## How is Clearance Height Calculated & How Does One Change It?

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ivxcvi
Posts: 17
Joined: Wed Oct 16, 2019 12:31 am

### How is Clearance Height Calculated & How Does One Change It?

Hello,

The title basically says everything. I am trying to use FreeCAD to output GCode for a Maslow CNC--which has minimal clearance & Safe Height. Right now Clearance is calculated at over 21mm. I would like to have that down to 6mm. I'm just not sure what I need to adjust to do that. Documentation doesn't appear clear on that issue.

Much appreciated,
chrisb
Posts: 28806
Joined: Tue Mar 17, 2015 9:14 am

### Re: How is Clearance Height Calculated & How Does One Change It?

Have a look at Job->Setup->DefaultValues.
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RatonLaveur
Posts: 803
Joined: Wed Mar 27, 2019 10:45 am

### Re: How is Clearance Height Calculated & How Does One Change It?

Be careful that in FreeCAD Clearance Height and Safe Height are inverted with regards to conventional machinimg nomenclature. So double check the heights and the travels.
Kunda1
Posts: 8667
Joined: Thu Jan 05, 2017 9:03 pm

### Re: How is Clearance Height Calculated & How Does One Change It?

ivxcvi wrote:
Wed Oct 16, 2019 7:01 am
Want to contribute back to FC? Checkout:
#lowhangingfruit | Use the Source, Luke. | How to Help FreeCAD | How to report FC bugs and features
geant
Posts: 37
Joined: Mon Mar 30, 2015 11:54 pm

### Re: How is Clearance Height Calculated & How Does One Change It?

RatonLaveur wrote:
Wed Oct 16, 2019 2:42 pm
Be careful that in FreeCAD Clearance Height and Safe Height are inverted with regards to conventional machinimg nomenclature. So double check the heights and the travels.
Thanks for saying that "out loud"; this has been bugging me for years!
RatonLaveur
Posts: 803
Joined: Wed Mar 27, 2019 10:45 am

### Re: How is Clearance Height Calculated & How Does One Change It?

Yep, Safe height is supposed to be the height for which any lateral movement in the machine will clear both part, features and fixtures.
Clearance height is a reduced retraction used to clear features on a single work-piece or work-piece area (typically, move from one pocket to another).

An overly cautious machinist or hobbyist will probably accept Safe height as the only default parameter. A machinist more interested in optimizing cycle times (or who likes to live dangerously) will happily rapid around at clearance height.

In FreeCAD: both are inverted. Hence why Clearance Height is by default higher than Safe Height. Since the automatic generation of travels was coded this way, I would not mess with their relative positions to "try" to emulate correct nomenclature.
ivxcvi
Posts: 17
Joined: Wed Oct 16, 2019 12:31 am

### Re: How is Clearance Height Calculated & How Does One Change It?

Hello,

I found that my issue was that I was padding my designs in a positive direction, causing the clearance height to be well beyond the Maslow's Z-height threshold. Padding designs in reverse & sticking to default values solved my issue.

Also of note for anyone getting started with FreeCAD+MakerMade/Maslow CNC, don't forget to set your feedrates & rapid mm/s (42 for H & V Feed, 100 for H & V Rapid). After I figured out the Z-height issue, I was wondering why my Maslow stalled before the first cut. Big thanks to Walt_Moorhouse over on the Maslow CNC forums for the FreeCAD guide which has helped me overcome these issues.

Thanks!
chrisb
Posts: 28806
Joined: Tue Mar 17, 2015 9:14 am

### Re: How is Clearance Height Calculated & How Does One Change It?

I see that there is a FreeCAD world outside of this forum. As you are active there, would you mind directing the author here or submit the following:

May I kindly suggest some corrections and improvements?

Issues:
- The sketch is created outside of a body adding unnecessary work
- The sketch is not constrained (not really a problem only an issue)
- In Step 6 you create already a body before even having a solid

I suggest:
Step 2: Open PartDesign workbench and create a new sketch. (This creates an enclosing body.)
Step 3: choose XY plane as before, but it will look different
Step 4: I would recommend to add dimensions for, lets say an 8mm bit
Step 6: move the images to the job creation step.
A Sketcher Lecture with in-depth information is available in English, auf deutsch, en français, en español.
ivxcvi
Posts: 17
Joined: Wed Oct 16, 2019 12:31 am

### Re: How is Clearance Height Calculated & How Does One Change It?

Thanks for the input. I've submitted the suggestions with a link back to your post. Much appreciated!