• Linear glass scales are more prompt to damage by coolant and chips.
  • IP or Ingress Protection is the degree of protection provided by the product enclosure.
  • Example: IP 53 would indicate a dust protected (first digit 5) piece of equipment which is protected against spraying water
  • What does the 1st Digit means:
  • 0  – Not protected.
  • 1  – Protected against objects greater than 50mm.
  • 2  -Protected against objects greateer than 12 mm.
  • 3  – Protected against objects greater than 2.5 mm;
  • 4  –  Protected against objects greater than 1.0 mm;
  • 5  – Dust Protected;
  • 6  – Dust Tight.
  • What does the 2nd Digit means:
  • 0  – Not protected.
  • 1 – Protected against dripping water.
  • 2  – Protected against dripping water when tilted up to 15N.
  • 3  – Protected against spraying water;
  • 4  – Protected against splashing water;
  • 5  – Protected against water jets;
  • 6  – Protected against heavy seas;
  • 7  – Protection against the effects of immersion;
  • 8  – Protection against submersion.
  • For most general applications IP53 is sufficient and value for money. In some cases, it is better to choose IP64 which has better protection. However these scales may cost more.
  • Taking the right preventive measures and doing periodic maintenance will make your linear glass scale last a long time:
  • It is important (and quite easy too) to use coolant covers to protect the linear scales.
  • Also the reader head should be installed so that it is not directly in the flow of the coolant.
  • Never use the air gun to spray at the linear glass scale.
  • After long usage, coolant and chips may accumulate inside the aluminium housing and cause the glass to be scratch. Gently removed the read head from the housing and clean up the linear scale.
  • In some cases, glass type of linear scale may not be the best choice, then it is better to explore metal tapes, etc
  • The ‘distance between centers’ will determine the scale length for the Z-axis or the carriage.
  • Measure the cross slide travel and this will determine the length of scale for the cross slide. The travel of the cross slide is not the same as the Swing over the center.
  • Similarly if you want to install a scale for the compound slide, just measure the actual travel on your lathe.
  • If you are refering to the machine manaul, check for these specifications:
  • Distance between centers
  • Cross slide travel or the Swing over cross slide. Some manufacturers provide both these information.
  • Top slide travel – if you want to install a linear scale for the compound slide.
  • You can refer to the machine brochure for the travel stroke:
  • X (longitudinal) which is the left-right movement of the table;
  • Y (traverse) which is the in-out movement of the table,
  • Z (Knee) which is the up-down movement of the knee; or
  • Z (Quill) which is the up-down movement of the Quill.
  • The correct scale length can be determined by looking at your mill table size too.
  • For example, a  9 x 42 mill table can use scales Y=30 inche, X=14 inch, Z (Knee)=16 inch  or Quill=5 inches travel.
  • Check the actual travel of the EDM and grind machines. The scales size would be based on these dimensions.
  • You can also check up the machine brochure or manual for the details. This is always the preferred method.
Digital readout or DRO systems help to improve accuracy and efficiency.  After you have decided which DRO is suitable for your lathe, mill or mill-lathe machine the next question is how do you buy the right linear glass scale ?

You should refer to the machine specification, product brochure or manufacturer’s website or the internet for the travel stroke of your machine. This information would be 100% accurate. If you cannot find the information, you can do a physical measurement. The danger of doing a physical measurement is that you may mistakenly use a different reference point.

Different manufacturers make linear scales with different dimensional specification, but all of them use the actual travel distance (measuring distance) when specifying the scale length. For example, we would say the scale has 26 inch travel. And this refers to the actual measuring distance and not the overall length of the scale.

Resolution has very little to do with accuracy. Consider your regular 12″ ruler. Let’s say it’s divided into Inches and 10th’s of Inches. The resolution, the finest division on the ruler, is one tenth of an Inch. But how accurate is it? If the graduations were spread over 12.5″ instead of 12″ the number of divisions (resolution) would remain the same but the accuracy would be 0.5″ different from an absolute measurement of 12″. If the accuracy of the ruler was stated as 12″ +/- 0.5″ then the ruler would be within specification. The same analogy applies to linear encoders and digital position readouts. If the accuracy isn’t specified, don’t be fooled into believing that resolution means the same thing.

The encoder accuracy is guaranteed by the manufacturer and unless it has been damaged mechanically, it is most probable that any accuracy errors are caused by the equipment the encoder is mounted to. Most errors are caused by problems with the slideway bearings. They may be worn, badly adjusted, misaligned or simply not up to the job. Whichever way, if the slideway isn’t running true you will get noticeable errors in the measuring system. This is a complex subject. Please contact us for more information if you need it.
Just follow the procedure to measure the “TRAVEL LENGTH” of the scale that you need.

(The physical length is 132mm(5.2inch) longer than the travel length of the scale, e.g. travel length is 800mm (31.5inch), physical length is 932mm(36.7inch).)

(We always mention the travel length for DRO as it is a more important piece of information than the physical length.)

1) Move your X axis to one extreme end and make a marking.

2) Move to the other extreme end and make another marking.

3) Measure the distance between the 2 marking, this is the TRAVEL LENGTH.

4) Select the correct travel length from our available list of travel length.

If the maximum horizontal travel of your milling machine is 420mm. Since scales come in 50mm increments, you need the next size scale which would be a 450mm scale

5) Do the same for the other axis/axes.