,I too have a similar problem. Built a rotary table (small, about 4" dia). Ordered a worm and wheel pair from Boston Gear, thought I ordered a 72 tooth worm wheel, which moves 5 degrees per one rev of the worm, divided by 400 steps, resolves to 0.0125 degrees per pulse.... Can't accurately read the catalog any more. Actually ordered and got an 80 tooth worm wheel.... 4.5 degrees per one rev of the worm, divided by 400 steps, resolves to 0.01125 per pulse. Looking into a gear pair from HPC gears to mechanically correct the problem.
----- Original Message ----- From: emc-users-requ...@lists.sourceforge.net To: emc-users@lists.sourceforge.net Sent: Sunday, January 3, 2016 2:04:39 AM Subject: Emc-users Digest, Vol 117, Issue 17 Send Emc-users mailing list submissions to emc-users@lists.sourceforge.net To subscribe or unsubscribe via the World Wide Web, visit https://lists.sourceforge.net/lists/listinfo/emc-users or, via email, send a message with subject or body 'help' to emc-users-requ...@lists.sourceforge.net You can reach the person managing the list at emc-users-ow...@lists.sourceforge.net When replying, please edit your Subject line so it is more specific than "Re: Contents of Emc-users digest..." Today's Topics: 1. Re: Lost fractions of a step (Valerio Bellizzomi) 2. Re: Lost fractions of a step (Dave Caroline) 3. Re: Lost fractions of a step (Dave Caroline) 4. Re: Lost fractions of a step (Dave Caroline) 5. Re: Lost fractions of a step (Tobias Gogolin) 6. Re: Lost fractions of a step (Dave Caroline) 7. Lost fractions of a step (Roland Jollivet) ---------------------------------------------------------------------- Message: 1 Date: Sun, 03 Jan 2016 07:51:05 +0100 From: Valerio Bellizzomi <vale...@selnet.org> Subject: Re: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <1451803865.3209.36.ca...@noc1.sel> Content-Type: text/plain; charset="UTF-8" Good year to all, I have a board that can do microstepping but I would not use microstepping because the manual says that while it rises the precision it also reduces the torque. On Sun, 2016-01-03 at 01:02 -0500, Cecil Thomas wrote: > My question is about what happens to the "leftovers" when the > precision of the g code commanded position cannot be met by the > hardware executing it. > Several years ago I wrote a program to "generate" involute gear teeth > by making multiple cuts of the same tooth from differing angles with > a rack shaped cutter. This eliminates the need for the different > cutters when making only one cut per tooth. I have used it many > times to cut relatively large gears with a relatively small number of > teeth with virtually no noticeable error. > > A few days ago a friend who repairs watches wanted to know if I could > figure out what gear (wheel to you watch guys) size, pitch or module > and number of teeth would be required to replace a missing one. (the > original was long gone). I had no problem working from the center > distance and the matching pinion coming up with the appropriate design. > > However, when I cut the gear I had the right number of teeth but the > last tooth was much too wide. > > It would appear that I had lost a bunch of steps on the rotary > axis. Further investigation reveals what I think is the root cause > but I would like someone with more knowledge than me to confirm or > disprove my analysis. > > The gear had 86 teeth (in the power train, not in the timing train) > and I made 9 cuts per tooth. That is 774 commands and about all but > 86 of them in the same direction. > > My rotary axis is a 200 step stepper into a 30 to 1 worm drive > microstepped by 10 so 1.8 degrees divided by 300 equals .006 degrees > per microstep or 166.6667 steps per degree. > > Unfortunately when the g code calls for a 1 degree move the motion > planner can only issue 166 steps since it can't issue .6667 > steps. That means that the actual movement of the A axis is only > 166/166.66667 or .996 degree. That is .004 degree lost as far as I > can tell. That might be close enough for one or even several > commands but after 688 comands in the same direction that constitutes > 688 x .004 or 2.7 degrees lost. > > That is a significant portion of a tooth on a high tooth number > wheel. Depending on the actual value of the command the actual lost > motion could be anything from nothing to essentially a whole step or > .0059999 degrees. > > I think that I can lessen the impact of the lost portion of the steps > by using the MOD operator to determine how much is left over after > dividing the commanded move by .006. Then use IF ELSE, IF the > remainder is Greater Than .5 steps then ADD a full step (command = > command PLUS .006 degrees) ELSE issue the commanded number (do nothing). > > This should statistically reduce the error by rounding up or down and > redistribute it randomly among all the cuts although it will not > eliminate it. The greater the number of cuts the better the > approximation will be. > > Sorry for the long post but I couldn't condense it much and get the > idea across. Can anyone confirm or disprove my observation or come > up with a better solution? Obviously I could add another reduction > stage to my rotary axis but I would like to avoid that if possible. > > Cecil > > > ------------------------------------------------------------------------------ > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------ Message: 2 Date: Sun, 3 Jan 2016 07:44:32 +0000 From: Dave Caroline <dave.thearchiv...@gmail.com> Subject: Re: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <CALfYgtn+STr-D8e-6+xmi7whO8EA+Xa+z6kGh=abpkknwkz...