Supported DRO Scale Information

Inexpensive Digital Calipers

Generic import digital calipers are the least expensive option for a DIY digital readout, selling for as little as $10 on eBay. They use the same 4-pin connector as the “standard” Chinese scales, which requires a proprietary (and hard to find) cable. They are available in lengths from 4” to 12” and can be easily cut down to a slammer size if desired. These calipers have one major flaw that makes them ill suited for a DRO application: after a period of inactivity they shut off, resetting the position. Their practical resolution is around 0.0005” and most retailer claim accuracy of 0.001”. In practice the latter is a bit optimistic, especially on some of the cheaper units with as much as 0.003" runout over a 6” span. This makes them the least desirable choice for use in a DIY DRO.

Pros:low cost; broad availability

Cons:lose their position on power-down; slow refresh rate; data cable expensive and difficult to find; low repeatability and high runout.

Shahe Remote DRO/iGaging DigiMag scales

Shahe/iGaging* DigiMag “Remote DRO” scales are slightly more expensive than the calipers but perform much better. The scales come in a number of sizes between 6” and 35” with the price ranging from $20 to $80 (US Dollars). The main disadvantage is that the frame is made of aluminum and the reading head is plastic, so correct mounting is critical. On the other hand, when properly calibrated in TouchDRO, they offer better accuracy and repeatability than claimed by the manufacturer. They are good for a digital readout setup where budget is the main considerations and flood coolant use is not planned.

iGaging "EZ-View" scales use the same reading head as the older DigiMag scales and differ only in the display unit. For the purposes of a DIY DRO they are identical.

Pros: inexpensive, easy to read, excellent refresh rate

Cons: not coolant proof, aluminum frame can wear out with use

*iGaging and AccuRemote are brand names used in the US and Canada. The scales are made by a Chinese company called “Shahe” and are sold under that name in the rest of the world.

** Many retailers have the word “magnetic” in the product name or descriptions. This is a bit misleading, since the scales are not magnetic. Instead, the DRO display can be magnetically attached to the machine. These are capacitive scales and should not be confused with magnetic quadrature scales.

AccuRemote Scales

AccuRemote scales use the same electronics as the iGaging DigiMag version and are made by Shahe as well, but use ground stainless steel frame and reading head. The tradeoff is the cost, which is about two times higher for the same lengths while the practical accuracy and repeatability is only marginally improved.

Pros: good refresh rate, good repeatability

Const: not coolant proof

iGaging Absolute DRO Plus Scales

Absolute DRO+ scales are relatively new offering from iGaging. They use ground stainless steel frames and reading heads that seem to be identical to the AccuRemote scales. Additionally, they use absolute encoder strips, so they don't lose position on power loss. In most other respects they are about the same, with almost identical resolution.

iGaging advertises these scales as being IP54, which has lead some people to believe that the scales are coolant proof. IP54 states that the scales have "Limited protection against dust ingress" and "Protected against splash water from any direction.". In reality IP54 rating means that the scale has some way to keep dust out, which is no different from any other linear scale on the market.

Pros: good refresh rate, good repeatability, absolute encoders

Const: not coolant proof

Standard Chinese Linear Scales

“Standard” Chinese scales (also called 24 * 2 and “Sylvac” scales) have been the mainstay of DIY DROs for years and are commonly available in most parts of the world. The price (excluding the data cable) is comparable to the AccuRemote scales. Their main downside is the proprietary data cable that is next to impossible to come by. Additionally, most of these scales use 1.5V power supply with the positive side connected to the frame, whereas most other scales and encoders have the frames grounded. This makes mixing them with other types of scales a bit problematic. Parameter-wise they are almost identical to the AccuRemote scales but as far as I know don’t come in lengths larger than 24”.

Pros: resolution and repeatability, good availability across the world

Cons: susceptible to noise, difficult to mix with other scales, requires hard-to-get data cable

Glass Scales

Glass scales are used in the majority of commercial DRO units. Most common glass scales have resolutions of between 5 micron and 1 micron (0.0002” - 0.00004”) with superior repeatability and reliability. They offer good protection from dirt/coolant and are much less sensitive to electric noise in the garage. The main downside is the cost that can be up to five times more than the cost of capacitive scales of the same length.

Pros: very accurate, real-time refresh rate, good protection and reliability

Cons: more expensive than capacitive scales, can’t be cut without special tools

Magnetic Scales

Magnetic scales are less common than glass scales but are gaining some momentum recently. They are very similar when it comes to resolutions and repeatability but have a few advantages over glass scales. First of all, they are virtually dust and coolant proof. Second, they can be cut to size. Finally, they have smaller cross section, making them easier to use when space is at a premium (for example on a lathe cross slide). Their main disadvantages are the high sensitivity to misalignment and the fact that they attract swarf.

Pros:very accurate, real-time refresh rate, dirtproof, smaller cross-section, can be cut to size

Cont:cost, lower availability, more sensitive to misalignment

The difference in quality between high-end and the less expensive Chinese glass scales is pretty minimal. This is not the case for magnetic scales, unfortunately. For a long time Electronica/EMS magnetic scales were most common and offered superb quality. As of late, less expensive Chinese magnetic scales started appearing on the market. Unfortunately magnetic encoder tape is the place where Chinese manufacturers can cut the cost. While these scales magnetic scales look good on paper, their overall accuracy is much more of a hit-or-miss than is the case with the glass scales.

Incremental Rotary Encoders

Rotary encoders are sometimes used in situations where a linear scale might be impractical. It can be either a rack-and-pinion setup, a shaft encoder on the lead screw or a similar application. The cost of rotary encoders varies widely, with low-end units retailing for $10 to hundreds of dollars for “industrial” grade encoders. Major drawback of rotary encoders is the fact that they don’t address the backlash, though.

Pros:can offer digital readout where linear scales are impractical, relatively inexpensive

Cons:don’t eliminate backlash