Info about DROs

Dunc1

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Wondering about the reasons for the large price difference between the glass-scale based and the magnetic-scale based units. A 3-axis glass-scale based unit (with read-out) is at least $500 whereas the magnetic scale (look like a digital electronic caliper with the measuring blades removed) could easily be under $100.

I am interested as a home hobbyist (intermittent use), not a production setting. I can't justify the higher cost for the amount of use.

My machines are non-cnc. Will these compensate for the backlash? In other words, will "dead" space (handwheel rotates but the table does not move) also show on the dro or must the table actually move before the indicator registers a change?

What are the shortcomings, compromises etc of the magnetic scale devices?
Are accuracy (or lack of) and repeatability, etc factors?
What makes one brand better than another?
What features are must-have, desirable and eye candy?

Finally, what, if anything, do I need to do differently now that dro's provide the readout?
 
I think the main difference between the more expensive DROs and the ~$100 units is the money buys you precision and accuracy, also maybe a wall socket powered control unit instead of battery powered.

How much P&A is enough? I'm guestimating that I'm getting within +- 0.0015 to 0.002" (good precision within this accuracy limit) with the AccuRemote unit I purchased for my mill z-axis. I can use my micrometer to get closer if I need to. I can't spend $500-$700 on this piece of equipment with all the other things I need. The DRO has been a great improvement over the etched scale on the feed crank of my mill. The z-axis has ~0.050" lash, but it's very difficult to track the lash because the friction in the slide and gibs makes the power head stick up, while gravity and cutting vibration pulls it down. The DRO is unaffected by gear lash, and gives a *much* more accurate indication of where the tip of the cutting tool is, at least in this case.

What you need to do differently? Not much. But mounting the scale can be a challenge. My machine has minimal clearance for the scale and I had to fabricate my own mounting brackets.

A really nice thing about the DRO is you don't have to count revolutions of the feed handle. It's still possible to loose track of where the cutter head is relative to the work piece, but a DRO make it a lot easier to track.

Hope this helps.

Walt
 
Wondering about the reasons for the large price difference between the glass-scale based and the magnetic-scale based units. A 3-axis glass-scale based unit (with read-out) is at least $500 whereas the magnetic scale (look like a digital electronic caliper with the measuring blades removed) could easily be under $100.

I am interested as a home hobbyist (intermittent use), not a production setting. I can't justify the higher cost for the amount of use.

My machines are non-cnc. Will these compensate for the backlash? In other words, will "dead" space (handwheel rotates but the table does not move) also show on the dro or must the table actually move before the indicator registers a change?

What are the shortcomings, compromises etc of the magnetic scale devices?
Are accuracy (or lack of) and repeatability, etc factors?
What makes one brand better than another?
What features are must-have, desirable and eye candy?

Finally, what, if anything, do I need to do differently now that dro's provide the readout?

There are low cost DROs that plug in the wall and have all of the basic features. At least one can connect to a low cost scale or to a glass scale.

Scales have two accuracy components. There is an absolute error of maybe +/- 1 count. More importantly there is a percentage error. The further your move, the larger the number of thou error you get. If you use a low cost scale and move many inches, the error is surprisingly large. But it is rare that I need much accuracy at that distance.

In general I need to move a large distance from a reference point with low accuracy. Then I need to machine a feature, move a small distance with high accuracy, and machine a second feature. I do this by first using the absolute mode. then I switch to incremental.

There is a saying: the cleanest area in any shop is the Function key on the DRO. Essential features, IMHO, are XYZ readout, absolute and incremental, and tool offset. This last one is nice but you can easily live without it. I can't think of any other functions that I use more than once a year. And it isn't that I don't know how to use these functions, I wrote a user's guide for the one I own.

I'm kind of a nut about accuracy yet am very happy with my low cost DRO. I do own a top of the line mic for really demanding work.

My lathe uses two really low cost digital calipers from Harbor Freight. they are modified to give me longitudinal and crossfeed readouts. Work great for me and cost less than $35 plus scrap from my junk bin.

On a related issue, having an edge finder is essential. You use it to set the zero point for a given scale. I have one wired to my DRO but having a stand alone edge finder is OK. If wired, you tell the DRO you are about to use the edge finder. Then you feed in until the cutter touches the workpiece. This causes the related axis to jump to 0. Handy.

Rick Sparber
Rick.Sparber.org
 
The table has to move to register on the read out. It has no clue of what the handles and knobs, or you, are doing. Only what the table is doing. The movable point versus the fixed point. I finally bought a low cost (cheap) one from SCAR? and could not be happier. I probably use about 4% of its features. My accuracy and finished results are greatly improved. I tell people "I can drill a hole in a hair now"!

