Sunday, October 17, 2010

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.

20 comments:

nophead said...

Hmm, I am sure Laszlo and Bogdan have asserted the BfB hot end is totally reliable.

BTW I think Laszlo sells a version with a resistor heater block.

How can firmware make the extruder leak? The worst it could do is increase the pressure due to feed rate too high or temp too low, but the design is fragile if it can't take the full pressure the motor can generate.

Why do you need a new MCU to use my style of hot end? It should be a drop in replacement for the nichrome and refractory heater as that is basically what a wire wound resistor is.

Forrest Higgs said...

"Totally reliable" is a relative term. In fact, it's not, as this latest failure shows. Heretofore, we've had a firmware problem that would stop xy movements while leaving the extruder running at full speed. If you weren't standing right by the printer, your hot end would quickly become buried in a huge blob of molten ABS. You coundn't get that off without destroying the thermistor connection, the nichrome connectors and the fire cement.

"Why do you need a new MCU"

The hassle is that because the firmware is not adjustable at all I would have to either use the same thermistor as is used in the BfB hot end, or something with the same parameters. While I have a few of those thermistors, the problem with them is that they're not on the market except in industrial quantities {thousands} in the US. It's a good thermistor, mind, but difficult to lay hands on.

BfBs fixed settings preclude their board from seriously being used except on the Rapman with their extruder. :-(

prusajr said...

Im much happier with Mega + Pololu duo. With original fw and hw I had few more features then you, like "Lets test to increase speed every layer", "Why not try to extrude peek at 300°C", "Bed diving", "Extruder vomiting giant blob of plastics"and so on :-)

But thing that pissed me most is, that when I told Ian about reseting, he said, he doesnt know about it, but there are two hundred posts threads on forum ... And they watch forums ...

Also, they bought one of my early prototypes of alu heatbed, havent heard a thing about it from them, then I sent them the PCB heatbed prototype, just for fun and for free, and same thing happen. I just hope that they understand what GNU GPL 2 means :-/

Wade said...

This is where open source and closed source don't mix well - when things start to break down.

When I only had a single printer running, I always felt like I was walking on thin ice, despite having plenty of spares around - it always seemed like I was about to break something I didn't have and couldn't get easily. Having two printers means you really have to try hard to get yourself into that mess. Especially when they're printed printers - spare parts a few clicks and some plastic filament away.

I'd vote for replacing your firmware with something open, so that you can fix it properly when it breaks, and not have to depend on BfB for updates.

Forrest Higgs said...

"I'd vote for replacing your firmware with something open"

That's rather why I suspect that I will have to design my own MCU board. Otherwise I will have to reverse engineer BfB's. That seems like just too much trouble for a MCU board that I would have difficult making copies of.

Unfold Fab said...

I completely agree that the firmware (and related hardware?) is still buggy on the Rapman but I can't agree on the hot end. I have had an even more dramatic ABS explosion in the past but that too was to be blamed on firmware. I don't think you can blame the hot end for not being able to resist the gulf of ABS and the related pressure that is build up in and outside of the hot end due to a firmware bug... The FM should handle this correctly. The current hot end is already the second design since I bough my machine and its a great improvement. The alu reinforcement does the trick for me, before the PTFE would tend to bend out of form easily.

Apart from that, I was interested in this part of you post:
"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."
Was this discussed in the forum? I had been following that topic closely since I started the discussion and never read about replacing the carriage with a metal one. I did ground the nozzle but that didn't work for me. Was this discussed in another thread?

Forrest Higgs said...

unfold: "Was this discussed in the forum?"

Indeed it was on multiple occasions, though not in depth, if my memory serves. Bogdan claimed that it effectively ended his reset troubles.

Mind, the supposition of a static charge building up on the plastic of the head as a result of the temperature is my own interpretation which I base on having had similar troubles with static interference in another instrument that I built back in the 1980s. I don't think I ever put forward that in the forums since I thought and think that it ought to be obvious. :-)

laszlok said...

> Hmm, I am sure Laszlo and Bogdan have asserted
> the BfB hot end is totally reliable.

I dont know where I claimed that, but to say the true, having a reliable
bfb hot-end meant for me:
1. machine a real PTFE tube on a lathe
(and not some hand cutted silicone thingy)
2. machine the peek tube to have the right size.

I cant imagine how you guys can have this big mushroom of ABS on the
hot-end. For me the threaded rod simply bites off the plastic, and
cant push it down anymore.

I think a proper machined ptfe and peek tube is required for this.

I have many problem lately with my bfb hot-end. I cant reliable print
with it, sometime it pushes only thin filament. It is especially a
problem with bigger prints (200x14x14mm object). So Im eager to
switch over to my design.

> BTW I think Laszlo sells a version with a resistor heater block.

One eye cries while the other eye smiles.

