Archive for September, 2010

Update for the sake of an update.. State of my Mendel

Monday, September 20th, 2010

Enough time has gone by since my last post that many are wondering how things are going and why I haven’t updated yet, so I’ll post this update just for the sake of an update, rather than waiting for a moment-worthy moment. Work and the release of Halo: Reach aren’t helping either, so I might as well post this stuff now.

At the time of my last post, I’d just had my original non-geared Mendel extruder push the heater barrel out of the PTFE which was JB-welded to it (preventing me from easily fixing it). Here was what the barrel looked like:

And here a picture of the whole thing just lying on the bed:

I could have heated up the barrel outside of the PTFE to melt the PLA, pulled it out and cleared out the barrel the best that I could, and then use a soldering iron to melt some of the PLA in the PTFE, but I’d still be left with a PTFE insulator whose inner threads already deformed enough to let the heater barrel escape.. so I’d still have to try removing the PTFE (even though it’s JB-welded into the extruder). I’ve read some hints that that can be done with a chisel, but that didn’t sound too fun.

While I still may do some repair on that extruder down the road (as a backup), luckily I didn’t have to go down that road. Spacexula offered in the comment section of my last post to send me the printed parts for a Wade’s extruder (since I had the rest of the hardware ready already) as long as I agreed to print out and give away two once I’m up and printing. Since I was going to do that anyway, it was easy to say yes. One quick paypal for shipping later, this arrived in the mail:

(Thank you, Neil!) The four parts on the right were the parts for Wade’s extruder, while the others on the left were extras worth having spares of to help fill out the box and justify shipping. More pics:


Those bottom two holes on the last picture are where you screw in long M3 bolts that go through the PTFE insulator, so you don’t have to glue it on, so I won’t be in the same situation I was in with my last extruder.

One other picture I wanted to show (ok, two) before going on was the cool look of how the bottom flat part of the large gear looks from how this part was printed (on a shiner surface than the masking tape I’m using, that’s for sure.. Probably kapton or PET, on a heated bed?):

Ok.. So here’s what the back of the extruder looks like when assembled.

The idler bracket is the piece on the right, held on by four screws. There are supposed to be springs on there – the springs I bought from McMaster must have too many coils or something, because when I had the springs on there was no way the bolts would reach the trapped nuts on the other side.. I need to find suitable springs, but the springs aren’t 100% necessary (they even out pressure when the diameter of the filament changes or turns, etc).

The nut shown above was a temporary M8 nut I used initially until I had everything going, but I eventually replaced it with a nylock M8 nut so it’d stay on through the vibrations.

The big mistake here was even mounting the motor at this point at all. You need to mount the extruder on your Mendel first, before mounting the motor within it, because the screw sits directly below the motor (which was actually a problem for me, fitting the motor in, but I got it to work).

More pics.. Here’s the front of the extruder. The stepper motor shaft (with a flat filed onto it) can be seen in the middle of the small gear on the right. That turns the large gear on the left, which has a large M8 bolt trapped in it (the same one you saw a nut on in the back picture). Two skate bearings in the structure hold the nut so it can spin. The nut has a knurled notch cut into it, which I don’t think I did a very good job of, but it does the job at least for now. The plastic to be melted gets pushed between that M8 bolt on the big gear, and the third skate bearing in the idler block which is held on as seen in the pic above (with the four bolts that should have springs).

Here’s a close up of the bolts holding the PTFE insulator into the extruder:

And here’s a picture showing the two gears meshing from the side. Here you can see the filed down stepper shaft (knew I’d use that skill again), and the grub/set screw going through the trapped M3 nut in the gear to dig into that flat in the shaft:

I put it all together (without the heater barrel assembly) to see if the M8 bolt I’d cut could grip any plastic at all. It turns out it was good enough. Here is the motor just turning the gears:

…and here is the extruder actually pressing plastic filament through the extruder (again, without the heater barrel):

Ok so now I needed to create another heater barrel (so I could leave the one in my original extruder intact). I had two unsuccessful attempts at drilling out M6 rods – they came out way off to the side at the bottom. I spent a few days fixating on finally getting around to buying a mini-lathe, until I read up on what the differences between a wood lathe and a metal lathe were, and saw that a metal lathe would cost me at least around $400-$500. So I resisted that desire by doing what I’d attempted to do before – hollowing out a heater barrel by putting the barrel itself in my drill press, and lowering it onto a fixed drill bit (now an M3 bit, since I just purchased a metric drill bit set recently.. no more converting to imperial measurements).

With the barrel successfully drilled, it was time once again to wire up a heater barrel assembly. I’d previously made a checklist for myself of what tools/parts to have on hand to build one, but that was for the MakerBot RepStrap, so I made another for rebuilding the heater for my Mendel:

..except that those hose clamps don’t fit in the x carriage..

This time it took me 1 hour 12 minutes to get to a barrel in a nozzle wrapped with crimped nichrome, with a thermistor connected, and even wrapped in ceramic tape.

There was no convenient place on Wade’s extruder for me to mount a piece of stripboard with compatible headers for connecting to my Mendel, and I didn’t have the desire to spend lots of money on shipping for a few proper headers with polarized locking connections for this new extruder, so I just used some breakaway headers and created a small unpolarized plug inline to plug them into (which I’d later connect with tape):

I connected it all up again, and finally, I was extruding!

As I said, I was not using the right E_STEPS_PER_MM yet, so the speed was off.

Now with a geared extruder, I printed one mug that filled up 90% with water but then leaked (a JeffTry30 print). Then I did another of an earlier model (JeffTry22) which always looks good but has a horrible leaking bottom. This one didn’t print its shield well, so it resulted in burned blobs everywhere while it tried printing and kept dragging plastic where the shield should be.

I think I need to try using a hairdrier to heat up the bed a little before the first layer goes down, or adjust my z-opto-flag again to mash the plastic into the bed more.

Then one day (I don’t remember how long after that) I read that someone said the value usually used for E_STEPS_PER_MM for a standard Wade’s extruder was actually 2.02, which was larger than what I’d obtained from the spreadsheet I had. That night I got home extremely late, everyone was asleep, and I decided to upload new firmware with the correct value and try printing again.

Here’s a picture of the bottom of the mug being made.. Note the brown spots, because there was way too much plastic being output and the nozzle would plow through it, burning it at points.

Again the shield wasn’t printing correctly but I let it go on anyway. Here’s the ugly result, with a very thick/tight bottom:

That was also a JeffTry30 (but again, now with 2.02 for E_STEPS_PER_MM). I went into the bathroom, and filmed this:

Sadly, the next morning was not a time for celebration. I actually tried filling the mug with my as-of-yet-undisclosed drink, and it sadly spilled all over the table. Now would be a horrible time to find out that alcohol dissolves PLA or something, wouldn’t it? 🙂

Haven’t had time yet since then to print another, and I’m going to be slowed up a bit by events over the next few weeks.

One of which, by the way, is Makerfaire NY, on September 25-26, 2010. I’m up in the Boston area, but I’ll be heading down Friday night (the 24th) with my Dad, we’ll stay at my brother’s, and the three of us will check it out Saturday. Mid-summer I’d considered bringing my Mendel down, but I deliberately let the deadline for registering pass, which I’m glad I did because while deadlines do help motivate progress on projects, they also tend to add stress, and in this case I’d rather see others’ RepRaps and walk around the faire than stand in a booth explaining why I still don’t have it calibrated correctly for a watertight minimug. 😀

So there you go – the most recent state of my Mendel. More later (after I’ve had a few weeks to get a few hundred hours of Halo: Reach under my belt, which is another distraction, but a welcome one). 🙂