DRO Advice

M

macardoso

H-M Supporter - Silver Member
H-M Supporter - Silver Member
Hi All,

I tried searching for DRO advice, however the HM search function filters out short words like "DRO" so it has been difficult to find what I am looking for.

Issue: Something is up with my lathe and the carriage hardweel readings can be off by 1/4" or more over lets say 4" of travel. They also don't repeat, so if I back off and return to the same number, the carriage is in a slightly different position. This leads me to use the compound slide for any precision work in the Z axis of the part (limited to 3.25"). I fear something is loose or broken in the apron gearbox, but I haven't had it apart to see.

Specs: I would like to get a DRO that can offer basic features plus maybe a tool offset table. I would like the cross slide to read in 0.0001" in diameter mode (1um scale) and the carriage to read at least in 0.0005" (5um scale). My cross slide travel is 6" and my carriage travel is 31.5".

I talked to DRO PROS and they quoted me $600 for a basic glass scale setup and $1000 for a magnetic scale setup. I was hoping to spend not more than $600. The EASSON EL-8A with the $600 kit seems super basic (but maybe does all I need). They get great reviews so I'm open to spending a bit more for the good stuff.

I also looked on AliExpress and found several kits which meet my specs for under $200. I think I've seen people on here say they have DROs from China that work perfectly and are accurate. I've also seen complaints about accuracy. Does anyone have any definitive advice on if I can trust the accuracy of the Chinese DROs? If they're pretty much the same as the DRO PROs models then I would be very tempted to try it out at $170.

I was looking at this one. They offer slim 1um scales at no added cost over the basic package. LINK

Thanks for any advice and sorry for doubling up on a question I know has been asked here a thousand times.

Mike
 
I would be hesitant to trust those overseas distributes, they wont have the same warranty or customer service of domestic distributor should a single component fail.
What lathe do you have? is it consistent enough to justify the 1um scales? Those high resolution scales are intended more for grinding and EDM machines that necessitate them. Exception being tool room machines that are accurate enough to benefit.

Be sure to read the manual, the recent DRO I installed at my workplace required calibration after installation. Basically the increments on the scale are not truly 5um apart, so you need to lay gauge blocs along the bed and traverse the slides towards a high resolution indicator with and with out the blocks., then enter in a compensation value in the display unit.
 
I installed the Magnetic scales from DroPros and could not be happier. Being able to easily cut the scales to the exact length I needed help to make the installation a breeze
 
I agree with Alexander on alot of this. I dont deal much with Chinese DROs, but my main question would be are you willing to be out $170 if it doesnt work?

As to the calibration he spoke about, it is always good to check this with any DRO install. The biggest issue I find with installing a DRO and not having accuracy later is that the scale only shows actual movement between the reader head and the scale. The accuracy issue can be compounded with the addition of a compound on a lathe, tool, table/saddle on a mill, etc. So it can quite often be that your scale is "reading wrong" but it could be that where you are testing is off mechanically.

As long as the scale repeats, you should be able to perform error comp to make it read accurately.

Jon
 
Make sure that the scales will fit your lathe. This can be a problem with smaller lathes, especially for the cross slide.. There are dimensional drawings on line for the various scales and pickups. Think about your mounting scheme. There are slim versions of the glass scales and magnetic scales tend to run smaller. I used the iGaging scales and Yuriy's TouchDRO for my Grizzly G0602 lathe because of size issues.

For a lathe install, you might want to consider a 1 micron scale for the cross slide. I have my DRO set up to display diameter on the cross slide which cuts the resolution in half.


.
 
@macardoso I'm in the process of installing the 3-axis version of the DRO you linked.
I looked at DRO Pros and others but I could not justify the price for my needs. (the cost situation is compounded for me because of US-->Can exchange)
Nevertheless, when I got the Y-axis installed it tested it quickly with a DTI and it was dead accurate out of the box.
There's been a number of posts recently on DRO accuracy etc which are worth a read. @RJSakowski and @hwelecrepair raise good points about mechanical accuracy and the actual size of the gear for the intended machine.
 
Thanks for the quick response all. I'll try to respond to some of the direct questions.

Alexander McGilton said:
What lathe do you have? is it consistent enough to justify the 1um scales? Those high resolution scales are intended more for grinding and EDM machines that necessitate them. Exception being tool room machines that are accurate enough to benefit.
Click to expand...

I have an Enco 12x36 import lathe ('94 vintage) which is nearly identical to the Grizzly G9249. It is not a high end south bend tool room lathe, but I frequently am doing smaller part and hitting diameters with a couple of tenths so I don't want to shoot myself in the foot by buying a scale with less resolution than I work at with the handwheels.

Alexander McGilton said:
Be sure to read the manual, the recent DRO I installed at my workplace required calibration after installation. Basically the increments on the scale are not truly 5um apart, so you need to lay gauge blocs along the bed and traverse the slides towards a high resolution indicator with and with out the blocks., then enter in a compensation value in the display unit.
Click to expand...

Is calibration required for all DRO's? I don't have anything of precision that could be used to calibrate them over the 32" of travel. Best I have is 1-2-3 blocks. I'm not going to be saving money on a cheap DRO if I need a $400 set of gage blocks to calibrate it.

hwelecrepair said:
As long as the scale repeats, you should be able to perform error comp to make it read accurately.
Click to expand...

Same comment as above.

RJSakowski said:
Make sure that the scales will fit your lathe. This can be a problem with smaller lathes, especially for the cross slide.. There are dimensional drawings on line for the various scales and pickups. Think about your mounting scheme. There are slim versions of the glass scales and magnetic scales tend to run smaller. I used the iGaging scales and Yuriy's TouchDRO for my Grizzly G0602 lathe because of size issues.
Click to expand...

I still have to look at sizing these, but I was planning on buying the slim scales for at least the cross slide.

RJSakowski said:
For a lathe install, you might want to consider a 1 micron scale for the cross slide. I have my DRO set up to display diameter on the cross slide which cuts the resolution in half.
Click to expand...

That was definitely my plan.

JimDawson said:
Maybe take a look here https://www.hobby-machinist.com/threads/lathe-dro.58063/
Click to expand...

Thanks!

DavidR8 said:
@macardoso I'm in the process of installing the 3-axis version of the DRO you linked.
I looked at DRO Pros and others but I could not justify the price for my needs. (the cost situation is compounded for me because of US-->Can exchange)
Nevertheless, when I got the Y-axis installed it tested it quickly with a DTI and it was dead accurate out of the box.
Click to expand...

Would LOVE to hear a review of how the unit works. Right now I have no way to trust my carriage handwheel so if $170 gets me pretty good performance then I'm pretty sure I'd drop the money on it.
 
For that particular DRO I used a combinations of blocs descending down from 6 inches long. I had them so I may well have used them. Do you have Micrometer calibration rods? those 123 blocs will get you through in a pinch. All dependson what degree of accuracy you wish to work with.
 
I have micrometer calibration rods 1-6". Not sure how I would stack them, or how to sub divide between 1" marks.
 
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