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| Digital Readout Question |
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| Bogstandard:
There will always be arguments for and against almost everything, and of course, depth of pockets comes into the equation. In fact, I would love to fit the Newall read heads, they work in a totally different way, but for me, way beyond my finances. I already have seven glass read heads, and some time next year, that should grow to nine, when my small surface grinder gets a couple during it's refurbish. If I had continued to use the scale type, I am sure that I would have spent the same sort on money as I have already spent on the glass scale systems, purely due to failure of the units. These ones I have haven't missed a beat since they have been fitted. How you operate your machine also has a great bearing on the longevity of the digiscale type. Most home model engineers rarely use flood coolant or even any lube or coolant at all, but if you do, then digiscales are at risk of failure, the same goes if yours is a cold and damp shop, they will play up at the least excuse. So if you can keep them warmish, swarf protected and bone dry, then you stand a good chance of having a reasonable life expectancy out of them, if you can't, then I really do feel sorry for you. Digiscales use a metal to metal contact in their workings, and are not even water resistant, and that is their downfall, whereas glass scales, even though they have mechanical workings inside (for support of the optical read head), their method of operation is purely optical with zero contact between the read head and the etched glass scale, plus if covers are used, they are in fact very well protected. But even though good, they still have their weaknesses. A heavy jolt whilst in use or whilst fitting can render them useless if the optical head flexes on its mounting and then hits the glass scale. Luckily that has never happened to me, but it can happen. How the cables hang can cause weepage into the main casing over time, so you sometimes have to swap the read heads around inside so that you get the cables coming out at the lowest point, I had to do that when fitting the large glass scale to the Z axis on my mill. They have to be mounted thou perfect to get long life out of them etc etc. So they are not perfect, just that they are the best that are available for the price at this time. Eventually and hopefully, all will be like the Newall system, which can actually be used under water if needed, but until that happens, we are stuck with what we can afford. Dale mentioned about feeling guilty using DRO's. I have no such qualms, and neither should you Dale. They are a natural progression in manual machining, just like having HSS and tungsten tooling, when in the past all we had was carbon to work with. Wigglers and edge finders took over from the cigarette paper, and small home shop mills replaced vertical slides on the lathe. Eventually, I would expect all machines to have them ready fitted at the factory, as is happening now on the slightly more expensive home machines. I am sure everyone would enjoy not having to take into account the backlash present in all our machines, and having a method of achieving 0.0001" (0.0005" in the case of digiscales) accuracy as standard, rather than the accepted 0.002", without even having to think about it. Bogs |
| picclock:
Hi Bogs "Digiscales use a metal to metal contact in their workings," I don't think you are correct there. They work by measuring the change of capacitance between metal fingers under the read head and the spacing of an etched copper pattern on a strip of fibreglass on the rule. There is no metal contact. Most errors are likely down to swarf or lubricant getting in between the head fingers and the rule, causing a local change of capacitance and altering the reading. A clear piece of plastic sheet (acrylic) covering the rule and head improves this. Ensuring the ruler wipers are in place will also help a great deal. If you have a remote readout covering them with metal would be better, protecting against mechanical fumbles (I'm born climsy :hammer:) as well as ingress of cr*p, and you don't have to use batteries. I already managed to break the display window on my 30" DRO :( and made a new one from a CD case ::), so metal and cr*p proof is clearly best IMHO. picclock |
| tumutbound:
I modified my cheap scales before mounting on the mill (X2). This involved removing the LCD display, switches and plastic housing. I made up an insulating cover from FR4 material and protective cover from aluminium. In the aluminium cover I built in some brushes to wipe off any swarf. So far, so good. I agree with Bogs that having swarf get in and cause damage is only a matter of time. I've seen some cheap glass scales that have much better swarf/liquid protection at a price pretty close to the cheap digital scales so I'll install these if/when the cheap scales fail. |
| Bogstandard:
Have a look at the edge of the scale, there is, when you disassemble, a spring bronze wiper strip. You will find that metal tensioner plays a fairly important role in keeping the thing working, and was always one of the quickie tweaks I did to get the scale working again. Clean the edges down and retensioning on that resulted in about a 50% recovery rate. The other area is the finger edges of the board, there is a loose rubberised/graphite block connection to the display. It generally isn't the board going down (except for battery failure), that normally carries on working, it is that physical joint that gets wet, and that was the second place to try in an attempt to get them working, by cleaning off with methylated spirits. So I still reckon it is a mechanical method of operation, even though it uses a bar counting system for the actual measurement. But anyway, that is all beside the wayside. You just have to protect them as best as you can. Bogs |
| Ned Ludd:
One should not feel guilty about using DROs any more than when using any other measuring instrument, do you feel guilty using a vernier caliper or micrometer? DROs are just built in 'micrometers'! You can work very well without but, if you can afford to, why would you? Ned |
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