Repairing Heindenhain VRZ 753B + LS803 scales
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    Default Repairing Heindenhain VRZ 753B + LS803 scales

    My 1965 FP2 came with a non-functional 3-axis Heidenhain DRO, model VRZ 753B. The control unit displayed 5 on all three axes and was non-responsive. The sealing lips on the scales had disintegrated into a sticky mush, and the insides of the scales were full of dust and grease.

    Probably I should throw it out and start over, but I'm not good at that. The system seems to date from the early 1980s and appears to have been professionally installed. The mounting hardware is machined and blued, with fiduciary dowel pins. The wiring is in armored waterproof flexible conduit with gasket-sealed connection boxes. The scale covers are heavy-duty steel with matching gray hammer-tone paint. So rather than trashing it I'm going to try to fix it.

    As a first step, I took apart the control unit. The three unregulated DC power supplies, 5, 10 and 20 volts all were working OK, but I changed their electrolytic capacitors because these tend to dry out with time and heat. Cost 5 Euros. The problem turned out to be with the 12 volt regulated output: the three-pin 12 volt regulator (MC7812 in a TO3 package) was defective. I replaced it (cost 3 Euros) adding some Arctic Silver 5 thermally conductive grease to help keep the temperatures down . The regulator is supplying 980 mA of current, and has an 8 volt drop across it. So it is dissipating around 8W of heat and will eventually cook (again) if not cooled properly.

    Here is a photo of the old regulator sitting on top of the heat sink, just next to the mounting location (under the black plastic cover).

    photo-3.jpg

    This fixed the control unit!

    photo-1.jpg

    Then I turned my attention to the glass scales (all are LS803). I've started with the shortest one (220mm) from Y. I took out the reader head, removed the remains of the rubber lips, and cleaned the scales and the reader head with alcohol. For motivation and to be sure I was on the right track, I reassembled this and tested it with the display: everything works correctly, as far as I can tell. The rubber sealing lips were crimped into place, so now I need to open up the crimping slightly to get the new lip seals into place (I bought 4m of material). I also want to make sure that I clean the read head properly. So here is my first question. What is the best way to clean the read head? Should I, or could I immerse the entire head in cleaning alcohol? Here is an annotated photo:

    photo-2-marked.jpg

    I am particularly concerned about dust or dirt that has gotten in between the pea lamp and the glass window/reticule. I'm afraid to clean it with compressed air, as that would probably break small wires and throw off the optical alignment. Any suggestions? Or is it not important to clean out this area thoroughly? My goal is to do it well enough that the scales give accurate and correct results, and work reliably for some years to come (this is a home shop, so not heavy use).

    Cheers,
    Bruce

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    I've found a few more hours to work on this and have cleaned up and repaired the X (520mm) and Y (220mm) axes scales.

    The main thing that made it possible was this tool, which I made by taking a pair of flea-market nippers and then grinding down one jaw to make it thinner and grinding the other jaw to blunt it.

    img_2632.jpg

    I use this to open the crimp in the scales in order to insert new rubber lip seals. Here is the tool showing how one can open the crimped slot. The slot on the left has just been spread open using the tool. For comparison, the slot on the right is in the original crimped state.

    img_2633.jpg

    The reground nipper jaw varies in cross-section, so I work it in the direction from the thinner to the thicker end, moving down a few mm and then squeezing, a few more mm, then squeezing, etc.

    The scales were in terrible shape. The lip seals had completely disintegrated into a sticky goo, and the scales were full of sawdust and sticky stuff

    img_2624.jpg

    img_2626.jpg

    In order to remove the lip seals completely, I made the following "tools" out of 0.005" = 0.12mm shim stock. I have versions with 1, 2, 3 and 4 layers. I used these to clean out the lip seal slots, then used them to push acetone-soaked tissues along the slots to remove the last of the goo and get the slots "squeaky clean".

    img_2628.jpg

    I was concerned that the widened slots for the lip-seals would not hold the seals securely, as the 'bead' at the back of the seal did not have a substantially larger opening to engage it. But the seals stay in place nicely, because the pressure against one another and from the read head 'fin' forces the seals deeper into the aluminium slots. I thought about using cyanoacrylate adhesive to glue the lip seals into place. While it would be very easy to do, I don't think it is needed.

    (Continued in the next posting)
    Last edited by ballen; 05-05-2014 at 12:47 AM.

