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A comment on The Polar Bear – Open-Source, Multipurpose CNC Machine with a Rotary Axis. Parent comment

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by jerome-jh on Saturday August 21, 2021 @05:36AM (#28255568)
The rotary axis is controlled by a stepper motor. This is not a usual turning lathe. The rotary axis can be made as slow as necessary and the only relevant analysis is a quasi-static one. Answering to parent comments: there are usually no encoders on these machines. The controller firmware just counts the motor steps. If a motor misses a step, everything will be off from then. For the cantilever design: it is already used by Prusa 3D printers which are well regarded (in the field of amateur 3D printing) so I do not think this is an issue for the targeted accuracy which is typically 10 to 50 micrometers.

The only issue I have with this design is that the accuracy decreases with the distance from the rotary axis, hence it is not uniform over the building volume.

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Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by Accujack on Sunday August 22, 2021 @11:12PM (#28271964)
>For the cantilever design: it is already used by Prusa 3D printers which are well regarded (in the field of amateur 3D printing) so I do not think this is an issue for the targeted accuracy which is typically 10 to 50 micrometers.

3d printers don't have forces pushing back on the print head, nor the vibration from a cutting tool to deal with.

This design might work ok for 3d printing, or laser cutting, or anything else where no contact between the working head and the material occurs.

As far as accuracy and repeatability, it's going to be about as good as the average 3d printer design. It's a nifty idea for a system, but it's only a decent machine for cutting if it's scaled up massively and built of cast iron or similar materials.

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Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by kadirilkimen on Tuesday August 24, 2021 @02:31PM (#28292973)
Depends on what you cut. It cuts wood pretty nice. I couldn't documented the wood cutting performance on prototyping. I will demonstrate it's wood cutting capacity in v1 release. It's a 3d printable desktop machine and never intended to cut precise metal parts. May be I can design a full metal body version with professional components like rail guides instead of plastic v-slot wheels.
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Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by kadirilkimen on Saturday August 21, 2021 @12:39PM (#28258344)
It is 0.025mm on the outer edge of the table.
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