Cat feeder coupler

Tonight I built a really crappy coupler to connect the motor on the cat feeder mechanism to the drive screw on the slide. I was having some difficulty getting anything to work and started on a new slide with a scotch yoke design, but, not surprisingly, I had trouble connecting to the motor shaft for that too. So I poked around a bit and found a grub screw in the junk box that I figured would work to secure an adapter to the motor shaft. To make the adapter I cut a short length of aluminum rod which I then needed to bore out to the diameters of the two shafts.

Since I don't have the equipment to properly bore a shaft, I did it improperly, and with really poor quality. To do this I mounted the rod in the drill press chuck, put a drill bit into the vise, and made an attempt to set the bit vertical and on center, then drilled away. This technique can be used to put a hole exactly in the center of the rotating shaft, give or take a few inches. Flip and repeat with the smaller bit for the motor shaft.

I tapped the larger hole for the screw, then mounted it up and marked where the motor shaft flat was so I could drill a hole for the grub screw. I didn't have a tap small enough for the grub screw, but since the screw is steel and the shaft is aluminum, it can self-tap. I ground the outside of the shaft a bit to remove some of the worst of the imbalance from the crappy, off-center boring job, dripped some loctight in it, and mounted it all up. I'm too impatient to wait for loctight to dry though, so I crushed the threaded portion to secure it to the shaft.

It's working pretty well. I'm not sure how much torque this motor generates, but at stall it generates a reasonable amount of linear force through the screw, a pound or two. At stall the motor draws 2.5A, so I'll need to scrounge up some appropriate transistors for the h-bridge.

Evening Project: Automatic Cat Food Dispenser

I spent the evening working on the mechanicals for an automatic dry cat food dispenser. It consists of a screw-driven slide with a 2 inch hole. The assembly will be placed under a large cat food bucket with a hole in the bottom, with a chute directing dispensed cat food into a bowl.

At the moment the screw is driving the slide simply by threads cut directly into the wood. If necessary I will embed a nut in the slide, but I'm hoping the forces will be low enough that the wood will be sufficient. I've got the motor coupled directly to the screw. This means I'm using a far larger motor than is really necessary for this job. Unfortuantely I didn't have any gear drives that were really suitable. Also unfortunately I didn't have any reasonable way to couple the motor to the screw, so I just bored the end of the screw out to the diameter of the motor shaft and put some Loctight in it. This obviously won't last long, but it was a quick fix. I'll need to come up with something interesting to couple the shafts. Maybe it would be interesting to cast a three-part coupler for this.

The next part of the project will be the electronics for driving the motor. This will consist mostly of some end switches for the slide and an h-bridge driver for the motor. I'll probably put an AVR into it, just because they're cheap and I've got a bunch lying around looking for work. On the other hand, since it just needs to cycle once per input trigger, it might be fun to do it with something more rudimentary with some basic logic.

Spectralight mill update

We spent the afternoon tearing down the mill, cleaning and oiling the ways, and getting the tabletop painted. Its running pretty good now.

Zinc Casting

I picked up some casting sand from a local aluminum foundry this weekend and spent Sunday putting together a small test casting. Rather than using aluminum, which is a challenge to melt in a soup can, I used a few rolls of pennies as a source for some zinc.

It took a few tries to get the cope rammed up properly. I had trouble getting the sand inside the pattern rammed hard enough and strongly connected to the rest of the sand in the cope. It did work out nicely though. I took some pictures of the casting process and the resulting object.

From 2011-06-05

Makery Mill Progress

Spent the day putting together a bench for the Omaha Maker Group Spectralight milling machine. I took way too long tearing apart a pallet some of the guys pulled out of a dumpster and reassembling it as a table. Then we mounted the mill and started troubleshooting the crappy stepping.

We had the mill connected up to grbl and that worked pretty well, but when we connected it to the PC via the hacked up parallel to Spectralight cable, it gave really jerky movement. After an hour of poking around we figured out that the PC parallel port just doesn't have enough drive for the controller. That's a pretty common problem with on-board parallel ports, but I was hoping it would be able to drive the optoisolators in the Spectralight controller.

We're trying a PCI parallel card now.

Mendel X assembled

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.

Prusa Mendel frame

Assembled a Prusa Mendel frame tonight. Still need to get some smooth rod for the X and stainless threaded rod for the Z screws.