The importance of a machine’s true travels and other tips for mounting linear encoders

Rising cost pressure is driving a trend toward dynamic machine tools that produce parts economically with very high accuracy, even in small batches. As a result, the share of linear axes with direct drive is steadily increasing in the machine tool sector.

This has been driving the continuously increasing demands for accurate measuring technology and solid signal quality. This puts shops that are unable to invest in capital equipment at the moment in a tricky position: How do we keep up if we can’t add machinery?

One of best options is to upgrade the linear encoders on an existing machine tool. And when paired with the right digital readout (DRO), a machine can be brought back from the brink of the scrap yard. Whether using a DRO or not, proper mounting of the encoder to the machine axes is critical to realizing return on investment.

When it comes to mounting a new encoder scale on a machine, we find one of the steps customers have the most trouble with is measuring the proper travels. It sounds simple, and it should be. But, if it’s done wrong, replacing a damaged scale can cost of thousands and render a machine inoperable.

Remember: The length of the machine table is not the same as the true travel, or the best scale. Always measure from hard-stop to hard-stop, then choose the right size encoder scale.

We hear it all the time, “I have a 42-inch table, I need a 42-inch scale.” In reality, the travel is likely closer to something like 32 inches. If we were to send this customer a 42-inch scale, they would quickly find that it hangs off the end of the table and will likely cover coolant drain holes. If the scale is too short, the sensor will run beyond the end of the scale and damage it.

Let’s look at one scenario. Some lathes have a tailstock on the lathe itself along with a steady rest. When you remove those, the true travel is revealed to be more than when those items are attached. If maintenance comes to service the machine or there’s an exceptionally large part, having the correct length scale extending the full travel of the machine tool eliminates any potential damage to the scale.

While understanding the machine’s true travels is arguably the most important piece of advice (at least the question we get most) for mounting and encoder scale, here are a few other general tips for making the process simple and fast:

  • Unpack the encoder in a safe, convenient location. Do not remove the reading head alignment brackets until instructed.
  • Keep the reading head centered during installation – slide the reading head and brackets along the scale case until the center marks on the scale case and reading head are aligned.
  • Clean mounting surfaces thoroughly.
  • Move the carriage, spindle housing or table to its center of travel during mounting.
  • Mark the axis so that it can be re-centered easily.

Based on most machines’ table sizes, we generally know what the encoder length should be and can help identify the best match. What’s more, at ACU-RITE we have custom brackets for just about every machine make and model out there, grinders, lathes, knee and bed mills alike. Pair that with the advice above, and you’ll save dramatic time bringing your machines up to speed.