Recommended Scales and Touch Probes

We don't sell DRO scales directly to avoid unnecessary markups and shipping costs. Instead, you can purchase the scales directly from the supplier. Based on our experience, testing, and feedback from TouchDRO customers, we have compiled a list of recommended scales and suppliers.

Table of Contents

• Recommended Optical Scales
• Recommended Magnetic Scales
• Recommended Capacitive Scales
• Recommended Touch Probes

Optical/Glass Scales

Optical DRO scales (also called "Glass Scales") use a precision glass encoder strip that is read with an infrared sensor. They are commonly available with 5μm and 1μm resolution but can be specially ordered with sub-micron resolution. The effective resolution is the same as nominal resolution. Glass scales offer an excellent balance of price, accuracy, and reliability, and are virtually maintenance-free if installed correctly.

For most hobby and small commercial machine shops, optical DRO scales from well-known Chinese brands would work well. A good street price range for brand-name Chinese optical DRO scales is between $130 and $200 (including shipping), depending on the length and resolution.

Scales that sell for under $70 with included shipping (regardless of the brand name) are usually quality rejects or production overruns from larger manufacturers. Although the low price is very enticing, it's best to avoid these scales. Many TouchDRO customers reported problems ranging from incorrect pinouts to missing components or damaged encoder glass.

Recommended Optical Scales

Magnetic Scales

Magnetic DRO scales use a magnetic encoder tape that is read by an array of Hall effect sensors. They are usually more compact than glass scales and are very easy to cut to size. The main downside is that magnetic scales are inherently less accurate than glass scales. High-end magnetic scales (Newll, Sony, etc.) typically have declared error of ± 10μm over 1m of travel. On the other end of the spectrum, some inexpensive Chinese scale models have cyclic errors that measure in tens or even hundreds of micrometers.

IMPORTANT: After the installation, magnetic scales have to be thoroughly checked to ensure their accuracy. Instructions are provided in the TouchDRO calibration video.

Note about Magnetic Scale Resolution

Magnetic scale resolution should be taken with a grain of salt. The effective resolution of most magnetic scales (including Newall, Sony, etc.) is around 10μm; higher output resolution is often achieved by interpolation in the firmware. The exceptions are Chinese scales, which use coarser 5mm tape for 5μm scales and 2mm tape for 1μm models. Consequently, 5μm Chinese scales are much less accurate than their 1μm counterparts.

Moreover, real-world resolution and accuracy are affected by a combination of gradual/linear, cyclic, and random errors. A gradual error affects large workpieces and can be reduced by calibration. Cyclic and random errors are much harder to compensate for and have a much worse effect on overall system accuracy. As such, scales with gradual error are significantly more accurate than scales with cyclic and localized random errors.

Recommended Magnetic Scales

Capacitive DRO Scales

Capacitive scales are sometimes used for measurement of the quill travel on many table top milling machines. They are not ideal for this application due to lower resolution and high noise sensitivity, but on some machines are the only viable option.

TouchDRO TDA-400 and TDA-420 adapters (starting with firmware version 3.2) support BIN6 (used by many Chinese calipers and scales) and Mitutoyo SPC (used by Mitutoyo, Starrett, iGaging Absolute DRO and some others).

Recommended Capacitive Scales

Touch Probes and Height Setters

TouchDRO TDA-420 supports standard triggering [digital] touch probes and tool setters with NPN or Push/Pull output. This covers the vast majority of hobby grade and commercial touch probes on the market, ranging in price from $50 to many thousands of USD.

Note on Chinese Touch Probes

The most important touch probe parameter is repeatability. Even though a kinematic triggering touch probe is a very simple device, to achieve good repeatability it must have very precisely spaced contact points and spring rate matched to the stylus length and rigidity.

There are many touch probes on eBay and AliExpress in the $50-$100 price range. This is a very appealing price, but based on our testing and feedback from our customers, these low-cost probes are very inconsistent from unit-to-unit, and overall quality control appears to be non-existent. Some had excellent repeatability, and others (some times from the same batch) were completely unusable.

Recommended Touch Probes

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