I have a few questions about my new MOD-t. This is the first printer I have bought, rather than built, and I feel a little lost not knowing how things work. If you can answer these questions, I would greatly appreciate it.
1) The Cura instructions posted on your support page show the standard build envelope of 150 x 100 x 125. However, the default profile used by AstroPrint utilizes a different build volume of 155.4 x 104.6 x 130. What causes this discrepancy? Am I safe to use the larger build volume that AstroPrint uses?
2) This question is similar to #1, but about retraction and print speed. Your Cura profile uses a higher print speed than AstroPrint (60mm/s v. 40mm/s) as well as different retraction settings. What is the highest print speed I can use without sacrificing print quality? What about retraction speed?
3) If I add buildtak, PEI, painter's tape, etc. to my bed will the printer be able to detect the change in height? How does the bed leveling sensor work? Is it capacitive?
4) Printing at 210 or 220C is going to yield a lot of stringing. I would like to add GCODE to change the print temp after the first layer to reduce this problem. Will the MOD-t respond like a traditional RepRap printer, or have you modified the commands it will respond to?
Thank you very much in advance!
1. The MOD-t’s “offocial” print volume is 6×4×5 inches, larger than the round metric dimensions of 150 × 100 × 125. The nominal, physical limits of travel are about 155.4 × 104.6 × 130 (6×4×5 inches plus 3mm plus/minus adjustments for injection molding and plating thicknesses). The “default profile used by AstroPrint” that you are referring to is probably very out-of-date. Do not try to print anything above 6×4×5 inches (152.4 × 101.6 × 127). We recommend staying a bit inside of that. If you hit a physical limit of travel the system may detect a stall and/or shift the build tray on the pinion rods. Different versions of firmware do/do not enforce build volume limits and/or do so in different ways.
2. The maximum speed while extruding is 80 mm/s in X and Y. The maximum speed while moving but not printing is 200 mm/s in X and Y. For Z, it is 300 mm/min. For E is is 360 mm/min. Depending on the firmware revision level, these limits are enforced/not enforced in different ways. Configuration files exist that exceed these limits, and those files are out-of-date/incorrect. Print quality is impacted by print speed from about 20 mm/s and up, for example, printing perimeters at 40mm/s is often helpful. Enforcement of these limits varies by firmware version. The motors are capable of much higher momentary speeds, however, this extra torque is generally consumed in making sure the MOD-t can move the axes at a very controlled velocity.
3. While not required, adding BuildTak, painter’s tape, etc. to the print surface plate is fine. If you exceed about +/-3mm of height change, you may confuse the firmware. The homing of the vertical position of the carriage is performed by slowing bringing the nozzle down into contact with the print surface while measuring the transverse (horizontal) drag on the build tray. When a change in drag is detected, the height is determined.
4. Firmwares 0.15.0 and earlier respond to the M104 and M109 G-code commands to set the temperature at values less than or equal to 220C. Values above 220C are typically truncated to 220C. The temperature sensing circuit only works about about 105C. faults are generated is extrusion is attempted below something like 170C. Future firmware is likely to arbitrarily increase the setpoint by 10C for layers less than 0.45mm (up to 220C). The MOD-t supports a variety of standard G-code commands, however it is not a direct match up with some of the other flavors of g-code out there. We have not (yet) published a comprehensive list of the supported commands, and these are also generally subject to change. Experimentation with G-codes is not recommended or generally supported and can put your printer in a non-functioning state that may or may not require power cycling and/or reflashing of the firmware to restore function. If you need to accomplish a specific action, please let us know via email@example.com and we may be able to help.
Derek Schulte, Principal Engineer, New Matter
A few more notes:
80 mm/s is a maximum, not necessarily the fastest speed that yields high quality. The current, released firmware (0.15.0) often doesn’t reach the target speed for a variety of path segments, but the forthcoming firmware should get to the target speeds much more often. Yes, the build tray can fly away, but that’s an acceleration issue not a speed issue. We have the most problems with try skip in the extreme ends, esp. the corners of the build area and it varies printer-to-printer. For users that are having problems with tray skip, there are some “MOD-skis” that can be printed to retain the tray over the rods.
Regarding the temperature sensing: in order to gain resolution in the sensing circuit, while keeping the electronics simple, we mapped roughly 100C to 240C to the range of the A/D converter. Since we use a NTC thermistor, resistance values at or above those that correspond to about 100C are “read” as 105C. We fudge the “thermometer bars” below about 105C.
Regarding the 10C temp shift – first, this will only happen on some FUTURE firmware. We haven’t observed uncontrollable stringing at 220C, but some geometries do produce a lot of stringing. Note that 220C on some other brand printer may not correspond exactly to 220C on the MOD-t as the sensor mounting and materials in the various hot ends vary a lot (We use stainless steel nozzle, Taz uses a beryllium-copper nozzle, for example). M104 and M109 won’t brick your printer. Messing with M201 or M202 or trying to cycle through, say, all the RepRap G-codes to see what they do could brick things simply because I haven’t spent much time trying to make sure they won’t have an effect (and exposing some of those things has been handy during development, where bricking a board is no big deal (because I have JTAG access, for example). To null the effect of future firmware’s 10C shift, just set the desired print temp to 10C lower than you want up to 0.45mm, then put in an M104 or M109 to get back to your desired temperature. We might provision for some hidden command to disable this shift, but I may or may not get around to writing it….
Regarding 210-220 as our print temp: we did a lot of testing. That said, you can set your own temperature in Cura or via the “advanced settings” on the web interface. The printer’s max temperature is limited to 220C due to the teflon sleeving in the hot end. The hot end also contains a thermal fuse for safety, so hacking the hot end to get around this limit can cause the fuse to open in a one-time fashion.
Thank you for all the enthusiasm. We’re working hard to make the MOD-t a positive introduction to 3d printing, and while I certainly know that it has it’s weaknesses, we are working to remedy them. Your feedback is greatly appreciated!
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