What you need to know when buying linear glass scales

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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.

1.    What is the correct length of the linear glass scale for my lathe?

    • 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.
    • Similarily 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.

2.   What is the correct length of the linear glass scales for my mill?

    • 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.

3.  What is the correct length of the linear glass scale for my Electric Discharge Machine (EDM)  or grind?

    • 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.

What is IP 53 or IP 64?

    • 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 .. 

Thank you for reading.

Revised 13 Dec 07.

Apri 27 2007.


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