DRO scales

Good afternoon,

I've been looking at various bench-top milling machines, and from what I gather from this excellent forum, a DRO system is the way to go, if it's within your budget.

From what I can gather, there are two systems, magnetic or optical. I'm guessing that optical might be the best, but what's the difference/advantages apart from cost?

I've got both on my milling machine. I only did x & y originally, when I came to do z the magnetic scales had come out. I found setting up the magnetic a lot easier as you can actually see the gap between read head and tape

I have a set of these fitted on my mill; not had any probs with them since fitting over 6 years ago, batteries last quite well too, worth considering.

**LINK**

George.

I couldn't make the LINK work.

Brian

Thank you George, the link takes me to ARC, but it doesn't work. When I search "DRO scale" the only DRO scale seems to be a vertical one. Is that what you have?

Looks like George's link got mangled. I think he meant these, which I have too.

Although not coolant-proof they work well enough. The separate readouts are mildly inconvenient and don't do any of the clever stuff like PCD but they're streets ahead of dials.

Dave

I have just fitted magnetic with Eason display from Machine Dro. Magnetic are smaller then optical and more resistant to coolant etc. All the information is on their web site. I did fit a cheap scale on my previous mill but it only lasted about eighteen months when it started reading randomly even though no damage was evident.

In my opinion, the magnetic is the better type. Its more compact so does not take too much space especially on small lathes and milling machines. The magnetic tape can be easily cut to the required size whereas it's not that easy with glass scales.

The down side is it costs more.

I went for glass when I bought for home use - mainly for cost reasons, but having used glass scales for a great many years for work I am "comfortable" with them. I have found them to be accurate and very reliable and they have the advantage over the magnetic type of having some sealing, though other measures are required in arduous conditions.

Maybe a bit bulkier than the magnetic type, but easy to fit and align. Other than mechanical damage due to collisons or installation alignment issues etc. most scale failures I experienced used to be the demise of the filament lamp used in the read head - Heidenhain used to use a 12V lamp on 5V to get a very dim glow but long life. But many years ago Leds replaced the filament lamps for effectively limitless life. The last scale I replaced had had the read head punched out though the end of the scale !

I have done 2 installations with Allendale's magnetic systems at work - both replacements for failed or troublesome capacitive systems with fitting space restrictions. Both have worked fine, but a single axis system fitted to a linisher did grow a fine dust coat on the magnetic bit of the scale that caused reading errors. Fixed by a blow-out with an airline & much more reliable than the capacitive readout it replaced. My experiences with Allendale, both from delivery and technical back-up points of view, have been good.

I did find that the accuracy of the magnetic type varies according to the substrate that the magnetic tape is attached to when calibrating a 2 axis system fitted to a tool presetter - one axis is an aluminium extrusion, the other a stainless steel bar & the magnetic tape was attached to these directly without use of an aluminium backing spar. Different compensation values were required for each axis in the readout parameters to get the readings to correspond to slip blocks used in calibration - neither axis was accurate without compensation.

Most likely either system will give you good service - choice down to depth of pocket and / or fitting space restrictions.

Nigel B.

Once again, a picture paints a thousand words. I fitted a 2 channel M-DRO magnetic DRO to my mill 8 years or so ago and I wouldn't be without it now. I have a numerical readout which works well for me but I understand that a graphical display is now available (probably a bit more expensive).

Here is the Y axis scale:

The backing piece is held to the machine base with a couple of M5 countersink screws and then the magnetic strip is placed in to it and the cover plate attached. A mounting bracket for the read head was made up and bolted to the table base.

The X axis:

This was attached to the table in place of the stops and the read head is where the stop was. I put a piece of aluminium angle behind the scale to keep swarf from getting jammed in between it and the read head.

The system works well and has never missed a beat despite the scales and read heads being regularly doused in coolant and other miscellaneous fluids. Also, being mains powered there is no faffing about with flat batteries at inconvenient moments.

It wasn't the cheapest system for sure but I think it was well worth what it cost my good lady wife and was a great Chrissie present.

Jim

A straightforward digital scale I fitted to my previous mill, one of the Warco round- column machines, failed prematurely because I was unable to protect it sufficiently well from cutting-fluid and oil.

'

I'm happy with the Allendale 3-axis, magnetic-strip set I fitted to my Myford VMC mill, with a great deal more care in the light of experience.

It was a challenge to install and I had to sacrifice the long-travel stops in the process. Not to mention having to fabricate an awful lot of awkward bracketry. That is NOT a criticism of the DRO system, simply that the machine was not designed to carry any such luxury, and it is all curves and tapers.

To set the recommended gap between head and strip, after measuring various materials I found a strip cut from an expired association membership "card" of plastic was just right as a feeler-gauge - I was wary of using steel gauges.

I did add a shield over the strip and read-head - Allendale supplied the quadrant extrusion. The instructions also recommended additional protection for the metal hoses carrying the read-head leads. Ordinary flexible electrical conduit being too small for the head to pass though it, I used a very similar but larger version sold as caravan waste-water hose.

I hang a Cellophane bag very loosely (for cooling) over the display unit to protect it from my oily fingers.

'

Incidentally I do not use the DRO for each and every operation. I still use the dials for a lot of smaller, simpler tasks.