# My DRO accuracy test



## Charley Davidson (Mar 23, 2014)

Installed my X & Y axis Igaging DRO's from David on my Bridgeport. I was doing my second job on it and decided to test repeatability/accuracy. I was drilling 4 holes in a rectangular pattern so I located where I wanted my first hole and zeroed both axis. Spot drilled the first hole then went 3.75 -Y spot drilled, then went 11" X spot drilled, then 3.75 +Y spot drilled. Returned to zero and was spot on, same at the #2 position but when I went to my 11" position it read 11.080, I'm not sure if I read wrong initially because I was looking from an extreme angle, I ran to the #4 spot from there and was good then back to 0 and was good. I'm gonna try a couple more tests to see if it was opp. error or something else. I could have mistaken the 8 for a 0 at the angle I was looking from, I also did not lock table at each position either (bad practice).


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## Charley Davidson (Mar 24, 2014)

I threw another plate in the vice and redid my test, the only difference is I started too far inboard to get 11" so I did 10" this time I locked the table at each spot (very important I found out) as some times when I locked the table the reading would change .001 or .002. Another change I made in the test was eliminating the Jacobs drill chuck as it had a ton of runout. I used my largest center drill in a 7/16 R8 collet and it ran true. I repeated what I did in the first test plus went corner to corner and it was (or at least best I could see with my bad eyes) pretty much perfect.

I powered them off & when I return to my shop I'm gonna move the table in both directions before powering them up to see how well the remember where they were.

I'm very happy with the product, shipping, price & function of these.

Now to get the tablet all wired into these or visa versa


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## chuckorlando (Mar 24, 2014)

Awesome man. Locking the table makes alot of diff. I learned that the hard way.


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## brasssmanget (Mar 25, 2014)

That's good to hear Charley Davidson. I installed the DROs on my RF31 and noticed some variances, but I too did not lock the table at any point. I'll try it again this week when I'm out there working. I though I may have disrupted something because I took the reader of the bar a couple of times and slid it back on again. We'll see.........

Thanks for posting your info.


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## chuckorlando (Mar 26, 2014)

We have acu-rite dros on the bridgeports at school and they will change every time if you dont lock it down. Lock it down before you zero it as well as the lock will push it into the way just a bit. These are brand new dros and machines so as they wear, I suppose locks would be even more important. I have seen them walk on you just sitting and running. Not much but easy to notice with big green numbers ahahaha


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## Charley Davidson (Mar 26, 2014)

I'm gonna do one more more accurate test today, I'm gonna drill four holes in the plate and use pins and height gauge to check actual measurements. It seems my dial calipers don't agree with the igaging scales.


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## kizmit99 (Mar 26, 2014)

Charley Davidson said:


> I'm gonna do one more more accurate test today, I'm gonna drill four holes in the plate and use pins and height gauge to check actual measurements. It seems my dial calipers don't agree with the igaging scales.



I'm following this with great interest.  I'm very curious what the actual precision, repeatability and "backlash" of the igaging scales are...

One thing I would also suggest you try, is approach your locations from different directions and check whether or not you end up at exactly the same spot.  I swear when I do this with my scales I have what appears to be "backlash".

Looking forward to hearing about what you find.  Thanks.


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## Ray C (Mar 26, 2014)

The DRO scales are fine for what they are intended.  Keep in mind, they bend a little because they're only held at each end and this is a source of imprecision.  For their cost and versatility it's a fine tool and I don't think they're intended for much more than +/- 2 thou which is good given their affordability.  There's a difference between precision and accuracy.  The scale heads are probably accurate to a half thou but the overall assembly is not precise enough to give repeatable precision.  I don't think a $100 scale set can compete with a $500 DRO.

I have a set on my lathe and am perfectly happy with them and they seem to stay within +/- 2 thou which is fine to get you in the ballpark.  After that, the big guns come out.


Ray


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## brasssmanget (Mar 26, 2014)

I had a chance to use my DROs today on my small mill. Unfortunately, I was experiencing some way out in left field discrepancies upon returning to zero and set end points - as much as .250 in some cases over a 4.0" distance. This was after powering the table nearly full distance left to right to return to a start point. Anyhow - I think I may have to put a different unit in, as the one right now is not trustworthy at all. There is a chance I damaged it sliding it off and on the reader bar [reading unit module]. There is only one way to find out for sure. ) Sounds like everyone else has no issues with em', so......


