Best printer for gears and maybe camshafts?

[Roxy]

But things like 'circular pitch' and 'circles' are meaningless to me. So I've got to find a good reference for these values, especially in the context of the gear code. I ran into numerous threads in which people were guessing and getting weird results. There seems to be a lot of confusion about size units et cetera. I used a text editor to study the gear code and I didn't see any embedded documentation or supplemental doc files. If anyone can direct me to a link where these terms will be explained, I'd be most grateful.

The easiest thing to do is get OpenScad installed and figure out how to pull files into it. The good news is you are trying to use a fully debugged and working module. So pull that module into OpenScad. And then tell OpenScad to render the objects created by your source. (Or in this case, put this code into OpenScad and make sure you have the /inc/ directory populated with the right files)

include <inc/configuration.scad>
use <inc/parametric_involute_gear_v5.0.scad>


make_gear();


module make_gear() {
gear (number_of_teeth=43,
circular_pitch=268,
gear_thickness =gear_thickness,
rim_thickness = 7,
rim_width = 3,
hub_thickness = nut_trap_thickness+ nut_trap_depth,
hub_diameter = 22,
bore_diameter = 8,
circles=4);
}

gear.jpg

In order to speed up the print and make the gear lighter, you can cut circles out of it. I'm using a version of this gear file that cuts tear drops out instead. They look better!

Here it is with the circular_pitch set to 120 and circles=8 :

gear2.jpg

[TimM]

Thanks for all the help! Perhaps this is the wrong forum or I am pushing my luck, but you have been so helpful that I'll ask a bit more. I've studied the gear() code and done a lot of Google search for terms. I learned a lot, but a few issues remain unresolved:

1) The usual definition of circular pitch is the distance along pitch circle from one tooth to the same point on the next tooth, with circular_pitch = pi / diametral_pitch, but the gear() code has circular_pitch = 180 / diametral_pitch which radically changes the meaning of this parameter.
Is there a reason for this apparent major departure from what appears to be standard practice? And in view of this, is the diametral pitch the usual 'Ratio of the number of teeth to the pitch diameter in inches' or is it also nonstandard?

2) the 'clearance' parameter seems to be a nonstandard term. I could not find it anywhere. What does it do, and how does one determine a reasonable value?

3) After considerable study, I basically understand backlash. But again, what exactly does the specified number mean, and how does one determine a good value? Is it an absolute distance? In inches or millimeters? Or is it a relative distance, a fraction of the diameter?

4) The 'twist' and 'involute_facets' parameters are similarly undefined and unclear. I can't find online references to them anywhere.

I know this is a lot to ask, but I would be grateful for any information. If I can become clear on the exact definition of all of these parameters, I'll write them up and post them for use by others. Thanks!

Tim

[Roxy]

Thanks for all the help! Perhaps this is the wrong forum or I am pushing my luck, but you have been so helpful that I'll ask a bit more. I've studied the gear() code and done a lot of Google search for terms. I learned a lot, but a few issues remain unresolved:

1) The usual definition of circular pitch is the distance along pitch circle from one tooth to the same point on the next tooth, with circular_pitch = pi / diametral_pitch, but the gear() code has circular_pitch = 180 / diametral_pitch which radically changes the meaning of this parameter.
Is there a reason for this apparent major departure from what appears to be standard practice? And in view of this, is the diametral pitch the usual 'Ratio of the number of teeth to the pitch diameter in inches' or is it also nonstandard?

So I don't know the answer. But I have a couple of comments. The person that did this code was really into gears. And he used all the standard names for things that are important to define a gear. My gut hunch is he has it right. But with that said,

	 // Calculate and display the pitch angle. This is needed to determine the angle to mount two meshing cone gears.


	// Base Circle for forming the involute teeth shape.
	base_radius = back_cone_radius * cos (pressure_angle);	


	// Diametrial pitch: Number of teeth per unit length.
	pitch_diametrial = number_of_teeth / outside_pitch_diameter;

And also, looking through the code, there seems to be some alternate way of interpretting this term when you are doing bevel gears. Because they have different sizes on the two edges, something has to give.

2) the 'clearance' parameter seems to be a nonstandard term. I could not find it anywhere. What does it do, and how does one determine a reasonable value?

