Temperature Sensor, Frame Design and News

Last post I said I would get my thermistor temperature sensor working by the next post (ie this one). I have it working but its not calibrated and thus gives the temperature a few degrees out.

The picture above is a bit deceiving as the thermometer was next to the heat sink in the background as there wasn't any other position that I could take the picture without the LCD being white from the light, and thus is showing a temperature higher than it should have. I'll calibrate it soon but I've had some ideas about the frame and other mechanical elements of the printer so I'm having a small break from electronics. One last thing though before I start talking about the mechanical elements is that for getting the temperature from the thermistor, I'm using linear extrapolation of points along the equation (equation stated in the last post).

This graph shows the points I'm using. There is an orange line connecting the points to show that they are basically the same as the real equation. The calibration I'll use will be to get a more accurate reading on the resistances and if necessary, shifting the graph left or right.

Now back to the mechanical side of things. I changed back to a mechanical state of mind as I have drawings surrounding my desk and one of them had a problem. This was how to physically connect the wheel to the carriage. I already had how it was going to work in theory but had not thought of how to bolt these parts down. So during the week I had a moment of inspiration and came up with how to fix this.

The squiggly line is the spring which is screwed down to the carriage, while the supports for the week are connected to a block that is then screwed to the carriage once again. No sooner had I thought up this solution, had I realised a much better way to do the carriage in total.

This came about as once the carriage was designed, I had realised I needed to work out how to have the Z slide work. At this point I decided aluminium profile was the best option again. Then the idea struck me that I should be using a linear bearing style slide.

This basically works by pulling down the carriage onto the metal and slides along the metal. Its far far simpler to build and is more accurate. This I understand to be similar to dovetail bearings used on industrial machinery. As dovetail bearings use cast iron, it would be too heavy and expensive to use dovetail bearings for this project. This is design allows easy ways to bolt on bits to the side such as the drive shaft. Talking of which I'm still hoping on using ball screw but I think now, I will build it without and then will later add them as an improvement.

After redesigning the carriage I decided I would do a better drawing of the frame in total as the previous ones I had were very rough.

With this new carriage design, I think they should be strong enough to cope with moving the entire frame so I'm going to try and use them to slide the frame rather than moving the print. After drawing these and talking to my father, I'm thinking I might use ground rods for the X slide (not named as I rubbed it out when I drew the plate holding the two sides together). This is so I can have the head of the extruder (and other tools) in the middle of two slides/rods where its much easier to attach a motor and the rest of the components rather than having to work round a box between the motor and components on the other side as I would have had to with the previous design. I'm still planning on using threaded rod/ball screw rather than a belt driven system. I'm hoping to do a basic mock up in inventor in the next week to get a better idea of how it will work.

In other news, my book on doxygen turned up. It was just a ripped off version of wikipedia, I think someone was just wanting some quick cash. So I printed out the doxygen manual, all 200+ pages, and I'll start reading it soon.

I was watching ABC 24 (a 24/7 news channel in Australia) and a story came on about 3D printing. It didn't say much but was good to see the style of manufacturing getting onto mainstream media a bit more. Here's the video:

I've decided I would like to print some Lego-like figures out for testing once I've built the printer so in the next few weeks I'll hopefully measure and create Inventor models of Lego Minifigures. This will also be a nice break from other parts of the project while still helping me improve my skills on inventor.

Finally, University goes back next week which will be nice, thus I've had my last shift of work for the time being. I'm not sure if this will mean more or less time able to be spent on this project, but I'm hoping more as I can spend lectures using CAD and reading up on background information such as GCode.