Pocket with 30mm tool fails, yet 29.999999999mm tool works?

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russ.northrup
Posts: 2
Joined: Thu Nov 16, 2017 7:38 pm

Pocket with 30mm tool fails, yet 29.999999999mm tool works?

Postby russ.northrup » Thu Nov 16, 2017 8:22 pm

I've simplified the project as far as I can to illustrate the problem. It consists of a 30mm pocket cut from a larger block.

I expect a straight path down the center of the cut. A 30mm tool does not generate any g-code.

However, a 29.999999999mm tool generates the expected path shown here:

Image

Any idea what am I overlooking?

[edit]
Very similar to the error in https://forum.freecadweb.org/viewtopic.php?f=15&t=25278, I get the following g code when the tool width matches the pocket width.

(Pocket)
G0 Z25.000000
G0
G0 Z0.000000
G0 Z25.000000


OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.12223 (Git)
Build type: Release
Branch: master
Hash: 917e61a3be12f3316d571ebf6fd6e3c537691c14
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.1.0
Locale: English/UnitedStates (en_US)
User avatar
JoshM
Posts: 419
Joined: Thu Oct 05, 2017 5:34 pm
Location: New Hampshire

Re: Pocket with 30mm tool fails, yet 29.999999999mm tool works?

Postby JoshM » Fri Nov 17, 2017 12:07 am

I think you're right Russ. I'm no expert, but have read that FC generally does better when we are able to avoid doing things like a Boolean cut between objects with Faces on an identical plane where the option to offset them slightly is harmless.

I see the same thing here with Tool-Diameter must be less than slot width for Path Operation to work. It's not a big deal for me since my machine tolerances are worse than the FC resolution.

Regards,
Josh
chrisb
Posts: 19722
Joined: Tue Mar 17, 2015 9:14 am

Re: Pocket with 30mm tool fails, yet 29.999999999mm tool works?

Postby chrisb » Fri Nov 17, 2017 12:11 am

A pocket is not a slot. The latter is not yet existant in Path Workbench. Due to the well known problems with rounding errors I am afraid that automatic recognition may not work reliably.