Gear formulas question.

[hobby]

Hi everyone,

I looked on the innernet, to find out about making gears, a lotof info, out there, but I'm not grasping the main concepts, yet,

Could someone please explain in detail, what formulas and procedures do you use to make a gear.

To make a gear from a blank, with a specified number of teeth, do you have to know diametral pitch and things, or just divide the circumfrence by the tooth number.

Just for example, if you were to make a gear with 40 teeth on a blank that is 2" diameter, is it as simple as dividing the teeth into the circumference, or what procedure from start to finish would you do to accomplish this.

Excluding the actual machining, with a hob, or gear cutter.

Thankyou...

PS.
I'm not making gears yet, but always wondered about the formulas involved.

 

[John S]

Look for a book called Gears and Gear-cutting by Ivan Law.
It's in the workshop practice series and isn't expensive, plenty of copies on both sides of the Atlantic as you haven't said where you come from. This book is based on simple home shop gear cutting and doesn't try to cover loads of extended maths that you have no control over anyway.

 

[Richard1]

This website seems to have most of the formulas listed that you would need.
http://www.engineersedge.com/gear_formula.htm

In your example of a 40 tooth gear on a 2 inch diameter blank the formula for DP is Number of teeth (N) + 2 = 42 divided by the OD of the gear so
P= (20 + 2) ÷ 2 so you would have a DP of 21.

Depth to cut = 2.2 ÷ P +0.002"
Depth is 2.2 ÷ 21 + 0.002 = 0.107"

You would however be better working from a known DP and number of teeth and making the blank to the right size in which case the formula is
OD = (N+2) ÷ DP

The above is just very basic and assumes ordinary spur gears in DP pitches.

 

[hobby]

Thanks guys.

Using the formula DP = ((N) +2) / OD

Then I could rework the formula back and forth to solve for gear blannks and OD's.

And I could then take a ready made gear, count the number of teeth, and measure its outside diameter, to be able to calculate the DP so as to make mating gears.

That's simple enough.

Thanks again...

 

[mklotz]

You might want to get a (free) copy of my GEARSPUR program. Given any two facts about a spur gear, it will calculate everything else you need to know - including whole depth which you'll need to cut gears.

Here's a sample output using your example data...

[I]mperial or (M)etric units?

Enter whatever data you know. Enter zero (0) for unknowns
You must enter two data items to obtain an answer.

OD of gear [2.35 in] ? 2
Number of teeth [45] ? 40

Diametral Pitch = 21.0000
Module = 1.2095
Number of teeth = 40
Outside Diameter = 2.0000 in = 50.8000 mm
Pitch Diameter = 1.9048 in = 48.3810 mm
Addendum = 0.0476 in = 1.2095 mm
Dedendum = 0.0571 in = 1.4514 mm
Whole Depth = 0.1048 in = 2.6610 mm
Circular Pitch = 0.1496 in = 3.7998 mm
Tooth Thickness = 0.0718 in = 1.8239 mm

B & S cutter number used to cut this gear = 3

 

[hobby]

Marv
Thankyou for the link.

A lot of good info on that site.

I'll be sure to use it from time to time.

Thanks again...

 

[Mainer]

What John said..... Get "Gears and Gear Cutting" by Ivan Law.

 

[tel]

I'll third that, that book is pure gold.

 

[hobby]

Thanks guys.

That book must be excellent, according to amazon.coms customer reviews, it got a 5 star rating, no one had a bad review.

I'll get that book when I am ready to pursue gear making.

Thanks again...

 

[precisionmetal]

Hobby,

Learning/understanding the basics will get you through 95% of anything you'd probably ever need, especially if the plan is to cut typical/standard gears using standard cutters (e.g. involute form cutters using a dividing head in a milling machine).

Beyond that, just fire away if you have questions. There's plenty of people here that will jump in and help.

PM

 

[Cedge]

Surfing on Youtube, I stumbled onto an interesting series of videos on making homemade hobs for gear cutting. http://www.youtube.com/user/Hobbynut . He shares enough information to get started, if you're interested enough to have a go at it.

