# How to make a gear for toothed belt

Hello there,

I would like to create different sized gears for a toothed belt.

I found plugins to create gears but I don’t find a way to tell any of them the distance I need to adapt the toothed belt.

The belt I’d like to use has got has a 3 millimeter distanced teeth. Right now, width and length of the belt seems unimportant but if I’m wrong, please tell me.

The system I’m trying to build will have two gears and their ratio will be 2:1. The “big” gear will have a pitch around 30mm and the “small” one, around 15mm.

This is maybe more a geometry or math problem than a specific Sketchup one.

Anyway, how do I create this in SketchUp?

Roger

You may find this discussion helpful, though you’ll have to test to see whether the tooth shapes generated are suitable for you belt.

The width of the gear should be simple to adjust. The length of a belt is always crucial. Normally one of the gears can be moved to adjust tension or there is an idler pulley that tensions the belt.

I saw this thread before but couldn’t find what I was looking for at least not at a first glance.

May I kindly ask you where exactly I should “dig” in this thread to find the info I need?

Roger

If you need a 2:1 ratio and want to use a 30mm pitch radius, start with the circumference of the gear circle:

2 * PI * R = 2 * 30 * PI = 188.49556

Divide this by your 3mm linear tooth spacing: 62.83185

This means you need about 63 teeth on the larger gear. Since the smaller gear needs half as many (31.5?) use 64 teeth on the larger and 32 teeth on the smaller. Working backwards, 64 * 3mm = 192 (circumference of gear circle). Pitch radius = 192 / 2 / PI = 30.55775mm for the large gear and 15.27887mm (half) for the smaller gear.

The plugin for this can be found at: https://sites.google.com/site/spirixcode/code/jimhami42_rack_and_pinion.rbz

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