Wednesday, July 11, 2018

Desktop thermometer

My office at work gets quite cold some days, and I wanted to know how cold. Also, I was at a loose end over the long July 4th break and looking for something to do. So I knocked together this project:


Inside the box there is an Arduino Nano, and a DHT11 temperature sensor, plus a 10k variable resistor to set the display brightness. The display is a 16x2 LCD. It displays the temperature and humidity and the range of temperatures it has seen. The readings can take a little while to stabilize, so until they do the C and F are displayed in lower case, and the % for the humidity is shown as H. The Arduino sketch is here, and the comments in this file also say how to connect it up. You might need to install the DHT library from Adafruit (info linked from this page). It uses a USB connector for power.

I designed the case with Fusion 360. It holds together with friction. I undersized the hole for the DHT11, meaning it's not quite large enough for the sensor to stick out. Rather that spend another 90 minutes printing a replacements, I just attached the DHT11 inside the case with hot glue, which works fine except that it came out a bit skew-whiff. But that's how you know it's home made.




Sunday, April 29, 2018

High altitude printing

Recently, I was printing a frame with a tall arch shaped part to it. The designer of the object  provides a version with built in support and one without. If I allow Cura to generate the support for the one without, the printing time is a lot less, so that's what I went with.

It was all going well until the support detached from the build plate. The printer then merrily continued, dumping the support material into thin air, where it gradually turned into a big pile of print snot. It is complete coincidence that I was using a green filament.


I trimmed away some of the slot and let it keep going. Amazingly, after a while, the printer managed to re-establish a bridge across the arch with a few layers of support to go, and get to the end of the print.
Here's the print with the snot that I trimmed away and the support that came loose.
After removing the support and the rest of the snot, the results are a bit ugly, but not too bad.

Sunday, April 22, 2018

Forcing variable layer heights in Cura

Recent versions of Cura have an experimental feature where it selects different layer heights according the slope of the model. As the slope changes from vertical to horizontal, it uses a lower layer height to get better shaped prints. Imagine a dome, where the later height gets smaller as it reaches the top, and you'll get the idea.

I have a piece that I wanted to print where I wanted most of it to print at 0.2mm or 0.3mm to keep the print time down, but wanted a small vertical extrusion to print at 0.1mm for strength and precision. As the extrusion is vertical, this won't trigger the adaptive layer heights.

A simple solution is to add a second object which has a dome at the same height a the extrusion. As the same layer height is used across all the objects, the low layer height needed for the dome also applies to the extrusion, while the remainder of the model prints quickly. Here is a screenshot from Cura to illustrate what I mean. I know it's a bit tiny; for a bigger version, look here. In short, the dark blue is 0.1mm layers and the yellow is 0.3mm.


Saturday, March 31, 2018

CoreXY frame

Continuing my noodling around from last week, I started to put together a frame for a CoreXY system. I could have done the right thing and designed this in a CAD package, got all the measurements right, blah-di-blah, but instead I'm just winging it and knocking together what I need in Blender. Here's the frame with motors and runners but no belts yet:
The motors are mounted on plates bolted to the bottom of the frame with spacers to raise them to the right height. These corners of the frame have internal L-shaped brackets.
The gantry is mounted on brackets with runner wheels:
They move quite smoothly, though I think the brackets will bend over time.

For the pulleys, I'm going to use flanged bearings. I really wanted ones with a 5mm inner diameter, but I would have had to wait a couple of weeks to get them, so I bought some with an 8mm inner diameter and added a insert.
I ran out of 5mm washers, but there is an easy solution to that:
The next stage will be to get all the pulleys set up. The motor height is designed to work with pulleys mounted on top of the gantry with a 30mm bolt as you can just see in the video clip. For the pulley fixed to the frame, I'll need a mount to raise them high enough. More to follow.

Sunday, March 25, 2018

Motion systems

I'm starting to play around with motion systems. I have no specific goal in mind: it's just noodling.

Here is a small testbed using a MGN12 linear guide that I bought for a printer upgrade and then never used, together with some parts salvaged from my now-defunct Folgertech printer and a few printed parts. There are printed T-nuts under there, though you can't see them.