Bevel Gears (again) - how to modify the non-tooth body of the gear

[Gary Barker]

I was able to create the bevel gear TEETH relatively quickly. But there is more to a bevel gear than just teeth - there is the cylindrical shank and the shoulder - and that is where I am having trouble...

We need a 3D model of these little 1.25" diameter 20 tooth bevel gears in order to have them plastic molded.

I was able to modify the sketch of the revolved center portion of the gear (the next to the last step generated by the Design Accelerator) to get most of the added cylindrical shank and shoulder shape I need. But I am having trouble "closing the gaps" to get a model that I can fillet and draft for molding. Here are the two problems...

1) picture a revolved T-shaped "body" below the gear teeth. How do you create a solid fill between the flat top plane of the T-shaped gear body and the curved back side (bottom side? large end?) of each of the 20 gear teeth?

2) how do you get the gear teeth and the revolved solid that connects them all be one solid piece? (I think they are not connected because I can't cut away any portion of the gear teeth, but I can cut away portions of the revolved solid)

Any help is appreciated, even it if is a referral to a video or a book. Thanks!

[JD Mather]

How much experience do you have with Inventor?
Attach the ipt file here and perhaps a hand sketch of what you are trying to do.

[Gary Barker]

Thanks JD!

I many years of AutoCad experience, and a few years of ProE time. I'm using a friend's Inventor to see how I like it. So far no problem using it for simple molded parts, but this little gear is a big headache.

I don't have access to the machine to get a IPT file tonight, but here is a JPG that shows the problem area. Hopefully it is self-explanatory. We need to fill the spaces behind each tooth so there are no undercuts in the molded part. Bevel Gear problem.jpg

[JD Mather]

This is so trivially easy in AutoCAD, Pro/E or Inventor that I feel I must be missing something.
I will have to see the ipt file.

[Gary Barker]

I have the IPT ready to share, but I can't attach it because it is larger than the max 500KB.

Is there anyway I can shrink the file size without opening Inventor again (it's on a friend's computer, not this one)

[Gary Barker]

I think I figured out how to shrink the smaller file enough. The larger version I can only send a picture of.

My first message was not very clear. I can "fill the undercut", but NOT in a way that is simple and elegant and clean enough to allow the drafting and filleting that I need to do to make a plastic 'mold-ready' part.

So the IPT file called "First Try" just used projected geometry to fill the gap. Pretty easy, but its not the style I want, And even with this "simple" fill method I then can not put clean fillets all around the teeth and shoulder.
(I suppressed most features to get the file size small enough. Start turning them back on at Revolution 3. Do not turn "Fix Body" or "Pitch Diameter" back on)

The attached picture shows what I want the teeth to look like, especially how the outer back of each tooth extends out to be part of the 32mm diameter shoulder of the body. I did a lot of crude steps to get it to look like this, and you can maybe see that the valley between each tooth does not actually line up with 32mm shoulder.

On neither of these models can I do all the filleting I want for molding - it's like the teeth edges don't connect perfectly with the revolved body, or the teeth have some sort of constraint that interfere with filleting.

So what I want is a gear model that is solid and connected enough to then draft and fillet.

I was thinking about starting with the face length longer and just cutting away some of the inner and outer edges of the gear - but I don't know if changing the face length will alter the tooth geometry so much as to cause other problems...

[JD Mather]

I think I figured out how to shrink the smaller file enough.

You are doing too much work.
To shrink the file size simply drag the red End of Part marker at the bottom of the feature tree up to the top of the browser - hiding all features in the graphics window. This will make the file significantly smaller (without the tedium of suppressing features). If you wanted to get it still smaller - save the file with the EOP in a rolled up state and then in Windows Explorer right click on the filename and select Send to Compressed (zipped) Folder. Then attach the *.zip file.

The larger version I can only send a picture of.

As I suspected - it would be trivially easy to get the desired geometry - but as I am using 2012 you would not be able to open my solution (but the procedure hasn't changed in years - so roll up your EOP, attach your file and I'll post screen shots of how to do that easily (and correctly).

When you attach the "finished" file - also attach at the state before you did anything at all to it (or I will have to recreate it myself) as I need to see it in a virgin state before it is "messed up" in the attempt to get the desired geometry.

[Gary Barker]

OK, moving the "End of Part" up near the top is a cool way to decrease the file size

While doing so I temporarily stopped right after the step where the portion of the gear is made that the teeth are cut from. Very strange that they cut so much of that thin ring away just to later fill the center back in. Seems like that early step has potential for altering to a bigger revolved section that looks like what I wish to create...

In a moment I'll post the shrunken files.

[Gary Barker]

For some reason I can't upload the IAM file. Perhaps at 54.5KB it is too big?

Anyways I did upload the virgin Bevel Gear21 that the Design Accelerator created as part of the assembly

Also attached is Bevel Gear21test which is the copy of a copy that I monkeyed with so much to make the JPG posted earlier.

If you can show me how to alter Bevel Gear21 to have the same shape as Bevel Gear21test, without all the bad practices I did, that would be very much appreciated!

[JD Mather]

Before I spend too much time on this - are you going to use this geometry for manufacture - or simply to represent in your assembly and then purchase the gear off-the-shelf from a gear manufacturer?
The reason I ask is because I think the Inventor Gear Generator toothform is a simplified representation - check in the assembly to see that the gears aren't actually intersecting.