Rapman assembly part 9

There's not much left to do on the cartesian bot now. I have to mount the Y stepper motor (on the top frontmost corner), one Y drive belt and the X drive belt.

The Z belt took a couple of attempts and a fair bit of fiddling to successfully splice the ends together; the second photo shows the jig I threw together using scrap acrylic and some polymorph. That attempt failed because I tried to do the splice whilst the belt was under tension - whoops.

The last attempt was also nearly a disaster when I discovered that the belt went the wrong way around one of the diagonal rods; I ended up having to completely remove the rod to get the belt where it was supposed to go. And then completely disassemble the belt tensioner that was on that rod, because it was impossible to realign the rod with my measurement jig while it was still on there.

The tensioner is a bit of a problem, because the belt doesn't have enough slack to fit it in the appropriate place! I ended up having to remove some of the nuts in the tensioner to reduce it's profile, and I spliced the belt together with a two tooth gap instead of just a one tooth gap to make it a little looser... and the tensioner barely fits. I don't have enough spare belt to make a replacement Z loop - in fact, I seem to only just have enough belt for the remaining belts with no spare left over. So it's probably just as well I made the Z belt as tight as it is!

Dear god, it smells like death!

The hot end of the extruder is a spiral of nichrome wire wrapped around a piece of brass tube, smothered in fire cement and shrouded in a piece of copper tube.

Well, it would have been fire cement except Buzz had a small amount of high-temperature epoxy available instead. Which was nice because it cures by itself in an hour instead of requiring a couple of days or a trip to an oven.

What wasn't so nice was what happened when I fired up the heating element. Fire cement would have happily taken the abuse, but instead the epoxy emitted incredibly foul smelling smoke. At this point I don't actually have the temperature control loop in place, so I probably exceeded the epoxy's max temp (260C, which isn't much above our desired working temp). The rest of the afternoon was pretty miserable, waiting for the smell to dissipate. People walking past the windows started coughing, including Paul - and he was smoking at the time! Even after the smell had abated from the room, I still had it clinging to the skin on my hands and suffered whenever they got too close to my nose.

The hot end is still in working order, thankfully; but I'm leaving it till the very end of the build before doing anything more with it...

Rapman assembly part 7

I've been in a Red Queens Race with this damn thing for the past few days (running as fast as possible just to stay in the same place) and it's only now that I have some true progress to show off.

I spent a lot of time on the extruder; it looks the same but it runs much more smoothly now. The gears that were slipping are much improved, and I learned a considerable amount about how to fine-tune the spring-loaded bearing. When you tighten the spring bolts too far it acts like they aren't tightened enough, but the real solution is to back them off. I originally had them done right up, which did nothing but grind the reaction washer on the other side of the extruder and eventually force it out of place. After replacing the washer (backwards, as one side is now badly gouged) and releasing the spring bolts it came good.

I was forced to remove the top frame from the cartesian bot and disassemble it a few days ago, so I spent a long time getting everything perfectly aligned before trying to reassemble it. I made a measuring jig out of a long strip of acrylic with rod-sized holes at the appropriate distances, and it's been far more accurate for getting the frames perfectly sized than the original sizing bars that came with the kit. Once I reassembled the full frame and put another couple of holes in the jig it made setting the diagonal tie bars effortless.

Unfortunately I discovered after the top frame was on that one of the opto-endstops was on the wrong bar! There was a short panic as I contemplated disassembling the top frame AGAIN - the only way to move the endstop - but thankfully it was possible to rearrange things so that it's only slightly different to the instructions, but all the endstops can still do their job. A big sigh of relief there, I must say!


Tonight Buzz and Andrew were also at the hackerspace, and Buzz decided to MacGyver a stepper-driven extruder from a large stepper he had in his bag, along with a bunch of scrap acrylic from my rapman kit. It works amazingly well for something thrown together in a couple of hours! It's a bit large and ungainly to fit on my rapman, but a bit more work and it'll plonk straight onto his repstrap. It was also a good test of my stepper drivers, as we watched a piece of ABS filament go back and forth, and back and forth, and back and forth...

Rapman assembly part 6

Progress is slowing as I get closer to the end. Things don't just need to be assembled anymore; it's all 'align this perfectly' and 'file this to exactly the right size'.

Case in point is the extruder, which I've got the top half assembled here. It's already been disassembled, filed, and reassembled once; and I'll be doing that again tomorrow. As things stand it does work; I've applied power to the motor and had a piece of PLA filament move through it. Unfortunately the top gear linkage slips at one point each rotation and I've need to figure out how to fix it.

I also need to disassemble the frame to a large extent; all those rods that I cleaned have now got a nice new layer of rust on them that I need to remove again. Gah! Hopefully a layer of 3in1 oil will keep them from rusting again (and the lubrication can't hurt.)

