Chinse DRO accuracy

K

Knick

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I have a DRO on my mill (dont have the brand name in front of me) and was checking it for accuracy.
I did the check with 123 blocks and checked it across 5". One block I used was .0005 small and the other was
maybe .0002 big so I called that a wash. When I checked it the DRO was off almost .003 in 5 inches.
My questions are:
Is this about the norm?
Is there a way to correct this on all DRO's? (did not see anything in the manual)
I am aware of rounding issues but I was thinking it would be closer than this.
Thanks for your time
 
To some degree you get what you pay for. I have installed 6 DRO's Easson, DROPros DRO's/magnetic scales, SRA magnetic scales, Newall, Acurite, etc. and worked on other peoples machines with them. I have yet to setup one where the scales were off by that degree. In all cases they met their resolution spec. I have noted more postings about scale resolution errors and accuracy recently (Ditron and a few others), so maybe something is amiss. The most common problem I see is more rounding errors and calculation errors, in particular when using scales in diameter mode that are not 1 micron. My mill uses 4 magnetic 5 micron scales (EL700), on the 123 blocks they measure within 0.0004" when I installed them, the magnetic and glass scales on my mill all track the same as the dials if I zero everything and then check the 0 point after X revolutions. This assumes they are accurate, but I also check two 123 blocks end to end.
 
0.003" in 5" does seem like a lot- do you know what the resolution is supposed to be for your scales?
Did you just recently buy these? Have you asked the vendor about it? Remember your credit card company can help you if you feel you didn't get your money's worth
-Mark
 
Knick said:
I have a DRO on my mill (dont have the brand name in front of me) and was checking it for accuracy.
I did the check with 123 blocks and checked it across 5". One block I used was .0005 small and the other was
maybe .0002 big so I called that a wash. When I checked it the DRO was off almost .003 in 5 inches.
My questions are:
Is this about the norm?
Is there a way to correct this on all DRO's? (did not see anything in the manual)
I am aware of rounding issues but I was thinking it would be closer than this.
Thanks for your time
Click to expand...
I was having accuracy problems on my Ditron scale on lathe-turns out it was getting bumped very slightly, so I redid the holder to ensure better clearance and also made the holder more robust.
 
Question: When you installed your scales and mounted the read heads did you indicate everything in within the installation tolerances? My DRO required everything to be within 0.003" over the entire length. Head alignment is also critical for accuracy. If you did all these, then linear compensation adjustment should help. If you didn't install correctly, backup and get things aligned.

Ted
 
I recently bought a PM mill with factory installed DRO. Also recently installed a new DRO from TPAC Tools (Thanks, @BGHansen for your help and advice!) on my lathe. Though both units are "branded" with the names of the suppliers, they're quite obviously from the same factory. I've heard the name "Sino" mentioned, and maybe that's the source(?)

Anyway, like @Knick, I've been curious about accuracy. I have a gauge block set that goes up to 4" and recently bought additional 8" and 10" gauge blocks from Shars. Once I get done with a couple of "hot" projects, I plan to do a careful study of all the DRO scales. I'll add linear compensation as needed, based on the results. I'll also post my procedure and results here. Stay tuned!
 
I briefly discussed how I did linear compensation on my Bridgeport install here:

www.hobby-machinist.com

TPACtools DRO Bridgeport Mill Install

Received the DRO via FedEx late this afternoon. Great shipping/delivery time since I only ordered it two days ago. Everything seemed to be well packaged. Got the 3 slides (each one came with its' own bag of hardware and cover), display unit (with collet rack and mounting bracket), aluminum angle...
www.hobby-machinist.com www.hobby-machinist.com

Ted
 
Technical Ted said:
Knick said:
I have a DRO on my mill (dont have the brand name in front of me) and was checking it for accuracy.
I did the check with 123 blocks and checked it across 5". One block I used was .0005 small and the other was
maybe .0002 big so I called that a wash. When I checked it the DRO was off almost .003 in 5 inches.
My questions are:
Is this about the norm?
Is there a way to correct this on all DRO's? (did not see anything in the manual)
I am aware of rounding issues but I was thinking it would be closer than this.
Thanks for your time
Click to expand...
Click to expand...
First off thanks for all the quick responses!

I checked this again and this time around it came out much closer, maybe half of what I had the first time. I am going to try this again after reading
some of the info that was referenced above. I will be back and post what I get in the end. IT may be a week or so as I get somewhat caught up.
Thanks again everyone.
 
Knick said:
First off thanks for all the quick responses!

I checked this again and this time around it came out much closer, maybe half of what I had the first time. I am going to try this again after reading
some of the info that was referenced above. I will be back and post what I get in the end. IT may be a week or so as I get somewhat caught up.
Thanks again everyone.
Click to expand...

Hey Guys

Ok so I got a chance to dig into this some more. I cleaned up the 123 blocks and things were closer. I checked it again over 8" and its about .002 difference.

The brand name of this DRO is Ditron D80 with 5um scales. One thing I could not figure out was how to do Linear compensation.
They show a screen shot on page 11 But I cant seem to find that on the DRO. I will play with this some more tomorrow.

Thanks everyone
 
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