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Modifying the Print Head to use an 8mm Rod

Discussion in 'Mods and Upgrades' started by Lance Weston, Jan 5, 2022.

  1. Lance Weston

    Lance Weston Active Member

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    First: The parts look much better than photo. Attached are the STL's for the three bottom plastic parts. I went to a brass tube for two reasons. The brass tube forces perfect alignment and it is smooth and replaceable/cleanable if you get a clog. It uses different length screws as I had to increase the height of the top piece to accommodate the 8 mm bearing.

    I used Fushi bearings LM8LUU from Amazon. They are verry tight and smooth. On my proto tyoe Robo Clone I only use the 8 mm rods. Picture attached.

    This week I should get to the bearing block drawings and STLs. An 8 mm rod is 3.17 times stiffer than a 6 mm rod and weighs less than two 6 mm rods.

    A single 8 mm rod improved my finish over two 6 mm rods. I did not try both 8 mm and 6 mm together, but it is not disallowed.

    I will specify all of the screws and little parts required as I upgrade my R2. Tools required: A cheap hand reamer set (about $25 on eBay or Amazon). 4 pieces of 8x11x30mm sleeve bearings. Available from eBay or Aliexpress, The graphite infused bearings are tighter but need lubrication anyway. A small plumbing tubing cutter to cut the 3mm OD,2mm ID brass tube I use for the internal filament guide.

    picture shown is my R2 modified to use an 8mm rod with a 6mm additional rod optional. My print head has the same bottom as the Robo Print head and attached are all of the STL's to print out the plastic parts that will use the Robo Print top.

    A note about rods. I bought Fushi LM8LUU bearing which are tight and smooth. I first tried the original 8mm rods from the Robo and they were sloppy. I tried other rods that I had used through the years and they were all sloppy or too tight. It was only when I got to the PDtech rods that I have been purchasing recently that the bearings had a perfect smooth fit.

    So far the printing is excellent and I am looking forward to next week when the sleeve bearings will be broken in.

    When comparing to my Robo clone that has four posts and two z steppers the print is not quite as good. It may be that the standards sleeve bearings in the blocks being more sloppy than the graphite infused blocks is the cause. I have ordered more graphite infused sleeve bearings from Aliexpress and will update after arrival.

    I found the assembly manual for an ultimaker printer on github https://drive.google.com/file/d/16G8-A61nS2UjkxCwoYU7rlxFhtmoZYCD/view?usp=sharing and the Robo is a clone, with the exception that Ultimaker uses a sinigle 8mm rod instead of two 6mm rods. I suspect that the Ultimaker has better quality (toleranced bearings and rods) than the Robo. I would expect the Robo to perform as well as the Ultimaker just by upgrading the rods to PDtech the bearings to NTK and finding a source for tighter sleeve bearings.
     

    Attached Files:

    #1 Lance Weston, Jan 5, 2022
    Last edited: Jan 8, 2022
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  2. LordPeq

    LordPeq Member

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    Using this for my rebuild right now!
     
  3. Lance Weston

    Lance Weston Active Member

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    posting my latest files: https://drive.google.com/drive/folders/1Tjq8ZB8Swx-kUXOQ98DMF_7EAtGby2IV?usp=sharing

    Right handed aluminum arm by itself is $5.77, If you need the spring and the cap on the spring order the $7.59 part. You have to drill and tap a 4mm hole for the adjusting screw . drill and tap for the pneumatic holder. I prefer the PC6-8 but a 1/8 NPT also works.

    https://www.ebay.com/itm/125251924171
    https://www.aliexpress.us/item/3256...2e13cNw&gatewayAdapt=glo2usa&_randl_shipto=US

    I prefer the graphite infused bearings. I break them it with black axle grease and then just keep the rods clean:
    https://www.aliexpress.us/item/2251...tewayAdapt=glo2usa4itemAdapt&_randl_shipto=US

    I used Fushi bearings for the 8mm rod in the print head because I could not find American or Japanese. They work fine:
    https://www.amazon.com/gp/product/B083XQTH41/ref=ppx_yo_dt_b_search_asin_title?
    ie=UTF8&psc=1

    I only use PDtech rods as they seem to be the best quality.. Then replace all of the carriage bearings with motor quality or better:
    https://www.ebay.com/itm/303359820363?var=602491967388

    You will then have a zero play print head.
     

    Attached Files:

    #3 Lance Weston, Nov 13, 2022
    Last edited: Nov 13, 2022
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  4. LordPeq

    LordPeq Member

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    Working on reassembling the motion system with the latest 8mm carriage and bearing blocks… what a chore lol
     

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  5. Lance Weston

    Lance Weston Active Member

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  6. Lance Weston

    Lance Weston Active Member

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    It is not obvious but the Robo holds the 6mm rods at points at each end. I simulated that with tapered holes in the bearing blocks. It is a good idea to have a cheap 8mm reamer if your print is a little too tight.. if the hole is too long then the block will try and aim the rod.

    I suspect there was a patent issue so Robo went to two 6mm rods.

    attached picture shows hole locations. Use 4mm thumb screw.

    The dual gear screw works sooo much better.
     

    Attached Files:

  7. LordPeq

    LordPeq Member

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    Thank you..... the LMU Bearings I have are very high quality, but the OD is 15mm so I either need to redesign your bearing plugs to allow a larger bearing OD or, I have to order the bearings you suggested and wait 6 weeks.... yea, I tried boring out one of the bearing blocks already and will now need to reprint.... Since I am bored on a Friday night, I think I'll try to modify them in Mesh Mixer
     
  8. Lance Weston

    Lance Weston Active Member

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    15mm is the correct OD, I found 15.2mm gave me a nice tight fit.
    If you have autodesk inventor I can send you all of the project files.
     

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    #8 Lance Weston, Nov 18, 2022
    Last edited: Nov 18, 2022
  9. LordPeq

    LordPeq Member

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    Oh??? The bearing holders I printed have an ID of 10.8?
     

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  10. Lance Weston

    Lance Weston Active Member

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    The bearings I use are 11mmODx30mmL. I use an arbor press to insert, but a vice works just as well. I press the bearing in the side of the 8mm rod flush to the block. Your 10.8mm sounds correct.

    I used LLLDmax PETG for the top and bottom of the print head where heat is present. For everything else I use GST3D PLA+ which is the strongest, hardest plastic I have found. Much stronger than PETG,
     

    Attached Files:

    #10 Lance Weston, Nov 18, 2022
    Last edited: Nov 18, 2022
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  11. LordPeq

    LordPeq Member

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    I have fusion 360 if that would help but I’m trash at it
     
  12. LordPeq

    LordPeq Member

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    What is going to be your replacement material with GST3D going belly up? I have had some great luck with Hatchbox PETG on structural stuff
     
  13. Lance Weston

    Lance Weston Active Member

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    Hatchbox is the best PETG I tested. It produces the best finish and is the strongest, but not close in strength to GST3D PLA+. I have been only using made in the USA filament because it is obvious we are preparing for war with China and I like to support local. I still get ads for GST3D filament every couple of days by text. I knew early on that they were not reliable suppliers and I keep a 100 roll buffer. For best finish in PLA I find Sunlu PLA+ works best, but again it is made in China. I have purchased enough printer supplies that are only made in China to last me the next five years. By then the USA should be making these parts.

    I just opened a box of GST3D PLA+ rolls, all rolls are labeled as such, but about half are PETG. Must have been dumping whatever they had.
     
  14. Lance Weston

    Lance Weston Active Member

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    I just realized I had added the non R2 bearing blocks attached are the R2 Bearing Blocks, sorry.
     

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