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# DRO - Educate Me Please

#### Rick_B

##### Stainless
I am leaning strongly towards a DRO purchase for a Bridgeport mill. The mill is a Series 1 J head with a 9 X 32 table and X axis power feed. With the power feed the table movement is 16-1/2" in the X direction and 12" in the Y. I know VERY little about DRO's so I thought I'd start a discussion relating to some high level questions and working down into the details. Please don't consider any of the following as factual statements - they simply represent what I think I know today. At a 50,000 foot level:

What a DRO isn't - it is not a CNC type of functionality. It cannot be programmed to perform a series of steps that can be executed by the push of a button.

What a DRO is - in simple terms it is a tool to measure and monitor table movement but the movement is executed by either manually using the the lead screw or a power feeder in one or more axis. In other words a DRO replaces the standard lead screw dials as a means of measuring how far the table has moved in any of one, two or three directions (depending on what you buy). As a result, any lead screw backlash is no longer significant because the DRO is measuring only actual table movement where as the dials are factoring in any backlash in the lead screw/nut configuration as well as table movement.

If the above is correct then let's drop down to 5,000 feet
the DRO uses a scale on each axis to measure movement and reports that back to a display - Question - how does the scale actually measure the movement?

When using a DRO I believe you can set a zero point and then measure from that zero point and return back to the zero point. question - does the zero point represent the tool center - in other words can the tool diameter be reported to the DRO and then it compensates for that diameter or is that an operator calculation?

What can I do with a DRO beyond the elimination of backlash issues. Some examples - touch off the end of a work piece and measure the distance a slot has been cut, touch off the work piece and find its center, touch off a work piece with a hole and find the hole center. Are these typical DRO features? What else can be done with a DRO before you need to consider full blown CNC functionality?

That's probably enough for now - thanks for any thoughts/comments you may have.

Rick

#### wawoodman

##### Hot Rolled
It's simply a measuring tool: it tells you how far you have moved from wherever you started.

It has a sensor attached to the moving part (the table) that moves along a scale attached to the solid part (the machine) and sends the dimension to the display.

There are other features, like calculating bolt circles, finding centers, etc, but it's nothing magical. Everything you can do with a DRO, you can dowithout it. But it sure makes life easier!

#### Rick_B

##### Stainless
Thaks Woodman - this could turn out to be a short lived discussion. I just took a quck look at pricing and have sticker shock. If I can't get into a 2 axis DRO in the \$300 range I will likely setriously reconsider whether I want to make the leap or not.

Rick

#### steve-l

##### Titanium
Rick,
Everything is much easier with a 3 axis DRO, you won't regret the purchase. The Chinese Sino DROs are actually quite good and reasonably priced. They are sold under many different brand names. Most of the modern DROs use glass scales in protected housings. If you do get one and I suspect you will, take great care mounting the scales spaced correctly and parallel to the moving surfaces. If you get that part right, they are pretty much plug and play. You should expect to pay around \$700 for a 3 axis rig for your machine.

#### Sendit

##### Aluminum
I sprung for the Acurite because they have brackets already made for the BP. It's a lot more coin than I wanted to spend but long term it will bay for it's self. It better at least.

#### MICK 1958

##### Stainless
If you think 300 dollars is too much money for a DRO.... You don't need one!

What you need is to find a different hobby.

I am not being a smart ass, if you would use one and see the repeatability, ease of use, bolt hole calculations, making hex's, etc... you are only limited by your imagination... and money!

Really, the Sino's are close to 900 bucks, I recently installed one on a friends Grizzly mill... the mill was only a little bit more money than the readout... He is very pleased and his product that he makes has increased in quality and speed.

Think about it! I would not listen to the guy who says you can do anything without it.... he is either being sarcastic or he just don't know.

Happy hunting!

Mick

#### JRIowa

##### Diamond
As Mick said, you might need to find a cheaper hobby. Or you could get really good with reading dials and making sure you always approach a part in the same direction.

