Repairing a catastrophic failure of the Rapman 3.0

Little did I know when I was upgrading Slice and Dice to do prints of laser-cut Rapman parts that I would soon be confronting the problem of replacing such parts without having a 3D printer to print the parts. That is an ENTIRELY different problem.

I had upgraded Slice and Dice to do a better job of printing my sample laser-cut part from last time and was doing trial prints when I noticed that I was getting an enormous number of resets. This was odd because ordinarily I only get one or two resets per month since I uploaded firmware version 4.0.2. I checked the humidity and it was a bit dry, so I fired up the hot mist humidifier and drove the relative humidity up to 52%. No joy.

The next morning I undertook a new print and noticed a mushroom of ABS had formed under the extruder.

When I attempted to remove the extruder, the mushroom of ABS proved to be too big to easily get out of the mounting hole.  I then began to disassemble the x-axis carriage that holds the extruder only to discover that the top plate was being held together by the grace of God and nothing else.  It crumbled into two major pieces and half a hundred small fragments when I began to remove the bolts.

As well, one of the tiny little bars that hold the x-axis belt had also broken in half as is readily visible in the previous picture.

As you might imagine, this all made me very cranky.  A quick calculation revealed that I had historically been spending considerably more on preassembled BfB hot ends that I was on the filament that goes through them.  I run a lot of filament, too.

I spent several hours chatting with both Iain and Andy at BfB.  They were attempting to be as helpful as they could, but somehow I came away with the same feeling that I get when I take my car into the garage and they say recursively, "It MIGHT be X.  We could work on that and see what happens."  I began to steam up a bit when they started talking about my not using "BfB gcode".  They'd latched on to that fact that I'd written my own STL processing software that produces gcode right out of their manual and tagging this as a possible problem.  They then started talking about the fact that I was using very short line segments {0.1-0.1414 mm} and that was possibly touching off heretofore unsuspected bugs in the firmware.  I pointed out that the Rapman is supposed to have 0.1 mm resolution and you can't print objects at that level of resolution unless the firmware can handle that short a line segment.

I finally decided that I had to stop talking before I said things I'd regret later {I do that a lot}, and have a good think.

Here's what it came down to...

• I needed a new top plate for the x-carriage and a new hot end.
• I was going to have to pay for these and it was going to take a week to get them
• It was entirely possible that the hot end had been destroyed by a firmware bug
• There was nothing to say that the new top plate would last any longer than the last one, viz, ten months.

No matter how I looked at that equation it just didn't seem to balance.  A big bone in my throat was the fact that BfB wanted me to pay to replace a hot end that it was very possible that their firmware had broken.  A bigger bone was that there was no guarantee that if I put the new hot end that I bought into the system that the firmware wouldn't ruin it, too, in short order.

It seemed to me that the most reasonable course was to see if the problem was with the firmware.  I typically print with a 0.3 mm hot end.  I like what that kind of resolution does for my prints.  Before I settled on 0.3 mm, however, I bought two, preassembled 0.5 mm hot ends, so I had those in stock.

I also had Bogdan's experience that replacing the top plate on the x-carriage and grounding the hot end to it would stop the resets.  This from the observation that resets were most often caused by a static charge building up on the plastic of the x-axis carriage and extruder and then discharging, causing a reset.  BfB which is apparently located in a damp environment had never encountered this issue.  I noted that resets tended to get quite common when the relative humidity in the room holding the printer dropped  below about 42%.  I'd sorted out resets, except for the ones I encountered most recently which have led to the hot end failure, I think, by using a hot vapour humidifier.  After seeing how the top plate had crumbled, however, the notion of replacing the acrylic one with an aluminum one began to sound very attractive.

I decided to acquire the means to cut both acrylic and aluminum.  Harbour Freight in Salinas had a very nice scroll saw on sale for $69 which would reputedly do the trick.  

I bought that, a sheet of 0.22 inch (5 mm) acrylic and a billet of 3.35 mm aluminum plate.  I decided to cut an aluminum top plate first.  I began the process by simply tracing the bottom plate, which was identical to the top plate onto the aluminum with a fine tip marker.

I did the rough cut with the scroll saw and dressed it with a grinding wheel and a half round ring file after having set the plate in a small vise.

I then remarked two holes at diagonal corners of the plate, drilled 1/16th inch guide holes and widened them to 13/64th inch {as close as I could get to the 5.2 mm holes as I measured them on the original piece.   I did this with a hand drill after securing the plate in a vise. 

This done I then bolted the acrylic bottom plate to the developing aluminum one and drilled the guide holes for the rest of the holes using my Dremel drill press.

I then removed the acrylic bottom plate, secured the aluminum plate in the vise again and drilled out the rest of the holes.  

Afterwards I cleaned up the finished plate with a wire wheel and checked it for fit on the x-axis.

At this point my dyslexia set in.  The plate is not symmetrical and I'd got it flipped and completely reassembled and tested the carriage this way.  I didn't notice the problem till I tried to fit the extruder into the top plate assembly and discovered the symmetry problem.  The next pic is from the original, incorrect assembly.

The new top plate works smoothly.  Now I've got to swap out my ruined, 0.3 mm extruder with one of my spare 0.5 mm ones.  I will be able to see if I have a serious firmware problem or whether I just have a design fault with the hot end.  It could be either, or both.

I'm entering a big of a crisis with respect to 3D printing.  I bought into BfB's Rapman because I wanted to do some printing instead of screwing around with printer design and problems all the time.  At the time, a year ago, it was a good move.  Rapman was a bit pricy, but it was solid and the components of it were affordable. The 32bit MCU board was a delight after all of the Linux/Arduino/Sanguino/Bullshitino nonsense.  Some months ago there was talk of extending the Rapman MCU to where you could parameterise the firmware setpoints to deal with different machines and extruders, like the Mendel, for example, or even machines you'd designed yourself.  As it stands, it's not clear that BfB can design reliable firmware for their own machine, much less a parametric firmware app that would make it applicable to a wider range of machines.  

On top of that, they've recently jumped the price rather dramatically.

As it stands, BfB's Rapman has two Achille's heels; their firmware and their hot end.  Neither are reliable and the hot end is very difficult to repair.  I'm told that BfB is working on successors to the hot end, but that does me no good at all.  I'd like to shift over to something like Nophead's power resistor driven hot end.  The problem with that, however, is that I'll have to design a MCU to drive it and the printer both.  By the time I've done that,  BfB is out of the picture, since the those two components are what is defensible as corporate worth in the BfB.

I don't know quite what to do.