if the error is small , it may be the actual distance of a single step or less being 1.8 deg , and due to the ballscrew it does not allow the the measurement you want see if the step size equals the error , or less .
changing the steps if your using a microstep driver , will sort it On 11 December 2015 at 20:19, Viesturs Lācis <viesturs.la...@gmail.com> wrote: > Hello! > > This is more like a hope that somebody (especially any fellow > jewelers) might share their experience, where to look for source of > problem. Please feel free to suggest whatever possible ideas that I > already have not tried out. I will try to provide as detailed > description as I can (sorry, if it ends up too long and boring to read > all the way through). > > The machine is relatively small bench-top mill, used by jewelry maker > to mill wax models to be used in lost-wax casting process. That is a > 4-axis machine with rotary head (I do not have particular data of what > motors and stepper drivers are used there). Original controls come > with mach3. I only tested with my replacement control pc with Mesa > 5i25 and LinuxCNC 2.6.8 > > The problem is this: when milling out a ring, the tool passes back and > forth on X axis (parallel to center-line of rotary axis) and changes Z > height during those passes to create the profile of the ring. Between > the passes there are small indexing moves of A axis to make for 0,02 > mm stepover from previous pass. The ring is about 23 mm diameter, so > it takes something around 6000+ passes to complete whole circle. The > problem is that the Z position in the last pass is approximately 0,5 > mm lower than in the first. > Here is a picture that shows the issue (as they say something about > one picture being better than 10^3 words): > http://picpaste.com/IMG_8289-lyaSJDQI.JPG > > Things that have been tried: > 1) looked at the code and Z heights match (at least to +/- 0,01 mm, > which could not be observed to human eye), so it is not direct issue > with the code; > 2) checked for any hardware issue: loose clutch on motor shaft, any > slop in linear bearings; > 3) swapped the stepper drivers and motors > 4) I reorganized the wires on the machine to move any motor power > wires as far from incoming step/dir signal lines as possible > > The end result from these actions - no improvement at all. Client says > there are total at least 4 attempts of milling the ring, no > improvement has been observed. > > There are 2 things that have affected the result that do not make any > sense to me and I would also appreciate any hints for these: > 1) we made "test code" - the same 3d model was used, but code was > generated with 0,2 mm stepover (instead of 0,02) to make for shorter > run time - the result: _no problem_ at all; IMHO this excludes any > effect from actual cutting forces as there was 10x more material to > remove; I would have expected 10x smaller error (still easily > observable, compared to overall surface finish roughness), but it was > all equally smooth; > > 2) the same original code was executed on a smaller workpiece (tool > was touched off closer to centerline of rotary axis, actual diameter > reduced from ~23 mm to ~14 mm); the position drift was smaller (client > says 0,3 mm instead of 0,5 mm). IMHO reducing the actual diameter > decreases actual stepover distance and distorts overall proportions of > the part produced, but it should have _zero_ effect on Z axis > positioning precision. > > Thanks in advance for any [almost] meaningful ideas! > > Viesturs > > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- The information contained in this message is confidential and is intended for the addressee only. If you have received this message in error or there are any problems please notify the originator immediately. The unauthorised use, disclosure, copying or alteration of this message is strictly forbidden. This mail and any attachments have been scanned for viruses prior to leaving the RcTechnix network. RcTechnix will not be liable for direct, special, indirect or consequential damages arising from alteration of the contents of this message by a third party or as a result of any virus being passed on. RcTechnix reserves the right to monitor and record e-mail messages being sent to and from this address for the purposes of investigating or detecting any unauthorised use of its system and ensuring effective operation. (c) RcTechnix ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
