One of the Omaha Maker Group's generous members donated some robot arms a while back. A couple of them had some mechanical issues, and we've stripped those for parts. Some of the remaining arms are reserved to possibly share with some other groups. This leaves a few that are mostly just being stored. Today while I was at the Makery I claimed one of the remaining arms and brought it home. I'm not down at the space often enough to make much progress working on an arm there, so I figure I'll work on it here at Whelwick.
First step is to hose the danged thing off; it's incrusted with old oil and grease, into which is embedded dust, grime, and cat hair, all of which is infused with a funk of barn with overtones of old machine shop and dank basement.
So, first a spray with the garden hose, then couple of good soakings with engine degreaser (my phone ate the picture of it coated in nice white foam :( ). This was followed by a couple more sprayings. This removed the bulk of the grime and cat hair. I followed this with some paper towels and Simple Green, some Oops for the tape gunk, etc. Then I spent a while blowing it all out with the leaf blower to get it reasonable dry.
As part of the cleaning and drying I removed the cover panels and discovered that the cast iron base on this particular arm has cracked. I could probably braze this, but since we scrapped a couple of identical arms, we've got a couple of spare bases sitting around. I'll pick one of those up next time I'm there and replace this one.
After a couple of hours of cleanup work, it still has a little bit of an odor, but it's fit to sit on the bench and wait for more technical attention.
For the sand casting demo for the Omaha Maker Group, I picked up some beads at Hobby Lobby to use as patterns. I thought that since these were convex they would make for an easier demo than the glass dish I used in my first attempt. These turned out to be pretty good patterns.
The two at the top are the original metal-finished plastic beads, the rest are my zinc castings. You can see on the larger casting on left that I had insufficient metal coming in to avoid a little bit of a shrinkage cavity at the top. The four smaller castings at the right were done in one pour. They came out better, with somewhat less shrinkage, but I didn't do quite as nice of a job of packing the sand, so the surface finish wasn't quite as nice. I took the best one and colored it with a sharpie and then polished it with a rag to remove the ink from the high points.
Casting these was pretty much like any other simple casting, nothing much to say about the process. For the demo I did a pretty rushed job of making the mold, so the results were fairly low quality, but the pour went well.
I picked up some drill rod today at the local Fastenal store and put the X axis together.
We used smooth rods out of various printers and a scanner for the other axes, but we didn't have any rods long enough for the X axis, which needed rods of at least 16.5". So I spent some time looking at drill rod suppliers before I discovered Fastenal. It turns out there is a store here in Omaha, and the company keeps inventory info online so you can see what is available at the stores and what will need to be ordered.
I stopped by after work on the way to the Omaha Maker Group 'space and picked up a 36" piece of 8mm drill rod for $5, and also a couple of scrap pieces of 3/8" threaded rod that I thought might be useful as the Z axis screws.
The drill rod fit perfectly,but the threaded rod was a bit big. to make it work we tapped the holes in the plastic parts out to 3/8" and then dribbled some PLA around the rod to build up the cavity where the nut was intended to go.
Next we need to turn down the ends of the screws for couplers, build the couplers, and get the motors mounted. Then we'll be looking for electronics.