Hobbing contrate/frontal teeth

[stephenmcd74]

Good afternoon everyone

I wanted to model some contrate teeth which have been hobbed/generated.

Outer radius of hobbing cutter is 6mm.

I modelled the cutter, and  then implanted this 20 times in an assembly which contains the pinion to be hobbed. The aim is to break down the continuous process of hobbing into 20 steps for a half of a single tooth space. This could then be mirrored to create a single tooth, albeit with slightly jagged areas because of the 20 steps.

From within the assembly, I edited the pinion and used copy object to bring the 20 cutters into the pinion part file. I had hoped to use combine to then cut away the material where the cutters intersect with  the pinion. This could be done by either combining the cutters into a single larger object, and then subtracting this from the pinion (the combining didn't work at all - WHY??). Or, individually subtracting each cutter form the pinion using combine: this also didn't work, as combine fails after a maximum of 4 combines.

Alternatively, in the assembly I edited the pinion, and drew a new sketch on the tangential face of the cutter, which gives me the profile of the cutter. I then drew a second sketch at right angles to, and through the centre of, the first sketch, and drew an arc of r=6mm from the tip of the cutter to use a a guide. So I then used Sweep to move the profile in the first sketch along the arc in the second. This worked once, but failed on the second (out of 20!!) cutter.

Can anyone see a way to get this to work, or even see a better way of solving the problem?

Some files are attached

Many thanks

Stephen

[JDMather]

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@stephenmcd74 wrote:

Can anyone see a way to get this to work, or even see a better way of solving the problem?

Inventor 2020 - Swept Solid

[stephenmcd74]

Now admittedly I don't have Inventor 2020, and so have not had a chance to try Swept Solid.

But does it really have to capability to model the complex motion involved in hobbing teeth, in that the pinion must rotate while the cutter translates?

[JDMather]

Might have to do multiple Swept Solids - similar to the way you are attempting to model.

I think I would try to model the volume that the cutter would occupy over time rather than the static geometry of the tool.

Think of it like this - if I wanted to model the side cut of an end-mill, I wouldn't model and pattern the individual flute positions over time. Your geometry is more complex, but it is enveloped by a certain volume over position/time.

[andrewdroth]

I think you can accomplish this within the part by using your layout sketch and a sketch driven pattern. The trick is to extract the base points for the pattern, and make a new surface (face) to use as a guide.

Let me know if this is what you are after.

[JDMather]

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@andrewdroth wrote:

I think you can accomplish this within the part by using your layout sketch and a sketch driven pattern.

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OP is using 2015.

I don't think sketch driven pattern existed back then.

[andrewdroth]

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@JDMather wrote:

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I don't think sketch driven pattern existed back then.

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That's right...

[johnsonshiue]

Hi! If possible, please try Inventor 2020. Like JD and Alex mentioned here, Solid Sweep can create the desirable geometry very easily.

Many thanks!

[stephenmcd74]

Hello again

Yes, Johnson, I appreciate what you say about Inventor 2020, but I would just like to be absolutely sure that it is really capable of doing this.  I know this may be a big ask, but is there any chance you could show me it hobbing this pinion?

Also, I have to admit that I made a mistake with the files I sent previously, as I had used the wrong radius to arrange the cutters. Sorry about that. The newly attached files are definitely correct. Look at sketch 17 of "BWC2-2001-3 for hobbing". The red lines show the path of the cutter for each of the 20 steps. 

Thanks

Stephen

[johnsonshiue]

Hi Stephen,

Absolutely! Talk is cheap. I will try it first thing in the morning tomorrow and share with you the STEP file as a proof.

Many thanks!

[stephenmcd74]

Also, sorry Andrew, but the sketch driven pattern you have done isn't correct. 

To show you how it should look, I have hobbed a single space with just 3 steps. So the geometry of either side of the space is correct, but it is jagged because of the small number of steps. See "pinion 1 space hobbed".

Then I have mirrored that and done a pattern to give all 16 teeth ("pinion 16 teeth hobbed"). This is how the finished teeth need to look, but without all of the jagged stuff, and all smooth at the roots.

Are you all really certain that Swept Solid in 2020 can do this?

[stephenmcd74]

Johnson that sounds brilliant.