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## Ray C (Mar 26, 2014)

brasssmanget said:


> I had a chance to use my DROs today on my small mill. Unfortunately, I was experiencing some way out in left field discrepancies upon returning to zero and set end points - as much as .250 in some cases over a 4.0" distance. This was after powering the table nearly full distance left to right to return to a start point. Anyhow - I think I may have to put a different unit in, as the one right now is not trustworthy at all. There is a chance I damaged it sliding it off and on the reader bar [reading unit module]. There is only one way to find out for sure. ) Sounds like everyone else has no issues with em', so......



Check for water, oil, grit or other stuff on the rails.  They'll go way off if they're dirty.

I use mine a lot and like them.


Ray


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## chuckorlando (Mar 26, 2014)

I ordered 3 of them today from David. He seems to have the best prices and is a member. As long as they get me close enough to start micing, I'll be happy. I will buy a "real" dro for the mill after a while and move these to the lathe  I figure. I got to much to buy right now to throw 400+ into a dro


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## Charley Davidson (Mar 27, 2014)

Ray C said:


> The DRO scales are fine for what they are intended.  Keep in mind, they bend a little because they're only held at each end and this is a source of imprecision.  For their cost and versatility it's a fine tool and I don't think they're intended for much more than +/- 2 thou which is good given their affordability.  There's a difference between precision and accuracy.  The scale heads are probably accurate to a half thou but the overall assembly is not precise enough to give repeatable precision.  I don't think a $100 scale set can compete with a $500 DRO.
> 
> I have a set on my lathe and am perfectly happy with them and they seem to stay within +/- 2 thou which is fine to get you in the ballpark.  After that, the big guns come out.
> 
> ...



I knew when I bought these they were the "Bottom of the barrel in accuracy" so to speak but still a valuable asset to our old machinery & eyes. That being said, My longest (24") scale when trying to flex it (by hand) and get a variance in reading mine only moved the reading .0005 and stayed there so I'd say I mounted it very nicely. On the other (12") not so good, I knew I had messed up the threads on one hole I tapped and used L brackets with only one screw holding each one so the resulting flex is terrible .005 or more.  I'm gonna fix that issue today. 

The reason for this accuracy test was two fold, to help others decide if these are right for them, and the other was to see what I was dealing with on my particular setup. Last night I blued the plate and today I'm gonna layout several points on it then using my wobbler center finder with the point I'll see how close things are. I also will wipe down my slides and instal covers to keep the gunk out.


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## kizmit99 (Mar 27, 2014)

brasssmanget said:


> I had a chance to use my DROs today on my small mill. Unfortunately, I was experiencing some way out in left field discrepancies upon returning to zero and set end points - as much as .250 in some cases over a 4.0" distance. This was after powering the table nearly full distance left to right to return to a start point. Anyhow - I think I may have to put a different unit in, as the one right now is not trustworthy at all. There is a chance I damaged it sliding it off and on the reader bar [reading unit module]. There is only one way to find out for sure. ) Sounds like everyone else has no issues with em', so......



I don't think that "everyone" has no issues with them...  I'm going the Yuriy Android-DRO route, using the AccuRemote version of the scales, and I am still fighting with significant "random" jumping of the scale positions.  I see a lot of similar complaints on the web from others who originally went the iGaging route (most from years ago using the supplied read heads) - and while there are many who claim to never have any issues, there are also a fair number who seem to have just given up on them and went with "real" (ie, glass) scales and an integrated DRO.  I know there are potential issues with ground-loops and other electrical interference, but I've seen some issues with the scales just sitting on a bench.  I will say though, I'm using a micro-controller (with my own code) to read the scales, not using the supplied read heads - so my experience is very non-typical.  I'm at the point that I still think I can either get the jumping to stop, or address it in the micro-code (detect and compensate for it).  I'm more concerned with how precise these scales actually turn out to be...  well, maybe "interested" is a better word than "concerned"; I know these scales aren't going to be perfect or on par with glass scales.

I hope you have good luck in getting your setup running stable.


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## brasssmanget (Mar 27, 2014)

I had to laugh this morning. I was cleaning up out in the shop and just for kicks I turned on the X axis dro and moved the table slowly by hand. The readings did not return to zero accurately - in fact they were off a lot in just 4 inches. Here's the kicker tho. I happened to glance up at the screen a few minutes later, and the numbers were actually increasing as I stood and watched the screen - and I was not touching the table or moving it at all. :thinking:

I'll try and get a crude video [its all I have] and post it her for your observations. )

OK Here it is. I am not touching the wheels at all, and no power to the power table feed. It's just doing this by itself. {chuckle}

[video=youtube_share;rP8DwaMhFMQ]http://youtu.be/rP8DwaMhFMQ[/video]


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## BenjamanQ (Mar 27, 2014)

I'm a Mechanical Engineer and not an Electrical Engineer by any stretch of the imagination, but, I have to ask; are the DRO cables running parallel to or in contact with a power cable or any other source of electrical interference?

