I?ve done it now. The cross slide on my lathe has been giving me problems. I hesitated to do anything because it meant that I had to remove the DRO scale. My cross slide is now working like new. But even though I handled the scale as if it were nitroglycerine, my worst fears have come true. When I reassembled everything, the read out now reads
0.000 no mater what the position on the cross slide is in. The other scale, that I didn?t touch works fine, as does the receiving unit.
I was not aware that Sargon is no longer in business. Now what do I do? Anyone have an idea on how I can fix this thing? I really don?t have a budget for a new DRO.
The scale itself is a Sargon LG330-8. Are scales of different brands interchangeable?
The scales are much sturdier than you might think. Are you sure you got the alignment of the reader head right? There's a link between the actual reader head (the part inside that slides on the glass scale itself) and the part outside that attaches to the machine. The link is rigid only in the axis that is being measured and is flexible in the other 5 (2 linear, 3 angular) so that the head aligns itself to the scale. Most scales are tolerant of a reasonable amount of misalignment, but will act as you describe if the alignment is too far off.
You may be able to get some tips on alignment on Acurite's website.
Most scales, but by no means all, are TTL level and interchangeable, though connectors and pinouts may not be compatible. The scale also needs to match one of the available resolutions on the readout.
The Sargon readouts that I have seen are quite adjsutable for the readout resolution. I have a Sargon readout, and a Heidenhain scale, and Hiedenhain interpolation unit. Most scales are TTL, and the signals are compatible, and just need new connectors, or adapters made. The Heidenhain scales that I used are not TTL compatible, but the interpolator box does convert them from analog to TTL. At that point they plug into a Sargon, or AcuRite, ir whatever box. Teh point being, I set up the Heidenhain scales for .0005 mm resolution, and the Sargon readout was able to accomodate that resolution. Now, my Diameter reads out to .0001" (That Diameter, and thats that many zeroes!!)
I don't know what is wrong with your scale. It is possible to troubleshoot it, but I can't type fast enought to write the book on it, before I am late for something else. Surely something you can do, with a little exploration. Maybe try here:
the Sargon scales have some electronics right insode the DB25 connector that plugs into the readout. If the readout head is not lined up, it will not see the grating on the glass scale, and won't "move". If any wires to the readout head break, it will not work.. Look it over very carefully. The majority (only?) problems I had with the scales was getting the readout head lined up. One Sargon scale did have to have the pots tweaked inside the cable plug end, on the little circut board. I don't suggest doing that unless you have an Oscilloscope to troubleshoot with.
This was intended to show what is possible. WORST case scneario, you need a new scale, but I doubt it. There are a lot of shops that do scale repairs. I have a dealt with a shop in the Minneapolis are that was able to get spare parts to fix scales with. Good luck!
Thanks for responding. At this point I don't think it is the alignment. Whether I tighten down the screws or not I get no change in the reading when I move the slide. There doesn't seem to be a signal to the LEDs.
With your description of careful handling, it's unlikely that any damage occurred while you had it off. It sounds as though a bad contact or connection might be the problem. The little cover on the read head can be opened for inspection, but it should be well sealed when replaced.
The cable conductors in the plug/connector end can be examined without the risk of breaking any seal. You might also inspect the connector pins with a magnifier to see that they are clean and bright. If you have a similar pin of the same size, you can check that there is sufficient tension in the mating connector contacts (with the power off).
Careful inspection of the cable might reveal a pinched spot or some other sign that an individual conductor might've possibly been damaged. With the scale connected and the display turned on, you might try rolling the cable between your fingertips and thumb, while moving the cross slide, to see if there might be an intermittent connection in the cable. This could also be checked with an ohm meter with the head cover removed and connector shell open, with the scale disconnected from the display.
The reader head should glide in the housing silently. Any noticable sound could indicate an alignment problem. The basic design of the actual internal pickup/reader device includes a wheeled trolley-of-sorts, that's intended to keep the pickup device in alignment with the quartz/glass scale (without direct contact).
Typical DRO scales aren't extremely complex, and can be disassembled fairly easily for cleaning, by removing an end cap. If there happened to be some loose debris in the housing, it may have found it's way onto the pickup device when the scale was moved around during disassembly.
