Acu-rite not Accurate!!!

[bill south]

I'm just installing a used Acu-rite III DRO (2 axis) on my bridgeport, and the installation went fine mechanically. However, when I do a quick check with a dial indicator, I found the axis to be off +.266" in a 1 inch reading and .2535 on the yaxis. I downloaded the accurite III manual from their website and tried the switch settings. However, their manual shows a 10 position switch and my 2 axis has only 9. I'm assuming pins 789 for setting the scales are the same!!! Also, the switches do not have much of an effect on the display for the 10 micron .0005 scales.
This is an old unit and I'm afraid the electronics may be suffering. Can someone with a Acu-rite III 2 axis DRO verify the switch settings for me? Does anyone have a schematic?
And most importantly, what is the best (lowest cost) DRO buy out there to replace this old work horse?
Thanks in advance.
Bill form Spartanburg.

[offroadxx]

Penn Tool has a Fagor DRO 2 axis for $700 w/ scales. Shooting Star has one for $700 as well for a 2 axis. I just installed a Fagor on one of my EDM machines and I have a Shooting Star on one of my big lathes also. It is an older model (5yrs) but works flawless. For the money, I'd say that is as cheap as you can get. My .02

[widgitmaster]

When you installed the scales on the Bridgeport, how accurately did you mount them?

They MUST be parallel and perpendiculay to the axis within .0005" or better!

This is not easy and is time consuming, but all the effort will pay off in the end!

I had to make little adjuster blocks to mount between the Bridgeport and the scales, they had little setscrew for fine adjustment which made the process much easier!

Eric

Difficulty of installing DRO on lathe

[gus]

how repeatable is the inaccuracy?

If it is just random, check grounding etc between the reader head and the box. Also check the alignment of the head itself[as opposed to the scale to the table] The head must be true and the proper distance from the scale body.

[One of Many]

Do you know if these scales were the original OEM scales.

I suspect that the pitch of the scales may be incompatible with the display head. The older scales I had seen could be english pitch while the display did the conversion to metric. Then some of the import scales came as a metric pitch while the display head converted to inch. Cross mating gives some very odd conversions that can't be resolved although the quadrature signals do trigger a count, they best be in the correct base pitch prior to the conversion.

The .2535 is close enough to the metric conversion factor........therefore possibly a clue?

I would set up a travel indicator and travel 1" in both english and metric displays. Since 10uM scales are actually 0.0003936996 there will be some error if the display is expecting .0005 pitch scales.

DC

[bill south]

Thanks Guys for the pointers. I re-instlled the scales in the same position from which they were removed. Same mounting holes and positions. And, forgive my ignorance, but the scales are off by pretty much the same amount on both axis. And, regrdless of where the table is. So, how could it be an alignment problem??? Seems that alignment would cause non-linearity issues.
I'm thinking more a switch setting somewhere in the counter. Does anyone have a counter manual for the accurite III which shows a 2 axis board with the 9 position switches s1 and s3 shown on the left side of the main circuit board viewed while facing the rear of the unit????
Help would be appreciated.
Metric/inch switch, thanks, good observation.
Bill

[unterhaus]

If it was an inch to metric problem, it should be off by more than 1/4" in an inch. You probably have the switches set wrong, I've looked at the guts of those counters, and I seriously doubt they make any effort to keep the switches the same between models.

There was a time when some of the American manufacturers actually made inch unit encoders. For the last many years, they've gone to metric. Don't know when Accurite made the switch, but that may be what you are running up against.

[gus]

first rule number 2 in asking for help on the internet: answer the questions that are asked, if you already knew the answers, you would not be asking the people here, so just answer the questions.

Ohh, what is rule number one?

Search freaking google first

http://www.acu-rite.com/act_Download...RiteIII%20.pdf

damn dude

[bill south]

Gus thanks for the help and the comments.
See post number 1.
Thanks
Bill

[gus]

yes, try the manual for the II, it shows a dip with the appropriate number of switches.

still didn't answer a single question........

hard to get quality help that way....


not meaning to be harsh

[Al_The_Man]

Actually on the older Accu-rite it was hard to be out of alignment, as although there was a procedure for mounting the reading head, they were spring loaded against the scale, this was one of their downfalls, the head was a plastic material and over time would wear, and eventually cause problems.
As opposed to Heidenhain (who bought them out), theirs had small roller wheels that did not produce wear.
Bill, Do you have the original scales that came with this display? If so, you would think the switches were set OK.
Al.

[bill south]

Hey Al/Gus;
Thanks for the info. The display is not the original that came with the machine. The original counter had a weak diaplay, not readable. So, I swapped the original "millmate" with the acu-rite III which according to my supplier (backyard machine reseller) was a direct replacement. The scales I'm using are the "Absolute Zero II" which are suppose to be compatible with the display. I've looked on the acu-rite site and cannot find any information on this particular scale. It is a ten micron .0005" scale as listed on the scale legend.
Also, the error is somewhat repeatable as measured with a cheap dial indicator. I've tried grounding and no help.
I've read and compared several of the manuals, including the accurite II which does not match my board layout. So, again no help.
Al, the scales are the old spring loaded finger type heads so wear is an issue. But, I'm puzzled why both axis have approximately the same error knowing they both should not have the same wear (I guess). It still seems to me a setup problem with the counter but I just can't figure it out. None of the acu-rite manuals match this board layout. I'm going to send acu-rite the serial number tomorrow and see if they can help. I guess I should have done that before bothering the members of the forum.
I do have an electronics/mechanical background so, I shoud be able to figure this out. I really don't want to spend any more money on this manual setup because I'm eventurlly going the switch the bridgeport to cnc. I've already installed ball screws and purchased the mounts. I just wanted to get some manual time on the machine since my rebuilding it. I already have a sherline cnc and a lathemaster cnc so I'm not in any hurry. Just want the bridgeport quality and mussle.
Sorry this post is so long guys but I'm kinda frustrated trying to find the answer to a simple question. How do you set this damn thing up????
Best regards!
Have a good day.
Bill