My DRO accuracy test

Charley Davidson

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