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Polycarbonate - warning - newbie question!

Posted: Sun Nov 18, 2012 10:58 am
by chocman
Hi all,

I've been researching CMC mills for over a week now and have only just found the Shapeoko. I believe it's exactly what I've been looking for and am really excited about getting my hands on one. Before I place my order I was hoping to get the collected wisdom from this forum. I have a very specific purpose in mind for the Shapeoko ... specifically, milling chocolate moulds out of blocks of polycarbonate. Has anyone milled with polycarbonate on the shapeoko before? What would be the best types of cutters to get for this material? I need to have a very smooth surface so I can produce quality chocolates at the end of the process. Will the spindle that comes with the basic package be sufficient for this purpose, or would I have to upgrade the spindle and/or the motors?

Thanks in advance for your help.


Re: Polycarbonate - warning - newbie question!

Posted: Sun Nov 18, 2012 3:17 pm
by jluther
Well I haven't milled polycarbonate. I am curious as to why polycarbonate is the choice, most food contact materials are specific stainless steel alloys. However, if the FDA thinks it's ok, it's food grade, and you can keep it from fracturing, then I guess it'll be fine. The spindle is a dremel tool so expect to do some polishing after milling, you're not building a tool and die mill like a makino. Also most molds get polished after initial machining to get the surface finish.

I'd recommend rough machining an arbitrary plastic then coating with a food grade epoxy to smooth out the surface. Should reduce finishing time and still fullfill food grade contact requirements. As well as remove the risk of having a crack collect bacteria over time.

Re: Polycarbonate - warning - newbie question!

Posted: Mon Nov 19, 2012 4:53 am
by fito
The spindle should be alright, the real question is what end mill to use? I haven't done any polycarbonate but you should look for bits specifically made for polycarbonate, probably a ball end. How much detail at what size are you looking at?

Re: Polycarbonate - warning - newbie question!

Posted: Mon Nov 19, 2012 12:17 pm
by chocman

Thanks to both for your replies.

I chose polycarbonate because it seems to be what professional chocolate moulds are made from ... although they're definitely not milled into shape. As for the choice of mill ends, I was planning on trying this as recommended here ... age/127560. This link also says I need high RPM for polycarbonate. Am I right to assume I'd need to upgrade the spindle to achieve this? Perhaps I can use the dremel-style spindle with the kit to do some hand polishing at the end, but I'd obviously like to minimise any post-processing.

Thanks for the suggestion re the epoxy, but I think that would blur out the detail I'm looking for in my moulds. I was hoping for features about the 1mm size, but I don't know what is possible with polycarbonate. Any suggestions on how to get the best detail would be much appreciated.



Re: Polycarbonate - warning - newbie question!

Posted: Tue Nov 20, 2012 7:06 pm
by Aaron Seltzer
One popular technique is to cut in wax, then pour a rubber into it (see Smoothon) to make a mold, then pour your chocolate into into the rubber mold. Rubber is nice as it lets you pop out our pieces easily.

There are lots of tutorials online.

Re: Polycarbonate - warning - newbie question!

Posted: Wed Nov 21, 2012 7:53 pm
by jluther
just run any plastic endmill and you'll be fine for the PC, typically plastics are high rpm because of the tooth load but the dremel will do fine, maybe even with standard bits.

I'm more concerned about getting food grade PC and milling it. I'd think you could make a negative out of anything then use a food grade resin or silicone like was suggested (smoothon and any number of other sources) and then you have some solid backing. Otherwise you need to use food grade equipment and processing. You can't just take any ordinary buffing compound and use it on food production equipment. Also you need to make sure that you didn't put microcracks or anything for bacteria in it also.

Typical cleaning is with alcohol (special alcohol) and that will possibly crack your mold during cleaning...