# A dro idea



## gadget_lover (Aug 29, 2005)

I've been thinking about how to make an amateur DRO setup for my mini-late and micro mill. I had the idea that I could use a braided steel wire and a couple of guide wheels to let me mount a digital caliper behind the back-splash and move the slide remotely. 

The wire would be in a loop, attached to the carriage and the slide of the caliper.

It looks like this;









Are there any gotcha's that would prevent this from working?


Daniel


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## gadget_lover (Aug 29, 2005)

!2 views and no comments. That's generally a GOOD thing.

I guess I should have mentioned how it works.

The idea is to have the caliper move the same amount as the carriage moves. As the carriage moves right it pulls the Caliper's slide to the left. The caliper will read in the positive As you move the carriage right, the slide will go to the left, reading negative. It can be zero'ed at any point.

The guide wheels keep the wire taut and out of the way. I think the only critical dimensions are that teh carriage wire will need to be alligned with the movement of the carriage and the slide wire with the movement of the slide. 

I can get a cheap 8 inch caliper at HF for under $25, and little guide wheels for a few bucks. I figure a light framework would be needed to keep everything aligned.

I think this can be adapted to my minimill too.

Daniel

(BTW, does the animation show OK in I.E.? kinda cool, huh  )


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## PEU (Aug 29, 2005)

I tought many times of doing something like this, but shipping from usa and lazyness kept me from advancing on the idea 

I tought about the idea mainly for the tailstock.

I guess it should work, but the road may be bumpy  

Good Luck


Pablo


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## Anglepoise (Aug 29, 2005)

I do not think it will work. Great idea, but the repeatability just will not be there.
For me the whole idea of DRO is for absolute repeatability and accuracy.


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## greenLED (Aug 30, 2005)

I hereby declare myself the ignorant of the night. What is DRO?


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## gadget_lover (Aug 30, 2005)

DRO is a device that you use to get a direct reading of where your tool is positioned. I think DRO is short for Direct Read Out.

You can see a real DRO at http://littlemachineshop.com/products/product_view.php?ProductID=2016

A DRO usually has a sensor on the moving part and the base and a display somewhere that you can see clearly. A 2 axis DRO sells for more than $500.

The DRO is most useful when you are trying to create a part acording to a specification. Say you want to put a groove .7255 inches from the end of a tube. With a DRO you put the tool at the end of the tube, push a button to mark that as 'zero' and then move the tool till the DRO reads .7255 and that's where you start cutting.

Without a DRO, you have to count the revolutions of the handwheels on your compound to tell when you reach .7255 inches. With my lathe, that's 14 complete turns (.050 each) and then 25 and 1/2 marks. Alternatively, you can use a caliper to measure the distance from the end. It's easy to see that if you miscount you are off by 50 thousandths or more.

Often, when we are creating lights we simply move the tool to what looks like the right spot. For custom lights it usually makes little difference if we make a section 1.104 inches long instead of 1.00 inches. It's almost freehand.

Did that help?

Daniel


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## greenLED (Aug 30, 2005)

yes, thank you, "bro"!


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## gadget_lover (Aug 30, 2005)

A question for the math majors:

In the picture I posted the wire travels a path that is basically a polygon where the sides may not be equal lengths and the angles as the wire passes around the guides may not be the same for any two. 

I'm concerned that this might effect the relative motion of the caliper's travel. The concept is supposed to be that the caliper moves the same amount to the right as the carriage moves to the left.

What little I remember of my high school math tells me it would be OK as long as the plane of movement aligns with the wheels.

Can someone confirm this for me? 

Thanks


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## gadget_lover (Aug 30, 2005)

Anglepoise said:


> I do not think it will work. Great idea, but the repeatability just will not be there.
> For me the whole idea of DRO is for absolute repeatability and accuracy.



You are probably right, but I'm thinking that it might be good for getting me to the right spot. With the compound I currently count the handcrank turns and then measure with a caliper to make sure I did not mis-count. The carriage has no markings so it's a hit and miss proposition.

I think I need to do some expriments to see what happens.

Daniel


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## Anglepoise (Aug 30, 2005)

Gadget,
I think you are making extra work for yourself.
The idea is great but you can buy the scales alone with the digital head that slides back and forth, just like your calipers.
These Chinese made scales cost under $100 and are available in lengths up to about 4 ft.
Do not have a link but Google "DRO Chinese".
Now this could be mounted conventionally with two brackets behind the bed.


