Machining materials questions


(Gary C) #1
  1. Has anyone tried milling any cocobolo wood? It machined very nicely on my wood lathe. And I have a ton of it.

  2. Has anyone tried working with any of the polyester resins such as marine resin? Renshape is so expensive and hard to get in anything but full size $heets, other than the small pieces Carbide3d sells. I did a little searching was I was waiting on delivery and I found some guy saying he was in Peru and in addition to the high cost availability was really difficult for him. He said after hundreds of hours of experimentation he found that the best solution (pun intended) was marine resin with cornstarch mixed in. He said he had tried over 500 different things and this was pretty dang close to renshape. He added that marine resin was critical as other types of resin were “tacky” after curing.

Below is his recipe, if anyone is interested. I have a gallon of marine resin and intend to try it. I’ve always been interested in casting.

Take a cup of corn flour, or corn starch whatever you call it. A cup of resin ( I use a polyester resin), mix and stir well (slowly so as to not cause too many extra air bubbles (not important as you will see in a few minutes).
Their is a reaction that takes place between the polyester and the corn flour. It degasses itself!!! After about 20 minutes the resin is degassed.
AMAZING! Maybe an industrial chemist could tell us why.
Now add your hardener but do not stir too much. We don’t want those bubbles coming back.
In 10 minutes your block is set, in an hour you can machine with it.
Now because we use fifty percent volume (actually about 10 percent of the finished block (you will see what I mean) the plastic is less fragile and less prone to break outs. It is fairly soft on the tools and no louder than wood to machine.


(Jonathan K) #2

I know this is an old thead, but I’m curious how this turned out :thinking:

Can you fill us in?


(Adam Albert) #3

I missed this post from a year ago; thanks for bringing it back up!

I hope Gary had success; I’m interested in the outcome as well.

BTW, I found what I think is the original post here.
Note that further down, the same guy says “This type of resin is designed to be mixed with a substrate (fibreglass sheets) so don’t try making a solid block of it. It will be brittle and probably crack while curing.”


(Dan Nelson) #4

I’ve added cornstarch to regular old 30 minute epoxy to use as a filler/smoothener/thickener on foam RC airplanes, it makes it much easier to sand. Very similar to micro balloons that are used for the same thing, except cornstarch is cheaper and “possibly” less of a health hazard to handle, when I say possibly I mean in raw uncured form, I’d bet breathing epoxy dust from a router is “probably” a really bad idea. I don’t know if a whole big block of this would work as a machining medium, but it may be cheaper to just buy the real renshape since epoxy and/or polyester resin isn’t super cheap. Just my $0.02 from some observations I’ve made, YMMV.

Dan


(Gary C) #5

Sorry, I never got a chance to try it. My Nomad is buried somewhere in my garage while I’ve built a new shop. The shop is done but I still need to run electricity to it. Hopefully in the next month or so.

Maybe we could get some renshape group buy together…