[Emc-users] Creating Screw Compensation Table
I've RTFM and Googled but I can't find an idiot's guide to creating a lead screw compensation table for Linuxcnc. Is my googlefu weak or is there no such thing? ...or do I actually need one at all? As background (Hello! and Warning Newbie Alert!) I have a metric WMD30LV (big brother to the G0704) mill using the standard lead screws being driven by 7Nm NEMA 34 steppers (oldham couplers), DQ860MA drivers and a cheapy BOB connected to a parallel port with Linuxcnc 2.5.3 in control. The mill has glass scale DRO's on all axis (fitted when I thought I could resist going CNC... Pah! :-) However, I think I might have a problem with the accuracy of my lead screws or perception of accuracy and/or something else... which is why I'm thinking that a lead screw compensation file might be better than a crude backlash setting (yes I have backlash and no, I'm not surprised but I'd like to make chips before embarking on a ballscrew conversion). If I do: G90 G0 X0 X50 reset DRO to zero in the X axis X100 and take a reading from my DRO I get slightly under 50mm shown. I've tried various microsteppings with the following results on X Y: Micro Steps X-Axis Y-Axis 40049.960 49.950 80049.960 49.930 100049.970 49.970 200049.965 49.970 400049.955 49.970 Max variation: 0.015mm (0.59 thou) in X and 0.04mm (1.57 thou) in Y. Does that look like lost steps? or as much accuracy as I'm likely to see? (one can get hung up on accuracy reading the various cnc lists'n'forums and watching the DRO for that +-5 flicker in the third decimal place :-) Is this the sort of thing that a screw compensation table is meant to deal with? If so, how do I actually measure the numbers for the table? Are the measurements absolute or relative to the previous move? How do I get the reverse or reverse trim numbers? Sorry for being a thickie. If I do use a compensation table, ISTR that there's a limit of 256 entries and the table on my mill moves +-300mm. Is a table entry for every 2.34mm what I need to generate? Thanks in advance. PS - If I do need a compensation table and work out how to generate one I'll put something on the wiki for future newbies. -- Regards, Russell | Russell Brown | MAIL: russ...@lls.com PHONE: 01780 471800 | | Lady Lodge Systems | WWW Work: http://www.lls.com | | Peterborough, England | WWW Play: http://www.ruffle.me.uk | -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Creating Screw Compensation Table
On 5 September 2013 19:08, Russell Brown russ...@lls.lls.com wrote: Were the 'errors' I showed (~.015mm over a 50mm move) in the right ball park for a non-ball-screw benchtop mill driven by steppers? Not brilliant, but then I doubt that the machine is driven by super-precision screws. Should I expect a commanded 50mm move to travel 0.040mm less than 50mm ? Does the variation in actual distance moved indicate missed steps? (the actual move varied with different microsteppings) You may be missing steps, it is always a possibility with stepper machines. I don't suppose you have any way to get the DRO feedback into the PC? Closing the loop might be a fun project. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Creating Screw Compensation Table
Quoth bodge...@gmail.com. On 5 September 2013 16:33, Russell Brown russ...@lls.lls.com wrote: Is this the sort of thing that a screw compensation table is meant to deal with? If so, how do I actually measure the numbers for the table? Then just run up the table, G0 X10, note the reading and make a comp file entry of 10,9.92, and so on to the end of travel, then come back the other way, filling in the third column. OK. If I do that, given my X backlash of 0.165mm and an assumed feed of 9.92mm for every 10mm commanded, then I end up with a table like: 00.00 00.00 0.165 (10.085-9.92) 10.00 09.92 10.085 (20.005-9.92) 20.00 19.84 20.005 (29.76-9.92+my_backlash) 30.00 29.76 Does that look right? Given 600mm travel on the X-axis, what table intervals make sense? Or have I misunderstood the question? Well. You missed bits... but it was multi-part :-) Were the 'errors' I showed (~.015mm over a 50mm move) in the right ball park for a non-ball-screw benchtop mill driven by steppers? Should I expect a commanded 50mm move to travel 0.040mm less than 50mm ? Does the variation in actual distance moved indicate missed steps? (the actual move varied with different microsteppings) Am I trying to fix something that's 'normal' ? -- Regards, Russell | Russell Brown | MAIL: russ...@lls.com PHONE: 01780 471800 | | Lady Lodge Systems | WWW Work: http://www.lls.com | | Peterborough, England | WWW Play: http://www.ruffle.me.uk | -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Creating Screw Compensation Table
