Saturday, June 06, 2015

3D Printer Project, Part 6: Joining The Dots

First, I need to note a duh moment regarding step 10. I damaged one of the linear bearings in this step, but decided to proceed anyway, as it still seemed to move OK on the chrome rod. I forgot that Folger include two spare bearings in the kit. By the time I realized this, I had completed several more steps and didn't want to undo them (including taking the end pieces off the Z carriage). Maybe I'll fix it later.

Step 12: attach the chrome and threaded rods; 5 mins. Easy.

Step 13: front pulley; should have been 10 mins. I forgot the M3 washers at first and had to redo this. The parts list includes two M4x8mm pan head bolts for this, but they aren't needed as they were already attached earlier.

Step 14: attaching the Y belt; about 20 mins. Most of the work in this was trying to get the belt even across the Y motor, the pulley and the Y belt carriage. The position of the last of these in the X direction is fixed, so I took a measurement from it to the side extrusions (170mm from the end of the belt to the inside edge of the extrusion). Then I adjusted the position of the motor and pulley to make this the same. This puts the back of the motors right up against one of the chrome rods, and puts the pulley off center. Both of these seemed odd, but are consistent with the pictures in the construction guide.

Step 15: attach the couplings and SHF8UU; 10 mins. Easy. A tiny error in the guide: it says the M4x14mm bolts are black, which they aren't.

Step 16: attach the X/Z assembly; about 50 mins. To raise the motors I had to completely remove one of the screws holding each motor mount to the uprights. I found it easiest to lay the whole printer on its back while I worked on this step. It went together fairly smoothly on one side, but the other one didn't quite line up. I found that loosening the screw on one of the L pieces underneath the top bar meant I could move the upright in by about 1mm, and it then all fitted together nicely. Doing this also made the motor shaft and the threaded rods looked straight (coaxial) with respect to each other. You probably can have it slightly unaligned and be OK: the point of the helical couplings is to allow this. After tightening everything up, I manually turned the couplings to move the carriage all the way up and down the X axis, making a point of turning both couplings at the same time to keep it level. This proved to me that the alignment was good enough. Step 16 is the trickiest step since step 10, and it left me with a sense of satisfaction. It is just about the end of the mechanical construction, and it's really all come together.

Steps 17 and 18: power supply and acrylic mount; 10 mins. Easy.

I started on step 19, but was pretty unhappy with the quality of the RAMPS board. Here is what I wrote on the forum:
The quality of the RAMPS board is really horrible. Firstly, it was badly packaged, so that the power transistors and the two large capacitors were bent over. The pins on several of the connectors were bent out of shape. I've straightened them up, but it means extra care when attaching the other parts to it.

Worse that this is the quality of the soldering. There are two diodes which are not flat to the board. They are floating in mid air about 15 mm above the board. Then the really nasty bit. Turning the board over the solder side shows:
- many solder bridges. I picked off at least 10 with a scalpel plus as many other random blobs of solder in places they should not be.
- the board is covered with the resin (flux) from the solder. This tends to degrade the board over time. Back in the days when I was an electronics engineer building embedded systems, we would not have allowed something like this out the door. We would have cleaned it with Arklone first.
- many of the solder joints are dull and blobby, the hallmarks of a dry joint. I will go over those with a soldering iron before using the board.
- a few joints which were not soldered at all.

I decided to order a new board on next day delivery from Amazon, as I just don't trust the one that came with the kit to work without risk to the other components. The last thing I want is for a solder bridge to send 24V onto the Arduino board.

The other components look OK, apart from some damage to the Arduino board, again due to poor packaging. Two of the header sockets were bent over and the plastic shroud was not pushed down on the pins. This was easy to fix.

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