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I lost track of the thread where I was going to post dual head calibration tips. Here is a link to the post I made on the topic to the 3D printer forums. Still working up very detailed instructions specific to our Rigidbot and ReliaBuild 3D printers. Even generalized this should be a help to some of you.

https://plus.google.com/u/0/113930448883604105560/posts/bepoTcLLkLH

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Here is a link to detailed assembly instructions for the stock ReliaBuild 3D extruder for both Single and Dual heads. These instructions apply to extruder upgrades for the RB1and RBB and when porting over the guts of an RB2 to the new RB3 or RBB3 frame.

The effectiveness of the dual head leveling is based on a machine that has milled aluminum parts for the carriages and bed resulting in very flat surfaces and travel.

Let me know what you think!

http://reliabuild3d.com/product/reliabuild-3d-extruder-assembly-instructions-single-dual/

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For those that did not saw it already.
There are many options for a 3D printer's bed sensor and even more misconceptions about what they can and should do. So after a ton of testing with a custom-built precision test apparatus (TM), 12 sensor options and 9 myths about these sensors have been examined - and we got a ton of data about how precise each one can be!

All the raw data here: https://docs.google.com/spreadsheets/d/1QDtd-0IK79gme_f80Rw_PB-nIActKWJJJvvAYd4u2uM/edit?usp=sharing
IGUS W-compatible printed parts https://cad.onshape.com/documents/576f471b5dc2c3a9c19b7010/w/eb450345dab529c4eef1f05f/e/cf0671a5d51803413c1d74f7 (built from a free IGUS sample kit)

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There is a dearth of decent 30mm 24V extruder fans on the market so I got myself some nice 30x30x10mm 12V SUNON MagLev fans and added a resistor. They run super quiet as the MagLev technology has virtually no friction as the shaft is floating in air.

Here is the formula for working out the Resistor Value working back from the fan Wattage which in my case is 0.44W and the amount of voltage you want to drop across the resistor which is 12V.

P = V x I
0.44W = 12 x I
I = 0.44/12 = 0.0366Amps

R = V/I
R = 12/0.0366 = 327 Ohms

Standard resistor value is 330 Ohms (0.5W)

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Nice article on designing for screws. Applies well to filament printing as well as SLA.
https://formlabs.com/blog/adding-screw-threads-3d-printed-parts/

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This is a preview of the tutorial "Teach yourself to Migrate Marlin Firmware in 24 minutes"

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Here is how I successfully bypassed the DAC chip that was inop on my RB2 board. The symptoms of an inop DAC chip would include not being able to boot any RB2 firmware that would call upon the DAC to control the steppers. RB1 firmware, and Marlin would not do this, unless modified to do so. Also there would be almost no current going to the steppers, just enough to do very slow movements/prints. Even with that, you may still run into a bunch of layer shifts and what not.

Now the fix: While I am certainly no coder, or professional solderer, this fix was fairly easy for myself. In the picture below, you will see 5 sets of solder pads for jumpers all side by side. One side labeled D (I assume for DAC) and the other side labeled V. The DAC side will have jumpers soldered to them completing the DAC circuit. The V side will be empty with nothing there completing the circuit.

What we are going to do in this case, is take all of the DAC jumpers off (GREEN) being careful not to get solder on any of the other connections on the board. then once all the DAC jumpers are off, we will bridge the connection to all of the V circuits (RED) to complete that circuit.

Once this is one, you must, must, must, make sure that you upload a software that does not call on the DAC to control the stepper motors. You should be able to just the code calling on the DAC in the firmware in order to prevent it loading and upload that.

Now that the DAC is bypassed, and it is geting full power (I think it is 98% of the full power that the NEMA can handle is the way it is set up) and yes the steppers do get warm. I have taken a cheap heatsink and fan on one of the steppers and made it more than manageable. I plan on using these: http://www.thingiverse.com/thing:22449 for the time being.

Once I see how they work or if I need a heatsink, I will adjust aim from there.

I hope this helps as I am sure I'm not the only person that has had this problem.

A few words from the Mastermind that made this all possible:

"I would not recommend adding a pot to those footprints. there used to be footprints in my design but they were removed as a result of too much space being spent on a device that was A: very unreliable, B: impossible to determine what the actual drive value was, C: inaccessible. Adding a pot to the undersized pads runs the risk of pulling a pad unintentionally when adjusting said pot. Careful rework of those pads with an appropriately sized part should give quite a few tries at correcting the drive issues, although 2amp drive shouldn't blow those motors, they should just get pretty warm. (particularly the Y. In fact in qualifying this design for the rigidbot big I ran the Y axis at 98% drive in order to keep the tray from skipping, and eventually added a small heatsink to the Y motor to help dissipate heat.). The only reason to down tune is thermal management of the driver ICs and then the thermal issues with the motors. From what I've observed, the driver ICs seemed to fail long before the motors skipped due to being over driven, but I have a pretty small sample size to test with.