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    ballen
    Great work as usual thanks for posting the info and photos. I have read several other post about how the seals can be tough to work with. Your idea of the modified nippers seams to work well. Keep us posted
    Is there any place that has an interchange list between scales and readouts for Heidenhain? I just picked up two sets for lathes one is missing a scale one is missing the power cord. The power cord although the normal 110 v used here In the states has an unusual receptical on the box. Any place to download manuals for these?
    Andy

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    (continued from earlier post)

    To clean off the glass scales, I pulled tissues and then lint-free lens paper through on both sides of the glass scale, using a piece of cotton string with a loop on the end. I soaked the paper with reagent-grade (pure and clean) isopropanol (also called 2-propanol) and continued this procedure until the tissues and lens paper came out clean. Then I dried off the inside of the scale assembly using a "puffer" meant for blowing dust off camera lenses.

    img_2629.jpg

    I avoided using compressed air for two reasons. First, I'm not confident that the in-line filter of my compressor will remove all the oil and water from the air. Second, I was afraid that the high pressure might fling grit at the scale and scratch it or break it. So I picked a gentler alternative.

    To clean off the read head I used the same solvent, but also made use of a spray-can of purified isopropanol/2-propanol intended for cleaning optical devices and videotape read heads. Again, the puffer was used to blow away and dry off any excess.

    Here is the X-axis scale after reassembly, showing the replacement lip seals (green). The replacement lip seal material is Heidenhain part # 222282-03, with a US list price $ 37.13 per meter.

    img_2637.jpg

    Here is the X-axis scale mounted in place (without the protective shield/cover):

    img_2638.jpg

    The scales appear to work perfectly. One thing that give me some confidence is the following test. Both scales have reference marks 35mm from the nominal end. If I set zero at one reference mark, then traverse to the other reference mark, I get exactly 150.000 mm (220 - 2 x 35) for the shorter scale, and exactly 450.000 mm (520 - 2 x 35) for the longer one. I think this means that they are not skipping any counts in between the two reference marks. They also agree very closely with the lead-screws, with a maximum deviation of about 0.02mm.

    I have one question, at the moment the "increasing" direction is not what I was expecting. What is the standard for the direction in which the X and Y counts increase? I would have expected the X axis count to increase as I move the workpiece to the left, and the Y axis count to increase as I move the ram towards the back of the machine. Is that correct? Can anyone tell me which pair of wires to swap to reverse the counting direction?

    Cheers,
    Bruce
    Last edited by ballen; 05-05-2014 at 12:52 AM.

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    Hi Andy,

    Yes, the modified nippers make it straightforward to replace the crimped-in lip seals. It took me five or ten minutes to grind the nippers to shape. Using them to open up the longest scale I have (520 mm measuring length) took fifteen or twenty minutes. (The cleaning process took considerably longer.)

    Quote Originally Posted by Andy St View Post
    ballen
    Is there any place that has an interchange list between scales and readouts for Heidenhain? I just picked up two sets for lathes one is missing a scale one is missing the power cord. The power cord although the normal 110 v used here In the states has an unusual receptical on the box. Any place to download manuals for these?
    In trolling around the internet for information, I have not found an interchange list. But I have found on-line manuals for all the VRZ display units. I've also been able to find manuals for some scales using Google. For example manuals for my LS803 scales.

    I think to check for compatibility, you need to first consult the manual for the display (mine specifies 11 microamp scales with 20 or 40 micron gratings) and then check the manual for the scales to see if they match that spec.

    Cheers,
    Bruce

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    Thanks for the help and the link Bruce.
    So this is the front and back of the unit that is missing the X scale. Still not sure what model this is?
    Looking again at your first photo it looks like your power cord plug might be the same as my other unit. Do you have a photo of it without the cord in it? Is that a common plug in Germany?





    Thanks
    Andy

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    Never mind I found it.
    http://content.heidenhain.de/doku/om...n/28802824.pdf
    It was the ND 530
    For some reason I thought 530 a CNC unit.
    I'd still like to know about the plug.
    Andy

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    Andy, please post a photo of your power connector. From the manual that you sent, it looks like a standard C13 computer power plug. If so you can get the power cord from any computer store or just from an old PC. Cheers, Bruce

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    Quote Originally Posted by ballen View Post
    (continued from earlier post)


    I have one question, at the moment the "increasing" direction is not what I was expecting. What is the standard for the direction in which the X and Y counts increase? I would have expected the X axis count to increase as I move the workpiece to the left, and the Y axis count to increase as I move the ram towards the back of the machine. Is that correct? Can anyone tell me which pair of wires to swap to reverse the counting direction?

