My DRO accuracy test

[chuckorlando]

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

 

[Charley Davidson]

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 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.

 

[kizmit99]

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.

 

[brasssmanget]

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]

 

[BenjamanQ]

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

 

[brasssmanget]

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!

 

[BenjamanQ]

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.

 

[brasssmanget]

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.......

 

[f350ca]

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

 

[Charley Davidson]

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

Greg

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