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3D Printer - Have Any Experience Using A 0.125 Inch DIA. Core Bore For 3MM Filament? — Parallax Forums

3D Printer - Have Any Experience Using A 0.125 Inch DIA. Core Bore For 3MM Filament?

idbruceidbruce Posts: 6,197
edited 2014-05-11 18:34 in General Discussion
Hello Everyone

Please excuse another thread for 3D printing, but this thread pertains to a very specific question.

I am designing an extruder for a 3D printer, which will use 3MM filament. 3MM is the nominal diameter of the filament and the actual diameter of the filament is 2.85MM. To simplify this discussion, 2.85MM equates to 0.112IN, which is the actual imperial measurement of our filament.

To put it all in a nutshell, this thread pertains to the bore of the core, but more particularly the minimum and maximum bore diameter, for 3MM filament.

As we all know, or at least a fair portion of us, drilling deep accurate holes is not an easy task. To be perfectly honest, this is the machining task that I hate the most, because it oftens results in failure. However the fact remains that I need a deep hole for the 3MM filament to pass through. As applied to the imperial conversion completed above, I have several common options available, which are:
  • #33 Drill bit 0.113" (0.113" hole - 0.112" filament diameter = 0.001" clearance) (way too tight for my liking)
  • #32 Drill bit 0.116" (0.116" hole - 0.112" filament diameter = 0.004" clearance) (seems perfect to me, but maybe too tight)
  • 3MM Drill bit 0.118" (0.118" hole - 0.112" filament diameter = 0.006" clearance) (seems perfect to me, but maybe too tight)
  • #31 Drill bit 0.120" (0.120" hole - 0.112" filament diameter = 0.008" clearance) (seems a little loose to me, but I could be wrong)
  • 1/8" Drill bit 0.125" (0.125" hole - 0.112" filament diameter = 0.013" clearance) (seems extremely loose to me, but again, I could be wrong)
As you may have surmised, the easiest possible solution would be to use some brass tubing with a 1/8" inner diameter for the filament to pass through. Just cut it to length and BAM. However I am concerned that the +0.013" clearance might be a bit too much, which might allow the melted plastic to creep back up into the core and cause a filament jamb.

Does anyone have any experience with the optimized bore diameters for 3D printer extruders?

EDIT: I now see that several extruder barrels utilize a 3.2MM (0.126" rounded) bore. However this size bore still seems excessive.

Comments

  • kwinnkwinn Posts: 8,697
    edited 2014-05-10 10:08
    Only suggestion I have is to start with the smaller diameter and drill it up to the next size if it does not work.
  • garyggaryg Posts: 420
    edited 2014-05-10 20:43
    As you already may know,
    Materials change in diameter as you heat them.
    It's quite possible that the 0.113 clearance measured on a cold piece of
    plastic might quite possibly be needed to push it through the tube when
    the plastic is heated above about 175 degrees F.
    In a past life, I've had lots of trouble with not allowing enough clearance
    when running warm materials through a not large enough orifice.

    Just my 2 cents worth.
    I follow your 3d printer related threads each day.

    Thanks
    Garyg
  • W9GFOW9GFO Posts: 4,010
    edited 2014-05-10 21:07
    When I have need for a precise bore (not very often) I drill slightly undersize then ream.

    Having said that, I think you want the bore, at least the portion that conducts heat, to be a short as possible. The original MakerBot sort of solved this by using a PET(?) tube. Now they just use as short of bore as possible. If the filament spends too much time in the bore it will soften, expand, increase the amount of force required to feed it, strip more easily and possibly jam.

    Unless you are dead set on 3mm, I would recommend switching to 1.75mm. It takes less force to feed and spends less time in the bore.
  • idbruceidbruce Posts: 6,197
    edited 2014-05-10 21:31
    @ Garyg - Point well made and taken. I agree 100% now that I think about it. I am sure the closer it is to the heat and considering the amount of pressure applied to the filament, the more the filament will expand. So by the time it actually reaches the heat source, the filament may in fact be 0.120" dia. instead of the original 0.112" dia.

    @ Rich - In all likelihood, my design of the core and heatsink are probably inefficient, but as mentioned elsewhere, I like the concept and theory, so I at least want to try it. If necessary, I may add a thermal barrier of PEEK. As far as going all plastic, I don't want to go that route, because they have problems also.
    Unless you are dead set on 3mm, I would recommend switching to 1.75mm. It takes less force to feed and spends less time in the bore.

    I agree 100%, however with the current design, I am going for a centered 3MM filament, with the hope that the required offset for 1.75MM will not be too great for the extruder to overcome. Luckily I have plenty of material on hand to make various design changes. I was originally shooting for a 1.75MM filament and then later opted for the 3MM, but in reality, I want to be able to use both.
  • Mark_TMark_T Posts: 1,981
    edited 2014-05-11 05:55
    idbruce wrote: »
    As we all know, or at least a fair portion of us, drilling deep accurate holes is not an easy task. To be perfectly honest, this is the machining task that I hate the most, because it oftens results in failure.

    The important thing with deep holes is to keep clearing the flutes on the drill bit - otherwise
    it jams, friction rises dramatically, bit heats up and expands, siezes and snaps. Aluminium
    is bad for this IMO. Don't even think about doing this without a good drill press and vice.

    So peck-drill, withdraw frequently to clear flutes (a pointy tool of some sort is needed, and
    use oil liberally. Choose an alloy with good machinability (not pure Al, a hard alloy will
    cut better).

    Definitely drill slightly undersize then the final drill will have no problems and cut cleanly
    with no danger of jamming.
  • T ChapT Chap Posts: 4,223
    edited 2014-05-11 06:07
    In some cases, I do not drill at all. Instead, take two pieces of material, make a slot in each that is 50% deep of the desired hole diameter. Add holes with a thread tap diameter on one side, and holes sizes for a bolt on the other. Once you have 2 slots, mount the 2 pieces together with bolts. Now you have a hole similar to as if drilled, any length is easy. I often use a square end mill or single flute router to produce a resulting square "hole" versus a round hole, but a rounded end mill will allow a more accurate true "hole" if needed.
  • idbruceidbruce Posts: 6,197
    edited 2014-05-11 15:56
    T Chap
    In some cases, I do not drill at all. Instead, take two pieces of material, make a slot in each that is 50% deep of the desired hole diameter. Add holes with a thread tap diameter on one side, and holes sizes for a bolt on the other. Once you have 2 slots, mount the 2 pieces together with bolts. Now you have a hole similar to as if drilled, any length is easy. I often use a square end mill or single flute router to produce a resulting square "hole" versus a round hole, but a rounded end mill will allow a more accurate true "hole" if needed.

    I will have to remember that.... I think Walt was talking about something similar for his project, but he did not say it the same way, or go in depth.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2014-05-11 18:34
    garyg wrote: »
    I've had lots of trouble with not allowing enough clearance
    when running warm materials through a not large enough orifice.

    Lights cigar, lifts eyebrows, then deadpans to audience
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