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# Does anyone have an online calculator for small gears/cogs/belts/pullies?

We are building a small CNC machine and were looking into using gearing to turn the lead screws, but we don't know where to start? We use online calcs all the time and just couldn't find what we are looking for. Can someone help? I'm sure there is a formula I can type into my calculator and figure it out myself, but I want easy! Thanks!

## Discussions

If you can get access to a laser cutter you can produce very accurate and workable gears like this

Ply wood works amazingly well for gears if they are lightly loaded, Making very small sizes however is a pain and not so successful - for that you need to go to Acrylic plastic & a laser cutter.

This works well if you need a template for more normal shaped teeth

Auto desk inventor (there is a trial version that should work for you) will generate gear patterns and produce DXF files you can print or get cut.

Actually for a lot of the CNC home made machines - and not a few commercial once aluminium pulleys and toothed belts are the way to go - these can be bought at reasonable prices from online sources.

If you need metal toothed gears either find a friendly hobby engineer who has a lathe/milling machine and pay them to make what you want - should be reasonable or you should be able to find a gear making specialist you can use if you search. Often they will send you a catalogue of their stock gears and you just choose and pay.

What kind of calculations do you want ?

Steve

lol, I'm not really sure I guess. I just don't know what gears will do what, that's why I was looking for a gear calc so I could mess around with it to figure out what I needed.

Calculating the things is a lot easier than assembling them well !

Understand that gears must be of the same "DP" (diametral pitch) to mesh. Think of DP as the number of teeth per inch of circumference. so 15dp gears would mesh with 15 dp gears, but not 20dp gears.

Getting Single reduction ratios of more than about 10:1 tends to expensive, but gear ratios multiply,so making a 10:1 reduction with a 2:1 followed by a 5:1 is more economical, though there are more parts.

Steve

On the other hand, a single larger reduction would have less slack in it so would improve performance, especially in a CNC machine. You could avoid the issues with gears by using toothed belts, the ratio of which can be calculated in the same way as normal gears.

Belts are a good idea in many cases - but again, extreme reductions are expensive.

If you're worried about slippage (brings us back to the question of how much error you can tolerate), chains may or may not do better than belts.

If you're trying to calculate the ratio a pair of gears/pulleys will increase or decrease rotation speed, that's the ratio of the circumference of one to the other, or for gears the ratio of the number of teeth on one to the number of teeth on the other. Their meshed edges have to travel the same distance in the same time, and there have to be the same number of teeth per inch of circumference for the teeth to stay meshed.

(Actually, for gears I think that number of teeth is a better calculation -- easier to measure exactly, and avoids questions of whether to use the radius at the top of the teeth, their base, or somewhere between. For pulleys, remember to use the innermost radius rather than that of the raised edges which just keep the belt from slipping off.)