# Homemade DRO for $3.99



## Robo_Pi (Mar 2, 2019)

I know this is silly and will be laughed off the face of the forums, but hey, it's working for me!

Obviously this isn't an actual DRO.  But here's what I did:

I bought some $3.99 plastic digital calipers on Amazon.  I ordered 5 of them for about $20.  Free shipping. 

I didn't expect much from them.   In fact I figured they'd be total garbage, but boy was I surprised!

Ok, to begin with they only measure to 0.1 mm or 0.01 inch.  So they don't even read out the thousandths.   However, what shocked me is that they actually are pretty darn accurate to a hundredth of an inch.   By purchasing 5 of them I was able to measure objecting using all five calipers and then comparing how close they were to each other.   To my utter shock and amazement they all gave the same reading to within a hundredth of an inch.   So they are actually accurate to the tolerances they are advertised for. 

Anyway, why did I buy these?  I bought them to use as crude digital readouts on my lathe.   And today one came in extremely handy just for that. 

I'm boring a hole that I don't want to go clear through and hit my lathe spindle.   So I clamped one of these digital calipers between my lathe table and the tailstock.  You can see it in the photo below.   The c-clamp in the middle of the picture is clamping the end of the caliper to the lathe table, and the digital readout is clamped to the tailstock.




Here's a better picture of the actual digital caliper. 




The -0.75 is how far I am backed out of the hole.  I have set this caliper to read zero when I'm at the depth of the hole I want. 
This way when I bore to the bottom of the hole I can see on the caliper when I'm approaching the end of the cut. 
It works PERFECTLY!

You could no doubt do this reading dials on the lathe too, by my Z-axis table feed dial is at the end of the bed and is hard to read.   This DRO caliper made things much easier.  It truly did. 

If you look in the hole I'm boring you can see the thin lip at the bottom of the hole.  That's because I'm stopping at ZERO on the caliper. 
Later I'll remove this backing plate, turn it around and finish cutting off that little bit of extra material. 

The reason I'm doing this is because I didn't want to bore clear through and potentially damage the MT3 Taper in my lathe spindle.




So anyway, I thought I'd post this.  For $3.99 these plastic dial calipers can be a really economical way for someone to add a DRO (digital readout) to a machine. 

I mean, how can you beat the price?

This worked for me so well that I'm going to make up some nice sheet metal brackets to mount these on and use them when I want to see if I'm approaching a specific place.  The thing that makes them so useful is their ability to be zeroed out anywhere.   Just zero them out where you want to end up and you're all set.  Just aim for that zero. 

I'll probably put one on my drill press for a depth gauge too.    For $3.99 how can I resist?

Obviously this thing returned to zero accurately with every cut.   That left-over metal at the bottom of the hole looks to be pretty darn even. 

So have a belly roll, and when you're all played out from laughing so hard stop and think about the fact that this actually worked out pretty darn well.


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## hman (Mar 2, 2019)

"I know this is silly and will be laughed off the face of the forums, but hey, it's working for me!"  No way.  If it works, it's good!  What really surprises me is that there are now plastic calipers that are digital.  I think I still have an old plastic dial (analog!) caliper kicking around somewhere.  Nice price, too.


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## Robo_Pi (Mar 2, 2019)

hman said:


> "I know this is silly and will be laughed off the face of the forums, but hey, it's working for me!"  No way.  If it works, it's good!  What really surprises me is that there are now plastic calipers that are digital.  I think I still have an old plastic dial (analog!) caliper kicking around somewhere.  Nice price, too.



The accuracy just blew my mind away.    I mean, let's face it, I was taking quite a chance buying 5 of these.  I could have been flushing $20 right now the toilet.    In fact, I kind of thought that I probably had done just that.  But surprise surprise!!!  They actually turned out to be extremely accurate and dependable.

I'm amazed to be honest.   They are well worth $3.99.  And free shipping to boot.


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## markba633csi (Mar 2, 2019)

Actually you're not the first to do that- I've seen it done on a milling machine too with metric table feed screws- great bang for buck
mark


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## FanMan (Mar 3, 2019)

Robo_Pi said:


> However, what shocked me is that they actually are pretty darn accurate to a hundredth of an inch.   By purchasing 5 of them I was able to measure objecting using all five calipers and then comparing how close they were to each other.   To my utter shock and amazement they all gave the same reading to within a hundredth of an inch.   So they are actually accurate to the tolerances they are advertised for.



Not necessarily.  By comparing them to each other you've established that they're _consistent_ to each other, not that they're "accurate".  They could all be off by the exact same amount.


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## Robo_Pi (Mar 3, 2019)

FanMan said:


> Not necessarily.  By comparing them to each other you've established that they're _consistent_ to each other, not that they're "accurate".  They could all be off by the exact same amount.



That's true.  But I actually did compare them with a high quality calipers as well.  I just didn't report that part of the testing.  

I suppose I should have mentioned that.   I was so excited about the fact that they were all giving the same readings that I got totally carried away with that.   I didn't expect them to be so consistent.   That was the surprise for me. 

Plus the way I intend to use them it really wouldn't even matter if they were off from standard measurements.  All I plan on using them for is zeroing them out where I want to end up, and then just using them to head toward that zero.   So it wouldn't matter if they give bogus numbers on the readout in my application anyway.   As long as they always end up at the same place when they get back to their zero that's all I need.


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## Suzuki4evr (Mar 4, 2019)

Robo_Pi said:


> I know this is silly and will be laughed off the face of the forums, but hey, it's working for me!
> 
> Obviously this isn't an actual DRO.  But here's what I did:
> 
> ...


Nothing to laugh at. You used your head and what was available to you so I applaud you


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