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  1. #1

    Buy a new printer or fix my old printer? Reprap prusa mendel

    My 3D printer is a total basket case. My question is, can I rebuild it into a reasonably decent functional machine, or am I better off buying a whole new machine? Would this machine be on par with newer machines if fixed up properly? If I can fix it up, what parts do I need to replace, and with what should I replace them? My goal is that I want to be able to print random replacement parts for stuff (brackets, gears), mainly centering around my vintage computer collection and other hobby projects. Biggest "accuracy" issue for me is that I will need to create housings for small projects, and I'll need screw holes in the housing to line up with the mounting holes in the PCB. I'll need to make boxes and lids, and the lip of the lid will need to line up with the box so it can be screwed together nicely.

    The printer is a RepRap Prusa/Mendel V2/V3. It has a horizontal carriage assembly. Originally designed for the filament feed motor to be mounted directly on the carriage, however has been modified with a bowden type remote extruder. Hot end is some no-name off of ebay, held in place by a piece of paint-stirring stick (because the bracket was made for a direct drive not bowden. It's got a genuine arduino mega 2560, and RAMSP 1.4A board. Yes, it says "RAMSP" not "RAMPS" Heated bed, all steppers are "Kysan 1124090". Frame is thick acrylic, plexiglass, or similar. "Geeetech" LCD display with rotary encoder, speaker, and momentary switch.

    What are the problems:

    - Weak gear in servo motor ocassionally causes arm to partially extend for z-axis autolevel switch, causing hot end to ram into and shatter glass bed. (I think some sort of fixed-mount optical sensor would be better.)

    - Z-axis motors make "jamming" sound, even with threaded rods disconnected from motor. I've tried adjusting the little driver boards on the RAMSP. It works more reliably at extremely slow speeds, although never 100% reliable.

    - Intermittent yet frequent random heater error messages (thermal runaway, etc...) causing print job to halt.

    - Filiment jams up inside of hot end causing print job to be ruined.

    - After completing a layer, the printer does not correctly increment the carriage up "one notch" (z-axis) causes filament to be dispensed too far above the object being printed. By about a quarter inch worth of layers, the item being printed is a mess and ruined.


    I would imagine the thing to do is replace the carriage assembly with one made for a bowden filiment feed, and perhaps replace the arduino/ramsp board with something newer. Replacing the carriage could include an optical Z sensor, and proper cooling for the cold end.

    So, is this machine worth putting a few $$ into? Do newer machines spin circles around it? Time to toss it?

    Thanks!
    Last edited by Stu FL; 12-23-2017 at 03:59 AM.

  2. #2
    Technologist
    Join Date
    Jul 2017
    Posts
    145
    I'm not too sure what you mean about a servo, is it a flip down leveling switch? Maybe ditch it and just use manual leveling to save some headache now, get a working printer and then upgrade to a better sensor down the line.

    "jamming sound" is a bit vague, and odd when there is no load at all attached to the motor. Is it a 'click' like when you hold an axis and tell it to move, that sort of jamming? If so, try lowering z axis accelerations (this theory is sort of supported by the fact it works at low speeds).

    I can't really reccomend a safe solution to this, and I don't know what could be causing it without knowing more about your printer/workspace. Does it run in a particularly hot/cold environment? You could have a loose thermistor wire which is randomly connecting/disconnecting. Could you perhaps copy/paste some error messages here?

    The hotend jamming could be due to a couple of things. Cheap, knock off hotends are more prone to jamming due to poorer machining. e3d type hotends in particular are super fussy about retract settings, which can be a pain on bowden set ups. Try lowering your retract settings and see if that helps, but yes a proper bowden hotend mount would be a good idea. If you don't have a fan cooling the heatsink, this would almost certainly be causing the hotend to jam.

    As for the funky Z axis movement, what layer heights are you printing at and with what size nozzle? You could be trying to print at too thick of a layer height. Another alternative is that your Z axis steps/mm is incorrect and the z axis really is moving too far each time.

    Most of these fixes should be free to at least check/try and buying a few fans wont set you back much even if you don't have them on hand. Worst comes to worst you've already got a couple of fans for your printer build. Your electronics are fine for now, best not to try and change too much at once.

  3. #3
    Student
    Join Date
    Dec 2017
    Location
    North Carolina
    Posts
    5
    Quote Originally Posted by Stu FL View Post
    My goal is that I want to be able to print random replacement parts for stuff (brackets, gears), mainly centering around my vintage computer collection and other hobby projects. Biggest "accuracy" issue for me is that I will need to create housings for small projects, and I'll need screw holes in the housing to line up with the mounting holes in the PCB. I'll need to make boxes and lids, and the lip of the lid will need to line up with the box so it can be screwed together nicely.