Im sad, because you see my new hot-end design as a simple ripoff of
bfb hot-end.

Also Im happy too, as you think Im already finished and Im *selling* it.
Im not there yet. Im only at prototypes, and I dont sell them until
it is not perfect. (yes it means, maybe I will never sell them;-\)

I was at prototype version 2.5 (which I have not published, because
it didnt work), before I completely reworked the hot-end.

Im waiting to my new hot-end to finish manufacturing, sadly the cnc
guy got sick, so its delayed a lot. (Im waiting to it more then a week
now).

> How can firmware make the extruder leak?
> The worst it could do is increase the pressure due to
> feed rate too high or temp too low, but the design is
> fragile if it can't take the full pressure the motor can generate.

Completely agree.

> "I'd vote for replacing your firmware with something open"
> That's rather why I suspect that I will have to design my own
> MCU board. Otherwise I will have to reverse engineer BfB's.
> That seems like just too much trouble for a MCU board that I
> would have difficult making copies of.

I dont really get this argument. If Im well aware, you are on the
pic bandwagon. So why would be your own MCU board any easier then
simply rewriting the firmware to this board?

I want to switch to arduino mega+pololu myself.

> While I have a few of those thermistors, the problem with them is
> that they're not on the market except in industrial quantities
> {thousands} in the US. It's a good thermistor, mind,
> but difficult to lay hands on.

That is true I was forced to buy 200 of it. I still have more then 180,
the others were sacrificed in prototype hotends...

I used to sell it for 2EUR...
Sold less then a handfull (4 pieces in total if I remember right).

Best regards,
Laszlo
http://blog.arcol.hu

Forrest Higgs said...

Lazlok: Many good points!


>I dont know where I claimed that, but to say the true, having a reliable
>bfb hot-end meant for me:
>1. machine a real PTFE tube on a lathe
>(and not some hand cutted silicone thingy)

I suspect that the silicone instert in the BFB hot end is where the failures happen. It's flexible and not proper PTFE at all.

>2. machine the peek tube to have the right size.

Agreed

>I cant imagine how you guys can have this big mushroom of ABS on the
>hot-end. For me the threaded rod simply bites off the plastic, and
>cant push it down anymore.

Most of the time that seems to be the case. In this case, however. :-(


>I think a proper machined ptfe and peek tube is required for this.

Agreed

>Im sad, because you see my new hot-end design as a simple ripoff of
>bfb hot-end.

I think no such thing. I've seen the pictures. It uses the BfB fitting to the main body of the extruder. After that it is nothing like the BfB hot end.


>I dont really get this argument. If Im well aware, you are on the
>pic bandwagon.

I've actually been thinking about using an ARM prototype board and I2C for connection to Pololu stepper controllers.


>So why would be your own MCU board any easier then
>simply rewriting the firmware to this board?

The BfB boards are complicated and hard to make. As well, BfB has raised the price on them, I believe.

laszlok said...

> I suspect that the silicone
> instert in the BFB hot end is
> where the failures happen. It's
> flexible and not proper PTFE at
> all.

Yes properly machined PTFE tube should seal good the plastic from the outside world.

However in my 2.0 hot-end design I used a PEEK tube which gone under the ptfe tube, so basically it sealed the plastic alone.

It didnt leaked, only some vein styled a hair width plastic managed to creap under the PEEK tube.

I learned since, that the PEEK is worse heat insulator then PTFE, also this idea didnt helped, so I abandonned completely.

My only point is, even if the ptfe tube leaks, the PEEK tube should stop the leaking. It could only leek between the ptfe/silicone tube and the peek tube.

So I think the stock bfb hotend has a poorly machined peek tube, and also the ptfe tube is mostly a joke. So the problem is twofold.

Best regards,
Laszlo
http://blog.arcol.hu

Forrest Higgs said...

That's very good information, Lazlo. Thank you for sharing that experience. :-)

Erik de Bruijn said...

It such to have your main machine break!

I've tried to launch http://www.reprap.org/wiki/RapManFirmwareDevelopment
At the moment there wasn't the momentum to develop an open source firmware. I hope that BfB users can at some point free themselves from the dependence on closed firmwares. I bought their electronics and it was a waste of money, but especially a waste of time since they didn't allow me to modify its firmware for my Mini-Mendel. Now my Mini-Mendel has been in several newspapers with "BitsFromBytes" on it and people interested in the RepRap open source project started buying proprietary machines confused that they're not really open source.

I've had my fair share of problems with pre-built BfB extruders too. And taking a lot of trouble putting new thermistors in there, but that didn't work.

I was hoping that there was something reliable on the market by now and these extruder were expensive, but it looked like it was engineered a bit further than other things available.

