An argument for indicators & gages in lieu of a DRO system for work positioning

[marka12161]

A few months ago i brought home a bridgeport mill and Monarch 10EE lathe both of which were equipped with CBX DRO systems (3 axis on the mill, 2 axis on the lathe). I've never used a DRO system before and had grown acustomed to using a combination of machine dials, gage blocks, planer gages, micrometers and dial indicators for work positioning. While at first look, the DRO system promised to reduce/eliminate the need for these methods. However, I found that in order to compensate for cumulative error (.001 or ,002) inherent in the DRO system, I was checking dimensions using my old methods. In conjunction with this, I grew tired of working around the transducer wires and the scales when cleaning the machines. I finally made the decision to remove the DRO systems all together and revert to my old ways. I have not regretted this decision. Has anyone else made this decision and if so, what was your reasoning?

 

[GeneT45]

Might just be the DRO in question. I had a Shooting Star DRO on my lathe at one time, which I think is the same thing. At first it was fine, but it definitely developed problems with age (which never got to be that old). When it started outright 'jumping' I replaced it with a "better" DRO and it's been fine since.

GsT

 

[benmychree]

I like Travadials, have one on my 19" Regal, also I use step block gages and 123 blocks for measuring to a stop, and also use a 1" travel micrometer stop for much the same purpose, it was original equipment on a Monarch toolroom lathe. I only ever has one DRO on a mill in my shop downtown, it was on an Induma 1-S just two axis, all the scales and readers were out of the way and it was easy to clean up.

 

[verbotenwhisky]

A few months ago i brought home a bridgeport mill and Monarch 10EE lathe both of which were equipped with CBX DRO systems (3 axis on the mill, 2 axis on the lathe). I've never used a DRO system before and had grown acustomed to using a combination of machine dials, gage blocks, planer gages, micrometers and dial indicators for work positioning. While at first look, the DRO system promised to reduce/eliminate the need for these methods. However, I found that in order to compensate for cumulative error (.001 or ,002) inherent in the DRO system, I was checking dimensions using my old methods. In conjunction with this, I grew tired of working around the transducer wires and the scales when cleaning the machines. I finally made the decision to remove the DRO systems all together and revert to my old ways. I have not regretted this decision. Has anyone else made this decision and if so, what was your reasoning?

I do not see the DRO as a replacement for Ganges nor any other measuring methods, I see it as complimentary. I use my DRO to get into the neighborhood I need to be in (I do not use the dials a great deal) then the finer devices come into play.

 

[PNW_Guy]

I've used mills without a DRO, and don't enjoy the experience. It's worth it to me to have a DRO.

I don't feel it's as important on the lathe, but I like being able to set the stock diameter on the DRO and know where I am.

I don't have a problem hitting 0.001", but I usually don't need that level of tolerance anyway.

 

[SouthernChap]

However, I found that in order to compensate for cumulative error (.001 or ,002) inherent in the DRO system

Can anybody tell me if this is this a common level of error in DROs?

As a beginner in machining, this is not what I was expecting. I mean a few tenths I'd not be surprised about but a couple of thou, regularly?

That seems like it would make the DRO 'chocolate teapot' useless. One would be better off, as the OP says, relying on the machine dials, clocks and gage blocks/pins.

 

[Dabbler]

I have had the opposite experience. Two of the mills I have purchased came with antiquated DRO units.

One, a Sony (one of the very first companies to offer any kind of electronic DRO) from 1981 is so old the EPROMs in it keep forgetting their programming. (It is okay, however, we read and saved the images years before its occurrence, so now we just erase and reprogram them... - This is needed every 6 or 7 years, as the EPROMs have aged.

The other, a Mitutoyo, is from 1991 or 1992. Its programming is fine.

They both read well within their original accuracy claims: +/- 2 tenths for the Sony with cumulative error over the entire 23" range of 6 tenths.

The Mitutoyo is accurate to .001 over short distances, and cumulative error is less than a half thou.

This has been verified wioth gauge block stacks and half tenths test incidator. So I just use the DRO nowadays.

 

[PNW_Guy]

Can anybody tell me if this is this a common level of error in DROs?

As a beginner in machining, this is not what I was expecting. I mean a few tenths I'd not be surprised about but a couple of thou, regularly?

That seems like it would make the DRO 'chocolate teapot' useless. One would be better off, as the OP says, relying on the machine dials, clocks and gage blocks/pins.

Modern glass scales generally have a 2 or 5 micron resolution - your endmill will flex more than that.

I use the DRO to get me close, and make a final measurement before my last cut.

I use a DRO for multiple reasons, and getting a few microns accuracy isn't one of them. Here's why I like a DRO:
BIG numbers that my crap eyesight can see - most of us have used equipment and the numbers on the dials are worn off. Elimination of backlash errors (dials measure the leadscrew movement and the DRO measures table movement). Shortcuts like the 1/2 key, bolt circles, etc. Switching between metric and inch measurements in the same part. Never wondering if I turned the handwheel 25 times or 26 times. Being able to work in thousandths or tenths (and hiding the tenths), axis summing (knee and quill). Seeing the feed rate on the DRO.

None of those are required items, and we went to the moon without any of that. I do this for a hobby, and a DRO makes it more enjoyable. The guys who use the old school ways are probably retired machinists. Both are valid, but a DRO works much better for my situation.

 

[Mini Cooper S]

A couple of things to remember about Bridgeport type mills and DRO's. First the nature of a knee mill, especially an old one, is that they are not capable of machining to very close tolerances. The tables tip as the machine moves and the heads are never perfectly trammed. The second thing on an old mill is that the lead screws wear and the wear causes the table to actually over travel! As the nut moves from the worn section of thread where the thread is thin, to a less worn section to where the thread is full thickness, it is essentially moving up hill causing the table to over travel. Now if you do your work in a less worn part of the screw, you have table tip to contend with. When the shop that I served my apprenticeship at installed DRO's on their mills back in the early 70", we found the dials were under reading. Upon checking with Jo blocks we found the readouts to be much more accurate than the dials.

On my mills I have the readouts set to .0005" resolution instead of .00001", the machine is not capable of that close of a tolerance. If I need that kind of accuracy (.002" or less) I use my surface grinder.

I would keep the DRO but see if you can set the resolution to .0005"

Richard

 

[marka12161]

Can anybody tell me if this is this a common level of error in DROs?

As a beginner in machining, this is not what I was expecting. I mean a few tenths I'd not be surprised about but a couple of thou, regularly?

That seems like it would make the DRO 'chocolate teapot' useless. One would be better off, as the OP says, relying on the machine dials, clocks and gage blocks/pins.

I suspect much depends on the quality of the DRO and the nature of the scales. The DRO in question is a CDX which as I understand is a hobby grade unit. It uses a rack and pinion as the scale mechanism. Lke anything, the accuracy and the resolution of the DRO system (hence the cost) needs to support the work being done and the rigidity of the machine. By the way, the subject DRO system is for sale for not much money and is listed in the Craigslist, Marketplace, Offer Up adds forum.