[CAD] My Involute Gear Cutter

[LightningEngineer]

When I first started my interest in the mechanical world involute gears were always something of interest to me. I just thought I would share this little CAD model I made this evening for those that have any interest, and maybe get some feedback from the more experienced crowd.

I'm happy to share the original design files if anyone wants to toy around with it.

 

[Seagoon]

I'm the total opposite of an expert so please can you tell me the purpose of an involute gear? I have never heard of such a thing.

 

[philthy]

can you draw back rake on the model?

 

[LightningEngineer]

I'm the total opposite of an expert so please can you tell me the purpose of an involute gear? I have never heard of such a thing.

I'm sure others could probably explain a lot better than I, but I'll give it a shot. An involute is the profile or shape of the gear. They are quieter, produce less vibration, and less wear than a straight gear shape.

Involute: "a curve obtained from another given curve by attaching an imaginary taut string to the given curve and tracing its free end as it is wound onto that given curve"

The difference between an involute gear and a "straight" cut gear is that an involute always makes contact as it moves in a "steady line of force"

The gif is of the involute and a "steady line of force". Do you see how it always makes contact as the gear turns?

can you draw back rake on the model?

I will have to change a few things on the model since this is my first time playing with the involute concept. I should be a bit more aggressive in the front, and add some back rake. I have a gear book around here somewhere that I'll try to redo the model to complete specs, and add measurements. I intend to make a cutter here so I'm trying to learn the mechanics of it.

 

[Kevin54]

LightningEngineer....Welcome to Garage Journal. I think you will like it here.

As far as being an Engineer....what do you specialize in mainly?

And I read this three times and it's still a mouthful. All I can say is that it's pretty curvy

Involute: "a curve obtained from another given curve by attaching an imaginary taut string to the given curve and tracing its free end as it is wound onto that given curve"

 

[LightningEngineer]

LightningEngineer....Welcome to Garage Journal. I think you will like it here.

As far as being an Engineer....what do you specialize in mainly?

And I read this three times and it's still a mouthful. All I can say is that it's pretty curvy

Thanks!

Electronics is my specialty. Particularly RF, Power, and Analog. Electrical and mechanical mesh so much, and right now I'm working on a high power flashlight and lighting design which is what brought me into practicing my CAD.

Once I manage to finish the design I'm going to build myself up a thermal vacuum evaporator to make some reflectors, and do some anodizing. My goal is to have 90%+ done in house to keep the costs down. That means I could even do nitride coatings in the future!

 

[A_Pmech]

If you're planning to make it, I would reduce the chip clearance by adding a larger "shoulder" behind the cutting edge. A gear of that DP doesn't need anywhere near that much chip clearance. Other than that, it looks good!

Don't forget that the cutter needs back and side relief so that it will actually cut. You can get away without relief in brass, but most other materials will require relief and it will improve the surface finish on aluminum.

Regarding the involute form, have a look at how it is generated as opposed to directly machined in modern practice. A hob, having a straight tooth form like a rack gear is used to generate the involute profile on the gear by rotating the two in time. As the hob profile intersects the gear tooth, it generates a perfect involute tooth form.

The difference between an involute gear and a "straight" cut gear is that an involute always makes contact as it moves in a "steady line of force"

A "straight cut gear" is also known as a spur gear. That is, the involute profile is cut straight across the face of the gear blank. Straight cut gears are used primarily because they are easy to make and are adequate for a very large percentage of commercial products.

Helical gears use the same involute tooth profile as a straight cut gear, except that the teeth form a segment of a helix across the face of the gear. Helical gears don't suffer as much from the radius of action differential shown in the animation you posted. Note that as the gear on the left drives the gear on the right, the radius of action or "leverage ratio" between the two gears changes. Because a helical gear is operating at multiple leverage ratios across the width of it's face, it transfers power smoothly and with less noise.

 

[BLUE72CAMARO]

A couple things that jump out at me right away is the keyway is very odd sized on your i.d. there are standards out there for keyway sizes for size of bore.

Second it doesnt look like you have any relief on the cutter, what I mean by that is that your profile is on a common diameter and what you really need is the point where the cutting surfaces are to be the largest o.d. and the rest of the material behind it to have a couple degree relief to allow clearance and not rub on the part. With out this your tool will generate an extreme amount of heat.

I also agree with A_Pmech that you should have less chip clearnace and either a larger shoulder or more cutting teeth. I think I would prefer more teeth as a cutter like this is going to take minimal chip load per tooth and move pretty darn slow when cutting.

 

[srmofo]

maybe this can help you guys understand the involute gear a little easier
http://woodgears.ca/gear_cutting/template.html

 

[Kevin54]

Thanks!

Electronics is my specialty. Particularly RF, Power, and Analog. Electrical and mechanical mesh so much, and right now I'm working on a high power flashlight and lighting design which is what brought me into practicing my CAD.

