'Lost Wax' bronze caster wonders about CNCing machinable wax to...cast in bronze!

[gravus76]

Hi CNC zoners


Apologies up front, this is a bit of an essay for a first time poster..I've already searched various user groups and forums but essentially what I'm looking to achieve is a little bit different, I think, and in any case I humbly tip my hat to your wiser heads!


I'm from Meridian Sculpture in Melbourne Australia; we do lost wax art castings in bronze, a pretty rare and very old world process. This coming year I've promised myself to properly investigate some modern machining and manufacturing opportunities in the hope of remaining competitive and relevant. 3d printers present an obvious one but I'm in the near term more enamoured by CNC options.


We've zero CNC capability at the moment and only fledgling CAD skills but ultimately what I'd like to do, among other things, is achieve high quality high resolution machinable wax parts for direct casting to bronze. Surface fidelity and accuracy is paramount for us and that's where the size, quality, time and cost trade off for external 3d printed wax or plastic parts still isn't quite good enough, actually a long way off, at least in Australia.


So Ive been investigating compact routers like the Shopbot desktops and Sharks etc and of course these aren't 3d but we see an opportunity to create reliefs and plaques and other flatter 2.5d parts - think name plaques found with a large public sculpture - that are superior in choice and finish to that supplied by the single operator in that market locally. This company supply bronze cast plaques but they can't/wont do engraved patterns and always have a rough sand cast like appearance as the flat background to raised lettering, symbols or imagery. We are often re-finishing their product and our clients often ask for a humble variation they can't achieve.


So to get to the point..assuming the required software skills, I'm wondering whether a machine like the Shopbot desktop (or max) or indeed other machines are up to reliably producing high fidelity 2.5d parts from wax (sheets) that might for example have lettering and patterns either engraved OR low relief embossed? Also when carving wax would a router be sufficient or would a spindle be smarter as a business investment? I suspect so..


My research so far seem to show good availability of machinable waxes here, that tool life is good with such material, and that the desktop's step precision is reasonably 'pro' at 0.006mm..but please educate me, I know there's many other factors when considering accuracy. There are cheaper machines than the Shopbot but, inexperienced as we are, we can't afford to muck around with the likely sloppy build of the cheaper enthusiast machines and if we do this we need to do it well.


Love it if you CNC pros could de-bunk any of my assumptions or provide advice, particularly if you've experience in tooling wax parts.


Thanks again for your time
Gareth.

Similar Threads:

• gibs from oilite bronze sintered bearing material instead of brass/bronze
• Bronze Rabbit Plaque done with Lost Foam
• 954 bronze
• Need Help!- Need to put a spline in cast bronze
• Two bronze nuts better and cheaper then one bronze nut ?

[awerby]

Yes, it's perfectly possible to get good results with a Shopbot carving machinable wax; not sure about the Sharks. You're wise not to mess with the cheap Chinese imports; people are always asking for help here trying to get them to work. You seem to be a bit confused as to the difference between 3D and 2.5D, though. Any relief with compound curved surfaces would be 3D, even if it's not "in the round". 2.5D parts resemble a topo map composed of layered cutouts; the top-facing surfaces are flat, but the edges can be curved.

Yes, a 3-phase spindle run from a VFD is worth getting; they are much quieter, stronger, and longer-lasting than a router intended for intermittent hand use. For decent fidelity and reproduction of details without too many tool marks, you'll need to run the thing for a long time; parts often take 8 hours or more to complete the finishing pass if you're using small tools. This will destroy the bearings of your router, which aren't meant to run for long stretches.

You might be better off, though, if you treat the machinable wax as a master to make molds from, rather than trying to burn it out directly. It doesn't flow out of a mold like regular wax; it acts more like plastic, and expands quite a bit before it melts, which tends to crack molds. Also, unless you create a shell in software then flip the part over to carve the back (being careful not to lose registration) it will be uneven in thickness, which doesn't work well in cast metal. If you make a rubber mold from your carved wax part, it's easy enough to slush-cast a contoured wax model that will cast better in bronze. Also, of course, if there's a casting mishap or you need more than one, you won't have to carve another master.

Andrew Werby
computersculpture.com