Quick and dirty extruder design

Combining several recent ideas from the forums, I've put together a quick and dirty extruder design. It uses many of the labour-saving tips (welding tips, the BfB 'big washer' design, Nophead's excellent resistor work) provided by others.

The PTFE runs right into a copper pipe end stop, which has an M5 drilled and tapped hole to allow a welding tip to be screwed in. The welding tip is *carefully* drilled out to provide minimal resistance to the extrusion.

Heat is provided by 2x 12Ohm resistors (wirewound, 6W, max 350degreesC) wired in parallel (which I reckon should give me a 6ohm load). Two resistors - one for either side of the nozzle - and they're squashed between the copper pipe end, nozzle, and a big washer on the bottom.

The big washer provides support to the PTFE barrel and is attached to the motor through long bolts.

I'm now soliciting any comments or advice before having a go at building this.

Possible problems:

• ABS melt leaking along the side of the PTFE join?
• Not enough thermal inertia to keep the melt hot?

Possible improvements:

• Pack the gap around the resistors with FireCement to improve heat conductivity?
• Use silicone 'washers' to help seal the joint between PTFE and copper pipe?

Any comments or suggestions welcome.

My Reprap

Added some static pages describing My RepRap and my current setup. I'll post updates and built objects on the blog too, but it's sometimes easier to have a static list. I've added some pages for planned/built objects and ones found on the web.

My 'Workshop'

On the RepRap forums, there are several users who have access to some pretty good workshops, either using college or school facilities, even those with lathes and CNC machines at home.
I'm not one of those users.
Here's a picture of my workshop:

It's my dining table, covered with an old curtain. I have a box of tools containing the following items:

• several small screwdrivers
• allen keys
• some small pliers, needle nose and flat
• two small wirecutters
• soldering iron, stand, helping hands
• some small needle files
  

I've also got a garage full of junk, but it's also got a black'n'decker workmate, and some standard DIY tools,including a small hacksaw and electric drill.

That's about all you need to build a RepRap from a BitsFromBytes kit. Obviously, if you have a full-size workshop, things are much easier - but my RepRap sits behind the TV most of the time. Building from scratch or from a RepStrap would probably be a bit messier and needs a bit more time and equipment, but building from a kit can be done in your living room.

It helps a little if you can dedicate some space for a permanent setup (a boxroom or office would do nicely) but my RepRap is sturdy enough to get it out when I'm experimenting and put it away between times.

Choi Hawarang Do

I've just finished a session of Choi Hawarang Do at the Martial Arts Leisure UK. It's a martial art, based on effective self-defence and personal development - a really positive direction.
Inital impressions:
Everyone was really positive and friendly. Right from when I first walked in, Jenny , the assistant instructor, was welcoming and helpful, and everyone was willing to help along a new person, explaining what was going on and making sure I was OK. I was surprised and pleased at the mix of ages and people there - there was a good selection of older and younger students, right down to age 10 or so, and several ladies. There was none of the 'macho' atmosphere that is sometimes associated with martial arts and it all felt warm and friendly.

After the standard line-up and introduction, we did some guided stretching as a warm-up, and then onto the lesson. I was quickly paired off with one of the senior grades to show me the basics of the stance, and a basic block, punch and kick, and to run through the first block/punch/kick sequence. Once I'd shown that I was no ninja by wobbling through the simple kicks and punches, we rejoined the main class for a 2-on-1 exercise - where you simulate two 'attackers' (holding pads as targets) against one defender. After a few minutes, there was a quick break for a drink of water and then we ran through several self-defence techniques, including getting out of a headlock, a choke hold and a bear hug. A final line-up ended the lesson.

It made me breathe pretty hard at a couple of points - perhaps I shouldn't have spent the last couple of years on the sofa watching TV. That's good, because I needed a bit of exercise.

I'll definitely be back next week.

Configuration of XYZ axes

I spent some time writing a long blog post about some testing and configuration, and then realised it was almost a set of instructions. I re-wrote a few lines and posted it on the RepRap Builder's Wiki, in case it was useful for anyone else. You can find it here:
http://objects.reprap.org/wiki/Builders/Config/Getting_Started
and a couple of pages here:
http://objects.reprap.org/wiki/Builders/Config_Methods

Basically, I've configured the X, Y and Z axis, so that if you tell them to move 10mm they move 10mm.

I did find that the x-axis stepper was slipping, as the x-axis wasn't consistent. I disassembled the stepper and took off the grub screw. I filed a larger flat on the shaft of the stepper, and re-assembled, making sure the grub was tight on the flat. It moves much better now.

I have just started to test the extruder... more soon.

It's alive! It's alive! The beast is alive!

I finally got round to applying the electrodes and waking the beast from it's slumber (I plugged in my RepRap).
It's been stuck behind the TV for a while until I had a free evening to start configuring and testing everything. I spent an hour sorting out an Arduino communication issue (I'd foolishly uploaded the firmware compiled in test mode, and it kept saying 'start' down the comms channel).

Using ReplicatorG, I was able to jog the x-axis a little back and then forth - which worked!
I then wiggled the y-axis a bit - and that worked too! Then Z - both up and down worked!

With my hand on the PSU power switch, I gingerly pressed the 'home' button for the x-axis. The x-axis moved back to the home position, triggering the endstop and stopping on it's own! Then the same for Y - and Z - Things are going really well!

I spend a few more minutes winding the x, y and z back and forth. All was well until a z-home caused the wobbly z-flag to hit the side of the endstop, meaning the bed tried to ascend to the attic, winding itself into the print head on the way. The z-axis on the motor slipped, meaning that the bed was badly skewed before I got to the power switch. The z-belt also fell off.

I put it back together again - I don't think it's damaged but it gave me a scare.

Note to self: Hand on panic button ( the PSU power switch) until I'm really confident it's working.

Java! Reprap Host software!

I spent most of the weekend getting the official host software working. The 'host' software is written in java, and uses several external libraries. After lots of fiddling, I got it working. The biggest problem was getting the RXTX libraries - I had set the LD_LIBRARY_PATH but I'd misspelled the directory name. The java software compiled OK, but didn't run as the native .so files were missing.

Once I'd got that running, I was getting preference file errors - all sorts of missing settings. Eventually tracked that down to a reprap.preferences file in ~/.reprap that came from a previous attempt early last year - well out of date. I replaced that with the latest reprap.preferences.dist and all was well.

The latest software looks much better - a better UI, and easier to understand controls. Skeinforge looks great for complete end-to-end prints, for dumping 3d models to a configured system, but the host software has easier options for configuration and testing. I've still got a bit of tweaking the options to match my setup.