Guerrilla guide to CNC machining, mold making, and resin casting

Poor choice of working materials is one of the most common mistakes made by hobbyist machinists; quite a few people stick to workpieces that offer poor accuracy, get damaged easily, gum up the tool, or simply cost way too much. For moldmaking purposes, your best bet is one of the little-known materials: an extremely accurate, low cost piece of plastic known as a medium-density modelling board, originally devised for the automotive industry. It’s essentially a mix of medium strength polyurethane, and a combination of soft fillers such as calcium carbonate and aluminum hydroxide. There are many types of machinable boards, but the one we are interested in has a density of about 0.70-0.78 g/cm³, and vaguely resembles wood:

Prototyping boards of this particular variety include Huntsman RenShape 460 (or sligthly less dense BM 5460), Axson ProLab 65, Sika SikaBlock M700, BCC MB2001, Necuron Necumer 651, and several more. The material is typically sold in bulk, in sheets of about 50 x 150 cm, 25 mm thick. This may sound like a lot, but I recommend buying a full board, rather than grossly overpriced cut-to-size bits. The material lasts me for about a year, and costs about $12 per liter (roughly $250 for the whole thing). It’s much less than what you’d pay for a similar slab of HDPE or acrylic - and it machines easier, too. (Planks of dense hard wood, when glued together and planed, may be a cheaper alternative for uncomplicated parts.)

Buying prototyping boards is actually pretty easy. If you are in the US, you can simply go to Freeman Supply, and order RenShape 460 online (search for item #075229). In other places, simply look at the manufacturers’ websites and find local distributors, then send out several e-mails or make some calls (online ordering isn’t common in the industrial world). Be aware that prices may vary significantly, so shop around.

Freeman Manufacturing and Supply

materials supplier for making parts, patterns, tools, or molds.

RenShape 460

Mold Making

Resin Casting: Going from CAD to Engineering-Grade Plastic Parts

By Michal Zalewski March 21st, 2014 1:35 pm

Machinable Wax

Freeman Supply Welcome to the #1 manufacturer of Machinable Wax!

Originally invented by Freeman, Machinable Wax is a unique medium for carving and/or machining precise shapes. This user-friendly, hard, synthetic wax machines faster than most other media while being self-releasing, self-lubricating, non-abrasive, and capable of producing very high qualities of finish, surface detail, and dimensional accuracy.

1.5” X 12” X 12” Single Block for $44