For the Ultimaker we now have a heater cartridge system is very repeatable and easy to build. This way everyone can share PID settings. We're working with hybrid PTFE in PEEK insulators but we just started ordering prototype polymide thermal barriers to see if that works better.

laszlok said...

Erik:
I have always planned to build a 3D printer made some of its bits from laser cutted mdf, primarily something ready for heated chamber.

Looks like you already created this (ultimaker).

There are so many 3D cartesian bot on the market, that it is almost impossible to sell a new one even if its outperforms the currently available ones.

I wish you good luck with your printer by the way. But Im a bit sceptical here (mainly because of the low interest what I got on my hot-end design: I see things a bit too negative).

Bogdan Kecman said...
This comment has been removed by the author.
Bogdan Kecman said...
This comment has been removed by the author.
Bogdan Kecman said...

> Hmm, I am sure Laszlo and Bogdan have asserted the BfB hot end is totally reliable.

It is very reliable, I pushed over 15kg of PP, over 10kg of HDPE, over 20kg of ABS and over 20kg of PLA trough single one. During this the only issue I had was that PEEK tube darkened on one and and pressed on the PTFE tube a bit, I solved the problem in 10min by rotating PEEK tube.

What is the big issue with this hot end is the heater part with nicer and fire cement that's heated trough partially opened FET. This keeps the heater on the limit as if you add 0R5 of nicr wire more or less the heater will not be able to maintain needed temperature. I modded mine using 10R of nicr wire (instead 4.5R) and running 24V trough it via relay that is controlled by the half open FET on the pcb. If you don't have enough power (as you don't trough partially open FET as it overheat and shut down) the pressure in the nozzle is too high as extruder is pert powerful and the orifice on the extruder is too small and too cold so filament try to go somewhere else. Now if your PEEK is bit deformed (for e.g. if one of three screws pressuring PEEK and Al tubes into Al barrel is loose so hot end tilt to one side) the filament will find that to be easier path then to cold / blocked nozzle. Often the firmware will stop XY movement so there's just no way you can push more ABS trough nozzle as it is blocked by the cold ABS below it...

Bogdan Kecman said...

So, I still (after this one, and few other failures I seen) think that bfb hot end design is good. The overall rapman design is not perfect, but the hot end is imho great. Few improvements are possible
- the inside PTFE tube originally provided from bfb is from some "soft transparent ptfe", replacing this with "real machined ptfe tube" makes extruder much more sturdy
- double locked nuts on the triangular plate

on top of that - providing power to it bypassing the error on the PCB (half open FET)


> While I have a few of those thermistors, t
> he problem with them is that they're not on the market except in
> industrial quantities {thousands} in the US.

min order is 100pcs and it cost 150$. I ordered the package from usa.
They are great but fairly expensive (1.5$ compared to some honaywell ones I paid 0.3$ in 5pcs quantity)

Bogdan Kecman said...

> Was this discussed in the forum? (Al top plate solving resets)

Not sure I mentioned it on forum, I noticed that resets were gone when I earthed top plate that I made out of Al, mentioned that to Forrest. I might wrote about it on forum, no idea. It might be reason for why resets stop (they reduced significantly when I earthed nozzle, stopped completely when I earthed alu plate that is x-carriage), maybe it is not, I see so many reasons for the resets and I can't exclude any of them because not pcb nor firmware are open, on top of that, I'm note sure it is worth it. I already started working on my own pcb.

Wrt static, plastic, rubber and metal … on top of that, plastic being extruded … all of that creates static. I don't have experience with hydraulic but Tony mentioned that biggest sparks (many cm) he seen from static electricity was from unearthed hydraulic pistons as huge amount of static is generated when fluid is pushed trough small hole. We are pushing molted plastic trough a small hole .. I see a pattern there. Also, thermistor wires go directly to ADC on the pic. Note that ADC input is not even 5V tolerable so any spike here will do "who knows what" to the mcu. This is something I'm redesigning on my new board as well, I want to insulate thermistor input from mcu (Still not sure how to do it, started with basic op-amp linearisation…must do some tests)

> For me the threaded rod simply bites off the plastic, and
> cant push it down anymore.

It happens if you tighten the screws too much.

Bogdan Kecman said...

> I've tried to launch

old sd library used there does not help, it is not available from microchip and moving to new one require a lot of rewrites. Furthermore there are still 2 nasty problems with the board - FET being opened "barely" and wires going directly from hot end to the pic pin.

> low interest what I got on my hot-end design

when they are tested and you show how great they are, I'm sure things will change :D I for sure am anxious to come to .hu next week to check them out :D

Unfold Fab said...

Hi Forrest,
Are you referring to the discussion about grounding the nozzle, I followed that but never heard of using an alu carriage plate to do the trick. Probably your own solution but it is something I will give a try when my new machines start resetting. The problem is definitely in the extruder since we never have any resets with the syringe tool.