Please help! Having difficulty trimming the included model

Rhino Rhino for Windows
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Hello. I have been trying to trim the attached model and have been experiencing a lot of difficulty getting it to fully trim, to look like the included screenshot, (a result only derived with much effort trying different order of trimming operations, etc. and generally failing to get the model to completely trim per the example.)

I tried a number of different ways to model this part, including sweeping all of the recess cutouts in one operation, which worked great, but because of the 3 degree angle of the outer face of the disk and the way it will connect to adjacent similar pieces which also have the 3 degree angle on their disks, I was ending up with undercuts happening in those recesses, so I had to abandon that idea and go with what you see in the attached model.

I have used Rhino a fair amount and honestly do not understand why Rhino is being so particular in allowing/ not allowing me to successfully trim this model. I spent the better part of two days working with variations of the design and even started over from scratch a few times thinking perhaps I had a corrupt drawing or some other issue. I’m at a loss at this point and could really use some help! I would very much appreciate any assistance any of your can provide!

Thanks in advance!
Abel

Example of successful trim of problem part
Example of successful trim of problem part901Ă—926 146 KB

XW_Bent Lam - CD - Design - 2.8 - Send to McNeel to be analyized.3dm (239.2 KB)

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Is this what you want?

XW_Bent Lam - CD - Design - 2.8 - Send to McNeel to be analyized.3dm (321.2 KB)

I trimmed the slot surfaces first with the base plane and then with the dome surface.

Trimming the slot surfaces with each other worked on one end but not the other, so I went back to the untrimmed slot surfaces to get the full intersect curve, which worked to do the final trim step on the slots.

Finally, I joined the slot pieces and used them to trim the dome.

1 Like
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Hi Measure. Thank you very much for your assistance! I opened the completed trimmed object you attached and that IS what I am looking for as an end result, the problem is that I have a number of such items to model and trim and they are often attached to each other and I am questioning if Rhino is up to the task as I have had a lot of difficulty so far with this project. More importantly, I don’t understand why Rhino is struggling to do what I need it to do and questioning if I have done something wrong in my modeling process, or if it is just something that Rhino is struggling with..? I was planning on Rhino being my primary if not only 3D modeling software, but not knowing what or who is to blame for my difficulties has me questioning, perhaps unfairly if Rhino will meet my needs. Can you provide any insight regarding why what I have modeled is not trimming up easily and what I may be able to do differently to get such a model to trim fully/more efficiently for this and different iterations of the same design?

I think I am following how you stated you successfully trimmed the model except for the following part: “so I went back to the untrimmed slot surfaces to get the full intersect curve, which worked to do the final trim step on the slots.” I’m not sure what you are saying there. Can you please clarify this with additional detail?

I have some additional questions if you and/or others are able to answer them:

How long did it take you to get the model fully trimmed and what was the logic you used to be successful? Was it mostly trial and error or something more specific?

Do you have any opinion as to why Rhino is being particular regarding the order in which things are being trimmed when it seems logical that the trim should have happened the way the trim selections were being made?

Is it typical to have such difficulties with Rhino regarding trimming such models?

I was often able to get the model close to fully trimmed, but not all the way in most instances. Sometimes Rhino would leave one surface part not trimmed or two or three parts, sometimes it would leave just a remaining profile curve not trimmed having successfully trimmed all of the surface shapes, sometimes it would remove a large portion of the disk/dome surface and successfully trim the rest, but rarely have I been able to get the whole model piece trimmed.

Are there tools other than trim that would allow me to go in and remove the surface pieces that Rhino did not trim?

Is there a list of best practices regarding trimming these kinds of objects regarding the process to do so efficiently?

Thanks for helping me!! Also, if other users could attempt trimming my model and give me feedback as well, I would really appreciate it! It is possible that I am doing something or multiple things wrong, so please assume I don’t know what I am doing. I could well be the entire issue. I just don’t know but I need to find out so I can proceed with my project either with Rhino or undesirably so, with a different modeling software. I’m quite frustrated over here, but trying to stay positive! :slight_smile:

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image
image1390Ă—1369 102 KB

I used Intersect on the untrimmed surfaces to get this curve, then after trimming with the dome, I could use the curve to trim the remainder of the slot surfaces.

image
image1023Ă—1141 76.7 KB

1 Like
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Its a bad idea to make surfaces that are coincident (or nearly coincident). That will often cause trimming problems.

I would make the slot like this (see file):
slot.3dm (2.5 MB)

To do the trimming select both objects at the same time then run the Trim command and pick the part you want removed on each object. When that’s done hit the Join button and you have a closed solid.

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Oh, wow, Jim! The tool you made does exactly what I am looking to do and the piece trims up perfectly. Can you PLEASE walk me through how you made this tool? I looked in the file you attached but there don’t appear to be any of the curves you used to make this cutting tool still present in their original forms, or any other signs of how you constructed it. It looks like the tool was made in multiple steps..? I need to do this same basic process a number of times on similar disks with different curves and of course I need to learn how to do this correctly myself. Please help!

As I stated in the post, I had previously tried something similar but my result caused undercuts to happen, which will not work for my need, so I abandoned that approach and a different approach of using Sweep 2 Rails with one curve used as the item to sweep caused some funky additional geometry to happen when it turned the sharp corner while doing the sweep.

Thank you very much for your response and help so far! I obviously have a lot to learn!

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I didn’t need any curves. I used your existing surfaces just in a different arrangement.

The slot is basically 2 sides and a bottom. The bottom is composed of 3 surfaces. Those five surfaces are connected by fillets to make the slot.

I don’t have time right now, but if i get chance this evening I’ll send another file showing the steps.

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Hi Jim! Thanks for the quick response! I am actively trying to figure out what you did in Rhino. That said, I am struggling. I will use what you told me here to try and figure out the process you used. I’m not sure I will be able to though. If you do get time tonight to do a file showing the steps, I would be grateful for sure! Thanks! Abel

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XW_Bent Lam - CD - Design - 2.8 - Revised per Jim’s direction.3dm (913.0 KB)

Hi Jim! I was able to figure out how you likely constructed the cutting tool from what you told me earlier and doing some experimenting. See the attached if you are interested.

I really appreciate the help you gave me today! This made all the difference and allows me to trim up the disk model without any issues now. What a relief! I can see what you are saying regarding having surfaces that are coincident or nearly coincident and such causing issues with trimming. I will keep that in mind for the future and seek to make one piece tools where possible.

I hope you have a great night! Thanks again and thanks also to @Measure for your help as well!

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That looks good. Probably better than what I did.

I compared it to your original model and noticed that the new slot is in a little different position. I point that out just in case you inadvertently moved it. That’s easy to do accidentally in Rhino.

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Thanks, Jim! Yes, I worked directly in my original model to try your solution. The one I uploaded as an example was more eyeballed because I was concerned that maybe my original model was corrupted in some way so I didn’t want to use anything from it while trying to get a solution. The most recent upload is the correct placement of things for my actual project. Again, thanks so much! I was becoming pretty disheartened about what to do and you gave me the solution. Have a great night!