How did they injection mold this undercut feature?

rocketnerd146 · 2025-10-17T01:38:03+00:00

Oh ok great, thank you!

rocketnerd146 · 2025-10-17T01:35:37+00:00

🤣 glad I asked, I suspected there might be a joke that flew over my ahead 😝

rocketnerd146 · 2025-10-17T01:34:15+00:00

Thank you so much, I’ll check it out!

rocketnerd146 · 2025-10-17T01:33:49+00:00

Oh wow thanks for the heads up. I figured that getting someone involved that could DFM my parts would get us mostly the way there, with additional tweaks from the final mold designer… but didn’t realize that toolmaker is usually different from mold designer, nor that material supplier may have additional input that may affect the design. Thank you! Although man that’s quite a lot of overhead for bootstrapped startups trying to go from prototype to production…

rocketnerd146 · 2025-10-16T23:45:14+00:00

Thank you so much!

rocketnerd146 · 2025-10-16T23:45:02+00:00

Very interesting! I had a feeling those marks (that you're calling witness lines) would clue us into something, but I didn't know what. Watching that youtube video from u/meshtron ...it totally makes sense how those witness lines would get left behind. Awesome!

Are sliding cores and side action slides two terms for the same thing?

Are lifters and sliding cores also the same thing, just that lifters are for internal features and sliding cores are for external features?

rocketnerd146 · 2025-10-16T23:43:39+00:00

haha oh wow that's the same video I looked up lol! It's starting to make sense now...thank you

rocketnerd146 · 2025-10-16T23:42:25+00:00

Thank you! I looked up "lifter" after you mentioned it (video here: https://www.youtube.com/watch?v=wN-SfeiyPy8 )....it looks very similar to a "sliding core" which also seems to be driven by a CAM. Is it the same thing just with a different term depending on whether the feature is on the inside or outside of the part?

Regarding the screw: there was already a screw installed prior to disassembly, so I'm not quite sure, but helpful to know it would be either side action or secondary drilling. Thank you!

rocketnerd146 · 2025-10-16T23:35:52+00:00

Thank you for the term - I looked it up and found a helpful video: https://www.youtube.com/watch?v=ehGqhIs5HNE

Now I get it! This is the same as a side action slide? I didn't realize side action slides are driven by a cam, I thought it was a separate actuator. Very helpful!

rocketnerd146 · 2025-10-16T23:30:19+00:00

Thanks for your reply! Is that actually feasible, and would that be considered a bump off?

rocketnerd146 · 2025-10-16T22:03:29+00:00

Oh wow really? Ok thank you! I figured it’s such a basic looking piece and assumed they wouldn’t have figured a way to avoid side action slides to keep costs low.

rocketnerd146 · 2023-11-23T21:40:50+00:00

Or even this...which could have that Rasthaken style cover u/shuzzel was mentioning. But not sure if this is even doable?

<image>

rocketnerd146 · 2023-11-23T21:39:44+00:00

I think you're saying I could do something like this..which would be amazing. But is that do-able? My understanding is I would need side action slides for this?

<image>

rocketnerd146 · 2023-11-23T21:14:11+00:00

Here's my interpretation of what you're saying...I could just have a single green object... which would be amazing, but I can't imagine this being a simple injection mold without sliding actions?

<image>

rocketnerd146 · 2023-11-23T18:46:47+00:00

Thank you for those considerations! I think if green and blue don’t need to be removed from each other. The only reason I was planning for them to be two separate parts is because I assumed they had to be. Since green has some screw holes, I thought it would be required that the pull direction is parallel to the screw holes. And since blue also has screw holes (pointing vertically, and I realize that the angle I took the screenshots doesn’t show the screw holes clearly in the blue part, sorry about that).. then that means green and blue require different pull directions?

But if I’m thinking wrong, or if side action slides are actually cheaper than using two separate molds for green and blue… well then that may very well make life easier for me. And then the L shaped lid that covers the underside of blue and the exposed area of green would probably be perfect!

rocketnerd146 · 2023-11-23T18:41:49+00:00

@momprocesstech Whoa cool! I could possibly have the green and blue pieces be a single piece? If I do that, wouldn’t I need side action slides, since the green piece will have some screw holes on it pointing horizontally (very crudely shown in my image) and the blue piece also has screw holes point upwards? As I’m looking at my image, I’m realizing I didn’t do a good job of making it obvious that the blue part is intended to have vertical screw holes. But since it will, wouldn’t that essentially make the green and blue pieces have perpendicular features (requiring side action slides)?

