foam) to mill my molds out of.
that stuff is awfully expensive though, so i started looking for alternatives and found some interesting materials. only problem is, i'm not sure if i'm interpreting the data right...especially on compressive strength.
i figured that we're actually getting about 30 psi on the laminate (area of roughly 160x30 cm).

finding data on compressive strength for MDF is kinda difficult. the only number i could find was 34 Mpa (5000 psi).

now here's the data on a couple different materials i'm looking into along with the tests used:

Obomodulan 502: 13 Mpa (1900 psi), tested according to ISO 604
Puren / Modur 145: 2 Mpa (290 psi), tested according to DIN EN 826
Purenit 550 MD: 6.5 Mpa (950 psi), tested according to DIN EN 826
Renshape BM 5440: 22 Mpa (3200 psi), tested according to ISO 604

i'd love to use the Purenit since it's the cheapest one out of the four. i'm just not sure if it'll hold up...

funny enough I was thinking about this today whilst sanding a new MDF mold!

Hi all,

I am about to order some paulownia wood for cores and I was considering ordering some blocks for mold as well. Do not like MDF. Does anybody here see some bad things about using paulownia for mold?

From what I heard it is easy to machine and strong.

Some data,

• English Paulownia
  
  Density (Kg/m3) 280-300
  Tensile sthrength (N/mm2) 64-80
  compression strenght (N/mm2) 25-28
  bending strength (N/mm2) 31-40
  modulus of elasticity (N/mm2) 5000
  shear strength (N/m2) 5.5
  N/mm2 = MN/m2

English Paulowina ... I don't think there is such a species.

haha, sorry for that, the word 'English' ended there due to some copy/paste ..