Machinable mould making materials

[Musht]

Returning t`mill after a break, partly spurred by Sketchup getting .stl export that works.

Wanting to mill smallish, 3040 , mould masters for dolls house and model railway building features.

Take molds from master machined plug is the idea, but what to use for the plug is the question that would appreciate the input of the panel.

1. Modelling Board , as in high density PU foam, am already a fan of using celotex/kingspan for trial cuts , lot more forgiving on wrong Z than MDF :-) and cheap. HD PU is hard to obtain in small quantities or prices below what presume McLaren F1 pay, also wondering about surface finish unless go to very high density/cost board. Any hints on suppliers?

2. Machinable Wax, as in blue Trycut or mix your own with paraffin wax and poly bags, looks like an economcal possibility, but wonder about home mix inhibiting cure with latex or silicones. Any experience to share?

3. Plaster, read varying reports but seems if its machined a bit green or damp , dust shouldn`t be a problem, seems ideal for latex as it will release easily , wins on cost. Again any words of wisdom from anyone?

4. Balsa, Jelutong , bass wood seem to be traditional patterm making materials but guessing grain and splintering can be issues and will need coated with a release.

Appreciate any input

[Boyan Silyavski]

The junkyard is the best source for this kind of stuff.

For mold masters I use phenolic plastic, paper filled, gives great resolution, machines like wood with 6mm and 1/3 feed of wood with small <3mm cutters and V bits.. Think MacDonald toilet doors, airport toilet doors.

16000rpm 45-60IPM 6mm bit, 16000rpm 24ipm 3mm bit , with very sharp and thin 30degree V cutters, treat like aluminum 8000rpm 24ipm or slower

Tufnol is similar, make sure to get the paper filled. Check ebay, its quite cheap there on small pieces.

[Blackrat]

Corian ... Solid surfaces works great ! Easy to polish and easy to get parts to release

[Sven]

Don't use plaster, it is very corrosive on tools.
As far as machinable wax goes, I've read some info on disolving PE shopping bags in to candle wax (keep on disolving until no more gets disolved) gives you maxinable wax.

Mdf can work too, have tried but for bigger molds. Used epoxy to seal it, then sand smooth.

[Musht]

Thanks guys , thought had heard Tufnol /SRBP dust was bad, but looking up the MSDS just an irritant, bit on order from ebay.

Tried MDF but chepa stuff furrs really badly , especially at the scale and sheet of Valchromat bit more than need at mo.

Lost contact had for chunks of Corian like solid surface, if they were any bigger thna door wedge began to get expensive. Would use acetal as next favourite material to cut , not cheap though.

Looked at mix your own wax route , slightly concerened that any impurities might inhibit platinum cure silicones, dosent take much ;-)

For try before buy, committing decent cutter and material have settled on cellotex at moment.

Read abit about plaster not being as hard on tools as might think, its just calcium carbonate, and adding some PVA to mix helps bind it keeping dust down. Idea seems to be cutting it when its still damp or soaking the brick for a while before cutting, Ideal for taking latex moulds from but think shrinkage of plaster and latex will begin to add up.

Will report back on using tufnol clone