topic Re: Interference & Non-Interference issue in Inventor Forum

Interference & Non-Interference issue

Anonymous — Mon, 22 Aug 2016 12:54:54 GMT

As the Nut & Bolt thread surfaces are uneven different position of the Nut is giving different Interference result. How to overcome this issue?

Re: Interference & Non-Interference issue

mcgyvr — Mon, 22 Aug 2016 13:22:49 GMT

@Anonymous wrote:

As the Nut & Bolt thread surfaces are uneven different position of the Nut is giving different Interference result. How to overcome this issue?

You can't.. You need to be smart enough to ignore it..

Re: Interference & Non-Interference issue

JDMather — Mon, 22 Aug 2016 13:55:10 GMT

Your threads are not modeled correctly.

What is the Pitch Diameter for the Nut?

What are the formulas for the Nut?

Model the cut threads correctly and there will be no interference when in correct position.

Do you have any experience with Rotational/Translation Constraint?

Do you have any experience with Dynamic Simulation Screw Joint?

Using motion that mimics the real world will result in properly mating parts without interference.

Re: Interference & Non-Interference issue

swalton — Mon, 22 Aug 2016 13:40:22 GMT

Have you test fit a nut and bolt in the real world yet? Knowledge and experience with real-world components will help you answer some of these practical questions.

When I am checking a design and see an interference between two fasteners, I check each fastener to make sure that the thread specification matches. If they do, then I ignore the interference. If not, I make an engineering decision about the required thread spec and change the components as required.

I have not opened your parts, but it looks like you have modeled the internal and external threads for the nut and the bolt. You should see the amount of interference changing as you rotate the nut around the long axis of the bolt. If you don't want to see the interference, and you have modeled both threads correctly, apply an angular constraint between the nut and the bolt and adjust the angle value until the interference is gone.

This process can consume a large amount of time, so only do it if you have to prove that the threads don't interfere. I have done it when designing new thread forms for implanted medical devices. Standard threads don't require this level of detail.

Re: Interference & Non-Interference issue

Anonymous — Mon, 22 Aug 2016 14:07:30 GMT

Specification is 5/8-18 UNF 2A

If you can pinpoint the error I can correct it.

“Correct Position” means Rotational/Translation Constraint.

I don’t have any experience with Rotational/Translation Constraint but I can find out.

Re: Interference & Non-Interference issue

Curtis_W — Mon, 22 Aug 2016 15:10:23 GMT

HI fiatnm,

In your quest to understand threads in the other discussions, you've received a number of answers telling you not to be concerned with threads, and so on. Understand that many people (myself included) never need to be concerned with modeling, constraining, and driving realistic threads, in the course of normal design and engineering work.

Simply put, fasteners are pre-engineered, so that we can specify the correct fasteners and corresponding threaded holes.

I have had only two occasions over the years to see someone need to go beyond the normal use of threads, and do or use the engineering involved for themselves. One instance was a company who developed their own proprietary threads. I think they make fans, if I recall correctly. The other was a college professor who used the engineering concepts to animate a fastener in a threaded hole, using Inventor, for academic purposes as he was teaching a lesson. (this was not JDMather but he likely does something similar).

To most people, your question is academic in nature. And I point that out so that you can understand the difference in the answers you get.

And I'll give you a hint to this question, by pointing you to this example:

http://forums.autodesk.com/t5/inventor-general-discussion/motion-constraints-turning-a-screw-in-a-hole/m-p/5490998#M535426

In that example, JDMather has set up the model very close to what you are asking. I only looked at it briefly, but I think the value in the Drive This step value was "fictional" and not calculated, therefore it will show interference as it turns, but it does rotate as it moves forward. Calculating that step value will be key here. JDMather is welcome to correct me if I missed something, or misinterpreted something.

Don't let that example be a distraction, your bolt and nut is a probably a better example for you to concentrate on, because it is a simple example. But the vise example can help you understand the tools to use in Inventor.

One last hint, you'll want to use (or link) the pitch parameter from the parts into the assembly and use that value to calculate the constraints.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

Re: Interference & Non-Interference issue

Anonymous — Tue, 23 Aug 2016 10:07:15 GMT

Sometime when I select from this options Interference disappear. Actually what is happening?

Re: Interference & Non-Interference issue

JDMather — Tue, 23 Aug 2016 11:09:21 GMT

@Anonymous wrote:

Sometime when I select from this options Interference disappear. Actually what is happening?

Attach your files here that exhibit this behavior.

Re: Interference & Non-Interference issue

Anonymous — Tue, 23 Aug 2016 12:32:36 GMT

Re: Interference & Non-Interference issue

JDMather — Tue, 23 Aug 2016 21:18:23 GMT

1. My instructions were to attach the assembly that reported No Interference behavior.

That is not what you attached.

The part you attached has thread diameter set to Minor Diameter, not Major Diameter.

You should have gotten a warning message indicating caution - because that results in an incorrect hole size.

(If you Manage>Rebuild All on the part and watch the hole - you should see it grow in size from correct Minor Diameter size to incorrect Major Diameter size). To answer your question - that is what is happening. The hole is getting bigger.

This entire topic seems to have you really confused.

In general -

1. use the settings for cosmetic threads as generated by Inventor.

2. mating threads must use same specifications.

3. designers don't worry about interference with correctly specified cosmetic threads - because there should be interference.

3.b. if there is no interference as the result of changing to your Major Dia as you indicate - there is danger of wrong hole size being used if the 3D model goes directly into CAM without awareness by the CAM programmer that you overrode the correct tap-drill size.

4. Only model threads when you are going to 3D print or in special cases like very large special purpose threads for special visual applications.

Re: Interference & Non-Interference issue

Anonymous — Thu, 25 Aug 2016 08:23:48 GMT

This entire topic seems to have you really confused.
--------------------------------------------

Yes you are correct “I am confused” because sometimes assignment gives different size in mating thread.

It was from you I came to know that “Two mating parts must have same thread size.”

3. Designers don't worry about interference with correctly specified cosmetic threads - because there should be interference.
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It was from you I came to know that “There is no problem to have interference if cosmetic threads are correctly specified.”