First CNC project - Need help with excess stock and rapid collision errors

[Anonymous]

Hello,

This is my very first time working with CNC. I have a cheap 3-axis machine that I bought off of Amazon and I thought I'd start with something semi-complex because I learn best by diving into the deep end. So I thought I'd try to mill a 20 sided die (icosahedron). I imported a .stl from thingiverse and started playing around with generating toolpaths. I think I have the generated toolpaths that I like, but there's a couple problems. I'm attaching my .f3d file to help if anyone cares to look and I'm happy to answer questions, I'm just not sure what information I need to provide to be helpful.

First is in both my top and bottom operations I have a couple "Rapid collision with stock" errors during simulation that I just can't seem to fix.

Second is the remaining stock. Obviously I need to leave some so that it can remain connected to the stock so the piece remains stable, but right now with my generation there's at least 5 mm of uncut stock that I would have to try and sand off and hope I keep the correct angle. Is there any way I can reduce this amount? Another option would be to secure the piece with glue or double sided tape and let the machine cut the piece free of the stock such as enabling "Contact point boundary", but I can't find a toolpath generation strategy that doesn't try to cut all the way down to the bottom causing "Shaft collides with stock" errors.

Any help would be greatly appreciated.

[johnswetz1982]

1.) Use an adaptive or other roughing strategy first.

2.) You really should not use a square endmill with a parallel operation. Use a ball mill.

3.) Generally with a rapid collision, changing your leadin/out parameters to something larger will fix it but take longer.

[Anonymous]

Editing, this is a duplicate response by accident

[Anonymous]

Thanks for the reply. I've tried adaptive clearing but it seems to want to clear all the way to the bottom of the piece which causes shaft collision errors, not to mention that it will remove the piece from the block that I have clamped down onto the plate. I tried looking for a solution to trim the path off about halfway down but I can't seem to cut it off, any suggestions?

Also, what strategy would you suggest for a flat end bit, that's all I have at the moment and eager to get something cutting

[johnswetz1982]

Use 3D adaptive. 3D operations are model aware and SHOULD not collide with your part. 2D operations are not model aware.

You can limit how low you go on the heights tab. Default would be model bottom. Give it a positive value.

Though you will have a very tough time to do this because it is undercut. There was someone else doing exact project but they had 4th axis and rotated the part around. With yours you would have to go down past half way, flip it over and have a way to hold it AND find the origin to start a second/backside operation.

[Anonymous]

Ok! This is really helping, I'm getting somewhere! My plan with only three axes (I can upgrade to 4 later, my controller supports it) is to make the origin point the center of the triangle, these are equilateral triangles and the top and bottom triangles, while not in the same orientation, share a center point, so I should just be able to mark my center points and flip the piece and clamp it back down.

May I ask one additional question? I'm eager to get moving on this project, all I have are the square end milling bits at the moment. Which pathing strategy would you suggest for something like this?

[engineguy]

@Anonymous 

Been done, see images and attached file 🙂 🙂 🙂

My 2 Cents worth, is to try and do it the way it should be done, if you are going to fit a 4th axis then do that first and use a "Rotary" toolpath as in the attached file, IMHO to be trying to do this with just the 3 axis you will spend an inordinate amount of time trying to do it the hard way when what you should be really trying to learn is the right way, much better use of your time 🙂 🙂 🙂

Open the attached file and before doing anything else run it in the Simulation so you will be able to see how best to do this job 🙂

Of course you can do it in two halves, no argument there by using for example something like the 3D Adaptive and a Ball nose tool, I have added such a toolpath to the original file so you can see how that works as well 🙂 🙂 🙂

Stay Safe

Regards

Rob

[Anonymous]

Wow! Great info! I stepped away from the computer for a while, I'll look at these tonight. I'm probably going to try 3 axis first just to try and actually see this thing operate. If I spend too much time doing it wrong, oh well, I'm still learning. I fully intend to upgrade to a 4th axis whenever I find one that fits. Baby steps!