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Microstepping increases resolution but not accuracy, you can easily lose torque in intermediate positions, any stiffness in the rotary will just add error. Perhaps the worst thing I have seen though is rotary error itself, the lower the reduction ratio usually means a greater error from the worm/wheel in the rotary. Here you see tooth width error at worm wheel tooth rate. I was working at a clockmakers and I had some high count wheels rejected. This made me measure all the rotaries we had plus a gear set I had ready for the George Thomas design and a rotary we borrowed, only one a 1940's Boley was within any kind of spec. On this we made new dividing disks and cured our quality problem. As it happens my xmas project is to start to document the errors in this typical setup as used by many. http://www.archivist.info/cnc/wormtest/ The page is not yet finished I need to finish the tooth error average for the 48 tooth gear and the high resolution microstepping error, which currently shows as regular noise on the upper graphs. Dave Caroline ------------------------------ Message: 3 Date: Sun, 3 Jan 2016 08:03:28 +0000 From: Dave Caroline <dave.thearchiv...@gmail.com> Subject: Re: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <CALfYgtk=GdGc3nfcX_=TV7NaGoKyf+xBru4f1i9nJ8At9a=0...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 I forgot to mention, I had no accumulated step loss in my tests, I started each test with encoders at 0 and they completed with 48000 and 20000, not even a +-1 digit error which surprised me. Dave Caroline ------------------------------ Message: 4 Date: Sun, 3 Jan 2016 08:33:25 +0000 From: Dave Caroline <dave.thearchiv...@gmail.com> Subject: Re: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <calfygtmrnma7xaimcxadytxjnhiutiqru-mx4vzd5ymcwbq...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 And another thing, almost all rotaries have backlash, do make sure this is removed in gcode before you start cutting this will result in a single tooth error. Dave Caroline ------------------------------ Message: 5 Date: Sun, 3 Jan 2016 09:51:19 +0100 From: Tobias Gogolin <usert...@gmail.com> Subject: Re: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <CACCG-_Pgar=SoC20PYOrenzdyxnBcSyrcjRW=_trjop6uqh...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 I suspect that if you were indeed to cut each tooth completely and sequentially you could get the spiral wave of material heat extending that would cause even stranger errors! In the effort to cut a little of each I would use the Fibonacci number applied to 360degrees - as I remember aprox. 137 deg in the 'stepover' to find the next tooth do work a little upon... On 3 Jan 2016 07:25, "Cecil Thomas" <wctho...@chartertn.net> wrote: > My question is about what happens to the "leftovers" when the > precision of the g code commanded position cannot be met by the > hardware executing it. > Several years ago I wrote a program to "generate" involute gear teeth > by making multiple cuts of the same tooth from differing angles with > a rack shaped cutter. This eliminates the need for the different > cutters when making only one cut per tooth. I have used it many > times to cut relatively large gears with a relatively small number of > teeth with virtually no noticeable error. > > A few days ago a friend who repairs watches wanted to know if I could > figure out what gear (wheel to you watch guys) size, pitch or module > and number of teeth would be required to replace a missing one. (the > original was long gone). I had no problem working from the center > distance and the matching pinion coming up with the appropriate design. > > However, when I cut the gear I had the right number of teeth but the > last tooth was much too wide. > > It would appear that I had lost a bunch of steps on the rotary > axis. Further investigation reveals what I think is the root cause > but I would like someone with more knowledge than me to confirm or > disprove my analysis. > > The gear had 86 teeth (in the power train, not in the timing train) > and I made 9 cuts per tooth. That is 774 commands and about all but > 86 of them in the same direction. > > My rotary axis is a 200 step stepper into a 30 to 1 worm drive > microstepped by 10 so 1.8 degrees divided by 300 equals .006 degrees > per microstep or 166.6667 steps per degree. > > Unfortunately when the g code calls for a 1 degree move the motion > planner can only issue 166 steps since it can't issue .6667 > steps. That means that the actual movement of the A axis is only > 166/166.66667 or .996 degree. That is .004 degree lost as far as I > can tell. That might be close enough for one or even several > commands but after 688 comands in the same direction that constitutes > 688 x .004 or 2.7 degrees lost. > > That is a significant portion of a tooth on a high tooth number > wheel. Depending on the actual value of the command the actual lost > motion could be anything from nothing to essentially a whole step or > .0059999 degrees. > > I think that I can lessen the impact of the lost portion of the steps > by using the MOD operator to determine how much is left over after > dividing the commanded move by .006. Then use IF ELSE, IF the > remainder is Greater Than .5 steps then ADD a full step (command = > command PLUS .006 degrees) ELSE issue the commanded number (do nothing). > > This should statistically reduce the error by rounding up or down and > redistribute it randomly among all the cuts although it will not > eliminate it. The greater the number of cuts the better the > approximation will be. > > Sorry for the long post but I couldn't condense it much and get the > idea across. Can anyone confirm or disprove my observation or come > up with a better solution? Obviously I could add another reduction > stage to my rotary axis but I would like to avoid that if possible. > > Cecil > > > > ------------------------------------------------------------------------------ > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------ Message: 6 Date: Sun, 3 Jan 2016 09:11:39 +0000 From: Dave Caroline <dave.thearchiv...