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Digital Position Readout Comparison

A digital position readout (also known as a DRO, short for digital read out) provides a numerical display showing the position of your machine elements. On a milling machine a 3-axis DRO shows the X- and Y- positions of the mill table plus the Z-axis position of the cutting tool. On a lathe, a typical 2-axis DRO shows the positions of the carriage and the cross slide.

DROs help prevent common errors such as misreading the hand wheel dials or losing count of hand wheel rotations. They also provide capabilities that are impossible with mechanical hand wheels and dials, such as switching from measuring inches to measuring millimeters.

At LittleMachineShop.com, we carry several complete DRO packages. We have rotary encoder-based DRO packages that fit specific lathe. We have a selection of scale-based DRO packages that fit most bench top lathes and mills.

Rotary encoder-base DRO's for Lathe

These packages mount right on the cross slide and compound rest to give you accurate depth of cut readings.

Unlike our other DRO kits, these are not a true DROs. There are two things that differentiate these from a true DRO. First, they provide readouts for the cross slide and the compound rest. They do not display the position of the carriage at all. Second, they do not actually measure the position of the cross slide or the compound rest, but measure turns of the hand wheels.

Why are these distinctions important? The first is pretty obvious, if you want to know where your lathe carriage is. This product won't help. But if you want to measure along the axis of the bed, you can set the compound rest perpendicular to the cross slide and use it to measure.

The second distinction is a finer point. Because this product measures turns of the hand wheel, there is no compensation for backlash. On a milling machine this would make this product pretty much useless. But on a lathe, you are always cutting in the same direction (on any particular cut), so backlash doesn't matter.

  • Works on any 7x10, 7x12 or 7x14 mini lathe made by SIEG
  • Models for other SIEG lathes
  • Resolution: 0.0001", accuracy: 0.001"
  • Buttons for On/Off, Zero, and Inch/MM
  • Zero any axis at any point
  • Inch or mm display

This product is a good value. It provides most of the features of a 'real' DRO at a very attractive price. But don't try to use it on anything but the lathe it was designed for. It simply won't work.

Rotary Encoder-Based DRO Package Comparison Table

  Digital Position Readout, 2-Axis Mini Lathe Digital Position Readout, 2-Axis C4 Lathe
Part Number 2222 3463
Product Digital Position Readout, 2-Axis Mini Lathe Digital Position Readout, 2-Axis C4 Lathe
Repeatability 0.00050" (0.0127 mm) 0.00050" (0.0127 mm)
Resolution 0.00010" (0.0025 mm) 0.00010" (0.0025 mm)
Accuracy 0.00100" (0.0254 mm) 0.00100" (0.0254 mm)
Technology Rotary encoder Rotary encoder
Clear to Zero Yes Yes
Inch/mm Display Yes Yes
Made In China China

Scale-Based DRO Packages

These DRO packages include the digital display unit, 2 or 3 scales, mounting hardware, and complete instructions for installation and use.

Scale-Based DRO Packages are designed to mount on any machine within the range of the scales. They all come with 'universal' mounting brackets. These mounting brackets are probably all you need to mount the DRO on larger machines. On smaller machines (including mini lathes and mini mills) you will probably need to make some mounting brackets.

The biggest challenge is usually the cross slide on small lathes and the X-axis on small mills. On small lathes, the answer is sometimes to mount the DRO scale hanging in space behind the cross slide. On small mills, the smaller cross section of the Shooting Star and the DRO Pros magnetic scales can make it significantly easier to mount the X-axis scale behind the table without restricting the table travel.

  Shooting Star
Shooting Star
DRO Pros Glass Scales
DRO Pros Glass Scales
DRO Pros Magnetic Scales
DRO Pros Magnetic Scales
3 Axis Mill 2665, 3568 3811 4239
2 Axis Mill 2664 3976 4240
2 Axis Lathe 2664 3929 4241

Scale-Based DRO Package Comparison Table

This table includes one DRO package representing each class of DRO. The specs for the other packages in the same class are the same.
  Digital Position Readout, 3-Axis DRO Pros Mill Digital Position Readout, 3-Axis Magnetic Scale  DRO Pros Mill Digital Position Readout, 3-Axis Shooting Star
Part Number 3811 4239 2665
Product Digital Position Readout, 3-Axis DRO Pros Mill Digital Position Readout, 3-Axis Magnetic Scale DRO Pros Mill Digital Position Readout, 3-Axis Shooting Star
Repeatability 2 μm, 0.002 mm, 0.0001" 10 μm, 0.010 mm, 0.0004" 0.0005" (0.013 mm)
Resolution 5 μm, 0.005 mm, 0.0002" 5 μm, 0.005 mm, 0.0002" 0.0005" (0.013 mm)
Specified Accuracy 6 μm, 0.006 mm, 0.0002" / 50 mm travel 10 μm, 0.010 mm, 0.0004" / 1 m travel 0.002" / 12" travel
Accuracy / Foot 0.0014" (0.036 mm) 0.0002" (0.005 mm) 0.0020" (0.051 mm)
Accuracy / 100 mm 0.0005" (0.012 mm) 0.0001" (0.002 mm) 0.0006" (0.016 mm)
Scales Cut to Length by User No Yes Yes
Scale Technology Glass Magnetic Rack and anti-backlash pinion with optical encoder
Scale Protection Coolant & dust resistant Coolant & dust proof Coolant & dust resistant
Voltage 120-240 V 120-240 V 120 V
Clear to Zero Yes Yes Yes
Direct Entry of Position Yes Yes Yes
Inch/mm Display Yes Yes Yes
Power Off Memory Yes Yes Yes
Reversible Count Direction Yes Yes Yes
Find Center Yes Yes Yes
Bolt Circles Yes Yes Yes
Bolt Lines Yes Yes Yes
Preset Points No Yes Yes
Tool Offsets No No Yes
Radius/Diameter Yes Yes Yes
Incremental/Absolute Yes Yes Yes
Calculator Yes Yes No
Arc machinding Yes Yes No
Linear Error Compensation Yes Yes No
Made in China India Canada
Warranty 3 years 6 years 5 years
Phone Tech Support Free Free Free

Common features of DROs include:

Repeatability How closely can you return to a previous position.
Resolution The smallest increment that can be displayed.
Accuracy The accuracy specified by the manufacturer.
Clear to Zero Press a button to set the readout to zero.
Direct Entry of Position Enter your current position.
Inch/mm Display

Displays in inches or millimeters.

Power Off Memory Maintain your coordinates and settings even if the power fails.
Reversible Count Direction Set so the dimensions increase in either direction.
Find Center Find the center of a workpiece.
Bolt Circles Lay out a bolt circle with the press of a few buttons. Move to each hole position in turn.
Bolt Lines Lay out a line of bolt holes with the press of a few buttons. Move to each hole position in turn.
Preset Points Enter or move to points and store. Select stored points and move to them.
Tool Offsets Touch off each lathe tool in your quick change tool post and record the offset. Recover the offset when you change to that tool.
Radius/Diameter Good for lathes, displays the diameter of the workpiece rather than the radius.
Incremental/Absolute Tthis capability is good for making slots or other features where you need to work to the dimensions of the feature, while maintaining your position on the workpiece.
Calculator Use the keypad as a calculator.
Arc machinding Cut a radius or an arc by moving between closley spaces points.
Linear Error Compensation Correct for scale deviations.

 

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