Great on the mill but I am still out to lunch about the lathe. I use dial indicators there if I require real precision. Now the quill on the drill press there is another question. My radial arm drill press has a 10" stroke on the quill and a digital scale there would be sweet. Like most things, nothing time and money can't fix!
:thumbsup:​
 
There are low cost DROs that plug in the wall and have all of the basic features. At least one can connect to a low cost scale or to a glass scale....................................................................................................................................................................... This causes the related axis to jump to 0. Handy.

Rick Sparber
Rick.Sparber.org


Way to go Rick...Looks like I won't get anything done today. I took a look at your website, what a wealth of information.

Thank you
Bill
 
Rick
I'll start a thread with this same question, but will also ask here. What model and or brand of touch probe do you own? I have read several reviews with problems of some of them.
thanks in advance
Jerry
 
I have a DRO on my lathe and if you ever use one you will never go back.
 
Wondering about the reasons for the large price difference between the glass-scale based and the magnetic-scale based units. A 3-axis glass-scale based unit (with read-out) is at least $500 whereas the magnetic scale (look like a digital electronic caliper with the measuring blades removed) could easily be under $100.

I am interested as a home hobbyist (intermittent use), not a production setting. I can't justify the higher cost for the amount of use.

My machines are non-cnc. Will these compensate for the backlash? In other words, will "dead" space (handwheel rotates but the table does not move) also show on the dro or must the table actually move before the indicator registers a change?

What are the shortcomings, compromises etc of the magnetic scale devices?
Are accuracy (or lack of) and repeatability, etc factors?
What makes one brand better than another?
What features are must-have, desirable and eye candy?

Finally, what, if anything, do I need to do differently now that dro's provide the readout?

The differences are rather significant. What you are calling "magnetic" scales are probably "capacitive" scales. The big difference in using calipers or other common measuring scales with a remote read head is flutter. Glass scales provide a much more stable readout and can go to tenths. A good low cost way to equip a machine with DRO's to see if they are your cup of tea is the Grizzly self contained display units. These are very inexpensive (about $28 for a six inch unit including remote display head) and you can take the remote display heads and group them together so that you can see all of the axis without having to look at the physical scale. Take a look in the Grizzly catalog, the scales are from I-Gauging and are available from several sources.

I first equipped my mini-mill/lathe with DRO scales some years ago. The improvement in accuracy was rather astounding. Trying to obtain accuracy while dealing with large amounts of backlash became very simple. I cannot imagine using the imported Chinese equipment without digit scales of some type.

Jim
 
In general I need to move a large distance from a reference point with low accuracy. Then I need to machine a feature, move a small distance with high accuracy, and machine a second feature. I do this by first using the absolute mode. then I switch to incremental.



Rick.Sparber.org

Please explain this more. I never understood the difference between absolute and incremental, and why I have that choice on my dro's.

Thanks Randy
 
Please explain this more. I never understood the difference between absolute and incremental, and why I have that choice on my dro's.

Thanks Randy

Another way that I find it useful is sometimes I need to switch back & forth between two tools. I perform the first operation with the first tool zero'd on absolute mode. Then switch tools & zero that tool on incremental mode. After I'm done with that I switch back to the other tool & back to absolute mode, my settings are retained so I don't have to zero again. I could also set tool offsets but I haven't set up any tools in my lathe DRO yet.

Absolute would be your reference & incremental is based off abolute. So it you zero'd in incremental mode, if you change to absolute & zero again, you incremental values will change whatever that difference was when you zero'd absolute.


EDIT:

Here's a link showing the difference: http://www.mmattera.com/g-code/abs-inc.html

This past Sat I made a simple holder for screws. Occasionally I have to shorten screws to custom lengths & holding the short tiny ones to the belt sander is interesting.

I just took a strip & tapped all the sizes I think I might need. I spaced the holes 0.2" apart from each major dia of the different thread sizes. So with the DRO I zero'd at the edge in absolute, advanced 0.2" + the radius of the first hole. I use incremental to advance to the next hole to be drilled/threaded. Everytime I get to the next point where I would drill a hole, I switch back to absolute & record my reading. Then back to incremental to advance to the next hole. Now that I have recorded all my readings in absolute positioning, the next time I go to make another one of these I don't have to spend time calculating spacing, etc. I just use my DRO to move the table to the readings I recorded & drill away.


Img_7062_zpse73c3072.jpg

Img_7062_zpse73c3072.jpg
 
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