I have a lot of stuff on tomorrow, so please don't be offended if I don't get back to you until Monday.

I will be VERY interested to see how you get on.

Thanks a million

Stephen

[johnsonshiue]

Hi Stephen,

Here you go! The screenshot was taken on Inventor 2020. I used the SC Z3 R6.ipt as the Sweep tool to sweep along an arc path of 1.5mm radius in 20 degree (emulating your pattern).

Here is the circular pattern of 16 occurrences.

The attached file contains the parts with above features saved in 2020. Also, the STEP files are included so you can open them in 2015 to check.

Many thanks!

[andrewdroth · Accepted solution]

I think your missing a mirror there @johnsonshiue ,

[johnsonshiue]

Hi Andrew,

Many thanks for taking a look and recording the video! Yes, I did miss some detail. The sweep path is also a guess. I used an arc. I have marked your posting as the solution.

Thanks again!

[stephenmcd74]

Good Morning Everyone

Thanks for making the effort to send the various files and videos.

However, I am sorry to say that this is not the correct solution.

It is really important to understand the precise nature of the hobbing process, and therefore the geometry which underlies it. This is not an arc, but something more complicated.

During this process, the pinion rotates while the cutter teeth translate, but I believe that the Sweep Solid tool in 2020 will only allow a single solid to be swept, and not 2? So that being the base, it is necessary to move the cutting tooth in a more complex way, thus producing a compound motion of just the cutter which takes into account both the rotational motion of the pinion and the translational motion of the cutter. Please look again at sketch 17 of "BWC2-2001-3 for hobbing". The red lines show the 20 or so progressive positions of the cutter as it creates one side of a single tooth space.

As mentioned before, in my file "pinion 1 space hobbed" you can see exactly what 1 side of a single space should look like. Then I have mirrored this and patterned it 16 times to produce the full array of teeth which you see in "pinion 16 teeth hobbed". Apart from the jagged edges in these 2 files, the shape of the teeth is precisely correct, so if yours don't look like this then something is wrong.

What I really want to know is whether or not the Sweep Solid tool is capable of sweeping according to this complex geometry, or is there another way i can accurately reproduce these hobbed teeth?

Thanks again for your help

Stephen

[johnsonshiue]

Hi! I am sorry I did not realize the compound movement nature. I thought you had a tool moving along a path, based on the files you provided. Certainly, Solid Sweep does not allow more than one solid tool to sweep. But, you can create two separate Sweep features, right? Do they have to sweep along the path within one feature?

Many thanks!

[stephenmcd74]

Hello again Johnson

What about this:

I have done a new version of the file which is attached (BWC2-2001-3 for hobbing2). 

This time, you have the pinion, and the tool is in its starting position. Then look in Sketch 17. Here you have the 21 white lines which show the progress of the cutter as it forms one half of the space. But I have joined up the starting points of these 21 lines using an interpolation spline, which is in red.. So I was hoping that it would be possible to sweep the tool along this spline (using "profile held constant to path"/"follow path" - NOT "parallel") to give the correct profile.

Could you possibly give it a try it with the Sweep Solid tool?

Thanks for persevering with this.

Stephen

[johnsonshiue]

Hi Stephen,

I am not sure if I followed the instruction correctly. It can be done easily. I just picked one of the 21 lines. Then sweep the tool (see attached STEP file).

Certainly, you will need multiple solid tools to sweep along the paths. Please feel free to download Inventor 2020 to try.

Many thanks!

[stephenmcd74]

Hello again Johnson

Sorry to be such a pain. It's just that I am under a lot of pressure time-wise. Changing to 2020 will inevitably slow me down until I get used to it, so I really want to be certain that it will give me a clear advantage, and this stuff is a key area for me.

Could I possibly ask you to please have 1 more try at the Solid Sweep (using the same file: "BWC2-2001-3 for hobbing2" from my last post)? You have not used the interpolated spline as the sweep path.

To help you find the spline, here are 3 images of sketch 17 from "BWC2-2001-3 for hobbing2". The spline you need for the path (using "profile held constant to path"/"follow path" - NOT "parallel") is in red:

I would be so very interested to see the results if you could try this again.

Many thanks for all your help

Stephen