Question about gears.

[stevehuckss396]

How can I go about reverse engineering a gear. I have a starter and I need to make a flywheel with gear teeth to work with the starter gear. I also have an RC gear from a 20 year old car that needs to be replaced and is no longer available. Should I start looking for some kind of guage like a thread guage only for gear teeth? Is there another way to figure out what i have?

 

[Jordan]

I'm no gear expert. You should try to figure out if it's metric or imperial (module or pitch).
Some modelling clay (plasticene) can help figure out the pressure angle. Roll gear through it on a flat surface, cut along the resulting impression, measure gear flank angle. This assumes involute gear form (probable). It's effectively a rack form with straight flanks, which you can possibly find full scale drawings of, to help ID the tooth size.

 

[ironman]

Steve, what is the outside diameters of those 2 gears (the starter gear and the RC Car gear) and the number of teeth on each? Do you know if eithere is 32P, 48P or what?

Also, a few posts down here has good info on gear formulas. A good website mentioned is http://www.engineersedge.com/gear_formula.htm.

I use a little program called Gear Code It to make most of my gears (it makes the g-code for CNC ing the gears). It was written by Shorty Leatherwood in Kingsport, TN. His website is WWW.leatherwoodplayground.com. He also has Youtube videos on making cutters and hobs. He is a very nice individual.

Ray

 

[stevehuckss396]

Steve, what is the outside diameters of those 2 gears (the starter gear and the RC Car gear) and the number of teeth on each? Do you know if eithere is 32P, 48P or what?

Ray

I don't know what pitch they are. Could be metric.

RC = 2.188ish with 53 teeth

Starter = 1.607 with 14 teeth

 

[enfieldbullet]

to make a gear you lost you need a base diameter and a diametral pitch.

the gears must have the same diametral pitch to mesh perfectly.

what varies the gear ratio is the different base diameters.(which causes a different number of teeth in gears with the same diametral pitch)

so if you don't have the gear, measure the diameter it would have if it was in its journal or shaft(shaft position in design is defined after the gears, so it's position will correspond to the base diameter)

a tip:

try measuring the diameter of the gear from about the middle of the teeth and then divide this number by the number of teeth in the gear, if it gives you a round number it is probably right.

Edit:

in the missing gear case try to look to the gear that it should mesh with, that will give you more info.

 

[kvom]

I have a program called Gear Generator that is an inexpensive download. It allows you to input parameters for a gear, and then it will output both DXF and printed versions of the gear. In the case of the starter, you can play with the parameters until the on-screen gear look like what you have. Varying the pressure angle changes the tooth form, so you'll get a pretty good idea of the correct value. When it's as close as you can get, print out in actual size and compare the gear with the print version.

Once you're satisfied that it's as close as you can get, you can make a duplicate via DXF output and machine it from aluminum to check the mesh. If that works, then generate the flywheel with the same parameters but the larger diameter.

Of course, this assumes that you will mill the teeth on the CNC mill as a profile.

 

[cfellows]

Steve, the starter gear sounds like about a 10 DP. If you add 2 to the 14 teeth and divide that by 1.6 it comes very close. The other unknown is the pressure angle. Most common gears have a pressure angle of 14.5 degrees. However, a starter might have a pressure angle of 20 degrees or higher because of the stresses involved. To understand the geometry of gears, you need to first look at a rack gear. On a rack gear, the sides of the teeth are not curved but are straight forming a triangle with the top cut off. The slope of the triangle side defines the pressure angle. The higher the PA number, the fatter the gear tooth at the base.

The RC gear sounds like it's metric, which I don't have a basic understanding of.

Chuck

 

[stevehuckss396]

Thanks guys. I have a list of honey do's then i'm going to look into what has been posted

 

[Charles Lamont]

I agree with Chuck on the starter gear. The figure you give for the diameter of the 53 tooth gear is just 1% out for a gear with a metric module (D/T) of 1, which is a preferred value and seems likely. The 'correct' diameter would be 55 mm, or 2.165". The alternative would be 25 DP, which is not a 'known' size, 24 being the norm.

As to pressure angle, 20deg has widely been the preferred standard for three quarters of a century or so.

 

[enfieldbullet]

I agree with Chuck on the starter gear. The figure you give for the diameter of the 53 tooth gear is just 1% out for a gear with a metric module (D/T) of 1, which is a preferred value and seems likely. The 'correct' diameter would be 55 mm, or 2.165". The alternative would be 25 DP, which is not a 'known' size, 24 being the norm.

As to pressure angle, 20deg has widely been the preferred standard for three quarters of a century or so.

i saw it looked like metric too. maybe 53mm base diameter with 53 teeth, would be module 1. (which is tiny)

 

[stevehuckss396]

i saw it looked like metric too. maybe 53mm base diameter with 53 teeth, would be module 1. (which is tiny)

Not tiny at all. over 2 inch diameter is a huge gear for me.

 

[enfieldbullet]

i mean the spacing of the teeth.

the change gears in my lathe are 1.5 IIRC though.

of course considering that i am involved in horology i may have exagerated on the tiny. i have a few ladies watches which are REALLY tiny.

 

[Bastelmike]

I don't know what pitch they are. Could be metric.

RC = 2.188ish with 53 teeth

Starter = 1.607 with 14 teeth

Hi Steve,

I am famiiar with the metric world, but not with the imperial:wall:

The RC gear might be metric module 1, though the outer diameter You gave is a little bit too large.
Angle for metric gears is 20 degrees, with exceptions pretty rare. Another issue is there is the possibility of some shifting (german: Profilverschiebung)

It mightbe helpful to know the distance between the centers of the axles, and if You know it, number of teeth of the mating gear.

For the starter, I would assume imperial as I can't find any standardized metric modul for that gear.

Mike