Beginner - suitability of Cheetah3D?

B

bilbomacuser

New member
I'm just starting out with a project where I'm creating an stl file of a bone, and I want to then use software to make a drill guide that fits over the bone to allow precise drilling. I have no experience with 3D software but after watching a few tutorials I understand that I can create a box and a cylinder and using boolean to 'cut' the cylinder out of the box.

I assume that I should also be able to 'cut' the bone out of the box - so that the box fits perfectly in the correct position over the bone. However, when I try this the bone stl image disappears.

Finally - if I can get Cheetah3D to do what I want, I also need to check whether Cheetah3D allows accurate measurement. ie. I need the bone to be actual size, and the holes in the box need to be a precise diameter. I also then need to create other holes that are angled exactly the same.

Is Cheetah3D suitable for this type of project or should I be looking elsewhere? If it is suitable, any ideas why I can cut the cylinder out of the box, but not cut the bone out of the box using boolean?

Thanks for any help!
 
Hi and Welcome!
I guess the stl file is probably not watertight (or don´t contain connected polygons due its creation source maybe) - which can be checked by calling "Info" (icon or cmd+I)).
I made a funny cartoony bone drilled by a small cylinder:
Hole´nBone.gif

I don´t see any issues regarding your project - Cheetah3d uses units over real world entities like cm/mm/inch/etc.
Maybe this will help you out. If there´s anything else feel free to add more questions herein.

Cheers
Frank
 

Attachments

  • Hole´nBone.jas.zip
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* The geometry of the objects in a Boolean is critical. Minor inconsistencies (holes / not watertight, see Frank B above), maybe not obvious, can cause the Boolean to fail to execute as expected.
* Please upload a screenshot / a .jas of the bone.
* Similar to other 3D applications, C3D has no definite measurements. There is a decimal standard grid which permits metrics to be entered with 4 decimals. Depending on the model, one interval of this standard grid can be 1 angstrom, 1 cm, 1 mile or a light year.
* In the case of human (?) bones I guess that 1cm would be useful. This gives a precision down to 1 µm.
 
Thanks for the replies. I tried the same with the Hole n Bone example and what I had been trying worked - so it must be something with the stl file as you suggest.

The object info says it is watertight - but it is made up of 250126 polygons - could that be the problem, is it too detailed?

Thanks also for the info regarding scale - using 1 cm for one interval sounds perfect. Where do I go to set this? How do I make sure that the bone imported is the correct size? (it's exported from Osirix, the bone is from a CT).

Thanks again.
 
bilbomacuser said:
The object info says it is watertight - but it is made up of 250126 polygons - could that be the problem, is it too detailed?
Click to expand...
No - I believe the polygons/tris are not connected, please check out: go in polygon mode - select one polygon and try to drag it from the mesh - or hit cmd+G (for group selecting) when all turn red it´s one mesh - so the crux is elswhere. Any chance to link to the file? I guess 250k is too large as a zip-file for uploading into the forum.

Cheers
Frank
 
* There is no direct way to set the scale. You are advised to look into the preferences for importing documents where a scale factor can be defined. Sorry, I have no experience with .dcm formatted documents.
* In the sample, you have a humerus which is approximately 15 units long. If 1 unit were to be equal to 1 cm, this bone (and all others) need to be resized approximately x 2 (the mean length of the humerus in adult humans being 31/f - 33/m cm).
Screenshot 2019-12-05 at 15.52.54.png
 
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