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## unnerv (Aug 30, 2005)

Daniel, you might want to check out little machine shop, as they have the scales that you can attach directly. Below is a link for the 8 inch one, they have other sizes tho.

http://littlemachineshop.com/products/product_view.php?ProductID=2013


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## gadget_lover (Aug 30, 2005)

Thanks for the pointers, guys.


I guess I should have said up front the reason for the wires and guides was to move the readout to a spot where I could see it without having to be a contortionist. The scales are basically the same as the caliper without the jaws. They have the same electronics. There's a little data port on the caliper hidden under a plastic cover.

The other advantage to moving the device away from the bed is that it cuts down on the stuff that would get into it (way oil, cutting fluid, swarf, etc).

I was hoping to avoid buying the DRO display ( http://littlemachineshop.com/products/product_view.php?ProductID=2010 ) for another $249. Maybe I can find them cheaper somewhere???


The remote display and the correct set of scales is really the correct way to go.


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## pbarrette (Aug 30, 2005)

Hi Gadget,

If you're just looking for a cheap display, and you don't mind putting in a bit of work.. Take a look at the DRO-350 from ShumaTech. It's a 3-axis DRO display project as a DIY kit. The PCB costs $17.95, the pretty overlay costs $12.95 and you buy your own components from Digikey or Mouser.

If the DIY doesn't interest you, there's always the Zietlow DRO-2 which sells for ~$170, though they are currently out of stock.

If you are interested in buying linear quadrature scales instead of sticking with the chinese calipers, there is a website which has software and information regarding hooking them up directly to the parallel port of a computer and using the computer display as a DRO.

Also, there is a different DRO available at the Little Machine Shop which replaces the handwheels of the mini-lathe. There is a fairly positive review for this one here at mini-lathe.com.

If you are still looking for something different, then you could search through the Yahoo CAD CAM EDM DRO group or post a request for more information.

Hope this helps,
pb


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## Silviron (Aug 31, 2005)

Thought you already had one of these that pbarrette mentioned, already on your lathe?

At least one of the regular posters on this forum does, and I thought it was you.. I got tired of messing around this weekend and ordered a set myself. Should be here tomorrow, or maybe even today if I'm really lucky.

Seems like a reasonable price for them, should save a lot of time and wasted material because you lost count of the turns or just "eyeballed" a little too inaccurately. Will surely save the headaches of trying to adapt something..... I read a review on one of the mini-lathe related sites (if not mini-lathe.com itself) that said even installing one of the $700-$900 linear DRO kits that was designed for the mini-lathe was a total pain in the posterior, requiring "engineering", "Jerry rigging" and fabricating some mounting parts. 

The ones I ordered just bolt right in, and directly replace the cross slide screws and plates and stuff. (hopefully these don't have the slop that seems inherent in the OEM ones no matter how often you adjust the gibs.

I hesitated a while because they reduce the amount of rotation you can put on the cross slide.... But upon reflection, I realized that I don't rotate the slide all that much anyway, and can slap the old setup back pretty quick if I need to.

Also ordered the new A2Z QCTP. I have had the one HF sells, for a couple of years, but it kind of sucks. Hopefully this one is better and easier to use.


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## gadget_lover (Aug 31, 2005)

Yes, I have the DRO that replaces the leadscrews and cranks of the minilathe. The compound only moves about 2 inches with any degree of stiffness. After that you must crank it back and move the carriage.

While that DRO quite useful, there is nothing for the carriage itself. That's the one that I'm thinking about.

Daniel


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## Silviron (Aug 31, 2005)

OH! Well, that explains it 

Hey, it should be fairly easy to adapt one of the cross slide DRO units to the carriage leadscrew. The only problem I can see is do the TPI match what the DRO needs to calculate things right. Or if there was a way to reprogram the calculator _(But I guess if there was a way to do that, they wouldn't have to put new leadscrews and nuts in the kit.)_

If by chance they do match, it seems like it would be a pretty neat solution. Just a thought.:thinking:

EDITED: AH, Nevermind. 
That would only work when you are using power feed .:shrug:

I hardly ever use power feed except for threading.


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## HarryN (Sep 4, 2005)

Hi Dan - you can potentially gain accuracy if your setup amplifies the movement before it reads it out. Even a 2:1 or 5:1 could make a huge difference in achieved results.


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## paulr (Sep 4, 2005)

If you're just trying to move the readout where it's easier to see, I'm sure there's some kind of DRO that remote mounts the display with a cable, so you can put it wherever you want. If not, maybe you can adapt an existing one.


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