How To Model A Screw Locking Patch Feature

[ptc-2204087]

Would anyone know how to model a locking patch screw feature like the one you can find in the STEP files that are available from McMaster Carr with the threads modeled? As the picture shows, there is a very small protrusion coming off the screw threads to represent the locking patch.

I can easily create a datum curve and project it onto the threads, which for all practical purposes is sufficient. But I am quite annoyed that I cannot figure out how to actually make it as a protrusion. If McMaster Carr can figure it out, it seems like I should be able to.

I find the visible locking feature quite handy to make sure the locking patch is actually engaged with the mating threads. Eternal thanks if anyone has any suggestions.

[KenFarley]

You can model the threads using a helical sweep.

One possible way I would model this is to build the model as a solid non patched screw, then cut a very thin-walled oval where you think the patch is, to a sufficient depth to look like what you want. You could even modify the surfaces of the patch region making them white or something that approximates the look of nylon.

I don't know where you will get specifics about where the patch is actually located on these types of screws. Maybe there are some sort of standards about it.

Modeling fully threaded screws can cause a lot of headaches if you are using a lot of them in assemblies. They cause a slowdown in hidden line rendering. I've suffered the effects of someone putting hundreds of them in an assembly and it becomes a nightmare to deal with.

[ptc-2204087]

If anyone is curious, a very detailed standard exists for inch screws that actually defines the dimensions of the patch which is MIL-DTL-18240. No metric equivalent, and we are using metric screws  which is how life works 😉 ND industries has a downloadable PDF which states 1.5 to 2 threads left free, a minimum of at least four thread pitches locking area, and 90° of patch coverage. Long Lok fasteners also give similar dimensions in their handbook catalog for standard patches.

I know how to create the helical sweep to cut in the threads on a solid part, but I do not see how you could create a thin walled oval cut. What would the oval be extruding to since the depth constantly changes as it is moving along the sweep?

You would think by 2025 graphics cards and processors should be able to handle threads 😁 I have been hearing for over 30 years how 2D PDF drawings will be going away!

[KenFarley]

You're not sweeping anything to cut the "patch". A protrusion with a thin wall (0.002 inch or so should work) is cut so you are basically making a "moat" around where the patch is. You might start the protrusion from the center axis of the bolt.

Graphics cards are powerful and able to do shaded stuff remarkably fast, but to the best of my knowledge hidden lines still need to be calculated algorithmically, thus adding a large number of edges that need to be evaluated makes things slow.

[ptc-2204087]

Oh, that did work to visually show the locking patch 😁

I started at the tangent datum and cut inward. What I really need is to extrude a protrusion an offset distance past Thru Next. Then I could extrude .002" past the next surface and it would like the McMaster Carr screw.

BTW, it would not nicely color the surfaces inside the cut. I would pick a surface and it would extend outside the cut ☹️

[StephenW]

I would have a chat with you if you worked in my engineering group if I found you have modeled all the threads on all your parts!

You're thinking small picture...YES, you can model the threads and locking patches and all the engraved text and rivets and all that stuff and it looks great on your 8 or 12 part assembly

BUT, my assembly uses your assemblies, and 6 or 8 others groups assemblies. My assembly has 1000's or tens of thousands parts. Weighs over a million pounds in the real world. Everyone of these parts adds time to my work and especially my drawings. I spent a lot of time "simplifying" my assemblies to make them go faster. Sometime I have to put my assembly within larger assemblies to understand or explain interfaces.

And then there is the drawings that have black blobs on the PDF because of all the detail that is in small areas.

All that saying, if you are modeling for manufacturing, you need to include the necessary detail to get the job done and convey the information necessary to build the parts.

If you are modeling for visual presentation, that's different, and maybe it needs a little flair to make a sale!

[ptc-2204087]

Um,

My assembly is a $50,000 to $75,000 electronic unit that is the engineering heart of what we make. Shall I run all of the hundreds of electronic COTS parts in my assembly by you and get your seal of approval that they are acceptable for my model? Will you be there to troubleshoot and do the paperwork when all the electronic components in the model are a simplified block and they screw up the electronic assembly in a unit that has 1000 wires, hundreds of fasteners, and hundreds of electrical components?

I might suggest that if you are managing something that weighs millions of pounds and uses assembly after assembly that it is perhaps not wise to deal with detailed subassemblies that contain even a singe internal fastener. You could take every single unit I work on, turn it into a rectangle with connectors and then you never have to deal with any of my detailed fastener models.

I am not trying to be a jerk, but perhaps we have conflicting requirements. I really do not think it is me seeing only the "small picture" or doing things to "make a sale".

[StephenW]

@ptc-2204087  

Sorry, I worded my reply in the completely in the wrong way and you are correct, my situation likely doesn't apply to you.

[ptc-2204087]

I accept your apology!!! Thanks it means a lot to me.

Let me edit my response above. We would need to work together to figure out a way to best handle these screws and also my many detailed COTS electrical parts. If it is destroying the performance for the rest of the company that is a problem. One way would be to just model the screw as cylinder with a colored surface to show the patch. Of course I would not have started this thread if I did that 😀

BTW, my basement partially flooded this weekend so I was probably much too harsh in my response above. Sorry about being so grumpy. 

[StephenW]

Yes! Communication is the key! It would need to work for everyone as best it could. Of course, my point of view is always skewed to my work, but discussing the issues will help find that solution that works for all!

Sorry about the flooding thing. It's just not a good situation to be in.

[kdirth · Accepted solution]

I would suggest using Offset>Expand>Sketched Area.

[ptc-2204087]

Wow!!! That is awesome!! Exactly what I was looking. I bow down to your Creo knowledge in deep, arcane menu choices 😁

I tried it out, and it worked exactly as you have pictured. I would never have figured that out on my own. Thanks!

[ArnoldCollett]

If you only want a visual feature to ensure that the mating bolt is interfering with the locking feature, you could sketch a rectangle on the center plane and add a plane at the top and bottom of the feature, parallel to the bolt head. Those feature won't make the part much "heavier" and you can show them when needed for the visual inspection. You can then use those features in family tables to change the locations for different sizes and lengths.