Book terminology - hobbed gears

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Ryan Carlyle

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Apr 10, 2019, 10:05:21 PM4/10/19
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What's your preferred term?
  • Pinch wheel
  • Hobbed gear
  • Hobbed drive gear
  • other?
I don't really like "hobbed gear" since hobbing is a standard method of manufacturing spur gears and the term doesn't really differentiate between a regular gear versus a 3d printer filament drive thing.

Google has more hits for "hobbed gear" than "pinch wheel" but not by a large margin. 

Whosawhatsis

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Apr 11, 2019, 4:13:48 AM4/11/19
to Ryan Carlyle, 3DP Ideas
"Pinch wheel" is a general term for the type of extruder mechanism. The term has largely gone out of use as all of the types of extruders that are NOT pinch wheel extruders have gone out of use, thus making the term "pinch wheel extruder" synonymous with the more concise term "extruder".

I would not, nor do I think I've heard anyone else, call the *part* of such an extruder that grips the filament a "pinch wheel". When I hear that term used to refer to a part rather than to the type of mechanism, rather than the drive gear, I think of the idler (now usually just a bearing, but in earlier designs, often a larger-diameter wheel) that pushes (or pinches) the filament *against* the drive gear. These larger-diameter wheels were necessary in some designs, notably the MBI MK4, to reach inside the flanges on a repurposed belt pulley and/or to locate the bearing shaft far enough from the drive shaft that it would clear the extruder motor body.

Some early designs used a "hobbed bolt" or "hobbed shaft" that linked to a large printed gear (initially all home-made using a tap for hobbing, thus the inclusion of the term "hobbed" to describe them), but nearly all modern designs use a "drive gear" (or "filament drive gear", if you feel the need to be extra specific), usually affixed directly to the motor shaft, to grip filament. Though the tooth profiles used on these today are derived from the tap-hobbed profile on early hobbed bolts (and some early drive gears were no doubt made that way), actual hobs are now a more common tool, since nearly all of them are now mass-produced by professional machinists rather than one-offs made by hobbyists.

These are the usages of these terms that I would expect to see, and I think they're fairly universal within the community.
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Ryan Carlyle

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Apr 11, 2019, 4:45:14 PM4/11/19
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I'm on board with "hobbed" but it's really the term "gear" that bugs me. It's not a gear. It's a traction wheel or something.

In a MIG welder wire feed assembly, which is a functionally identical mechanism, it's called a "drive roll" or "drive roller."


On Thursday, April 11, 2019 at 3:13:48 AM UTC-5, Whosawhatsis wrote:
"Pinch wheel" is a general term for the type of extruder mechanism. The term has largely gone out of use as all of the types of extruders that are NOT pinch wheel extruders have gone out of use, thus making the term "pinch wheel extruder" synonymous with the more concise term "extruder".

I would not, nor do I think I've heard anyone else, call the *part* of such an extruder that grips the filament a "pinch wheel". When I hear that term used to refer to a part rather than to the type of mechanism, rather than the drive gear, I think of the idler (now usually just a bearing, but in earlier designs, often a larger-diameter wheel) that pushes (or pinches) the filament *against* the drive gear. These larger-diameter wheels were necessary in some designs, notably the MBI MK4, to reach inside the flanges on a repurposed belt pulley and/or to locate the bearing shaft far enough from the drive shaft that it would clear the extruder motor body.

Some early designs used a "hobbed bolt" or "hobbed shaft" that linked to a large printed gear (initially all home-made using a tap for hobbing, thus the inclusion of the term "hobbed" to describe them), but nearly all modern designs use a "drive gear" (or "filament drive gear", if you feel the need to be extra specific), usually affixed directly to the motor shaft, to grip filament. Though the tooth profiles used on these today are derived from the tap-hobbed profile on early hobbed bolts (and some early drive gears were no doubt made that way), actual hobs are now a more common tool, since nearly all of them are now mass-produced by professional machinists rather than one-offs made by hobbyists.

These are the usages of these terms that I would expect to see, and I think they're fairly universal within the community.

On April 10, 2019 at 19:05:23, Ryan Carlyle (temp...@gmail.com) wrote:

What's your preferred term?
  • Pinch wheel
  • Hobbed gear
  • Hobbed drive gear
  • other?
I don't really like "hobbed gear" since hobbing is a standard method of manufacturing spur gears and the term doesn't really differentiate between a regular gear versus a 3d printer filament drive thing.

Google has more hits for "hobbed gear" than "pinch wheel" but not by a large margin. 
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Whosawhatsis

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Apr 11, 2019, 7:35:34 PM4/11/19
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Well, it's certainly reasonable to include that note about how the term is used, but trying to call it something other than what the entire community calls it is probably counterproductive.
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Ryan Carlyle

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Apr 11, 2019, 8:41:28 PM4/11/19
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If it’s WRONG (like jerk) then I’m going to say so and use a different term. But “extruder drive gear” is probably fine. (Hobbed vs knurled vs EDM can be a different discussion.)

Where this gets painful is when you have extruder drivetrain gears driving an extruder drive gear...