    I make PCB at home sometimes as an eleectrical engineer and make cases for them with my 3d printer. The printer I use I bought from folgertech , the 20/20 model. After a lot of tinkering I have it where I want it, I guess it depends on whether you want a printer to just print something or if you like the tinkering aspect of it. Decide how valuable your time is vs your money.

    The printer is a RepRap Prusa/Mendel V2/V3. It has a horizontal carriage assembly. Originally designed for the filament feed motor to be mounted directly on the carriage, however has been modified with a bowden type remote extruder.
    Mine was the same way , but I now use a bowden extruder on the original carriage designed for a direct extruder. There are holders and mounts you can print on thingiverse that will make it work.

    Hot end is some no-name off of ebay, held in place by a piece of paint-stirring stick (because the bracket was made for a direct drive not bowden. It's got a genuine arduino mega 2560, and RAMSP 1.4A board. Yes, it says "RAMSP" not "RAMPS" Heated bed, all steppers are "Kysan 1124090". Frame is thick acrylic, plexiglass, or similar. "Geeetech" LCD display with rotary encoder, speaker, and momentary switch.
    You have to fix the bracket issue. You can't have the extruder flexing or movind during prints and putting something on the carriage that adds to its momentum or causes more jerking that the firmware wasn't set up to handle will lead to bad prints. So start with the carriage and mount of the extruder.
    The one I use is below and has the ability to add a cooling fan for pla if you want, not required to use the mount. It is minimal and doesn't add much weight to the carriage and works with the carriage that the prusa clone models have.
    https://www.thingiverse.com/thing:1632847


    - Weak gear in servo motor ocassionally causes arm to partially extend for z-axis autolevel switch, causing hot end to ram into and shatter glass bed. (I think some sort of fixed-mount optical sensor would be better.)
    Before you enable any auto bed leveling stuff , make the bed as level and rigid as possible. I don't use the spring design on the corners of my bed , instead I use lock nuts and the bed is always at the same height which brings me to another area. The PCB heated beds that ship with a lot of printers warp badly, both when heated and cooled and tend to require the bed to be leveled more than it needs to be. There are better solutions. Like aluminum beds that have the heater PCB as part of the aluminum bed itself, not glued on but done through the PCB on aluminum method like is done for LED lighting heat sinking.
    They are not overly expensive either, the one I use is :
    https://www.amazon.com/dp/B075375HBY/

    Cost is $30 and is a thick aluminum heated bead with thick glass that is coated with the PEI stuff (I still use glass with it and hair spray), but the bed works good and is ridid. I haven;t leveled my bed in 30+ prints and don't use auto level because the bed doesn't need it.

    - Z-axis motors make "jamming" sound, even with threaded rods disconnected from motor. I've tried adjusting the little driver boards on the RAMSP. It works more reliably at extremely slow speeds, although never 100% reliable.
    Connect each Z motor by itself , and then try connecting it to a different driver on the board and see if the same result. The servo drivers on the boards cannot be disconnected from the motor while powered or you will kill the driver. Bad driver boards sometimes appear to be ok but the stepping is wrong or skips because the fets have gone bad in the driver, you need to probably keep a few driver boards on hand as spares, they are cheap anyway.

    - Intermittent yet frequent random heater error messages (thermal runaway, etc...) causing print job to halt.
    Have you done the calibration of the heaters using the M303 commands ?

    - Filiment jams up inside of hot end causing print job to be ruined.
    Either the heater is running too hot, with something like PLA I try to stay at 200-210 max., or your fan cooling the heatsink on the extruder isn't working correctly.

    - After completing a layer, the printer does not correctly increment the carriage up "one notch" (z-axis) causes filament to be dispensed too far above the object being printed. By about a quarter inch worth of layers, the item being printed is a mess and ruined.


    I would imagine the thing to do is replace the carriage assembly with one made for a bowden filiment feed, and perhaps replace the arduino/ramsp board with something newer. Replacing the carriage could include an optical Z sensor, and proper cooling for the cold end.

    So, is this machine worth putting a few $$ into? Do newer machines spin circles around it? Time to toss it?

    Thanks!


    It sounds like the problems are really ones of calibration and configuration. I would fix the carriage, the ramps boards are fine, update the firmware . Newer machines do have some nicer features but the prints they produce are not going to be any better than a properly tuned and configured printer like you already have.

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