On 5 September 2013 16:33, Russell Brown russ...@lls.lls.com wrote: Is this the sort of thing that a screw compensation table is meant to deal with? If so, how do I actually measure the numbers for the table? Normally it is quite difficult. But as you have glass scales then it seems like it ought to be very simple in your case. http://www.linuxcnc.org/docs/html/config/ini_config.html#_axis_lt_num_gt_section_a_id_sub_axis_section_a You need to specify a COMP_FILE and COMP_FILE_TYPE in the INI file. You can choose to specify an absolute or relative file (that's the FILE_TYPE) I think what you need to do in your case is switch to machine coordinate view (#, or use the menu if you don't have a #, or Linux hasn't found it) Then G0 X0 and manually push the axis to the end of backlash (unless your config allows you to approach zero from the other side). First line in the comp file is now 0,0,? Then just run up the table, G0 X10, note the reading and make a comp file entry of 10,9.92, and so on to the end of travel, then come back the other way, filling in the third column. Or have I misunderstood the question? -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Creating Screw Compensation Table
What are the DRO readings vs. commanded position at regular intervals along the entire length of travel? On Thu, Sep 5, 2013 at 1:20 PM, andy pugh bodge...@gmail.com wrote: On 5 September 2013 19:08, Russell Brown russ...@lls.lls.com wrote: Were the 'errors' I showed (~.015mm over a 50mm move) in the right ball park for a non-ball-screw benchtop mill driven by steppers? Not brilliant, but then I doubt that the machine is driven by super-precision screws. Should I expect a commanded 50mm move to travel 0.040mm less than 50mm ? Does the variation in actual distance moved indicate missed steps? (the actual move varied with different microsteppings) You may be missing steps, it is always a possibility with stepper machines. I don't suppose you have any way to get the DRO feedback into the PC? Closing the loop might be a fun project. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Creating Screw Compensation Table
If you do bidirectional compensation then backlash does not apply. I think I would adjust the scale to get the numbers to match as good as possible. Then the compensation values would be small. On Thu, Sep 5, 2013 at 1:20 PM, andy pugh bodge...@gmail.com wrote: On 5 September 2013 19:08, Russell Brown russ...@lls.lls.com wrote: Were the 'errors' I showed (~.015mm over a 50mm move) in the right ball park for a non-ball-screw benchtop mill driven by steppers? Not brilliant, but then I doubt that the machine is driven by super-precision screws. Should I expect a commanded 50mm move to travel 0.040mm less than 50mm ? Does the variation in actual distance moved indicate missed steps? (the actual move varied with different microsteppings) You may be missing steps, it is always a possibility with stepper machines. I don't suppose you have any way to get the DRO feedback into the PC? Closing the loop might be a fun project. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- Addressee is the intended audience. If you are not the addressee then my consent is not given for you to read this email furthermore it is my wish you would close this without saving or reading, and cease and desist from saving or opening my private correspondence. Thank you for honoring my wish. Just for you NSA - think autointercourse terrorist suitcase bomb sarin hello -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Creating Screw Compensation Table
Were the 'errors' I showed (~.015mm over a 50mm move) in the right ball park for a non-ball-screw benchtop mill driven by steppers? This sounds well within then range if normal screws if not better than I would have expected. Another way of looking at this is it is 0.03% error. Very small. The trouble with non-ball-screws is wear from sliding as compared balls with rolling. The nuts and screws wear quickly and therefor the calibration goes out quite quickly. Cheers Wallace. -- Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391iu=/4140/ostg.clktrk ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
