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Who knows Gears?

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cclark440

Alibre Super User
Who knows Gears?

I am trying to reverse engineer a gear that I want to reproduce in aluminum instead of plastic. My problem is I know just about nothing about gears.
I really just need to figure out what cutter I need to buy to cut a few sample gears.

Yell I am not even sure which gear this is, it is either a 14-1/2 Degree full depth Involute, or it is a 20 Degree Stub Involute.

Anyone out there give me a clue as to how to figure this out?
 
swertel

swertel

Alibre Super User


Get yourself a copy of the AGMA standard and have yourself a great nap.

The Machinery's Handbook does have a reasonable section of general information about spur gears, including methods of cutting and formed cutters.

Is this a sprocket or a gear? Your most common pressure angle for gears is 20 degrees. Sprockets vary greatly and are often confused with gears.

I hope you have a good set of reverse engineering tools. Determining the characteristic dimensions of a gear is not very easy. But, that's where you start. Calculate out the various gear dimensions for the gear size you think it is, then start measuring to see where you measurements come closest.

Can't you find out the OEM of the equipment you took the gear from and follow the trail to get the gear maker and a catalog/part number?
 
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cclark440

Alibre Super User


I wish I could follow the trail. Unfortunalty the manufacturer of the part I am trying to reporduce would not be happy with me making these parts, as this will cause a direct competion to them.

Anyway I have measured the gear and think I have figured out what it basically is. I was just hoping that Someone might have a better knowledge of gears and can help me confirm what I have.

I do have the machinist handbook, I guess I should just try reading a little bit more. My main question is how do you know what the Diametric pitch is?

Here is what I know
The outside diameter of the gear is .933"
There are 26 teeth.
The teeth are .041" deep (radially)

Just to clearify, this gear is really more of a pully as it engages a cogged belt. But it sure looks like a Involute stub gear.

Maybe I am barking up the wrong tree here. Should I be looking at something different?
 
swertel

swertel

Alibre Super User


Yes, a cogged belt probably does not have the involute profile of a spur gear.

In the Machinery's Handbook, look up Flexible Belts and Sheaves. In there is a section on Synchronous Belt Sections which has a table for standard pitch lengths and tolerances as well as section dimensions. If you have access to the belt, or the belt manufacturer's catalog information (belt's wear, get the info from your "competitor"), you should be able to find the right dimensional information for the pulley design.
 
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dgstoll

Senior Member


Do you have a belt that the sprocket runs with? Any numbers on the belt would help identify the pitch.

Try the Stock Drive Components website for shot in the dark dimensions
daveS
 
E

ericle

Member


"Bo Knows Gears"

On a serious note. If you are the academic type, I would recommend you head down to your local college library and look for one of the following:

- Mechanical Engineering Design - Joseph Shigeley
- Design of Machine Elements - Spotts
- Handbook of Practical Gear Design - Darle Dudley

The first two have sections on gear design and should allow you to figure out what you have. The last one is gears from start to finish. If that doesn't help you, well nothing will.

If you digest all three, you will be a bona fide gear expert.
 
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cclark440

Alibre Super User


Thanks guys!

Stock Drive Products, lists a Timing pully that is almost exactly what I am looking for.

Now I just need to find cutter to re-produce this profile. Unfortunalty I can't use off the self parts for my application.

Swertel
Mayeb I am just having a sever case of Cranial Rectalitis, but I can't find a flexable belt and Sheave section in my MHB. I have version 21 what version are you using? I did find the Flat belt, and V-Belt and Sheaves section.
 
swertel

swertel

Alibre Super User


I have Mach Hdbk version 25. The index only lists Belts and Pulleys with flat belts and v-belts indented. The flex belt and sheave section is shown on the page headers within the list of pages for flat and v-belts.

I just had to thumb through the entire section on belts to find information closely related.

The SDP is a great resource.
You should also look up Emmerson Power Transmission (EPT).
 
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dave2962

Senior Member
Timing belt pulley

If it is a timing belt pulley but you cannot use a standard pulley, you can buy timing belt pulley bar stock, which already has the teeth cut in it. Then you can cut off a piece and machine whatever bore etc you need. I recently bought some of this from MSC for a job I was working on.
 
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markhas

Member
Re:

cclark440 said:
Thanks guys!
Now I just need to find cutter to re-produce this profile. Unfortunalty I can't use off the self parts for my application.
quote]

If you have an optical comparator (shadow graph) handy measure the profile and grind a half round cutter to cut a few gears till you get into production. Maybe!

I dunno!? Just an idea...
Click to expand...
 
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cclark440

Alibre Super User


Dave

MSC has exactly what I am looking for.
When I saw how much it costs I about died!

$52.50 for 5", Then I have to machine it. WOW I might be able to get 6 parts out of a 5" length.

This project of mine might not be cost effective. Now I know why the other guys get so much for thier parts. Its all in the friggen Pully!
 
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