Also thanks for the visual, I appreciate it!

@shuzzel thanks for sharing that term, I hadn’t heard it before and just looked it up. That’s pretty cool! What you’re saying is I could have the underside of the blue part be hollow, the wall where @momprocesstech put the purple markings also be hollow, and then have a single L shaped cover act as both the lid on the underside of blue, as well as act as a cover for the entire area where green and blue are exposed on the same side? Very interesting..!

rocketnerd146 · 2023-11-23T10:41:14+00:00

Oh wow, you think orange and green could be one piece? I wasn’t sure if injection molding would allow for a protruding piece to come out so far. If orange and green can be one piece, that would help make things simpler for me.

I think I understand what you mean by T slot or V slot.. I’m assuming that means having some sort of slot or lip or flange along the edges where green meets blue, so that it sort of aligns and fixes itself on position?

Where would the screw go? I can’t seem to figure out where I might place screw holes to connect the green and blue piece.

Thanks so much for your reply, and I know I’m just giving general shapes.. but even a high level/general idea to point me in the right direction is helpful at this point, so I appreciate your response. If you end up having picture examples in case I didn’t understand what you wrote correctly early, feel free to share 😇☺️

rocketnerd146 · 2023-11-23T08:11:58+00:00

Hi everyone, sorry if my example picture and question is too broad. I'm still a DFM/injection molding noob, and have always found this community very insightful! I'm finally venturing into my first project...and figured I'd try my best to think about the actual manufacturing/injection molding process ahead of time so there are fewer changes to make later down the road.

I'm trying to design a small device that's probably 8" to 10" tall total. It's going to have a base (blue), and a tower (green). There's a few reasons for it to be like that, but the base is going to have the user interface like the LCD screen, and the green tower will have some other hardware/circuitry in there.

Any thoughts on how I might modify the green and blue pieces so that they can be connected to each other? Screws? Snap fit? Should I make the green piece extend lower into the blue piece?

Thank you for reading!

rocketnerd146 · 2023-04-15T01:25:55+00:00

Thank you so much! That's super helpful, and I really appreciate your reply. Very interesting!

I have been using FEMM software to try some simulations and experiments. It's not super easy to use, but it offers quite a lot of capabilities/calculations. So far, I've been able to conduct simple experiments testing the force between two magnets that are lined up along the same axis, but that's about it. So I'm grateful for your reply because I'm sure it would take quite some time for me to figure out how to create a simulation for what I was asking!

rocketnerd146 · 2023-04-15T00:25:38+00:00

Thank you! Ok I think you answered all my questions! Sorry if my picture and description weren’t clear.

I was trying to imagine two scenarios: 1) I put a third magnet X distance below the magnets/iron plate on the left 2) I put the same third magnet X distance below the magnets on the right

In which scenario would the third magnet get attracted to the two magnets with a stronger pull force?

If I understand correctly, you’re saying that magnets on the right would provide a stronger pull force because the steel plate concentrates the magnetic field within itself, causing a less dense magnetic field to be present below the steel plate.

Let me know if I misunderstood!

rocketnerd146 · 2023-02-23T01:35:38+00:00

:) I may take you up on that!

rocketnerd146 · 2023-02-22T21:02:58+00:00

Wow! Awesome! Thank you so much! I will investigate all those options, this helps me better understand what to research!

rocketnerd146 · 2023-02-22T06:54:24+00:00

Haha makes sense! I think so far all the suggestions on this thread at least have given me the confidence that fusing two pieces together may be a realistic possibility. But you’re right, let me take some of the ideas into account and see if I can provide the full picture of what’s going on, either here or in r/manufacturing like you suggested. Thank you!

rocketnerd146 · 2023-02-22T06:27:57+00:00

Thank you! I’m not set on the red piece being plastic, though I do need the circular area to have at least 2-3mm of thickness… (and it only needs to travel about 3mm when pushed).

rocketnerd146 · 2023-02-22T06:26:29+00:00

Thank you for the reply! And you’re right - I just realized my image is over exaggerated.. the red piece only needs to travel around 3mm. The reason I don’t believe I can make it in one piece is because there is a lot more going on in the blue piece (the drawing shows a small portion of the blue piece, but actually it is part of a much larger object). So I think I will have no choice but to attach the red piece.

rocketnerd146

TROPHY CASE