Pocket Clearing_ Retract Height, Stepdown, Safe Distance warning for my values.

[Arthur_Hebert]

My case involves using the 3D Pocket Clearing option. 

I want the retract height to be 0.1 in.

I want the stepdown amount to be 0.5 in. 

What is the idea behind the recommendation that the safe height should be greater than the stepdown amount? That makes sense a little bit, but I think my simple example shows that the policy is lacking. Like others have said, I'm trying to correct warnings and not ignore them. 

Can someone agree with me or tell me that my approach is wrong? 

notes probably mostly for me: 
1) "Warning: Lifting retract plane to safe plane" message in Fusion 360 and Inventor CAM_  doesn't talk about Stepdown. 
2) Safe Height Bug?_ answer not complete enough (and difficult for me to reread). 
3) Warning: Lifting retract height to safe height._ trailed off into 2D Adaptive Clearing. 
4) How to get rid of - Warning: Lifting retract height to safe height. ?_ not what I'm after. 

[demong · Accepted solution]

Hi @Arthur_Hebert ,

This may be more of a discussion of machining best practices. If I understand correctly, leaving your retract height close to the surface of the part is to save time during machining. However, in my experience the machine will rapid from the feed height to the retract height and vice versa, negating appreciable time savings. 0.1" Retract Height also makes me very nervous when I think about clamping that part to the machine bed, but I suppose not everyone is stuck in the stone ages with toe clamps like myself. I would argue that your "Retract Height" must be equal to or greater than your "Safe Distance" or else your retract movement isn't 'safe'. As for the why you might not want your "Safe Distance" less than your maximum Step Down, it seems to me that if you had an issue where your setup wasn't perfect, you would be less likely to cut too deep or rapid into your part if you are a full stepdown away from your part.

Hopefully something there helps. Good luck!

[Arthur_Hebert]

Your answer explains what I was wondering about. I was guessing correctly at some of what you said, but I needed confirmation to close the case on this more. 

It's worth noting a reason why I was asking about this. I'm cutting wood with a small 700 dollar CNC machine. The Z axis is slower. If I cut 10 small pockets or holes, the Z time occasionally can add up enough for me to notice. 

A bigger problem can be unnecessary retracts, but that's a different issue. 

I take back my words saying 'the policy is lacking'. Sure, I'd prefer it be more adjustable, but simple is good to address the more common cases (general machining where being conservative is the way to go). 

[demong]

Ah, I definitely understand why you would want to minimize Z-travel time in this case. While I don't have a great recommendation to speed things up from a machining point of view, I've found that my overall workflow has been reduced significantly by using templates to cut down my programming time. If there is a machining strategy with similar heights, tools, and options that I find myself using often, I will save the toolpaths as a template.

Then I can quickly insert multiple strategies into a setup without having to reset heights and other various options.

Off the top of my head, my most used template has Pocket or Adaptive clearing, Horizontal Finishing, 2D Contouring, Drilling, Tapping, and Chamfering all with heights, stepdowns, feeds and speeds and a few standard tools preset for cutting the workpiece material (aluminum in my case).

I know this isn't helpful for your slow z-axis, and I would imagine a hobbyist machine may not include an automatic tool changer, but hopefully this is applicable to other areas of your workflow. Personally I don't like redoing all my cutting parameters every time I set up a new part. I think there are many comments about people wishing Fusion was a little more adjustable in a particular area, but at least you get about 80% of the results for 20% of the effort. Or maybe more accurately it covers 80% of the use cases for 20% of the cost of other software.

Hope your parts turn out well!

[Arthur_Hebert]

Templates is good to know. I was copying and pasting toolpaths to reuse. Thanks for taking the time to take the screenshots (particularly the 2nd one because I don't know if I would have clicked the setup to make a toolpath (and it's a little different from the ribbon option)). 

Typically I'm decent at playing around to find some of the shortcuts (example: assigning keyboard shortcuts to the constraints that get used the most). 

I have lots of praise for Fusion 360. It has lots of impressive features. 

The free version letting me test first to know what I was getting took out any surprises. 

Definitely worth the money even for my small scale work.