In order to run the system at ~50% drive strength loading about a 63K ohm resistor. The arithmetic is simple, no guessing at tuning, Vout = (R2/(R1+R2)) * 5V where R2 is fixed at 10Kohm, and R1 = 53.6K + whatever is loaded in the V jumper position. A Vout of ~.8V is 100% 0 is zero % drive strength. Anything less than 50% probably won't move the Y axis reliably. Typically I've been setting mine to 80%. This corresponds to an increase of resistace = 14.53Kohm, quick look at the parts kit says use a 14.7Kohm resistor in the V jumper position to obtain ~80% drive strength."

Keep that in mind when considering this
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Print recovery from jams, clogs, and power losses.

If during a print you experience a clog or jam or power loss you end up with a print half finished.  The tips below can help you recover from this and possibly save your print if it is still attached to the print bed.

Preparation tips:

If you are using Cura, leave the program open with your part orientation until you have a successfully completed the print.  This is just a precaution in case you have to make modifications.  Simplify3D saves it by default.

The RB2 firmware will make the steps below easier but is not necessary to utilize these tips.

Begin by carefully measuring the height of the failed print object.

In your slicer program cut off the base by the measured height so the model starts at the layer of the failure.  There is a direct feature in Cure to do this.  Re-export out your g-code.

Using the Z jog adjust the tip of the nozzle to just touch the print.  You can leave it there or raise it the thickness of your printing layers above that point.  Depends on how confident you are in your measurements.  If you leave it touching see the note at the end of these instructions.  You might want to carefully run the head around above the print to make sure it clears everything and is the right height.

While holding the Z limit switch down set it's value to 0 with the jog buttons.  This is so the gantry does not lower back to the bed.
If you have the RB2 firmware you can use the home XY function to move the head out of the way so you don’t string plastic over it while heating up the head. Otherwise continue to hold the Z down and home the head.

Now you have two options – Manual or g-code modification.

Manual option:
Start your modified print and hold down the Z limit switch until the head starts to move then quickly release it.  This will keep Z from homing below the top of your print.  The head will rise a short distance and then descend down to the level of the last layer on the print.  The printer will continue the print at the level you zeroed it and should line up with the last layer printed.

G-code modification option:
Open the g-code in notepad or some other text editor and comment out the G28 Z0 line in the top section like so: ;G28 Z0.  Save your modified g-code.

With the Z already zeroed out simply start the print.  It will home if not already there and then continue printing from where it failed.

Note: There may be some double-up or small gaps on the transition from the failed section to the new one depending on how far through a layer the process was before it stopped.  Tweaking the first layer thickness or the level of the head above the print can compensate for a portion of this.

Note:  Heating up the first 2 layers about 5 degrees hotter than what you were using previously helps the head not get hung up on the print if you are touching the top of the print which can cause a little over extruding when you begin to print again.  Once it completes two layers then turn it down to your regular print temperature.

I hope these tips are useful to someone in saving a failed print. 

I wish I had this figured out for the two kings on the right in the picture.  One failed from a power outage and the other from a slow speed clog.  Saved both, but this would have been a lot cleaner.  Can you see the failure points?
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Here's another post I've been meaning to put up here for a while.  This is my setup to replace the weak connection point for the stock heated bed cable.  Using a solid state relay, the PSU takes the brunt of the load going to the heated bed while the original heated bed cable only sends the signal.  IMHO this is the safest heated bed setup I've seen.  It's also pretty straight forward too.  I hope these instructions are easy to follow.
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2016-04-18
5 Photos - View album

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Rigidbot 2 unofficial assembly instructions are here!

Follow the link below to a PDF version and an editable Word document.

http://www.laserwelddesign.com/#!What-weve-been-waiting-forRigidbot-20-Assembly-Instructions/qi9z6/570fbd380cf20ee5e3c38c6f

These assembly instructions are for a stock build with the exception of mentioning a part cooling fan duct upgrade which is highly recommended.

While the assembly method developed has produced exceptional results we are open to suggestions from the community to make them better.  Please post your feedback and insights.  It is a great pleasure to turn on a well built machine for the first time and have it home perfectly with no binding.

With these instructions to start from, let's spread some of that pleasure throughout the rest of the community.

Enjoy!
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