# Create bone model with screw cavity

How can we create such this bone model having cavities that perfectly fit with its corresponding screws? I've tried boolean function (all of its variations from intersect, difference, slice, with slicer either bone or the screw) but all I got were the hole on the surface.

By the way the bone model that I'm working with is a bone having thickness of 3 mm, not like the image below.

My current attempt is to have both the portion of the screw 1 inside the box and the cavities on the box itself. But my attempt failed as the screw thread was all gone.

2nd edited: My intended goal was to recreate something similar with this model coming from a paper in 2015 (doi: 10.1007/s00264-015-3106-y). .

As you can see in the green circle, there were the cavity in the bone, prepared to be inserted by the screws. I would like to create that one, but in my own bone model, which is hollow inside and has some thickness as shown here .

• Can you show your attempt? It would be easier to answer seeing what does your mesh look like Jan 13, 2022 at 9:20
• you say that bool just made holes on surfaces. In that case your bool has wrong settings that doesn't work on your model... if you insert object into another and use bool it can and should make holes with same topology as inserted object, if it doesn't work as supposed, something is wrong with either settings, your topology or face orientation Jan 13, 2022 at 9:53
• As @Luciano says, it would be good if you could show your attempt. Because I don't know what the actual problem is, if I create some cylinder (to simulate the bone), put a Boolean modifier with Difference on it and take a screw model as the other object, I get a cavity fitting to the screw. What you mean your bone is 3 mm thick, you mean it's a very thin bone or it's a hollow bone with a wall thickness of 3 mm? If it's hollow, where should the cavity be in? When you're drilling a screw in a pipe there's also just a hole in the wall and no cavity around the screw. Jan 13, 2022 at 9:54
• I am sorry I am still new to stack exchange. I just edited my post by adding my attempt. In my edited post I made that box to be assumed as the bone. Jan 13, 2022 at 10:02
• wait, did you want it to show your screw inside of the box that has no mass? I am really not sure right now... I can see that you have thread in your box but it surely won't be visible if there was no mass inside of the box, it needs to be enclosed object to make a hole Jan 13, 2022 at 10:27

You state in your question that your bone model has a 3mm thickness (so hollow, like the box where you demonstrate the problem), but in the samples you show all the bones are solid. That's why you're having trouble showing both the bone and the hole.

1. Model the bone object (I added a Solidify Modifier just to make my sample hollow)

2. add the boolean modifier with the screw object(s)

3. hide the screw object(s) (Disable in Render) so only the bone with the holes is visible

4. select some of the faces to be the "window" and assign a transparent material (I added a simple Glass BDSF)

You can see that the bone object is visible, the walls are visible as a sort of x-ray view and the holes are visible (I didn't model a screw, but the basic principle is the same)

• Just one addition, although it doesn't matter much for the problem: if you put all the screws in a collection you wouldn't need multiple boolean modifiers ;) Jan 13, 2022 at 19:25
• @GordonBrinkmann oh good catch, I didn't know that! I was more focused on solving the transparent bone problem Jan 14, 2022 at 10:07
• yeah well, as I said it doesn't matter much in this case anyway. But it is quite useful if you have multiple (maybe even different) cutting objects and you either do not want to join them into a single object or if they are all the same like those screws but maybe high-poly so that you would prefer instances instead of separate objects. Oh and of course you can always add new cutting objects without having to set up new modifiers - just throw them into the collection. Jan 14, 2022 at 10:42