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PrintAir CoreXY

Discussion in '3D printers' started by Keith Davis, Oct 3, 2015.

  1. DarkAlchemist

    DarkAlchemist Well-Known
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    Ahhh, yes the missing third wheel and I never noticed that. I have seen 3 or 4 but not 2 before so interesting.

    How would you get the tension right? The third wheel is normally the eccentric so I am baffled at this.
     
  2. Keith Davis

    Keith Davis Veteran
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    Actually I'm not even sure I'll use the big wheels up there, I may use mini-wheels instead. That requires lifting the idlers up 4mm and attaching the Tee Plate to the top of the X axis with the mini-wheels pointing down. The Tee Plate holding the mini-wheels has to extend about 3mm out over the 20x40 side rails to engage the wheels in the v slots.
    Like So:
    [​IMG]

    Lifting the idlers 4mm also allows for use of a regular 90 degree joining plate on the two front corners, not a bad way in itself for tying those corners. And, note that two of the Tee Plate bolt holes are available for attaching to the X axis bar even if the outside hole and 20mm are removed. That can reduce overall width of the printer 1 1/2 inches.
     
  3. Keith Davis

    Keith Davis Veteran
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    DarkAlchemist - "How would you get the tension right?" Gently. All 4 of the wheel axles on the X gantry have eccentric spacers. Bore the two outside 5mm holes to 7mm and the eccentric fits right in to the Tee Plate.
     
  4. DarkAlchemist

    DarkAlchemist Well-Known
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    What I was thinking so all wheels are actually eccentrics and no stationary wheels were used. As far as the mini wheels go I don't actually care for them and couldn't design them in as easily as the regular sized wheels.
     
  5. Keith Davis

    Keith Davis Veteran
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    Actually I'm lazier than that. I'll leave the two on the right stationary and make the two on the left eccentric. Same for the Z axis wheels. Accurate alignment will be camming the two eccentrics against the two stationaries.

    The more I look at using mini-wheels for all 12 wheels the more I like it. Makes it look more like a "precision appliance" instead of an "industrial machine".

    It's true that both Josef Prusa (i3) and Brook Drumm (ThePrinterbot) produced flimsy machines to appeal to the "lady of the house". But they were on the right track. The photo of Brook's ThePrintrBot setting on the coffee table was iconic. Until printers appeal to the "lady of the house" we do not have a market, we're just guys selling printers to guys like ourselves - that's a niche, not a market. And, until we can actually sell to "ladies who print" we won't have a mass market. We are a long way from 3d printing as a kitchen table "craft" that Michaels or Hobby Lobby will cater to by selling filament.
     
  6. DarkAlchemist

    DarkAlchemist Well-Known
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    Right idea but a horrible implementation by Prusa.

    Look at the Tiko. For most of us that is a toy but it will have a great appeal due to how small, and self enclosed, it is. It is sort of cute and add a light to the inside (if it doesn't already have it) and you have the perfect "lady of the house" printer. Takes little knowledge with not much messing around, or tweaking, and away we go. I wouldn't touch it but for a child for school or for the lady of the house you bet your buttons it will sell.

    Back to your printer now.

    Having 2 in 2 (I feel like Chuck Woolery on the Love Connection, lol) is a really neat idea but I think it would be hard to get exactly right in your configuration. The 2 + 1 eccentric is dead sexy easy to get right though.
     
  7. Keith Davis

    Keith Davis Veteran
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    Women will not be buying toy printers. Tiko isn't even a toy, it's an ornament. Women will demand and buy the same quality, speed and size as men, or just not print at all. The difference is in it's use. Men will devote an entire room or shop to their hobby. Fly tying can be done on a TV tray but no "self respecting" man would do it in anything less than his den. In a den it doesn't matter if the psu and controller are feet away from the printer and it makes a racket that requires earphones or plugs. Women will not buy something that looks like a high school science fair project and sounds like a wheel barrow on a gravel road (Mendel). They are more apt to buy what I call a kitchen table design, something self contained that can be pulled off the table for supper , easily stowed away in the hall closet between sessions, and looks like an attractive appliance while running with visitors in the house. They just lead more fluid lives than we do.

    Setting one eccentric against two stationaries is indeed easy, but setting the 4 wheels on a mini v-wheel kit, universal build plate, print bed plate,or inside a C-Beam is hardly difficult. If the two opposing bars are truly parallel and rigid, it doesn't matter if the two slots are on opposite sides of the same bar with wheels on the outside of that bar, or 3 feet way from each other on the inside of two opposing bars.
     
