<story><title>The Polar Bear – Open-Source, Multipurpose CNC Machine with a Rotary Axis</title><url>https://www.kadirilkimen.com/thepolarbear/</url></story><parent_chain><item><author>SeasonalEnnui</author><text>Neat kinematics with a horribly flexible frame that denies any serious usage. That said - it&amp;#x27;s designed to a low budget that increases the potential audience, and that is something that can only be welcomed. I&amp;#x27;m particularly interested in the software as that will be an enabler for future variations that have mechanical rigidity.&lt;p&gt;Nice website!</text></item></parent_chain><comment><author>canadian_tired</author><text>Exactly.  I can&amp;#x27;t speak for laser, extruders, knives or such, but for subtractive work (i.e. milling &amp;#x2F; drilling operations with some form of rotary tool) this design would be an exercise in frustration.  Typically, you would have encoders on each axis to tell the machine where things are happening.  These encoders are excellent, but any flex&amp;#x2F;slop in the chassis or moving parts is not caught by the encoder... so the software will not know that the cutter is in the wrong place.  Thus, crappy parts.   Any reasonably useful CNC design takes rigidity and backlash prevention seriously. Take a look at PocketCNC for a good (and yes, expensive) design.</text></comment>
<story><title>The Polar Bear – Open-Source, Multipurpose CNC Machine with a Rotary Axis</title><url>https://www.kadirilkimen.com/thepolarbear/</url></story><parent_chain><item><author>SeasonalEnnui</author><text>Neat kinematics with a horribly flexible frame that denies any serious usage. That said - it&amp;#x27;s designed to a low budget that increases the potential audience, and that is something that can only be welcomed. I&amp;#x27;m particularly interested in the software as that will be an enabler for future variations that have mechanical rigidity.&lt;p&gt;Nice website!</text></item></parent_chain><comment><author>londons_explore</author><text>I would like to see software compensation for frame flexibility.&lt;p&gt;Either open loop (ie. use mechanical models to predict frame flexing and compensate for them), or closed loop (have sensors to detect realtime head position).&lt;p&gt;The whole idea of having a frame which is 100% rigid seems like a simplifying assumption that makes everything more expensive, with knock on effects too (eg. making stuff stronger makes them heavier, which in turn means a bigger motor is needed, which uses more power, so a bigger power supply is needed, etc)</text></comment>