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PM suggested using simple green, or "some other mild cleaner" in the region.
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How can I remove the x axis scale on a PM25MV?
- Thread starter WobblyHand
- Start date
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I got that. Your problem seems to be a dirty or defective scale. But the post previous to mine implied that we are at the mercy of our dials in checking the accuracy of a DRO.
As a side note, my Grizzly G0602 cross slide and compound lead screws are metric so Imperial dial readings are not accurate. IIRC, the same is true for the G4000 lathe and for the G0755 mill.. I would expect that this is common for many of the Chinese imports.
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I cleaned the scale glass with isopropyl alcohol and it got a little better, but the problem is still there. The Qtips were clean. Cleaned the seals and they had some minor stuff on them. Still have a 0.030" return to zero error, which seems to accumulate. Definitely not a good thing for a DRO.
@RJSakowski my G0752Z came from Grizzly with 0.001" scales. The native readout is in 1/1000" on the magnetic tape. It's ok for Z, but not so good for X. I may replace the X axis. Since I have my own ELS (and DRO is incorporated into it) I could change the scales without much problem.
@RJSakowski my G0752Z came from Grizzly with 0.001" scales. The native readout is in 1/1000" on the magnetic tape. It's ok for Z, but not so good for X. I may replace the X axis. Since I have my own ELS (and DRO is incorporated into it) I could change the scales without much problem.
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PM is sending me a new reader. I'm not sure of the nomenclature, is that the whole assembly? (Head, scale, housing, cable?)
They are a first class outfit.
Edit: they are sending me a new read head. Hope that does it. Hoping it comes with the cable, there's a lot of wires!
They are a first class outfit.
Edit: they are sending me a new read head. Hope that does it. Hoping it comes with the cable, there's a lot of wires!
Last edited:
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It's not only the scale that needs to be clean. There is also the read head which will have an LED source, and a photodiode detector, and some lensing arrangement which might be integral with the diode plastics. Just like in a kitchen in corners nobody can get to easily , over time, on a sticky film of condensing oil vapor, the dirt builds up.
Obviously, cleaning up a mucky read head can be a delicate procedure, even if the action is appropriate anyway. There are more things that can go wrong with optical sensors than can be put down to dirt film buildup. It's great that you get to have a new one, and I have to agree that PM is exemplary as a supplier!
Obviously, cleaning up a mucky read head can be a delicate procedure, even if the action is appropriate anyway. There are more things that can go wrong with optical sensors than can be put down to dirt film buildup. It's great that you get to have a new one, and I have to agree that PM is exemplary as a supplier!
@WobblyHand
Congrats on getting it loose.
I do not have an optical scale so hesitate to suggest how to clean it or even disassemble it. My DRO is magnetic and I have yet to need to clean it. But without other instructions I would clean it in a similar manner.
I am suspect that there is lots of info on either this forum or via the web on how to clean scales. Or better still go back to the manufacturer for suggestions.
Below I will provide some suggestions on cleaning optics, but first I must say I do not fully understand your statements about return to zero, skipped counts, etc. You want to make sure that the table is actually moving. Use the 123 block before you do a lot of work on the DRO. When I got my CNC mill from the factory... it did not work right. The dro is non-physical, built into the software, and merely counts the step signals sent to the CNC stepper motors not the actual distance. So this DRO would say that the mill had moved even if it was not moving. The z-axis Gib was too tight and while the steppers would work and the counts were correct when dropping the heavy head they did not always lift the head and so would miss steps, and the DRO would have the wrong value displayed. Hence, the error in motion, but it looked like an error in the return to zero on this axis.
Cleaning optics:
I do have considerable experience with other optical components and cleaning them as I have built experimental optical systems, lenses, devices, laser optics, etc. You must not scratch them as this is the equivalent of dirt and blocks, bends or diffracts the light from its intended path. Be careful, with a very gentle hand, and actually do not touching it.... Only as a last result does actually rub an optic with anything other than lens cleaning paper wet with pure (100%) methanol. You can get booklets of "lens cleaning paper/tissue" at a photography store if not on line. You do not want oil on the optic which you can sometimes see by holding the optic at an angle and looking at the grazing light reflected from it. If there is debris on the optic. Your hands have oil in the skin so the approach is to clean some metal tweezers with soap and water and then with clean water and finally with methanol, removing all oils and particles. Using the tweezers fold a piece of the lens cleaning tissue a few times so that it is a little stiff. With an clean eye dropper drop a bit of methanol on the paper while holding the folded tissue on one side with the tweezers. Now drag the wet paper along the optic once to dissolve the oils and transfer them from the optic to the paper. Repeat with clean paper. So you can sort of see that this technique limits the pressure that you can put on the optic and so limits the scratching. You will see lots of folks cleaning things with Q-tips. However, caution, caution, caution.... as you can exert lots of pressure with these and any debris that gets stuck in the cotton is just waiting to scratch the optic.