He also offers a neat little windows friendly freebie on his web site, called "gearcodit" for calculating all the needed gear cutting data, as well as G-coding for CNC. His web site is located at www.leatherwoodplayground.com . The gear utility is located in his "machine shop" area.

After having gone the single tooth cutter route, I'll be making up a few gear hobs of my own when I go back into the shop.

Steve

 

[Maryak]

After having gone the single tooth cutter route, I'll be making up a few gear hobs of my own when I go back into the shop.

Steve

Took the words right out of my mouth. I'm currently on the scrounge for a decent lump of drill rod. ;D

Best Regards
Bob

 

[shred]

I've seen a fair bit of debate online about HobbyNut's methods, but it looks like they work well enough. I'm plotting to try them at some point in the future as well.

 

[Cedge]

Jose Rodriguez shows the same basic technique in his instructional DVD "Making Gears the Easy Way"..... if you can stay awake long enough to get through it. He notes that once you have the created the hob for a given classification, you can cut any tooth count of that size with the same hob. With a matter of creating a few profiles, one can cut nearly any gear needed. Sure sounds cheaper than buying a full set of involute cutters.

Steve

 

[putputman]

Steve, that was a very good video. Thanks for posting it. I watch the complete series on cutting gears. Haven't watch all the series on making the hobb yet.
I have a question that maybe you can answer. When he cut the gear, he cut .005 depth at a time until he finally reached his .090 depth. He mentioned that you had to do it in steps to accomplish the profile.
I don't understand why you can't cut to the full depth the first time around. I wonder if his light cut where due to the fast he was using light equipment.
It just seems to me the profile would be generated as you rotate the gear.
All those .005 passes are fine with CNC equipment but would take forever manually.
I just can't get my head around it.

 

[Cedge]

Putput
He was working with Taig or Sherline sized machines, so lighter cuts were required. I'm sure, heavier equipment would have allowed him to be a bit more aggressive.

I was amazed that he's gotten so much negative response to doing the videos. Reading between the lines it seems he almost decided to stop doing them after "the experts" went at him. Being nibbled to death by ducks still means you're just as dead. I'm glad he got over the shock and went forward.

Steve

 

[shred]

Putput
He was working with Taig or Sherline sized machines, so lighter cuts were required. I'm sure, heavier equipment would have allowed him to be a bit more aggressive.

I was amazed that he's gotten so much negative response to doing the videos. Reading between the lines it seems he almost decided to stop doing them after "the experts" went at him. Being nibbled to death by ducks still means you're just as dead. I'm glad he got over the shock and went forward.

Steve

I'm not sure you don't need the steps to create the shape, but it's worth a try both ways if you've got more rigid equipment. Likewise, I was kinda surprised by how the keyboard commandos were (though he does throw out a blooper or two). For most of our purposes we don't need a perfect tooth form anyway, just something that will mesh and deliver power reasonably well.

 

[Cedge]

Shed
After the single tooth thing, I'm convinced model engineering doesn't always require NASA standards...LOL. I'd do it again, but getting that tiny cutter profile right was a bear.

Give the guy his due.... his gear change box for the Sherline lathe isn't something you'll see just everyday....LOL. He's obviously hobbed a few gears that worked.

Steve

 

[Blogwitch]

I am looking at the moment at cutting internal module gears by making a spur gear and grinding it up to make an internal hob. I will also be cutting external gears by using commercially produced gear hobs, and using them in a slightly modified way to how Jose Rodriguez does with his home made ones.

http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Gear-Hobs

I have found this program very useful for getting all the data I require, for all types of internal and external gears, for both DP and Module. All the inputs aren't required, just the size of the cutter and number of teeth, plus how you want the output, metric or imperial. You don't have to input your name for the program to work, that is only if you want to send the data to Berg so that they can make the gear for you.

Go to here

http://www.wmberg.com/tools/

and download the program 'GearSpec' and unpack and install it.

Blogs

 

[Cedge]

Putput
My last response was a bit quick on the trigger and made an assumption that wasn't justified. I had only reviewed his videos on making the hobs. In his CNC gear hobbing collection he explains that the movement in .005 increments assures that you'll have a smooth "rounded" transition on the involute surfaces.

Makes sense, I suppose, but I'd have to give things a try to be sure....(grin)

Steve