I have Sony DROs, if I was to replace, it would be Newell. They run about \$1,800
\$300! I've got 3 drill chucks that cost more than that. Probably got that much in just new 1/2" end mills.
JR

#### hobbyman

##### Hot Rolled
Bolt circles are not limited to actual circles. This includes dividing up an arc into hole positions. I have used it to locate holes on an arc and from that find chordal distance so that I can duplicate the holes on a matching flange.
Also if you have multiple hole locations you can put the locations into memory then move from location to location to do one part then mount another part and repeat the procedure over by simply calling up the hole location and zeroing your DRO.
I would be lost without mine. Backlash? I don't even pay attention to it.

#### Rick_B

##### Stainless
Thanks guys for the comments so far - I appreciate the honesty. I don't think i need to find a cheaper hobby but I do need to decide what level I want to be at. So far I haven't done anything I couldn't accomplish without a DRO - that is not a testament to my skills for sure - it really speaks to the level of simplicity I have been working at. Part of the reason for this thread was to reach some conclusions regarding my need for a DRO so all of the comments are appreciated.

It sounds like the advice is to avoid the less expensive versions of DRO's but I'm wondering if there isn't some middle ground.

Rick

#### aribert

##### Cast Iron
It sounds like my (personal, hobby) situation is similar to yours. I could (and did for a number of years) live without the DRO on my mill but it makes working with a well worn mill that much easier. At work my milling is frequently only to a scribe line (or even to a Sharpie mark) - where I am modifying a part for build clearance, driver access or the like during a build event.

If cost is an issue and you are willing to give up a lot of useful features, scrounge around for a used DRO. I found an old Mitutoyo DRO (this style of box, image off of web http://machineryrepairshop.com/wp-content/gallery/mitutoyo-digimatic-dro-982-537/p1040465.jpg ) for under \$100 for my Bport. It does not do much other than to tell me how far I have moved the table and it is as much effort to install an obsolete DRO as it is to install a new one. Recently I was using the one mill at work that has a dead scale - seemed primitive to have to read the dials and make sure I kept track of how many times I crossed the zero.

My goal originally was to see if I could upgrade the display (reuse the existing scales) so that I would have features such as bolt circles and tool offsets but I just have not gotten around to looking into upgrading the display in the past decade that I have owned it.

#### tubeguy

##### Aluminum
I am leaning strongly towards a DRO purchase for a Bridgeport mill. The mill is a Series 1 J head with a 9 X 32 table and X axis power feed. With the power feed the table movement is 16-1/2" in the X direction and 12" in the Y. I know VERY little about DRO's so I thought I'd start a discussion relating to some high level questions and working down into the details. Please don't consider any of the following as factual statements - they simply represent what I think I know today. At a 50,000 foot level:

What a DRO isn't - it is not a CNC type of functionality. It cannot be programmed to perform a series of steps that can be executed by the push of a button.

What a DRO is - in simple terms it is a tool to measure and monitor table movement but the movement is executed by either manually using the the lead screw or a power feeder in one or more axis. In other words a DRO replaces the standard lead screw dials as a means of measuring how far the table has moved in any of one, two or three directions (depending on what you buy). As a result, any lead screw backlash is no longer significant because the DRO is measuring only actual table movement where as the dials are factoring in any backlash in the lead screw/nut configuration as well as table movement.

If the above is correct then let's drop down to 5,000 feet
the DRO uses a scale on each axis to measure movement and reports that back to a display - Question - how does the scale actually measure the movement?

When using a DRO I believe you can set a zero point and then measure from that zero point and return back to the zero point. question - does the zero point represent the tool center - in other words can the tool diameter be reported to the DRO and then it compensates for that diameter or is that an operator calculation?

What can I do with a DRO beyond the elimination of backlash issues. Some examples - touch off the end of a work piece and measure the distance a slot has been cut, touch off the work piece and find its center, touch off a work piece with a hole and find the hole center. Are these typical DRO features? What else can be done with a DRO before you need to consider full blown CNC functionality?