Once I manage to finish the design I'm going to build myself up a thermal vacuum evaporator to make some reflectors, and do some anodizing. My goal is to have 90%+ done in house to keep the costs down. That means I could even do nitride coatings in the future!

Making tooling to make reflectors use to be one of my jobs, although we used aluminum to make the reflectors. If you are interested in going with an aluminum reflector, let me know, and I can show you some samples, and I probably still have some drawings of the tools. i was a Tool and Die maker in the aircraft lighting industry, and almost all of our lights involved reflectors. We can trade notes.

 

[E12-535iTurbo]

It's an interesting topic. If you make some changes in the design can you upload those too and not delete the original ones. It's nice to read along with the learning curve you'll go through for us newbies.

 

[LightningEngineer]

A couple things that jump out at me right away is the keyway is very odd sized on your i.d. there are standards out there for keyway sizes for size of bore.

Second it doesnt look like you have any relief on the cutter, what I mean by that is that your profile is on a common diameter and what you really need is the point where the cutting surfaces are to be the largest o.d. and the rest of the material behind it to have a couple degree relief to allow clearance and not rub on the part. With out this your tool will generate an extreme amount of heat.

I also agree with A_Pmech that you should have less chip clearnace and either a larger shoulder or more cutting teeth. I think I would prefer more teeth as a cutter like this is going to take minimal chip load per tooth and move pretty darn slow when cutting.

Updated teeth, changed keyway to specs of 3/32 Width, and 3/64 depth as per "English Standard Keyway and Key Sizes" chart. Added back rake angle of approximately 20 degrees.

Making tooling to make reflectors use to be one of my jobs, although we used aluminum to make the reflectors. If you are interested in going with an aluminum reflector, let me know, and I can show you some samples, and I probably still have some drawings of the tools. i was a Tool and Die maker in the aircraft lighting industry, and almost all of our lights involved reflectors. We can trade notes.

I'm quite interested in any goodies ya got!

It's an interesting topic. If you make some changes in the design can you upload those too and not delete the original ones. It's nice to read along with the learning curve you'll go through for us newbies.

Sure thing. I'm here to learn just like everyone, and happy to share. Updated images below!

 

[Kevin54]

I noticed that you drastically changed your design. I imagine that you have read up on the gears and that's how you arrived at your design, but you do know that with an involute gear, there are national standards for the cutters just as there are with woodruff key cutters? The higher number of standard gear, the less teeth of the gear being cut.

 

[LightningEngineer]

I'm reading a little bit at a time, the real use of the involute is to get more CAD experience. I was reading up on relief a bit. I still have tons more research to do, and since I have little mechanical experience I don't even know what I'm missing such as the standard keyways.

I'll have to look at some of those standards and see if I can try this again. You wouldn't happen to have any references for them would you?

 

[sanddan]

I'm reading a little bit at a time, the real use of the involute is to get more CAD experience. I was reading up on relief a bit. I still have tons more research to do, and since I have little mechanical experience I don't even know what I'm missing such as the standard keyways.

I'll have to look at some of those standards and see if I can try this again. You wouldn't happen to have any references for them would you?

Machinery's Handbook?

http://www.amazon.com/dp/083112900X/?tag=atomicindus08-20


I'll bet it's all there, very handy reference book to have.

 

[chris_1001]

I'm reading a little bit at a time, the real use of the involute is to get more CAD experience. I was reading up on relief a bit. I still have tons more research to do, and since I have little mechanical experience I don't even know what I'm missing such as the standard keyways.

I'll have to look at some of those standards and see if I can try this again. You wouldn't happen to have any references for them would you?

There is so much info on the web these days for standards and such. Ive looked up all sorts of stuff, I'd even look up a comparable gear and use their info for say the keyway.

In a few cases, I have made custom threads for non standard applications.

 

[BRIANBB]

Looks to me like we are not really talking gears here but cutters that look a little like gears. The cutters dont interact with other cutters that I can see. Correct me if I am wrong!

 

[chris_1001]

Looks to me like we are not really talking gears here but cutters that look a little like gears. The cutters dont interact with other cutters that I can see. Correct me if I am wrong!

Its a cutter to cut gears...

 

[A_Pmech]

That's looking better!

 

[gorilla]

Thanks!

Electronics is my specialty. Particularly RF, Power, and Analog. Electrical and mechanical mesh so much, and right now I'm working on a high power flashlight and lighting design which is what brought me into practicing my CAD.

Once I manage to finish the design I'm going to build myself up a thermal vacuum evaporator to make some reflectors, and do some anodizing. My goal is to have 90%+ done in house to keep the costs down. That means I could even do nitride coatings in the future!

I spent close to 40 years in the vacuum coating industry.I'll be interested to see what you come up with. I'm more than willing to offer any help that I can.