Tuesday, November 06, 2007


Extruder Casting Photos

I recently got a set of molds for the extruder from Adrian. After acquiring the proper casting goop, I decided to spend a day learning how to do it and see if its something I could do myself. Turns out, its really easy!

The basic process is this:

* insert cores into proper places
* spray with mold release (this definitely helps)
* mix and pour in liquid plastic
* wait til plastic hardens
* remove cores
* remove cast parts
* trim/clean up cast parts
* clean cores
* repeat

casting a set of parts from beginning to end takes about 30 minutes, although 15 of those are waiting for it to cure. this is good for someone like me who multitasks alot. i'll setup the molds in the lab, cast them, and while they are curing, i'll work on something else.

i plan on trying to make my own mold as well, because then i'll be able to double my production while only slightly increasing the time it takes. its pretty much just as easy to setup and pour 2 molds as it is to do 1 mold. i have an old, non-straight extruder that i should be able to get a mold of, so eventually people will be able to choose between old and new if they want.

there are pretty much only 2 or 3 major hurdles keeping these out of the RRRF store:

1. brass bearings. i dont have a supplier for these yet, but i do have an idea for how to make them rather easily from brass 10-24 nuts. i'll be trying it out this week, and if it works, then we'll be in business!!

2. assembling and testing it. i still need to fully assemble a cast version and test it just to make sure that it works 100% as advertised. this is still a research project and sometimes things wont work, but i certainly don't want to sell stuff to researchers that hasn't been tested yet. hopefully the resin i'm using is strong enough. we'll find out soon enough =)

3. get the final part list. i need to double check the part list in order to create the kits to sell on the store. this will also be helpful for people who want to order them directly from McMaster, etc. specifying the right nuts, bolts, washers, etc. will really help out alot.

we're close to having extruders generally available!!

More pix on Flickr.

Very nice. Looking forward to getting a full set of molded parts. ("collect them all!")

//i plan on trying to make my own mold as well, because then i'll be able to double my production while only slightly increasing the time it takes//

Can't help imagining Zach in a room full of molds, running around trying to keep up with the process a la Lucy in the chocolate factory.
Vis-a-vis bearings...A bearing has two seperate functions.
A: It provides two sliding surfaces in close contact;
B: It provides support.

I have found that wrapping the shaft in a single layer of brass shimstock provides the first function, and then supporting the shimstock with hot glue or similar provides the second.
I found this provided the fastest and easiest way, and have used it on many robots over the last ten years.
It supported loads of 500 lbs at 1250 r.p.m. using 24 gauge copper sheet around a 3/4" shaft, supported on a epoxy bed.
hey lobster,

thanks for the tip... i'll have to try that!
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