Spur gear mesh/backlash question

[Futterama]

Hi forum,

I'm working with some metric spur gears in azetal and steel, and need to know how far I need to place them from each other.

Module 1 gears: 80 teeth azetal and 10 teeth steel.
Calculated distance between centers without backlash: 45mm.

Module 0.7 gears: 75 teeth azetal and 12 teeth steel.
Calculated distance between centers without backlash: 30.45mm

Now I need to know how far to place the centers so there will be a bit of backlash to avoid overloading the gears. Also I don't know how much backlash I need, but I just need to know the exact distance between centers for both gear sizes (module 1 and module 0.7).

Is there a table for this somewhere on the web? Something like "add 0.1mm distance between centers for module 0.7 gears".

Thanks.

Best regards,
Futterama

[Oldmanandhistoy]

I believe you will find the information you are looking for here. http://www.roymech.co.uk/Useful_Tables/Drive/Gears.html

John

[HuFlungDung]

The center distances would most commonly be left accurately at the calculated seperation distance. Backlash is created by a slight overcut of the gear tooth's whole depth.

Commonly, one will use a gear tooth vernier caliper to measure the chordal thickness of the tooth right on the machine. However, these measuring tools do have limits on how small of a tooth they will measure. If you cannot get a caliper in to the pitch circle depth (the addendum deep), then you'd probably need to spring for a 3 wire measurement across the gear. There are tables or formulas in Machinery's Handbook to help you figure the pin diameter and the chordal measurement, so that you can infer the pitch thickness of the gear tooth based on how far a wire of a particular diameter fits down into the gear tooth space. The ideal wire is calculated to make contact near the addendum depth, which is where the pitch circle is located.

[RICHARD ZASTROW]

There is also a formula in the "HANDBOOK" for span measurement over a given number of teeth.

Dick Z

[Futterama]

Thanks for the replies. I'll place them with the nominal center distance and see how it works out. I have the possibility to try a few times to get it right.

[Mike Everman]

A workable method to get the mesh right is to put some plastic food wrap in the mesh between gears and tighten the movable one down, then run the plastic out. There is a product for that, though the name escapes me...

[Futterama]

Thanks Mike, I know this trick. The problem is that there is no movable part, since I will mill holes in an aluminum plate for the ball bearings to support the axles, so I need to know the center distance in advance.

[HuFlungDung]

Originally Posted by Mike Everman A workable method to get the mesh right is to put some plastic food wrap in the mesh between gears and tighten the movable one down, then run the plastic out. There is a product for that, though the name escapes me...

Plastigauge.