Obviously Methanol does not dissolve all materials and I have no idea about cosmoline, but the WD40 contains several solvents in addition to oils which could be dissolving the cosmoline. Acetone, Toluene, etc... Of course the WD40 is also a potential contaminate for the scales. (By the way when I cleaned the gooey shipping wax (cosmoline) off of my mill and lathe I used naphtha (lighter fluid ... by the gallon at a paint store, and does not attack most paints) rather than WD40 and it worked great and is much cheaper and does not contain unspecified oils in it.)
I "think" the glass scale patterns are etched and use these patterns for detection. You can see why the transducer might confuse scratches for etched scales marks! That is how the older glass scales were made, but it could be these days that they deposit a material onto the glass and you would not want to wash the pattern off with some solvent. Very last resort, just wash these things .... gentle ...starting with mild soap and water and work your way towards cleaner and cleaner wash systems. I used the word "clean" methanol as there are several solvents which are not clean and will leave residues of dirt. Acetone is one of these as it leave particles ... behind sometimes.
Now a nightmare story and the resulting optimism. I had a lower story lab in an old University building with a 4x5' optical table covered with expensive optical components for a laser interferometer experiment that I was conducting. Some vandal plugged up the drains and turned the water on in a bathroom that was a couple of stories up in the building flooding the place over night. The water made its way through the old dirty concrete and plaster and was dripping all over my lab with I arrived in the morning. Some of the water had already evaporated off of the optics leaving all kinds of stuff stuck on these delicate surfaces... These residues did not come off with the gentle processes I described nor did some of it even dissolve with water or other solvents. However, lots of gentle cleaning eventually got most of it off and in most cases we were able to save many of the parts. Yes, there was some rubbing, but always with a gentle hand and soft materials. (By the way, if you wear plastic eye glasses and need to clean the oils off never rub them on your shirt tail! I simply use warm soap and water... I find a "Dial Complete Foaming Kitchen Hand Soap" dispenser pump to work well for this as it makes foam rather than a gob of sticky soap. The dilute foam is easy to wash off. )
Good luck.
Dave L.
Congrats on getting it loose.
I do not have an optical scale so hesitate to suggest how to clean it or even disassemble it. My DRO is magnetic and I have yet to need to clean it. But without other instructions I would clean it in a similar manner.
I am suspect that there is lots of info on either this forum or via the web on how to clean scales. Or better still go back to the manufacturer for suggestions.
Below I will provide some suggestions on cleaning optics, but first I must say I do not fully understand your statements about return to zero, skipped counts, etc. You want to make sure that the table is actually moving. Use the 123 block before you do a lot of work on the DRO. When I got my CNC mill from the factory... it did not work right. The dro is non-physical, built into the software, and merely counts the step signals sent to the CNC stepper motors not the actual distance. So this DRO would say that the mill had moved even if it was not moving. The z-axis Gib was too tight and while the steppers would work and the counts were correct when dropping the heavy head they did not always lift the head and so would miss steps, and the DRO would have the wrong value displayed. Hence, the error in motion, but it looked like an error in the return to zero on this axis.
Cleaning optics:
I do have considerable experience with other optical components and cleaning them as I have built experimental optical systems, lenses, devices, laser optics, etc. You must not scratch them as this is the equivalent of dirt and blocks, bends or diffracts the light from its intended path. Be careful, with a very gentle hand, and actually do not touching it.... Only as a last result does actually rub an optic with anything other than lens cleaning paper wet with pure (100%) methanol. You can get booklets of "lens cleaning paper/tissue" at a photography store if not on line. You do not want oil on the optic which you can sometimes see by holding the optic at an angle and looking at the grazing light reflected from it. If there is debris on the optic. Your hands have oil in the skin so the approach is to clean some metal tweezers with soap and water and then with clean water and finally with methanol, removing all oils and particles. Using the tweezers fold a piece of the lens cleaning tissue a few times so that it is a little stiff. With an clean eye dropper drop a bit of methanol on the paper while holding the folded tissue on one side with the tweezers. Now drag the wet paper along the optic once to dissolve the oils and transfer them from the optic to the paper. Repeat with clean paper. So you can sort of see that this technique limits the pressure that you can put on the optic and so limits the scratching. You will see lots of folks cleaning things with Q-tips. However, caution, caution, caution.... as you can exert lots of pressure with these and any debris that gets stuck in the cotton is just waiting to scratch the optic.
