How to print sprockets and gears?

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Pak36
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How to print sprockets and gears?

Post by Pak36 »

Is there an easy, simple and accurate way to print up sprockets to fit a particular track?

I thought I would have a go at making a modified drive sprocket, but I am having real issues getting teeth that properly fit the track. I have been doing it by eye and by scanning in a photo taken of the stock part....but getting the scale to transfer into the 3D modelling software is not working well enough to get smooth running.

I also wondered about 3d printing accurate gears. I was contemplating a build project....but the motors cannot drive the drive sprocket directly....as they won;t fit. It's easy enough to make an ally cage with some top-hat bearings...but I would need to have a drive sprocket with a gear central to it's shaft driven by another gear. An opportunity also to gear down the drive to lose speed.

So that means also making 2 gears with compatable teeth, with accurate distances between centres....incorporating a drive sprocket that will fit the plastic HL tracks I have.

Can anyone give me any pointers/tricks of the trasde?
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AlwynTurner
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Re: How to print sprockets and gears?

Post by AlwynTurner »

Have a look here on thingiverse, theres loads of projects for gears

https://www.thingiverse.com/akaziuna/co ... ar-scripts

Good luck
Alwyn :thumbup: :wave:
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RobW
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Re: How to print sprockets and gears?

Post by RobW »

Gears aren't an easy thing to design, as you need to get the tooth spacing and shape correct. Any errors and they won't mesh correctly as you're seeing.

If you can put the gear onto a scanner you may be able to import the result into CAD and then trace it, or use the code to create a surface. Not sure whether the printers can put a high rez stl on the plane and then extrude the mesh for printing?
Pak36
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Re: How to print sprockets and gears?

Post by Pak36 »

Thanks for the input :)

Robw...that's pretty much the approach I have been trying, and it's not working. I use Lightwave as a modelling tool by choice, and I can import an image as a base to work from. You then have to manually construct the teeth over the top of hte image...but any error in scaling or parallax errrors on the picture....and hte end result gets wonky. Then you end up spending a lot of time printing stuff that gets thrown in the bin

Alwyn ... I have got the script...but have not figured out how to use it yet! I am like a chimp with a pocket calculator. I am randomly poking and prodding and will, by the law of averages, get it to say 'BOOBS' before I stop for a banana break or else start shrieking and throwing my own poop around.

oook
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AlwynTurner
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Re: How to print sprockets and gears?

Post by AlwynTurner »

OK there's one little trick that CURA can help you with. If you take a photo of a gear and load the image into CURA, it will ask you how thick to scale the image, and will then allow you to scale it and print it. I haven't mastered this myself, the only image I managed to print was a horseshoe commissioned by one of the forum members, but it does work. Wibblywobbly (Rob) has managed to make this work so he may be able to help you.

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Pak36
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Re: How to print sprockets and gears?

Post by Pak36 »

On the plus side.....I finally got the spur gear script to work...I had to have another script open for it to read and refer to .... and it will make gears. It lets me make a pair of gears with varying numbers of teeth that will mesh together.....which is hte first barrier crossed. I don;t seem to have any real control over how big the gears are...but I can export the STL, bring it back into modelling software and re-size the gears as well as modifying the centre to take a half-round drive.

Just leaves me to make a drive sprocket that works.

I presume I need to make a gear with the right dimensions...and then butcher it to remove every other tooth and get the gapping right for the track. Phew....
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AlwynTurner
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Re: How to print sprockets and gears?

Post by AlwynTurner »

Here's a sprocket design for KV1 track
module sprocket_hub () {
$fn=100;
translate([0,0,0]) sprocket ();
translate([0,0,25]) sprocket ();
difference () {
translate([0,0,0]) cylinder(r=6, h=20);
translate([0,0,-0.5]) cylinder(r=4.1, h=10.5);
translate([0,0,-0.5]) cylinder(r=2, h=24);
}
difference () {
translate([0,0,15]) cylinder(r1=6,r2=14, h=10);
translate([0,0,18.1]) cylinder(r1=6,r2=12, h=7);
translate([0,0,1.5]) cylinder(r=4.25, h=12.5);
translate([0,0,0.5]) cylinder(r=2, h=24);
}
difference () {
translate([0,0,2]) cylinder(r1=14,r2=6, h=10);
translate([0,0,1]) cylinder(r1=12,r2=6, h=7);
translate([0,0,1.5]) cylinder(r=4.25, h=12.5);
translate([0,0,0.5]) cylinder(r=2, h=24);
}
difference () {
translate([0,0,8]) cylinder(r=8, h=10);
translate([0,0,1.5]) cylinder(r=4.25, h=12.5);
translate([0,0,0.5]) cylinder(r=2, h=24);
}
difference () {
translate([0,0,27]) cylinder(r=17, h=1.5);
translate([0,0,26.5]) cylinder(r=16, h=3);
}
difference () {
translate([0,0,24]) cylinder(r=12, h=4.5);
translate([0,0,19.5]) cylinder(r=11, h=10);
}

