Sunday, September 7, 2008

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.

Saturday, September 6, 2008


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.

Tuesday, September 2, 2008

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.