Just my 2 cents worth


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## brasssmanget (Mar 27, 2014)

You know - that's a good point. I do have the cables wire tied to a work lamp cord - I'll check that and see if it is causing this phenomenon. Thanks for the tip/idea. I can also take the one off my Y axis, but that's a lot of horsing around and backing into what I did before. I guess I could bite the bullet and buy another one, but I am a little gun shy right now. :whistle:

*Follow up* - I just came in from the shop. I moved the wiring as suggested in the thread, and it appears that was causing a lot of the malfunctioning. Two test runs back and forth brought it back to withing .002 on the reader, so for right now all seems to be good. Thanks for putting up with a novice hobby guy!


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## BenjamanQ (Mar 27, 2014)

Hey, to help each other is why we are here. I'm just glad you got it going. I hope others can learn from this thread too.


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## brasssmanget (Mar 27, 2014)

BenjamanQ said:


> Hey, to help each other is why we are here. I'm just glad you got it going. I hope others can learn from this thread too.



Couldn't agree more. To me the whole purpose if Forums is to share info and learning experiences, and learn a little back in the process.......


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## f350ca (Mar 27, 2014)

I installed a set on my Logan shaper to aid in making a set of racks for a cmc plasma table. 
The racks are 58 inches long with reamed holes every 8 inches. This was done on the milll using a different dro. I then made clamping plates out of 1 x 2 flat bar and drilled and reamed holes 8 inches apart of dowel pins to locate the rack material. Three racks were done at once.
I would cut 8 inches of teeth then index the material and pick up the last tooth using the dro. Its 20 diametral pitch so 0.157 inches per tooth so 369 teeth. When I was done I could flip one end for end and the teeth would all mesh perfectly, so they have to be repeatable. I just assembled the table and checked the movement. Based on the theoretical tooth spacing the machine was out 1/64th in 41 inches of movement. so fairly accurate. That would be 0.0003811 per inch. Pretty good for a dro under a hundred bucks.



Greg


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## Charley Davidson (Mar 28, 2014)

f350ca said:


> I installed a set on my Logan shaper to aid in making a set of racks for a cmc plasma table.
> The racks are 58 inches long with reamed holes every 8 inches. This was done on the milll using a different dro. I then made clamping plates out of 1 x 2 flat bar and drilled and reamed holes 8 inches apart of dowel pins to locate the rack material. Three racks were done at once.
> I would cut 8 inches of teeth then index the material and pick up the last tooth using the dro. Its 20 diametral pitch so 0.157 inches per tooth so 369 teeth. When I was done I could flip one end for end and the teeth would all mesh perfectly, so they have to be repeatable. I just assembled the table and checked the movement. Based on the theoretical tooth spacing the machine was out 1/64th in 41 inches of movement. so fairly accurate. That would be 0.0003811 per inch. Pretty good for a dro under a hundred bucks.
> View attachment 73156
> ...



This makes me extremely jealous, I really want a shaper pretty bad.


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## BenjamanQ (Mar 28, 2014)

Yeah Buddy
I had a little Atlas back in the 90's. Like a fool I let it go. At the time I was doing so much machine work at work that I didn't want to do more of it when I got home, went fishing instead. I sure do miss it now. I hope whoever has it now is enjoying it as much as I would.
Very good job of machining that rack. A real good example of how the work you can do on a machine is not limited by the size of the machine. Good stuff!


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## f350ca (Mar 29, 2014)

BenjamanQ said:


> Yeah Buddy
> I had a little Atlas back in the 90's. Like a fool I let it go. At the time I was doing so much machine work at work that I didn't want to do more of it when I got home, went fishing instead. I sure do miss it now. I hope whoever has it now is enjoying it as much as I would.
> Very good job of machining that rack. A real good example of how the work you can do on a machine is not limited by the size of the machine. Good stuff!



Thanks, they're an interesting machine, as simple and crude looking as they are they're amazingly accurate. It's not hard to see why they were replaced by milling machines for surfacing and such but for some operations they're hard to beet and tooling is cheap.

Greg


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