difference () {
union () {
translate([0,0,24]) cylinder(r=12, h=1);
translate([0,0,20]) cylinder(r=5, h=5);
translate([0,0,24]) cylinder(r1=8,r2=6.5, h=2);
}
translate([0,0,19.5]) cylinder(r=3.5, h=9);
}
rotate ([0,0,0]) translate ([10,0,25]) nut () ;
rotate ([0,0,30]) translate ([10,0,25]) nut () ;
rotate ([0,0,45]) translate ([10,0,25]) nut () ;
rotate ([0,0,60]) translate ([10,0,25]) nut () ;
rotate ([0,0,90]) translate ([10,0,25]) nut () ;
rotate ([0,0,120]) translate ([10,0,25]) nut () ;
rotate ([0,0,135]) translate ([10,0,25]) nut () ;
rotate ([0,0,150]) translate ([10,0,25]) nut () ;
rotate ([0,0,180]) translate ([10,0,25]) nut () ;
rotate ([0,0,210]) translate ([10,0,25]) nut () ;
rotate ([0,0,225]) translate ([10,0,25]) nut () ;
rotate ([0,0,240]) translate ([10,0,25]) nut () ;
rotate ([0,0,270]) translate ([10,0,25]) nut () ;
rotate ([0,0,300]) translate ([10,0,25]) nut () ;
rotate ([0,0,315]) translate ([10,0,25]) nut () ;
rotate ([0,0,330]) translate ([10,0,25]) nut () ;
difference () {
union () {
translate([-12,-1,0]) cube ([24,2,3.3]);
translate([-1,-12,0]) cube ([2,24,3.3]);
translate([-11.5,-1,2]) cube ([23,2,2.5]);
translate([-1,-11.5,2]) cube ([2,23,2.5]);
}
translate([0,0,-0.1]) cylinder(r=4.25, h=12.5);
translate([0,0,0,5]) cylinder(r=2, h=24);
}
translate ([-3.5,-5.2,0]) cube ([7,2.2,10]);
}
sprocket_hub ();

module sprocket () {
$fn=100;
difference () {
translate([0,0,0]) cylinder(r=17, h=2.8);
translate([0,0,-0.5]) cylinder(r=12, h=4);
}
rotate ([0,0,0]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,30]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,60]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,90]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,120]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,150]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,180]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,210]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,240]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,270]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,300]) translate ([16.5,0,0]) tooth ();
rotate ([0,0,330]) translate ([16.5,0,0]) tooth ();
}

//sprocket ();

module tooth () {
$fn=100;
difference () {
translate ([0,-2.5,0]) cube ([5.5,5,2.8]);
translate ([0,2.5,-0.5]) rotate ([0,0,-16]) cube ([6,5,4]);
translate ([1.5,-7.5,-0.5]) rotate ([0,0,16]) cube ([6,5,4]);
}
}


module nut ()
{
translate([-0.6,-0.4,0]) cube ([1.2,0.8,0.5]);
rotate ([0,0,60])translate([-0.6,-0.4,0]) cube ([1.2,0.8,0.5]);
rotate ([0,0,120])translate([-0.6,-0.4,0]) cube ([1.2,0.8,0.5]);
}
//}
module nut_large ()
{
translate([-1.2,-0.8,0]) cube ([2.4,1.6,1]);
rotate ([0,0,60])translate([-1.2,-0.8,0]) cube ([2.4,1.6,1]);
rotate ([0,0,120])translate([-1.2,-0.8,0]) cube ([2.4,1.6,1]);
}

//copyright Alwyn Turner 2018

See how the tooth is designed first, then work out how many teeth, then space them around the hub.

Play with the design in openscad untilyou get the hang of it.

Alwyn :thumbup: :wave:
YOU'RE NEVER TOO OLD TO HAVE A HAPPY CHILDHOOD!

Saladin scratchbuild, Matilda scratchbuild, Churchill scratchbuild, Crusader scratchbuild, M10 Achiĺles scratchbuild, Universal Carrier scratchbuild
Pak36
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Re: How to print sprockets and gears?

Post by Pak36 »

Ahhh.....you do it that way round.....makes sense when you think about it.

I was going hte other way....making the round centre, then extruding teeth from the outer polygons. It is easier in conventional modelling software to do it that way, as the tools support that workflow. Trouble is...diameter of the disc determines the size of the outer polys....which affects the teeth. You have to juggle polycount with diameter to get the 'right' sprocket.

Your way, basically would involve me making a tooth that fits the track....then spacing them ( still going to be some trial and error here but it's measurable ) and then just merging those teeth with the rest of the mesh. OpenSCAD is quite counter-intuitive for me, as I have had a lot of years working with 3d software....but it certainly has it's benefits for this kind of application.

Thanks for the tips
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Will01Capri
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Re: How to print sprockets and gears?

Post by Will01Capri »

Some simple gear maths should help with calculating the correct pitch diameter for the sprocket.
Depending how good a mesh you want will depend also on how you design the engaging flanks, so that it rolls nicely in & out of mesh.

You need to get some good measurements of pitch of the tracks you have. Depending on the design of the track and how it engages will also give you an offset to calculate its pitch on the pitch line.

Best thing to do is to eye up tracks and sprocket and see how they engage etc and then it helps guide the mind if that makes sense
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