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Kerry Pinkerton
01-04-2004, 04:25 AM
Right in the middle of drilling a center hole for an anvil mounting plate, the "Y" display on the Mitutoyo display on my Bridgport mill got flaky.

It would work coming toward you but going away the display would stay constant, then jump a little. You could tap the box mounted on the side of the table and it would cause the display to jump also.

No knowing anything about DRO's, I took the Y senders off the machine, apart, and wiped everything down. It seems to work fine now.

Some questions:

- How do these things work? Is it reading resistance in that thin metal strip?

- What causes it to do what mine did?

- What are the odds that I did not fix it at all and it's something in the electronics??

bcarlson
01-05-2004, 05:37 PM
Hi Kerry,

let me first say I have no actual experience with DRO's (other than using them while machining things).

My background is in CMM's (Coordinate Measurement Machines) which are high precision quality assurance machines. I worked for Carl Zeiss, IMT (Industrial Messtechnik) for several years assembling, designing, installing and servicing these machines. There are many styles, but basically the tend to be three axis, CNC(motorized) inspection machines which use etched glass, or flexible strips in conjunction with optical readers.

I would assume this is very similar to how a DRO works (in fact, Mitutoyo makes CMM's, and very probably shares technology between their machines).

Either way, the principle is the same, there is a strip of glass with microscopic markings, and an optical reader, coupled with the DRO, which counts the marks. As you pass by the marks, the reader tells the DRO 'hey, I just moved, in x direction', and the DRO adds a ten-thousandth to the measured reading.

If something gets on the scale, such as coolant, metal chips, etc. the reader would read incorrectly, perhaps from being physically disturbed, or from an interruption in the optical path.

On the machines I worked on, we used rubbing alcohol and windex to clean the scale, and would use q-tips to clean the reader-head. Be VERY careful with the reader as, if anything like the ones I used (Renishaw brand, and our own proprietary design) if moved, the reading becomes completely inaccurate, and sporadic.

Anyhow, I hope this was a wee bit informative...

Ben

Brian McCollim
02-13-2004, 11:54 AM
Kerry, a lot of different styles of readouts out there. Most are of the glass with encoder, but some are actually a bit more mechanical. The Trak systems use a wheel that runs against the way of the machine or a bar attached parallel to the axis. These are set up a bit differently as they must be calibrated. Not hard to do, but takes a bit of time. If the reader slides through a tube or an extruded part with rubber seals then it is probably the glass style. When you put these back on the set up needs to be correct, also you should make sure that the rubber seals are in good shape. I would use caution with certain cleaners that may attack the rubber. I have taken these apart and cleaned them and got them to work well, but they are best cleaned with a spray cleaner and dried. Let me know which kind you have and I'll try to give you some more info. Brian Mccollim
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