Hot End Fail

I’ve had a bit of a break from my RepRap project recently, mainly caused by my disappointment when my first hot end lasted all of about 1 hour continuous printing before failing. It looks like the force of the filament being pushed down into the barrel was sufficient to cause the threads to slip on the PTFE interface. Probably partly due to heat making the PTFE more compliant. It does look like some plastic has made its way into the thread, but I’m not definite that it’s not just remnants of the PTFE tape. I’ve ordered the new design hot end components so looking forward to assembling that.

Meanwhile I’ve made a couple of adjustments. I’ve moved the USB connection from the top board to the lower board next to the power connection, I’ve added a switch (salvaged from a broken kettle) to the 12V power, and also added an LED strip to the underside of the upper board which nicely lights up the build area. Although I am now starting to think that it would be better to have all the electronics encased in a project box and have the rest of the machine stand alone.

I’ve also been working on a side project; using my android phone as a remote control for my Samsung TV using an Arduino connected via Bluetooth. It worked a lot easier than I thought and showed me how simple (and cheap) it could be to add wireless capability to any Arduino project. Documentation is a little sparse at the moment but hoping to add more soon, but if you’re interested the info can be found here:


http://sites.google.com/site/jsrsprojects/androidir

First Almost Print

Just thought I do an update on my initial testing of the machine. I was quite pleased that I have managed to get everything wired up correctly and the extruder heated up. I have spent a while trying to level the bed, a job that was more tricky than I imagined. I am not really happy with the way the bed bolts to the y axis plate. On the Prusa design there is a nut above and below the y plate, I find this a bit annoying when adjusting the bed level – I have to keep adjusting both nuts, I can’t see why there can’t be just one nut below the plate, I might test it out at some point.

At the moment I am using RepRap host but I have also been testing with ReplicatorG to see if that will work. I can connect with ReplicatorG fine using the “experimental” Mendel machine profile. The control panel jog’s the axis (although sometimes the distances seem a bit random and sometimes it moves 2 axes instead of just one). The control panel also controls the temperature of the hot end fine however it does not turn the extruder stepper. When I try and print an object with ReplicatorG it starts ok, but then extruder starts to cool down, it doesn’t seem to control the extruder temperature. Not sure how to access the temp settings, I assume it might be part of the Skeinforge profile, but not sure how to get to that at the moment.

With the RepRap host things are working pretty well. Below you can see my first attempt at printing the 40mm test cube object. As you can see I aborted the print part way through, the object is less of a 40mm cube and more of a 40mm filter. The extrusion seems to be patchy, and thin even when it is extruding. I think this could be caused by a couple of things. First my “hobbed” bolt on the Wade’s extruder could be not gripping in certain areas – or the springs set too loose. Second I might not have set the extrusion length correctly (the steps per mm value) so not enough filament is being supplied for the required extrusion. Third the temperature could be too low causing a blockage as filament is being melted. See the picture and video below and let me know if you think you know which of these it is. At least the x and y dimensions seem to be correct!

Another thing is the extruder stepper is getting HOT (on a long print I think it could get damaged), I have tried trimming down the pot but to get the current up enough to turn the stepper. I have decided to use a Pololu for the extruder stepper in the hope that the stepper will run cooler (and quieter).

Settings:

Host: RepRap Host
Electronics: Techzone Gen 3
Temperature: 200°C
Material: Black PLA
Extrusion Steps/mm: 2.508

From Mendel

X Axis Belt Tension

I noticed I little lashing on my x-axis, it looked like it was being caused by the slack in the belt. The tension is set when first using the clamps, keeping the belt tight whilst tightening the clamps is a little fiddly. So I decided to try and improvise a tensioner. I looked around the house for torsion springs that might be suitable, I found a promising one in a cheap clamp (Tesco DIY little hand clamps). The un-tensioned legs of the spring were set to about 110° apart, and had long legs that I could bend around to hook onto the belt. The spring works really well in keeping tension in the belt, I might need to do some more reshaping or use tape to ensure that it stays in position in the long term. Here are some pics:

From Mendel

From Mendel

From Mendel

From Mendel

Adrian's Geared Extruder Build Part 1

The RP parts I have are for Adrian's geared extruder see the wiki here. For this you need some pats not listed on the original BOM list. There are a couple of different screws you need, nothing hard to find on ebay. Main parts you need are a short piece of M4 threaded rod. An M4 "Insert" - this is a splined piece used to grip the plastic filament. An M4 wing nut, and 3 bearings. The splined piece I got from ebay here is a bit different to the one shown in the wiki but serves the same purpose. It doesn't have a grub screw but it is internally threaded so should stay in place with bolts either side of it. It was listed as "Ripmax DYCO M4 x 0.7mm Coupling Insert" looks like it is used in the clutch mechanisms of model cars, trains etc.
After a bit of drilling and shaping the parts seem to fit together ok.