That's probably enough for now - thanks for any thoughts/comments you may have.

Rick

475 bucks free shipping is about as low as I have seen recently. See Ebay.
They are chicom units but are fine for a ol'clunker. We got one last year and it arrived with a bad scale. Emailed the guy and had a new one in about 2 weeks. Since then its been on, and worked well since.

#### Rick_B

##### Stainless
I'm reaching the conclusion that I need to either go used or import to stay within a reasonable price range. I wonder how they imports perform when it comes to accuracy and repeatability?

Rick

#### onecut

##### Hot Rolled
"google" "DRO for milling machine",Seems you can get them for price you mention-Obviously wont match the higher priced ones

#### Rick_B

##### Stainless
So here's a high level question - I have a line on several acu-rite DRO's - both are two axis units. One is an ACU-RITE III and one is an ACU-RITE D200. Both include scales and cables as well as the read out units. I don't believe either of these are currently offered and may not be supported - I'm going to check that out. Cost is sub \$400 range.

I can get a 3 axis import unit for a little less money that seems comparable in terms of published specifications.

So the question - is an older used ACU-RITE 2 axis unit a significantly better buy than a 3 axis import - assuming the same price range?

Thanks
Rick

#### plastikdreams

##### Diamond
Having the additional option to have at least 3.5 digit readout after decimal on the quill is a great thing to have especially when doing final passes.

#### Rick_B

##### Stainless
Having the additional option to have at least 3.5 digit readout after decimal on the quill is a great thing to have especially when doing final passes.

Not being a smart%\$^& - but I'm not sure what that even means?

Rick

#### davehud

##### Cast Iron
Backlash... Back in my jig bore days even with a high end DRO we still made all our pickups and moves in one direction only. We were of the belief that the table would twist to one side or another depending on the direction it was being moved. Also, don't lean against the machine on finish cuts...

#### plastikdreams

##### Diamond
3.5 decimal means it will read 0-9 to the thousandths place and only 0 or 5 in the tenths place...examples:

1.9840
1.9835
1.9830

Some will read 0-9 in the tenth spot some will read even or odd.

#### wheels17

##### Stainless
If you are daring, Amazon has a 2 axis taishi for \$237 and a 3 axis for \$334. Longest scale is 1 meter. If you do dare, please let me know how it turns out.

2 axis: 2 Axis Digital Readout Dro for Milling Lathe Machine with Precision Linear Scale by Taishi: Amazon.com: Industrial & Scientific
3 axis: Mill Milling Machine Linear Scale Linear Encolde and 3 Axis Digital Readout Dro: Amazon.com: Industrial & Scientific

There are also the igaging linear scales with remote readouts. I have them on an unmentionable mill; a 3 axis set is \$135. Obviously no DRO functionality, but a lot nicer than counting turns on a dial. They seem to be a reasonable match to the mill. On 14" of travel, the mill and the scale disagree by .0015". Who knows which is closer to the truth?

This is a link to their new model. It's a lot nicer than what I have, as the readouts link together. It looks like it now has USB output as well?

iGaging Digital Readout DRO Set of 3 - 6" 12" 24" Travel X-Large LCD Display (3-pack) EZ-VIEW PLUS - - Amazon.com

I'm savaing my DRO money for when I get a real mill.

#### dkmc

##### Diamond
If you are daring, Amazon has a 2 axis taishi for \$237 and a 3 axis for \$334. Longest scale is 1 meter. If you do dare, please let me know how it turns out.

2 axis: 2 Axis Digital Readout Dro for Milling Lathe Machine with Precision Linear Scale by Taishi: Amazon.com: Industrial & Scientific
3 axis: Mill Milling Machine Linear Scale Linear Encolde and 3 Axis Digital Readout Dro: Amazon.com: Industrial & Scientific

My gosh that's cheap!
And they look "nice" too.
I wonder how nice and how reliable they actually are.
You can't have it all......but you can hope for a lot.

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