OK Ned, now I think I am getting it. My only other DRO experience was installing and later repairing a Shooting Star 3 axis DRO on my mill. On that, the alignment was pretty coarse. I presume that you are saying that the alignment is very critical,and not a situation of binding, etc.
I originally removed the 4 screws (which hold the scale bar and sliding component), noted where each of the mounting shims went and made no adjustments. I then replaced everything exactly as removed. I then turned on the DRO, zeroed it and everything stayed at zero when I moved the slide. I then removed the screw from the sliding component and moved it back and forth gently, the read out stayed at zero. So what you are saying is that I must fine tune the total alignment? If so, about how many thousandths alignment must be maintained?
The sliding component moves smoothly, so maybe I haven't broken anything yet. Whether I tighten down the screws or not I get no change in the reading
I'm not sure what the details of construction of that Sargon scale are, but if there is an end cap that is screwed on, take one of them off and have a look inside. Generally, there is a glass scale glued into the aluminum beam. A small read head that looks mostly like a thick circuit board on each side of the glass scale will ride on some sort of arrangement. The expensive scales have the head rolling on micro-micro ball bearings. The cheaper scales have the head riding on spring-loaded fingers with Teflon pads, mostly riding on the glass. With either design, it is not very hard when handling the scale loose from the machine to knock the head off the track. It will be pretty obvious when you get a look inside if that has happened. Moving the head while it is crooked is not a good thing, as it can damage the scale or the analyzer grating in the head, but that is not guaranteed. If the head is crooked, not close to the glass, etc. it should be fairly obvious which way you need to wiggle it to bring it back onto the track. You may be able to hold the flexible wiper material open with paper clip wire or similar improvisation to get a look at part of the head from a different angle. These units usually use a piece of music wire or a thin steel band to couple the internal head to the external slider part. Once the head is on the track, the wire or band may need to be adjusted to push/pull straight in the direction of travel, so it doesn't bow or push the head at an angle.
Many units have a square pin-type connector of some sort, so the external cable can be disconnected from the head itself. If there is a bind-up or overtravel when you reinstall the scale, this plug could have pulled out. That would be the easiest to fix.
One other possible condition is that swarf got inside the scale, and had been "swept" to the ends by the head over time. You may have moved the head farther than normal when it was off the machine, and the head is now dirty and can't see the scale. If you are careful and used to handling tiny stuff, these scales are not that hard to open up and clean with alcohol and Q-tips. I did my Mitutoyo scales on my Sheldon, and was AMAZED at the amount of gunk that had gotten in there!
I took everything apart today. Things looked good, no broken or loose parts. There was surprisingly very little swarf or grime inside. Upon inspection I found a broken orange wire. (Viola, I found it!) I repaired the wire and put everything together and tried it out. No change. Still registers 0.000" no matter the position. 8^(
I am interested in what you said about the bearings in the head. Mine has 2 silver colored rollers. The spring, which is very stiff, holds the head tightly to the base. It seemed to me that it should push in the other direction toward the glass. I guess now I will try it and see what happens.
As long as the read head is seated properly on the glass scale the alignment is close enough for the scale to output pulses to the readout. How far you can be off, and in which directions, and still have the scale work is a function of the scale's overall design, but most of the scales I've worked with would read if carefully hand guided. Jon described how the read head tracks on the glass, and I agree with his suggestions re peeking inside to see what's going between the read head and the glass.
The mounting requirements to maximize accuracy and minimize wear will be fussier than what's required to simply get the thing working.
It's helpful to understand that the read head doesn't pick up every line on the scale. The read head also carries a short grating similar to the main scale and the detector on the read head is looking at the interference pattern that results as the two gratings move relative to one another.
It may be helpful to post a photo of the scales as someone may be able to ID the manufacturer. It's my impression that there are more DRO manufacturers than scale mfrs and it's possible the scale mfr is still around even though Sargon is not. Ned Simmons
Well, be careful. But, the sensing part of the head should be REALLY close to the side of the glass that has the silver grating deposited on it. The lamp side of the head is often fairly far away, so the beam is pretty parallel.
