Sunday, 15 July 2012

Filament cleaning sponge...

As I blogged earlier today I had ordered some new black filament from Faberdashery. I was in the process of changing out the white filament as I want the black I ordered in the printer and thought I would take a look at my wiping sponge.

Dust from 200m of filament
I saw one of these on the printers at Bath when we built Huxley #710. I was chatting to one of the guys busy printing a Parliament of Owls. He told me that the filament has or tends to attract lots of dust. With the amount of printing he does, he found that it made a big difference.

I don't consider that I do a huge amount of printing but clearly there is quite an amount of dust and fibres that might block the extruder and contaminate the extruder mechanism.

Obviously if it doesn't get stuck somewhere,  it ends up in the plastic.

Tesco pan cleaning sponge
The sponge was peeled from one of those cheap rectangular cleaner sponge pan cleaning pads. But I imagine any foam will do the job nicely. I just wanted some white foam so I could readily identify if it was doing anything.

The sponge is simply wrapped around the filament and held in place with a cable wrap that came keeping one of the cables neat and tidy during shipping.

There are designs out there on Thingiverse such as this for example.

Some Stuff ...MH-201 3v Electric Motor Model

There are a few things that don't get to the Blog for a number of reasons. This one is part of an idea for example. In the past I used a note pad or paper for ideas and that's still the case for the early start of an idea. But now people expect at the least a rapid prototype, preferably with basic functionality.
Hing Lung MFY MH-201 Motor

So as part of that project here is a spin off that can be placed in the public domain. An MH-201 STEP 3D motor model.

The motor was supplied in the Sparkfun Inventors Kit that I purchased for my children last Christmas. It has an Arduino in with all the sorts of bits anyone with any interest in electro mechanical ( Mechatronics ) bits should have.

As best as I can tell from my research the motor was manufactured by the Hing Lung Motor MFY in Hong Kong. However I was unable to locate a CAD model for it to allow me to design a bracket ( a rather non de script name for the unit ) that I need to design and subsequently print
Sparkfun Inventors Kit

As I wanted to post the CAD file as well for the Blog I ended up creating a Google account. So I will use the Google account for all things public. The STEP model being the first of these. As it's a 3D Solid model it can be tweaked and imported readily into most CAD systems whilst retaining a significant degree of fidelity. If you find a better model please let me know.

I ordered some more filament from Faberdashery last week. I have ordered some black this time as well as white. Delivery was amazing and sneaked in the bottom was a lovely sample of clear plastic filament. It's not a material I would have tried but now I have a sample I will certainly try it out.

One of the more public developments is the seed of an idea for a remote processing system for a 3D printer under the currently rather cheesy name of RepRapS. This is indented to remove the burden of processing for the user, drive down cost and perhaps allow single click printing (possible with innovations such as Ooze free unattended start ).

Of interest is the report on printing using mixed colour filaments by one of Adrian Bowyer's Masters students Myles Corbett's report, you can find it here.

Sunday, 1 July 2012

Hot End Resisitor Fatigue...

After about 300m of PLA the hot end resistor gave out mid print today.

Now using the Marlin software, the machine stopped the extrusion stepper motor with messages indicating extrusion prevented due to low temperature. For a few seconds, before I saw the message I was confused as the machine kept merrily describing the print path. For one heart stopping moment I thought the stepper extruder driver or motor had died!
RepRap Pro Hot End Resistor Comparison

Having seen the message, I paused the machine and got my multimeter out to check the supply voltage and the resistance. The supply voltage was 19v D.C. whilst the resistance was in the Mega Ohms.
  
The poor little resistor beastie is open circuit and had to be stripped out from the hot end block. Having let everything cool and removing the hot end from the heat sink, a few taps with a small hammer and punch removed the little chap from its home.

When being fitted in Bath the resistor was very snug and then managed to wedge itself firmly into position. I spent a good while reviewing what I was going to do about the resistor and the risks entailed. This was one of the contributory factors that led to the machine not being completed before leaving. As they say measure many times and cut once, I should have filed some more I guess.

The issue is that the coating is easily cracked allowing moisture in and if the metal caps at the ends of the resistor contact the aluminium block, the resistor wire wound on the ceramic carrier is effectively shorted out by the hot end aluminium block.

So having assured my self the resistor would function as was, I elected to continue at the time. There was a lot of filing at Bath and attempting to file a round hole, even for those of us skilled in the art, is tricky over a length of 14.1 mm {the blocks aren't quite regular ;-) }.

The holes on the hot end blocks were too small and from that moment on I suspected it would fail at some point, I simply didn't know when.Well now we know.....

You can compare the two resistors both of which are RepRap Pro of the same batch supplied in Bath. Note how the coating and resistance wire on the failed device have changed.

There are two high points on each end of the resistor in the vitreous enamel over metal end cap diameters that are 4.99 mm; which is probably why the original stuck in the diameter of the 4.89 mm of the RepRap Pro hot end.

I passed a 5.00 mm drill through the hot end during the re-refurbishment, which allows the new 6.8 Ohm 5% RB59 (3 watt) resistor.

So we will order some more resistors and see how long this beastie lasts.

RepRap Pro Hot End Pack (April 2012)