I also have to fix another crack that showed up in a corner block whilst I was trying to square the frame. That job will be easier once the frame is rebuilt; I'm making various sizing jigs out of a long piece of scrap acrylic I had lying around to use together with the two that came in the kit.

Rapman assembly part 5

Here's what I did today; sorting out the diagonal tie rods and attempting to get the whole thing square. Haven't even nearly succeeded yet; a tape measure really isn't the best tool for the job. I have to dig into my post-move boxes and see if I can find my long straight edge.

I also discovered that the instructions suddenly end just before explaining how to set up the Y drive assembly. Tut tut. I've got enough info and photos from the reprap forums to get by, thankfully.

And here's what Buzz (assisted later on by Doug) did today. The driver boards are all nicely mounted on a sheet of cardboard, wired together and tested with a basic Reprap Gen 2 firmware on the Arduino. Sadly no 5D firmware for us until I get everything working and can look into replacing the dc motor extruder with a stepper driven one instead.

The ATX power supply I'd modified to use for the Rapman somehow died since the last time I fired it up a few days ago - which bugs me no end since I had pretty much used it non stop since 2001; it was the most robust PSU I've ever had. :(

Rapman assembly part 4

WORSHIP THE CUBE!

*ahem*

It's been a couple of days since my last post, mostly filled with "Disassemble... File... Reassemble... Repeat".

It kinda got to me (Disassemble - dead! No disassemble!) and so I took a day off.

I got the Z rods and X carriage finally moving smoothly (...ish), pulled all the top corner blocks apart and reassembled them (with filing in the middle, bah) and put together the top frame. I also built the parts for the Y drive assembly, which are pictured underneath the frame.

I managed at one point to cut the tip of my left index finger with a stanley knife, and it has been stinging ever since. One day I'll learn my lesson!

Eventually Andrew (who had been around all day) left, after I said I'd wait until another day to put the top frame on - and then I insanely went ahead and did it by myself. More filing (AAAH) and a rather ill-advised bump with a fist and the vertical rods slotted in where they were supposed to go... whereupon I discovered I had incorrectly reassembled one of the corner blocks (AAAAAAAH!) Another half an hour and a partial disassembly of the block in-situ and everything was as it should be.

Rapman assembly part 3

A bit more progress today, although it looks more impressive than it is. The frame is finally taking shape, although there's a lot more fiddling to do before the Z rods shown here move smoothly :(

I am having trouble with the X carriage binding a bit at one end of it's travel; until that is sorted I can't assemble the top half of the frame.

I'm also at a loss as to what to do with the Z belt - it needs to be a continuous loop, but I only have a cut length instead. So I have to join it somehow, and I can't find any reference as to how to do it properly. Thankfully the X and Y belts don't have to be continuous, as the ends are clamped to their respective carriages.

Edit: I just got pointed at http://reprap.org/bin/view/Main/AssemblingDarwinMachinery#Z_belt which explains how to splice a belt. While I don't have a belt splicer jig, it shouldn't be hard to make one out of polymorph.

Rapman assembly part 2

More parts assembled! Here are the eight corner blocks (one attached to the stepper) and the four Z rods. On the left end of each rod is the platform attachment assembly, and on the right side are the belt-driven gears.

Annoyingly, a bunch of the parts were only lasered through about 3/4 of the way through, and so I spent ages abusing a flathead screwdriver to try and break them apart, along with a heck of a lot of filing. :(

The good news is I had help today - Doug dropped by in the afternoon and was a massive help for several hours. Thanks Doug!

Rapman assembly part 1

A couple of years ago a bunch of people (including myself) here in Brisbane pooled their funds to buy a Reprap kit... and then never found the time to put it together. Oops.

Anyway, since I currently have oodles of free time I've taken over Hackerspace Brisbane the past few days and started assembling it.

It's taking forever going really well! I have all the electronics (early version Gen 2 RRRF boards as they were bought back in 2008) and the majority of the X carriage assembly put together. The carriage itself doesn't yet slide freely enough on the rails for me to completely assemble it, but I think I'll leave it for a while and move on to the corner blocks tomorrow.

One of the pieces was broken during delivery and I broke another piece or two trying to get some of the holes cleared where the laser didn't cut deep enough. So I whipped up a batch of acrylic cement last night ready for me to do field repairs. The cement is just acrylic chips (of which there are plenty left over once the reprap pieces are removed from the sheet) dissolved in acetone. Put the chips and just enough acetone to cover them in a container that won't itself melt in the solvent, seal the container and leave it for several hours. The acrylic doesn't so much dissolve as slowly soften as the solvent infiltrates the material. Once it's gooey enough you can smear some of it between the broken pieces and clamp them together. After leaving the piece for a couple of hours to let the acetone evaporate completely the resultant piece is as strong as if it had never been broken in the first place!

I did say I'd taken over the space, didn't I? :) We should probably clean up the other desk so I can spread across it too so we have some space for anyone else coming on Tuesday night...