That is almost for sure from the 3D Printing side of the world. Just because you say to make a 20mm cylinder, it never is quite that. Inside and outside diameters vary from printer to printer. It is very common to have the inside diameter be a little bit smaller than what was specified. So my guess is the clearance term is adjusting things so the gears will be the right size and mesh properly. You won't know the right value to use for this until you do some test prints on your printer.

3) After considerable study, I basically understand backlash. But again, what exactly does the specified number mean, and how does one determine a good value? Is it an absolute distance? In inches or millimeters? Or is it a relative distance, a fraction of the diameter?

I don't know the entire answer. But the backlash number affects the shape of the teeth of the gear. Depending on what is important, you might be better with one shape or another. Go ahead and tell OpenScad to render two gears side by side with different backlash numbers. You are going to be able to see the difference. When low back lash is needed, the herringbone gears help a lot with that problem. They don't have much slop when you reverse directions which is important on a 3D Printer extruder.

4) The 'twist' and 'involute_facets' parameters are similarly undefined and unclear. I can't find online references to them anywhere.

I don't know about these, but it has to do with bevel type gears where things are not cut straight across.

[printbus]

parametric_involute_gear_v5.0.scad must be from an openSCAD version beyond the March 2015 one I have running now. Unless it has changed (which I doubt), involute_gears.scad is very hard to grasp, especially when some parameters were "inadvertantly" left scaled by 180/pi.

Tim, if you do want to leverage the involute gears stuff in openSCAD, perhaps my openSCAD source for Greg's Wade extruder herringbone gears will be a helpful resource. I tried to scrub through the previous large and small gear scripts, focusing on trying to make them easier to understand. This in turn might help explain how the involute_gears.scad can be used.

Look for the herringbone_gears_9_47_RevA.scad file as part of this - http://www.thingiverse.com/thing:812899

[TimM]

Kevin - Thanks! I pored through your herringbone code and found the comments in it to be informative. I'm glad to see you also note the 180/pi factor that seems counterproductive and confusing. Given the obvious extreme skill possessed by the writer of the involute gear code, I don't understand why he did this. It just adds a layer of unnecessary complication to the parameter specification. At least now I know I'm not missing something important. Your comments on the other mystery parameters also clarified them. Now I'm ready to jump in and play with gears. I'm just anal enough to not want to do that until I had a decent understanding of what I was doing.
Tim

[printbus]

IIRC, the 180/pi was explained in the comments area of one of the series of openscad herringbone designs. What I remember is that the 180/pi was described as a mistake, or rather, a factor that was supposed to have been applied within the involute_gear script. But by the time the issue was noted, the involute_gear script had already been published or at least distributed to the community, and Greg Frost didn't want to rock the boat by correcting it. We've been living with this "error" ever since.

Depending on what you are looking for, there are multiple gear builders on Thingiverse. Search on "parameteric gear" or "gear generator" for some examples.

EDIT: By "series" of openscad designs, I'm referring to the Thingiverse trail starting with Greg Frost's 3575, followed by updates in 3752, 4305, 5268, 5275, and finally in what I consider the baseline herringbone design by Triffid Hunter in thing 10707.

[Roxy]

Hey! It is worth while to search on 'Involute Gear teeth' and look at pictures of them. I thought the backlash parameter changed the shape of the teeth. But that funny shape is what makes them 'Involute Gears'.

[printbus]

parametric_involute_gear_v5.0.scad must be from an openSCAD version beyond the March 2015 one I have running now...

Nevermind on that. Going back through my notes, I see parametric_involute_gear_v5.0.scad is the original script from thing:3572. The filename was simply truncated down to involute_gears.scad when it was incorporated into the openSCAD MCAD library in 2014.

[TimM]

The version I'm using is labeled 5.1.

[Mjolinor]

Well it draws very nice gears but I can't figure out how to use it.

Lots of demonstrations in the openscad file that give you no information whatsoever.

Anyone care to lead me down the path to enlightenment?

Lets assume:

1) I need to print two gears that mesh that are flat, need a 3:1 ratio and max diameter of 50 mm.
2) As above but I need them to be at right angles. (bevel gears)