    Cheers,
    Bruce
    Bruce:
    Early machines did not standardize on the direction of axis movements. Had this issue with an FP2 "Active" machine fitted with the TNC 113 Heidenhain box. Machine moved backwards from what i was used to on the "X" axis.

    Current standard on the lather machines ,which i use for all my Deckles, is that when standing at the operators position (where the controls are) When the "X" axis is moving away from the operator (table shortening closest to the operator,
    That is a positive (+) move......Table moving toward the operator...that is a minus (-) move.
    As to the "Y" that is easy. Visualize there being a drill in the horizontal spindle....A move (just like the "Z") that moves the drill into the work is a minus (-) move.....Moving the drill back for MORE clearance is a plus (+) move...
    However, if you aet teh DRO to the current movement direction standard it will likely be moving opposite to the "scales"(rulers) on the machine slides....Personally i do not find that a problem as the DRO pretty much removes the rulers
    from the picture. Guess it only becomes a problem if you also have other machines where the direction moves are different...you can run which ever way you wish. For me the CNC machines set teh standard, and i let
    everything else follow.

    If your DRO is a Heidenhain pretty sure there will be parameters that you can set that will change the direction of the move for that axis...shouldn't have to swap any wires. Solved my problem on the 113...and kept me from making stupid movement
    direction errors.
    The Heidenhain site has pretty much every DRO and control info on their site. Owners manual will give the sign change parameter if applicable.

    Cheers Ross

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    Hi Ross,

    Thanks for chiming in!

    Quote Originally Posted by AlfaGTA View Post
    Current standard on the later machines ,which i use for all my Deckels, is that when standing at the operators position (where the controls are) When the "X" axis is moving away from the operator (table shortening closest to the operator)
    That is a positive (+) move......Table moving toward the operator...that is a minus (-) move.
    As to the "Y" that is easy. Visualize there being a drill in the horizontal spindle....A move (just like the "Z") that moves the drill into the work is a minus (-) move.....Moving the drill back for MORE clearance is a plus (+) move...
    Yes, this is exactly what I would like. When standing in front of the machine, counts increase as the workpiece moves to the left, and counts increase as the workpiece moves towards the observer. It is the standard convention for a right-handed Cartesian coordinate system.

    Unfortunately there is nothing I can find in the Heidenhain VRZ753B manual about changing the sign convention. Probably this can be accomplished by swapping the 0 degree and 90 degree phase signals from the scale, or by swapping the polarity of the 0 degree and the 90 degree phase signals. Perhaps someone here knows the answer, or I can get it from Heidenhain support.

    Cheers,
    Bruce

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    Hi Bruce
    Sorry I can't help with your problem. Here is the photo of the other DRO. This one is in fine working condition but I do not have the power cord. It's VRZ 742C and the manual is listed in the link you sent. This is the one I thought might be the same as your first photo (looks like it has he same sheet metal flip up attachment). As far as I know this attachment is not common here.



    Andy

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    Bruce:
    Surly too simple and there are most likely good reasons to not go this way, but why not just turn the scale around?

    Cheers Ross

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    Andy:
    That is a normal Heidenhain power cord connection for the early boxes....
    Cheers Ross

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    Quote Originally Posted by ballen View Post
    Hi Ross,


    Unfortunately there is nothing I can find in the Heidenhain VRZ753B manual about changing the sign convention. Probably this can be accomplished by swapping the 0 degree and 90 degree phase signals from the scale, or by swapping the polarity of the 0 degree and the 90 degree phase signals. Perhaps someone here knows the answer, or I can get it from Heidenhain support.

    Cheers,
    Bruce
    Swapping the polarity seems to me to have potential danger. However swapping the signals should work. They are two 180 degree signals set 90 degree out of phase ("quadrature signals"), so swapping them should reverse the direction of the counter.

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    Quote Originally Posted by Andy St
    As far as I know this attachment is not common here.
    Hirschmann make them....available in this little backwater hole even.

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    Hi Ross,

    Quote Originally Posted by AlfaGTA View Post
    Surely too simple, and there are most likely good reasons to not go this way, but why not just turn the scale around?
    Two reasons:

    (1) The (10 cm long) cable from the read head runs through a long bracket hole and then into a wire channel. If I turn around the scale and the read head, the cable will no longer will run along this well-designed route. And the cable is too short. Yes, I could do micro-surgery and extend the cable, and I could channel out a new cable path. But I would rather swap a couple of wires if possible.