Whosawhatsis

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Apr 11, 2019, 10:48:15 PM4/11/19
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Yeah, jerk is a particularly problematic one, since you'll want to use the correct definition of that term as well. Bed "leveling" is another example (and the auto- version needs further correction). Even in these cases though, it's important to include the term that people commonly use, even if only to explain why how it is inaccurate. It might even be worth periodically (upon first mention in any given chapter, for instance) throwing in the incorrect term in quotes to remind the reader that the term you are using means the same as the more common but less accurate version.

It doesn't seem like it would be difficult to avoid calling one of the reduction gears in an extruder the "drive gear". You can always refer to them by (relative) size, or as "input" and "output", etc. If there's a chance of confusion, the term "filament drive gear" is always available to remove all ambiguity.

On April 11, 2019 at 17:41:30, Ryan Carlyle (temp...@gmail.com) wrote:

If it’s WRONG (like jerk) then I’m going to say so and use a different term. But “extruder drive gear” is probably fine. (Hobbed vs knurled vs EDM can be a different discussion.)

Where this gets painful is when you have extruder drivetrain gears driving an extruder drive gear...

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Ryan Carlyle

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Apr 12, 2019, 12:05:14 PM4/12/19
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There you go, "filament drive gear" looks like a winner. It's accurate enough if you imagine it's a rack and pinion mechanism. (Not quite right but close.)

I'm not writing all that much about extruders in Vol 2 or 3, but geared extruders are a big factor in the Vol 2 drivetrain discussions, and if I pick the wrong term now it'll make life difficult when I work on Vol 4 (extruders / build plates). I'm already struggling a small amount now to match up Vol 2 terminology to wording choices I made in Volume 1.


On Thursday, April 11, 2019 at 9:48:15 PM UTC-5, Whosawhatsis wrote:
Yeah, jerk is a particularly problematic one, since you'll want to use the correct definition of that term as well. Bed "leveling" is another example (and the auto- version needs further correction). Even in these cases though, it's important to include the term that people commonly use, even if only to explain why how it is inaccurate. It might even be worth periodically (upon first mention in any given chapter, for instance) throwing in the incorrect term in quotes to remind the reader that the term you are using means the same as the more common but less accurate version.

It doesn't seem like it would be difficult to avoid calling one of the reduction gears in an extruder the "drive gear". You can always refer to them by (relative) size, or as "input" and "output", etc. If there's a chance of confusion, the term "filament drive gear" is always available to remove all ambiguity.

On April 11, 2019 at 17:41:30, Ryan Carlyle (temp...@gmail.com) wrote:

If it’s WRONG (like jerk) then I’m going to say so and use a different term. But “extruder drive gear” is probably fine. (Hobbed vs knurled vs EDM can be a different discussion.)

Where this gets painful is when you have extruder drivetrain gears driving an extruder drive gear...

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Bob Bilbrey

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Apr 12, 2019, 12:40:51 PM4/12/19
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Eons past we used the term "Grit Wheel" to describe the abrasive toothed thingy that drove the paper through pen plotters.  For our filament pushers "Grip Wheel" is descriptive and historically similar sounding.

William Cook

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Apr 12, 2019, 2:42:20 PM4/12/19
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It is pretty close to being a "drive sprocket", although it doesn't exactly mesh with a chain.n I guess it could be said to mesh with an 'indented material', even if the sprocket itself is doing the indenting.

JasonB

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Apr 15, 2019, 9:58:15 PM4/15/19
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It not being a gear or a sprocket really, and most closely matching the part on a lighter that rubs on the flint, I'd say that friction wheel is the most accurate term.

Whosawhatsis

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Apr 15, 2019, 10:14:27 PM4/15/19
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Some of the wheels used for this purpose (at least the ones actually taken from flint strikers in lighters) are using friction, but the better ones are designed to press or cut indentations into the filament that are then used like a rack-and-pinion or belt drive drive to control the filament's motion. Once these indentations are made, backing over the same potion of filament will, at least in theory, continue to use those grooves rather than cutting new ones (though some designs achieve this more consistently than others). Given this, I think that it is more fair to call it a gear (or pinion) than a friction wheel.

Based on how it's used, I wouldn't call it a sprocket, though sprockets are often closer to the ideal tooth profile than most gears (due to the uneven hardness between the gear and the filament, and the fact that the teeth need to be sharp enough to create their own indentations in the filament). "Toothed pulley" would be a better candidate than sprocket, though in that case, I would expect the filament to wrap around it a lot more than it usually does.
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Steven Butterfield

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Apr 15, 2019, 11:58:08 PM4/15/19
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How about toothed filament drive wheel?

Ryan Carlyle

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Apr 17, 2019, 10:06:55 AM4/17/19
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If we're throwing around new terms, there's "traction" and "grip" so it's type-agnostic. There are true friction drives, knurled surfaces, hobbed teeth, EDM teeth, actual repurposed gears/sprockets/pulleys... 

Steven Butterfield

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Apr 17, 2019, 12:40:06 PM4/17/19
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Sounds like you need a new acronym to describe it.

Ryan Carlyle

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Apr 17, 2019, 5:48:49 PM4/17/19
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"Having Opposed Bearing Biting Extruder Drive Gear" or "HOBBED Gear" :-)

William Cook

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Apr 18, 2019, 11:48:10 AM4/18/19
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LOL
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