Finishing pass with the Helix toolpath?

Here's the place for discussion related to CAM/CNC and the development of the Path module.
Forum rules
Be nice to others! Respect the FreeCAD code of conduct!
Post Reply
Giulio Buccini
Posts: 541
Joined: Fri Aug 26, 2016 9:07 pm
Location: Munich - Gemany

Finishing pass with the Helix toolpath?

Post by Giulio Buccini »

Hello,

I adore the helix tool to make circular holes in my alu-plates. It is a pleasure watching the machne making the holes in this way! :D

Now I'm trying to understand why sometimes I get an (almost) perfect diameter of the holes, and sometimes not (around 0.1mm smaller diameter).
I'm preparing a test-plate to test the different approaches (helix vs traditional cylindrical cut / CW vs CCW / etc).

My question:
there is a way to to make a rough pass followed by a finishing pass with the helix tool?
Any trick/workaround?
(AFAIK there is only the step-over parameter available... :( )
Selection_7595.jpg
Selection_7595.jpg (30.81 KiB) Viewed 1135 times
--------------------------------------------------------
OS: Ubuntu 16.04.7 LTS (XFCE/xfce)
Word size of FreeCAD: 64-bit
Version: 0.20.25943 (Git) AppImage
Build type: Release
Branch: master
Hash: a65464b722a846bd2999aa2fecdff1132b15b297
Python version: 3.9.7
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: English/United States (en_US)
GeneFC
Veteran
Posts: 5373
Joined: Sat Mar 19, 2016 3:36 pm
Location: Punta Gorda, FL

Re: Finishing pass with the Helix toolpath?

Post by GeneFC »

Make sure that the preferences are set correctly.

Edit >> Preferences >> Path >> Job Preferences >> Default Geometry Tolerance and Default Curve Accuracy

I cannot tell you what they should be for you application, but try something tighter and see if the hole diameter behavior changes.

You might also look in the Properties panel (below the Combo tree) for the Helix to make sure the various numbers look OK. Right click and select "Show All" to see all available parameters.

Gene
Giulio Buccini
Posts: 541
Joined: Fri Aug 26, 2016 9:07 pm
Location: Munich - Gemany

Re: Finishing pass with the Helix toolpath?

Post by Giulio Buccini »

Hi GeneFC,

preference settings are ok: Default Geometry Tolerance = Default Curve Accuracy = 0.0001 mm

Also, I didn't find any useful property of the Helix-op to set some offset, even by using the "Show All" command.

As workaround, I will make first a rough pass by using the Profile command. Then I will use the Helix command as finishing pass.

I'm curious to find the reason of this erratic behaviour: some plates with the same nominal diameter of 5 mm have a resulting hole of 4.98-4.99 diameter on some shapes, while on other shapes/jobs my caliper give me 4.88-4.89 mm of dia.
Obviously, I'm milling the same material, with the same speed and feeds, the same machine and the same Mach3 settings and the same working offsets...

I would obtain a reasonable accuracy of the holes to use precision-dowel for flipping the shape on the working table more precise. (I need to make some milling on the backside too.)
Post Reply