More Mods

I've almost got the machine to the "set it and forget it" point. It's more like: set it, watch to make sure the first layer sticks properly and check once in a while to make sure it isn't completely messed up.

Here are some recent tweaks...

Floating bed, mounted on 3 springs and held down with bolts. Makes leveling a lot easier. Also takes some of the pain out of a head crash.


Z opto guide (the blob of polymorph). It's essentially an inverted V with the opto's gap at the apex. Keeps the Z opto flag from running into the opto posts.


Drilled a hole through the shaft couplers (both Y and Z) and inserted a pin.


Added a lubricator (oily rag) to the filament guide (bent paper clip).


Two-ply balsa raft (two sheets of balsa glued together cross-grain). Held down with carpet tape. I tried using antistatic foam but it works a little too well. It's extremely difficult to remove without ruining the foam.

Adjustments

Filament wasn't feeding at a consistent rate. Eventually figured out that the drive coupling was slipping relative to its gear. Had to remove the gear assembly to tighten it (added a bit of superglue to keep it in place) and took the opportunity to add grease to the gear motor internals.

Also noticed an increasing about of drift on the X axis. Tracked that down to the X motor pulley working itself loose. That was a bit more difficult to fix. Didn't really want to disassemble the X motor bracket just to tighten the set screws. Managed to achieve the same result by rotating the pulley until the set screw lined up with the X axis, then slipping an allen wrench between the belts. Did this for both set screws.

Currently trying to print a "motor holder" onto an antistatic foam raft.

Bed Covers

I've been experimenting with various raft materials. The MDF bed isn't suitable for a build. The melted plastic doesn't stick to it. What you need is something that sticks to the Here's a list of things I've tried:

Polymorph (ShapeLock)
- easy to use, sticks well, reusable
- heat from extruder softens it, allowing warping
- hard to get perfectly flat

Adhesive Paper (full-sheet labels)
- sticks to bed
- plastic doesn't stick

Adhesive Plastic (self-adhesive laminating sheets)
- sticks to bed
- plastic doesn't stick

Plastic Canvas
- doesn't work at all

Carpet Tape
- sticks to bed
- plastic sticks but not well enough to prevent warping

Balsa Wood (1/8" sheet)
- plastic sticks well provided first layer is low enough
- curls easily across grain, allowing warping

Balsa Wood (2 sheets glued together with orthogonal grains)
- plastic sticks well provided first layer is low enough
- minimal warping

I found it's critical to have a perfectly level bed. In order to get a good first layer, you need to get the nozzle extremely close. If you get too close, though, the nozzle will dig into the surface. This is especially bad if the head is moving in the negative Y direction. In that case, the surface catches the nozzle and drives it downward, resulting in either a gouged surface or a damaged head.

One thing I've been meaning to do is add a Z-bed like the one shown here. It's basically a secondary bed mounted on springs. This will allow easier adjustment and should also make head crashes less painful.

I also need to replace the Z opto flag with something a bit less flexible. There's a tendency for it to slip to the side a bit and miss the slot on the opto. Also, if I'm adding the Z-bed, it'll need to be longer anyway.

Best Laid Plans

Tried printing the "motor-holder" model. From left to right: 1) Y belt slipped a bit, 2) Y belt slipped a lot, 3) actually printed reasonably well.


This a first attempt at "gear-bush-holder", which I modified (hopefully correctly) to print without support. About 1/3 of the way through, the Y motor coupler came loose.

Mod Squad

Some modifications I've made...

Blobs of polymorph on the X and Y carriages to keep them from wobbling so much...



A bent paperclip to keep the filament out of the way...



A piece of plastic tubing clamped to a bookcase to feed the filament...

Growing a Part

Tightened up the X and Y axes a bit to keep the head from wobbling. Started on a motor bracket...



After a few layers, the Y axis skewed and I had to stop the build. Two things seem to be happening here:

1. I've set the layer height too small. After a few layers, the nozzle is dragging through the work.
2. The Y belts are too loose, causing them to skip off their drive pulleys under load.

The net effect is that the build runs fine for a few layers, then slips in the Y direction.

Tightened the belts and adjusted ExtrusionHeight. Will try again in the morning.

Supply and Demand

I tried printing off Vik's RepRap ring today...


...which the kids thought was really cool...


...so, to avoid sibling infighting, I had to make a second one. I imported the STL into Art of Illusion, converted it to a triangle mesh, scaled the mesh by 0.75 and exported the model as a new STL. This gave me a new ring at 3/4 size...


...for little hands...

The Ascent of Mug

Some attempts at the minimug model.

Containment

Found that my Y axis was slipping on one side. Tightened the Y belts, X belt and all of the pulleys. Realigned the Y axis. Adjusted the infill width from 1mm to .8mm.

Melted some ShapeLock and made a 3mm-thick raft, attached it to the print bed. Started a new build.

Got most of the way done and realized I was running out of filament. Did an "in-flight refueling" by patiently holding a new piece in place until the drive screw grabbed it.

Waited for it to finish printing (about 1 1/2 hours). Soaked in hot water and peeled off the raft.

Cleaned up the lumps and threads with a Dremel.

Here's the result. It may not be pretty but it holds water. Or, more to the point, it holds single malt. Cheers.

Zeroing In

After months of trying to get the original extruder working, I finally gave up and got a new one. Someone (I won't mention who, to avoid them being inundated with requests) took pity on me and sent me a fully-assembled and tested extruder. This one has a number of refinements over the original:
- the drive screw is straight, no flexible shaft
- the motor is geared down to improve torque
- the nozzle is smaller, machined from brass stock instead of an acorn nut
- all wires are soldered to a 15-pin D-sub connector

Another thing I noticed is that the springs are much heavier on this extruder. I'm not sure how important this is to the operation of the extruder but I suspect it's responsible for at least some of the problems I had.

I haven't opened it up yet but I suspect the bearings are done better than I managed as well.

Once I wired in the new extruder (I had to get my hands on a female 15-pin D-sub), I tried a few extruder tests, calibrated the heater and measured the extrusion rate.

The extra gearing makes a huge difference. The motor isn't under as much strain and the flow is much smoother. I'm currently extruding ABS (from McMaster) at a leisurely 3mm/s. I could probably go faster but I don't want to strain the PTFE barrel.

I need to update the PIC firmware and host software at some point but I want to print a complete model first. Trying not to change too many variables at a time.

Last night, I managed to get an entire shot glass printed. My infill is a bit too loose, so it leaks. It also looks like the Y axis slipped a bit part way through the build.

It's close, though. I suppose I should pick up some scotch at the liquor store, just in case.