Some more progress on the z-axis design:
I’ve set it up for 4″ of vertical movement.
The cart will slide on a single linear axis (rod and brass bushings). A second rod off to the side will only provide rotational constraint to avoid binding issues. The middle rod is threaded, and attached to the stepper. I think the drive rod will seat in a flanged bearing on the bottom rail to take the axial load. At the top I’ll use a flexible drive coupler to attach it to the stepper.
Mounted the electronics, completed all the wiring, and then fired up the bot for the first time:
X and Y axes only for now.
The NEMA 17 steppers are a lot more powerful than I expected. When they are moving, they set up some pretty significant vibrations in a couple of spots. I think I need to start by lowering the power settings. The higher feedrates also seem much smoother.
Can’t wait for the microstepping driver boards 
I completed milling the last stepper mount and installed the motor. The mounting holes were milled as slots to allow for belt tension adjustment. The drive belts are attached to each stage by clamping them between some small aluminum pieces. This seems to hold the belt nicely.
Next, I started work on the endstop switches. I didn’t think about their location when I designed the stages, so of course there wasn’t much room for mounting. After a couple days of fiddling with them, I finally got them attached.
A progress shot:
Here you can see some of the endstops mounted:
Next: Hook it all up and get the motors running.
Made a bunch of headway on the XY stage. Just need to mill the stepper mount for the x-axis and figure out how to clamp the stages to the belts.
A closeup of some mechanicals:
Using bronze bushings/steel rod seems to work well. There is very little breakout friction, and the movement is very smooth. I tried nylon bushings, but the breakout friction was suprisingly large. Didn’t try PFTE at $4/bushing — yikes!
The bronze bushings are finicky — they bind hard unless they are aligned well, which turned out to be pretty easy to do. The only issue I have now is that the 5/16″ rods I received from McMaster were precision ground, which I’ve found don’t work well for linear bearing use. They have very tiny grooves from the grinding process, so when you slide the bushing they buzz. I’ve had better luck with rolled steel, which has larger tolerances but has a smoother finish.
Next: Time to design the z-axis!
My extruder is pretty much complete (except for the wiring):
I milled the gearmotor mounting holes as slots so that the pinch gap can be adjusted.
Unfortunately, I don’t have any plastic to run through it, and Makerbot is out of stock.
Drilling the extruder barrel was a bit of a challenge, but the first one I made worked out great. Here’s a pic of the drilling operation, using a 0.5mm drill bit held in a pin chuck on my mini-lathe:
Completed assembly of the major electronics components over the weekend. Soldering SMD parts was a new experience for me — very cool stuff! First, using a magnifing visor, I placed tiny dabs of solder paste on the pads. Then using fine tweezers, I placed the parts on the board. Once they are all in place, the board is placed on a hotplate until the solder melts.
I am amazed at how nice it turned out. Here’s a pic of some of the boards (and the USBtinyISP which uses conventional thru-hole assembly), along with the solder paste syringe I used:
And after fiddling with bootloaders for a bit… it all worked! Here’s a pic of the whole power supply/controller/drivers/steppers mess printing out a virtual minimug:
I just finished assembling the base/y-axis drive. A couple of pics:
Haven’t hooked up the stepper yet — gotta finish the electronics first.
Just some photos of the first parts to come off my assembly line.
First, a pile of frame brackets:
And then some drive brackets which will accept tiny ball bearings for the drive axles:
I’m making these using a small desktop mill setup for CNC. I’m a CNC novice, so I’m pretty happy with the results. Here is a photo of my setup:
