Parametric Herringbone Gear Set for Greg's Accessible Wades

by triffid_hunter Aug 13, 2011
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I'm having trouble with my little gear breaking. I'm using PLA, but it's really my only option. It keeps either pushing the nut through the sidewall, cracking it, or cracking along a layer between the setscrew and teeth. Any way to add some strength to that, or do you have print settings you recommend?

If anyone needs it, in my firmware I've put 655 step/mm (1/16 driver and 1.8° motor) with a standard hobbed bolt

I just wanted to verify.....I am using a makerbot. When you say 0 extra shells (skeinforge)/ 1 perimeter (slic3r), does that correspond to 1 shell in makerware? Wouldn't having only 1 wall be bad for wear? Or are you depending on the 90 percent fill to compensate?

After just now downloading the OpenSCAD file, I noticed a visible difference between the STL model and output generated from OpenSCAD. I can only assume the MCAD/involute_gears.scad library has been modified since this thing was first published.

In the source file: "Gregs_Accessible_Wade_Herringbone_Gears.scad", lines 89 and 90 read:
g1twist = 360 teethtwist / t1 / 2;
g2twist = 360
teethtwist / t2 / 2;

By removing the divide by 2 factor, the OpenSCAD output now appears to exactly match the physical gears on my current machine:
g1twist = 360 teethtwist / t1;
g2twist = 360
teethtwist / t2;

Long term feedback: After a few years faultless service of a set of these (11:45 ratio in PLA) on my Prusa Mendel, I'm just about to integrate these gears into a derivative of the seminal Mendel90 by Nophead.

Thanks again for the great design triffid_hunter! :)

Great script, but a few questions:

1) The non-cone intersection cylinder on the large gear trims off a small amount of the large gear OD. Why?

2) As gears are changed, say from 11/45 to 9/47, how does one determine the optimal value to use for the gear separation distance?

3) I understand how the geometry connection tolerances are used, but what do the AT, ST and TT labels stand for?

Printed this out last night. Great dimensioning, m3 nut and m3 bolt fit in the smaller gear nicely! 5mm stepper motor shaft fit nice and snug in the smaller gear as well!

Printed mine at 100% infill and experienced overheating of the extruder stepper motor consistently for the first time. Had to add cooling fan on extruder motor to ensure a successful print(heat transferred from motor through shaft to the filament driving nut, softening it and causing jams(printer issue, not model issue).

Awesome gear design, Triffid!

Resliced in Kisslicer and the print is super clean. Slides easily onto 5mm shaft of the stepper motor. No bumps this time around. Very nice. Great modeling, triffid_hunter!

What type of bolt will fit the spur gear? I only have the M8 bolt right now.

Excellent design! Gears mesh really well.

(1) Downloaded the herringbone-gears_new_fixed.stl.
(2) Sliced in Slic3r 0.9.9 - Approx. 2 mins on a Windows box. (Quad core i7).
(3) Printed perfectly. Thanks!
Andrew (http://3dhacker.com3dhacker.com)

Gear2's setscrew's captive nut has a bug: It's always created right on the edge of the gear's shaft.

//setscrew captive nut

        translate([(gear2_shaft_outer_d)/2, 0, gear_h+gear_shaft_h-gear2_captive_nut_r-gear2_setscrew_offset])

Uses the diameter where gear 1 uses the radius; changing this paragraph to

//setscrew captive nut

        translate([(gear2_shaft_outer_d)/4, 0, gear_h+gear_shaft_h-gear2_captive_nut_r-gear2_setscrew_offset])

generates the nut trap in the right spot.

Fantastic, and thank you. But... I made the parts thinner to fit behind the belt in my Prusa setup and although the small gear looks great in OpenSCAD, whenever I put it through Slic3r 0.9.5 the "herring" is only at the top and bottom 2mm, the middle 4mm is just straight tooth (that's about 11 layers at my current .37 layer height... anybody have any ideas why that might be?


These gears look really nice but I just cant get them to slice ... using Slic3r 0.9.2 I get a bunch of spurious lines firing off from the big cog to what looks like infinity.

Any ideas?

I tried opening in SCAD and playing but A. it then rendered the small gear wrong and B. I paniced and decided
i really need to learn SCAD ...

Scratch that ... fixed it.

I think (though i changed a couple of things) it was to do with my infill shape choice, I had gone for honeycomb fill and concentric top fill. Changed them both to rectilinear and the errors are gone. Printing as we type

The Small gear is Broken, doesnt appear properly in openscad or Slic3r. I appears to have messed up facets.

Slicer v0.8.4
OpenScad 2011.12.30

http://cloud.netfabb.comcloud.netfabb.com is your friend. The gear script frequently makes gears that are less than stellar in terms of mesh.

If openscad won't export, adjust the number of teeth by 0.001 or so, eg gear1_teeth=11.001. this sometimes gives it enough wiggle room to make a better mesh.

also, try an openscad version that's less than 9 months old ;)

lt;3 the herringbone or 'Citro
ën' gears. (from the the inspiration behind the Citroën logo) Especially the math behind designing the perfect gearset. :-)

I've been using this gearset on my two Prusa's for 4 months. Just one issue this far. No matter how nice and strong I print them, I seem to wear them down quite fast. Every
400 hours I need to replace them. -Being every 3 weeks with my obsessive printing. The solution right now is to keep a spare set laying about at all times.

-I have two suggestions for improvement, if I may.

First off, a slightly larger tooth module to increase lifespan. Simply more tooth-materia
l to wear down before failure.

Second I looked up the formulas for designing helical gears in my machine-element book, and it seem that the tooth geometry is slightly simplified. A boring tooth-study is sure to improve lifespan further.

The latter however is a daunting task as the feature size of
the teeth no-matter module is so small that an ideal tooth-shape will never be possible to produce on a reprap due to print quality limitations.

Please don't look at my comment as a criticism. O:-) These gears truly rocks my reprap. No backlash, great for precise filament retraction before rapid m
ovement. :-D

you must be printing them in ABS for them to wear that fast, try PLA - it's significantly harder and should last a very long time.

If you want larger teeth, then put fewer teeth on each gear!

As for tooth profiles, I've used others' work for those, and I'm sure they're simplified. These gears take long enough to render and slice as it is! If you want to post an updated involute gears script with better tooth profiles, or for
greatest win parametric resolution on the tooth, that would be great!

I made a video of this print http://www.youtube.com/watch?v=uMqyVivzMQMhttp://www.youtube.com/watch?v...

Killer herringbone gear Hunter. Thanks for this quality piece of hyper functional art. RichRap gave a big recommendation to this set. I would slap this set on my RepRapPro Huxley today, but I have her running so smoothly right now, I dare not fix something that's not broken... this time ;) This proud set will be the extruder set for my Huxley's offspring.

Slic3r Settings I used:

; generated by Slic3r 0.7.1 on 2012-04-14 at 17:41:33

; layer_height = .25
; perimeters = 1
; solid_layers = 4
; fill_density = .90
; nozzle_diameter = 0.5
; filament_diameter = 1.70
; extrusion_multiplier = 1.0
; perimeter_speed = 50
; infill_speed = 40
; travel_speed = 130
; extrusion_width_rat
io = 1.45
; scale = 1
; single wall width = 0.36mm

191C Hot End (216C For First Layer), 75C Bed

I allowed Slic3r's cooling function to drop speed to 5mm/s if layer time ever dropped under 20 seconds. I also had two fans at 90 degree angles blowing on the bed. 8-)

Beautiful looking gear. Looking forward to printing this based on RichRap's recommendation. The small gear is failing to slice in Slic3r. The combo STL is working though. Any thoughts?

go with the combo, the small gear doesn't print well by itself anway, the teeth suffer from cooling issues although the base seems to do ok.

I'll upload new individuals since people seem to want them

You rock man! My cooling solution is a man sized fan... It works ;)

Great stuff, thanks! You might want to check the small gear stl is valid. First attempt, I printed both and the small gear was a little distorted (poss too fast/hot). So only needing the small gear, downloaded it and slic3r complained big time. And nothing showed up in the Pronterface gcode preview window. I didn't bother trying a netfabbing repair, just split the two gear stl with Meshlab.

The central part doesn't seem to slice properly using Skeinforge - there is no infill. Works in Slic3r though.

Skeinforge will not even print the infill for the central part of Greg's normal large gear. Frustrating.

Did anyone find out why Skeinforge won't slice the central part of the large gear correctly? I am getting reports of dangling edges during the slicing process. Any ideas?

try changing the number of teeth on the gears by 0.001 or so, eg put 45.001 teeth for the big gear.

Changing the number of teeth did not change anything, except the number of teeth. I still get no infill on the central hub of the large gear.

Well, after much trial and tribulation (thanks triffid, appreciate it!), I have completed my one-off 47t herringbone gear Hack-a Day logo skull mashup.

I'm not completely happy with it, and will likely polish and reprint with .35 tip and finer layer height to hopefully clean up th eskull faces.

See my "I Made One!"

At 51:11 gear ratio, the large gear may foul on your belt clamps, and if you turn the carriage around the other way, the motor may rub the belt.

Suggest using a lower gear ratio, so the big gear is a bit smaller!

Will post updated scad soon, is not hard to change yourself!

Excellent work triffid_hunter.

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