Obviously Methanol does not dissolve all materials and I have no idea about cosmoline, but the WD40 contains several solvents in addition to oils which could be dissolving the cosmoline. Acetone, Toluene, etc... Of course the WD40 is also a potential contaminate for the scales. (By the way when I cleaned the gooey shipping wax (cosmoline) off of my mill and lathe I used naphtha (lighter fluid ... by the gallon at a paint store, and does not attack most paints) rather than WD40 and it worked great and is much cheaper and does not contain unspecified oils in it.)
I "think" the glass scale patterns are etched and use these patterns for detection. You can see why the transducer might confuse scratches for etched scales marks! That is how the older glass scales were made, but it could be these days that they deposit a material onto the glass and you would not want to wash the pattern off with some solvent. Very last resort, just wash these things .... gentle ...starting with mild soap and water and work your way towards cleaner and cleaner wash systems. I used the word "clean" methanol as there are several solvents which are not clean and will leave residues of dirt. Acetone is one of these as it leave particles ... behind sometimes.
Now a nightmare story and the resulting optimism. I had a lower story lab in an old University building with a 4x5' optical table covered with expensive optical components for a laser interferometer experiment that I was conducting. Some vandal plugged up the drains and turned the water on in a bathroom that was a couple of stories up in the building flooding the place over night. The water made its way through the old dirty concrete and plaster and was dripping all over my lab with I arrived in the morning. Some of the water had already evaporated off of the optics leaving all kinds of stuff stuck on these delicate surfaces... These residues did not come off with the gentle processes I described nor did some of it even dissolve with water or other solvents. However, lots of gentle cleaning eventually got most of it off and in most cases we were able to save many of the parts. Yes, there was some rubbing, but always with a gentle hand and soft materials. (By the way, if you wear plastic eye glasses and need to clean the oils off never rub them on your shirt tail! I simply use warm soap and water... I find a "Dial Complete Foaming Kitchen Hand Soap" dispenser pump to work well for this as it makes foam rather than a gob of sticky soap. The dilute foam is easy to wash off. )
Good luck.
Dave L.
@RJSakowski
Having a 'known" reference is always an issue. Who says micrometers or blocks are accurate unless testing certificates are provide.... especially when one is trying to measure longer distances, inches, with accuracy of 0.0001" or 0.001 mm. I never actually do/can nor do I need to, but from a meteorological stand point, or just curiosity, one has to spend money and then maintain specialized tools. Anyway, we should not mess up this string by getting off topic.
Regards,
Dave L.
Having a 'known" reference is always an issue. Who says micrometers or blocks are accurate unless testing certificates are provide.... especially when one is trying to measure longer distances, inches, with accuracy of 0.0001" or 0.001 mm. I never actually do/can nor do I need to, but from a meteorological stand point, or just curiosity, one has to spend money and then maintain specialized tools. Anyway, we should not mess up this string by getting off topic.
Regards,
Dave L.
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Return to zero is simple. There is a scale (not super precise mind you) mounted onto the table edge. There is a pointer that is mounted to the base. When the pointer aligns to zero, I zero the X-DRO. I then move the table to +3.000 inches, by the scale. Then I move the table back until the pointer aligns to zero on the scale. This is not super exact, but more than adequate to see that counts are missed.
Another experiment. Start at 0 on the physical scale. Zero DRO. Move table to to 1.000" on the physical scale, but the DRO only indicates 0.8". If I move the table back to 0 on the scale, the DRO reads 0.2". The errors were so gross, I did not need a precision device to see the problem.
When I put in the new read head, I will check out the DRO with a 123 block and an Interapid DTI.
Hope to receive the new read head either tomorrow or Friday.
Another experiment. Start at 0 on the physical scale. Zero DRO. Move table to to 1.000" on the physical scale, but the DRO only indicates 0.8". If I move the table back to 0 on the scale, the DRO reads 0.2". The errors were so gross, I did not need a precision device to see the problem.
When I put in the new read head, I will check out the DRO with a 123 block and an Interapid DTI.
Hope to receive the new read head either tomorrow or Friday.
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- Dec 18, 2019
- Messages
- 7,333
Received the read head this morning. Will install it this afternoon. When I pull the scale I will check and clean the glass if necessary. I will take the old read head and put it under a microscope. Didn't think of that last time. Might as well, maybe it is recoverable and can be a spare? If not recoverable, at least I can learn something...