But, make sure the glass analyzer grating on the head doesn't scrape the silvering (usually tungsten or nichrome, actually) off the glass. There needs to be something that keeps the two glass parts from crashing into each other. If the analyzer grating is more than a mm away from the scale, that is definitely the problem. A kink or misalignment of the coupling wire could definitely shove the head the wrong way. The rollers could ride directly on the glass, or on the housing. Usually, they have MORE than just 2 rollers. I've seen some with 8, 4 on the glass and 4 on the housing, and some other combinations. There is usually also something to keep the head from twisting on the scale, as it has to stay parallel to the sliding direction for the tiny slots in the analyzer to stay parallel to the ones in the scale. (There are also Moire scales that depend on a precise tilt between the read head and scale. I hope you don't have one of those.)
Anyway, the analyzer glass should be something like .010 to .015" at most away from the scale.
Greetings Jay, I think, from your description, that the read head is now in the wrong position. What I think is happening is that the head is now on the wrong SIDE of the scale. The head should be held close to or touching the scale. The spring should be on the OTHER SIDE of the scale that the head is on. You are right (I think) in surmising that the spring should hold the head against the scale, not away from it. If the read head is pulled off the scale you may not know it because the rubber flaps add enough drag that the head slipping off isn't noticed. It's been a while since I took one of these apart to fix it but that's the way mine worked as I recall. ERS
Thanks again Ned. I just submitted some pictures to the dropbox under Jays DRO. On further investigation I think I have a broken LED (?) At least one of 8 somethings appears to have been broken. There are 4 of them across from each other on the opposing boards. I couldn't get the pictures up close enough to show the break.
For the life of me, I don't see how I could have broken the wire or the component in question. I cannot believe how delicate this thing is. I found someone on Net that has a scale he wants $200 for, but I sure would hate to buy a bad scale. Not much recourse
Your camera *has* a macro mode -- you simply need to learn how to turn it on. Here is part of the information from the EXIF data in your photos -- since you posted the whole image without cropping (which would have reduced the size significantly):
====================================================================== File Name : Jays_DRO_2.jpg File Size : 208KB File Type : JPEG Image Description : OLYMPUS DIGITAL CAMERA Make : OLYMPUS OPTICAL CO.,LTD Camera Model Name : C920Z,D450Z Orientation : Horizontal (normal) X Resolution : 72 Y Resolution : 72 Resolution Unit : inches Software : v873-75
[ ... ]
Special Mode : Normal, Sequence: 0, Panorama: (none) Image Quality : SHQ Macro : Off For the life of me, I don't see how I could have broken the wire or the
Did you remove the read head before the problem occurred? They are normally fairly well protected while fully assembled.
Granted -- if you tilt it to nearly vertical, and let the read head slide down to the end stops, it may well hit something which will break some part of the read head. Ideally, I would have put a cable tie around the spar of the scale and the armored wire to keep the head from sliding around loose while the scale was off the machine.
If it is shipped tied down as I suggested, it should be fine, if it was fine when he shipped it.
You might want to send the entire scale (cable and all), out for repair and recalibration. It's not really a DIY job, since the replacement components need to match the specs of the original parts, and it's highly unlikely that a complete parts list and calibration procedure is available. I believe the light emitters are infrared, for example.
If you have the Sargon model literature, including the scale specs, resolution and cable pinouts for the signals and power connections, you could select a suitable replacement scale of another brand, such as Anilam, Acu-Rite or similar 5 volt TTL scale.
Without unreasonably high expectations, you might be able to find a good replacement scale, or a NOS reader head on eBay, if you'd be willing to chance getting a working unit from a trustworthy source. I've bought numerous good DRO components on eBay, in new or good working condition.
The short (lathe cross slide) and the mini-scales will generally cost as much as a long scale because they're compact, and fit places that full-sized scales won't.
I found a scale that will work for a pretty reasonable price on the Net.
It seems that every time I took the damn thing apart I found something else wrong with it. I don't know if I am doing the breaking or it was just about to fall apart and my timing is bad. But my lathe has been down for days and I need to get it up to speed so getting a good scale for a reasonable price seems more cost effective than spending the next week up tuning up my poor electronics skills.
The glass is glued to the aluminum extrusion and there is no way to see if the silver grating is still in place.