    (2) The scale and head are not symmetric if flipped. According to the manual, one needs an offset of 0.5mm if it's mounted in one orientation, and 0.7mm if mounted in the other. So I would need to shim or re-machine the mount. Again, I'd rather just swap a couple of wires, if possible!

    In any case, if I can't find an simple electronics way to flip the orientation, then I'll turn the scale around.

    By the way, if I understand correctly how the scales work, if you modulate the X/Y of an oscilliscope with the 0/90 phase signals, it will trace a circle as the scale advances. Thus, simply changing the polarity (flipping the wires) of either the 0 degree or 90 degree signal will reverse the direction of the circle that is traced, corresponding to reversing the "increasing length" direction.

    [EDIT]

    Just got a very helpful reply from Heidenhain support. To reverse the scale direction one simply swaps the 0-degree and 90-degree signals. This means to swap I1+ (green) with I2+ (blue) and swap I1- (yellow) with I2- (red). Will try it at the next opportunity!

    Cheers,
    Bruce

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    Hi Andy,

    Yes, that's the same power connector that I have. I have seen them for sale on German Ebay and also I think from Singer Werkzeugmaschine. I don't know if they are standard or specific to Heidenhain. In any case, I suspect that someone in this group has an extra one and will give it or sell it to you.

    An easy solution if you like is to open up the box and simply replace the socket with a standard C13/C14 pair like on a desktop computer. You can buy the C13/14 pair from Radio Shack or Digi-key. You'll have to modify the hole in the back of the chassis to mount the fixed connector. Should be easy if your mill is in running shape (:-).

    Cheers,
    Bruce

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    Quote Originally Posted by swarf_rat View Post
    Swapping the polarity seems to me to have potential danger. However swapping the signals should work. They are two 180 degree signals set 90 degree out of phase ("quadrature signals"), so swapping them should reverse the direction of the counter.
    You are absolutely correct on both points!

    To reverse the scale direction (for scales WITHOUT distance-coded reference marks) you simply swap the 0- and 90-degree signals. This means swap I1+ (green) with I2+ (blue) and swap I1- (yellow) with I2- (red). I just used this to correct the sign of both X and Z to agree with the standard Ross described. It worked perfectly.

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    Default Repairs finished

    Well I am finished with the cleaning and repairs, and thought that I would post a few victory shots with all three axes completed and working. These might also be of interest to see one particular way that a "factory DRO install" was done. I am calling it a "factory install" because of the fact that all of the mounting blocks are pinned and blued steel and all the covers have hammer-tone paint that matches the other hammer-tone paint on the machine.

    First the display:

    img_2661.jpg

    The Z-axis. This is the only axis where the reader head moves with respect to the body of the machine.

    img_2662.jpg

    The Y-axis:

    img_2664.jpg

    The X-axis. The hammer-tone steel cover is flush with the vertical table, so does not interfere. The sealing lips are on the bottom side. However I might at some point re-machine the mounting blocks to move the body of the scale about 7mm to the right, because when the table is shifted as far away from the operator as possible, the read head comes right to the end of its travel in the scale (within a fraction of a mm) which makes me nervous.

    The gray signal-connection box was originally located in the middle of the area where I have added the one-shot oiler, so I have moved the box a bit towards the front of the machine.

    img_2667.jpg

    The cabling setup in back:

    img_2672.jpg

    My only gripe is that the Z-axis clamping lever is blocked in some positions by the scale. However since the Z-clamp doesn't work very well anyway, this is a minor loss.

    All of my tests indicate that the scales and reader work perfectly. Quite remarkable for what is probably a 30-year-old system!

    Was it worth fixing? Yes! I think that the time I spent fixing the system was probably less than it would have taken me to make up equivalently solid mounting blocks and covers and wiring conduits, and the cost was essentially zero.

    One final question:
    I'd like to add an inch/millimeter selector switch to my display unit (VRZ 753B). I suspect that there are a pair of internal contacts or solder pads inside the display unit which could be connected or disconnected to switch from metric to inches. If so, could someone help me to identify them? Then I can add a front or rear panel switch to go back and forth between metric and imperial units.

    Cheers,
    Bruce

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    Hi Bruce
    If looking inside either of mine will help you let me know. I can look and take some photos but it might not happen till next week.
    BillE thanks for the name of the manufacturer. Ill see what I can come up with here in the USA. Like I wrote I have never seen that plug on anything else. I have a box of the Micky Mouse shaped ones and the other C13 ones already. I just like to keep things simple and original.
    Thanks everyone
    Andy


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