  8. DarkAlchemist

    DarkAlchemist Well-Known
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    Disagree because the women I am talking about I have seen in focus groups who are not that tech savvy. We are not talking about the female geeks here we are talking about the LCD or the common woman. They like dainty cute things and from the two focus groups I was involved with that is precisely what they said they wanted. They were shown the picture of the Tiko and they loved it but I doubt the Tiko people have the money to advertise it to the non geeky women. That is what needs to be done is to take a printer like this and advertise it like it were Crayola Crayons on all the channels and it would blow the doors off of 3d printing.
    This is where the Tiko, and there was one other I forgot what it was called now, fit that bill exactly.


    Oh, and one thing will forever hold 3d printing back and can never ever be helped in FDM and that is how long it takes to print something. You can't tie up the kitchen table for 15-48 hours to make that really awesome print.
     
  9. KDan

    KDan New
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    Just joining in here. I've been looking at CoreXY designs for weeks and this one has really caught my attention. On the previous page in this section there was mention of the AZSMZ board as possible choice for this machine. I'd definitely go that route. I've been using one in a custom Delta build that has been printing very well for the past 7+ months. Actually, I'm the person who designed that AZSMZ case on Thingiverse that was mentioned.
     
  10. jezter6

    jezter6 New
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    I don't have a 3d printer, so I'm also looking at designs that don't use a ton of special parts. I was looking at the D-Bot CoreXY and was quoted like $160 in plastic bits alone. So it made that cost restrictive.

    Do you have a link to your build?
     
  11. jezter6

    jezter6 New
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    Please excuse my ignorance here, but...what makes the bed go up and down? I see a shaft with pulleys and 2 loops, but I don't see where they attach to the bed frame to move it? Is a BOM and other files still coming for this project?

    Aside from the Z axis rod pulleys, it seems most of the green material can be had with OpenBuilds or other hardware brackets/motor mounts that those are the only "must be printed" pieces?


    Also interested in your gantry design on the interior wheels only. Have you tested it? Is it still a good design?

    I was thinking of buying openbuilds plates placing the wheels under it, as well as mounting the print head axis (X?) rail to the underside of the plate.
     
  12. Keith Davis

    Keith Davis Veteran
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    That did not work well @jezter6 .

    I changed to using a min-v-wheel kit.
    [​IMG]

    But, the design is expensive and other than it's unique layout and belt system it offers no real advance in the state of the art and I am putting resources and time elsewhere for now.
     
  13. DarkAlchemist

    DarkAlchemist Well-Known
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    I do not and for some odd reason this forums no longer even notifies me of when messages are posted.

    All of my work is in the toilet as I spent from 1am to 7:30pm trying to recover my HDD after Linux Mint did me in. I am very numb at losing 200 gigs of work but it is what it is and that is the problem with all of these huge drives is they would take me a lot of blu rays to backup on so I stopped backing up. I am going to get an external to back up my designs once I build the new PC with USB3.x on it.
     
  14. DarkAlchemist

    DarkAlchemist Well-Known
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    Yep. See I used to be good about backing up but when drives got to be so big the dvd, then blu-ray, backups just were too small to handle so much data. I just checked and there are a lot of options but I am not sure which is the best with USB 3.x/UAS and will allow me to swap drives. If I want cheap WD has 1tb models for 60 dollars but you can't swap those out (I am leaning towards them but can't find any real reviews on them). I would just hook it up and unhook it from the back of the PC for backups so this doesn't happen again.
     
  15. KDan

    KDan New
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    Keith, have you abandoned this design? You said it did not work well... could you elaborate on that?

    Thanks
     
  16. Mark Rehorst

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    This design suffers from a very common coreXY layout error. The belt and pulley arrangement for the XY stage can't work the way it was done here.

    In the top view of a stacked belt corexy mechanism diagrammed below, belt segments labeled A-H must all be parallel to their respective guide rails or the belt tension will vary as the extruder carriage is moved. The way the coreXY belts and pulleys were positioned in this design, a belt may become so loose the motor spins without moving the belt/carriage, or it could go the other way and the tension could get so high that the mechanism will bind and the carriage will stop moving. More details, here.

    [​IMG]


    The other major problem with this design is that there is nothing to prevent the bed from crashing to the bottom of the Z axis if Z motor power is cut/lost. One solution to that problem is to use a worm gear drive reducer, but you must use high quality gears or you'll suffer repeating print defects in the Z axis with every complete turn of the worm gear.
     

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