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• I bought a CO2 laser on ebay and made one of these for my self.

  http://www.nilno.com/laser_intro/

  much more gratifying. there's a lot of people that make CNC laser systems, for a start go to:

  http://www.cnczone.com/forums/forumdisplay.php?f=79

  Posted by: smouldering-dog on January 20, 2006 at 10:11 AM

• I've been looking at the Epilog and similar laser systems. I recently bought a Roland EGX-300 3D engraver and a Graphtec CE3000-60 mk2 24" vinyl cutter/plotter. I'm also wanting to build a largish 4 axis CNC.

  Posted by: BrK on January 20, 2006 at 6:41 PM

• Roland DG EGX-300: Alarm over questionable resolution claims so don't plan any accurate work with this machine!

  No, this is not confusion of software/mechanical resolution figures. I understand those perfectly clearly. The EGX-300 printed and Japan-website specifications both claim:
  "Software resolution 0.01 mm (0.00394in.)/step or 0.025 mm (0.000984 in.) /step (XY axes only)" and
  "Mechanical resolution X, Y and Z-axis: 0.00125 mm (0.0000492 in.) /step (micro-step control)".

  Typographical errors are not the reason for my alarm. I have assumed that "0.00394 in." is a typographical error and "0.000394 in." was intended.

  However, the smallest mechanical step I can achieve using the X or Y axes under any circumstance is 0.01375mm (which is significantly larger than the claimed resolutions). I have tried issuing feed commands (constant speed), traverse commands (with acceleration and deceleration) and single steps under software control and I have also used the keypad on the machine. The observed movements have been validated under a microscope.

  No, the discrepancy is not caused by backlash on the X or Y axis drives, as they are both tensioned-wire drives with zero backlash. The motions I obtain are validated both when moving unidirectionally and when reversing the direction of motion

  It appears that the mechanical resolution is not eight times higher than the software resolution as claimed, but is actually 1.375 times lower than the software resolution! The claimed software resolution of 0.01mm is achieved by firmware interpolation. This can easily be verified using the keypad on the top of the machine. Each key-press for the X or Y axes increments or decrements the position display by 0.01mm, but only 8 out of every 11 key-presses cause any movement of the axes!

  For my work, which relies on the claimed 10µm step size (the reason I purchased the Roland) I have increased the mechanical resolution to match the software resolution, by reducing the diameter of the aluminum capstan pulleys so that each whole motor step corresponds to 0.01mm of linear motion. Then, by using a software algorithm to compensate for firmware interpolation 'steps' which do not cause any movement of the axes, I privately manage the phantom steps. It's a very complex matter, which is not cheap or easy to do. No, I can't simply send a program to another user, which will "fix" his own software. Your software has NO IDEA which 8 of the 11 steps to believe, or which 3 of 11 to ignore!

  Also, I have some reservations about the Roland brochure claim of "micro-stepping control". I can see from the board and the Roland service manual schematics that it is implemented in hardware, but I have made measurements under many circumstances and I don't think it's actually used. Even if 1/8 micro-stepping was used, it would only increase the actual mechanical resolution by 8 times to 1.71875µm, so it still would not meet the claimed mechanical resolution of 1.25µm.

  Perhaps the design engineer at Roland DG Japan could not get micro-stepping to work, was afraid to tell his boss, and devised the cheating technique of moving only 8 steps for every 11 commanded steps?

  Any EGX-300 owner can validate one aspect of my alarm, just using the position display and the motion keypad. Each key-press for the X or Y axes increments or decrements the position display by 0.01mm, but only 8 out of every 11 key-presses cause any physical movement of the axes!

  If I am correct, most US states have laws that require a buy-back. Just imagine advertising a "5-speed manual" car fitted with a gear-shift that has 5 slots, but 2 of them are extra neutral positions and there are only 3 gear ratios!

  
  

  Posted by: MiroD on July 1, 2006 at 3:47 PM

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