@gmail.com> Subject: Re: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <calfygtkbxg6rjzgu7geomxw16pmixzdfqmiwyy7jpz81vwo...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 In my experience of watch and clock gear cutting, heating is almost non existent as an error source, for steel one cuts under a lubricant which cools and brass is cut dry with a sharp cutter and often the clamping washers if used will keep it cool. Only one "brass" wheel gave me a problem and that was in naval brass for a tower clock, it is closer to a bronze. Dave Caroline ------------------------------ Message: 7 Date: Sun, 3 Jan 2016 12:04:01 +0200 From: Roland Jollivet <roland.jolli...@gmail.com> Subject: [Emc-users] Lost fractions of a step To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Message-ID: <caktodyjqgzwcsngoeitwdbzfypsas1ap0bdbywsyvhmepk1...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Just chipping in... So on your rotary axis, you have 60 000 steps per revolution. If you set up a dial gauge and do a simple G1 with 600 000 steps, or 10 rev's, is there much residual error? Otherwise, if the accuracy is good enough for one rev, then, in fake code; - home rotary - cut one tooth with +3 deg, - 3deg (or whatever one tooth requires) - home rotary axis - move to 6 degrees - cut one tooth with +3 deg, - 3deg - start again, for next tooth So now each tooth should be cut within the maximum error of a single rotation. Regards Roland On 3 January 2016 at 08:02, Cecil Thomas <wctho...@chartertn.net> wrote: > My question is about what happens to the "leftovers" when the > precision of the g code commanded position cannot be met by the > hardware executing it. > Several years ago I wrote a program to "generate" involute gear teeth > by making multiple cuts of the same tooth from differing angles with > a rack shaped cutter. This eliminates the need for the different > cutters when making only one cut per tooth. I have used it many > times to cut relatively large gears with a relatively small number of > teeth with virtually no noticeable error. > > A few days ago a friend who repairs watches wanted to know if I could > figure out what gear (wheel to you watch guys) size, pitch or module > and number of teeth would be required to replace a missing one. (the > original was long gone). I had no problem working from the center > distance and the matching pinion coming up with the appropriate design. > > However, when I cut the gear I had the right number of teeth but the > last tooth was much too wide. > > It would appear that I had lost a bunch of steps on the rotary > axis. Further investigation reveals what I think is the root cause > but I would like someone with more knowledge than me to confirm or > disprove my analysis. > > The gear had 86 teeth (in the power train, not in the timing train) > and I made 9 cuts per tooth. That is 774 commands and about all but > 86 of them in the same direction. > > My rotary axis is a 200 step stepper into a 30 to 1 worm drive > microstepped by 10 so 1.8 degrees divided by 300 equals .006 degrees > per microstep or 166.6667 steps per degree. > > Unfortunately when the g code calls for a 1 degree move the motion > planner can only issue 166 steps since it can't issue .6667 > steps. That means that the actual movement of the A axis is only > 166/166.66667 or .996 degree. That is .004 degree lost as far as I > can tell. That might be close enough for one or even several > commands but after 688 comands in the same direction that constitutes > 688 x .004 or 2.7 degrees lost. > > That is a significant portion of a tooth on a high tooth number > wheel. Depending on the actual value of the command the actual lost > motion could be anything from nothing to essentially a whole step or > .0059999 degrees. > > I think that I can lessen the impact of the lost portion of the steps > by using the MOD operator to determine how much is left over after > dividing the commanded move by .006. Then use IF ELSE, IF the > remainder is Greater Than .5 steps then ADD a full step (command = > command PLUS .006 degrees) ELSE issue the commanded number (do nothing). > > This should statistically reduce the error by rounding up or down and > redistribute it randomly among all the cuts although it will not > eliminate it. The greater the number of cuts the better the > approximation will be. > > Sorry for the long post but I couldn't condense it much and get the > idea across. Can anyone confirm or disprove my observation or come > up with a better solution? Obviously I could add another reduction > stage to my rotary axis but I would like to avoid that if possible. > > Cecil > > > > ------------------------------------------------------------------------------ > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------ ------------------------------------------------------------------------------ ------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users End of Emc-users Digest, Vol 117, Issue 17 ****************************************** ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
