Support > Knowledge Base > XL200 Series Controllers > Parameters > Shear Kerf
Shear Kerf
Help ID: 353
Initial Version: 1.0
Shear Kerf describes the amount of material removed during the cutting process. Some cutting processes include a forming process, so in these cases, Shear Kerf can also be the length of material "lost" during the forming process. The term kerf comes from saw cutting, where kerf is essentially the thickness of the blade.
Often, it is assumed that the thickness of the blade is a true kerf value. When cutting metal, the blade thickness is not sufficient to describe the kerf. Sometimes, the clearance hole is larger than the blade, or the material is soft and there is considerable deformation. In any event, measuring the blade, clearance hole, or slug is usually too inaccurate for a reliable kerf measurement. This is important for accurate part lengths across a range of lengths.
If Shear Kerf is wrong, the machine operator will calibrate based on an error induced in the programmed Shear Kerf parameter. This error will then become a percentage of the length the operator used to calibrate the machine. That percentage will then be applied to longer and shorter lengths.
The outcome will be that part lengths are consistent once calibrated, but if the programmed length changes, the new length will have a consistent error in it until calibrated again. This is a classic Shear Kerf error.
Shear Kerf for Post Cut Lines
The most accurate way to determine Shear Kerf is to perform the following procedure:
- Perform a standing cut on a "short" length of material that can be accurately measured to 0.001", approximately a 1' length.
- Measure the length as accurately as possible and record the measured value.
- Push the part back through the cutting tool and perform another standing cut.
- Retrieve both pieces and measure each as accurately as possible.
- Add the lengths of both pieces together, and subtract the total from the length measured in step 2.
- The final total is the Shear Kerf.
Shear Kerf for Pre-punch Post Cut Lines
On some machine applications, the kerf is actually removed by a pre-punch operation. The pre-punch operation removes the majority of material, but leaves a connecting tab that will later be removed in the cutting process.
Tab Left After Pre-Punch Operation
Even though the cut off removes the connecting tab, the blade doesn't actually touch the edges measured by the operator for a finished part. Technically, there is no "Shear Kerf", as such, but the same parameter can be used to account for the material lost.
Cut Off Does Not Contact Measured Surfaces
This type of process must account for material stretch within the roll former. When material stretches, so does the "gap" or hole punched before the material is stretched. Thus, it is not physically practical to measure the pre-punched gap, or simple to measure after the forming process.
A special procedure is required for this type of machine to calculate an accurate Shear Kerf value:
- Set Shear Kerf to 0 and Correction Factor to 100%.
- Run two sets of parts at two different lengths. The longer length should be the longest length that can be precisely measured. The shorter length should be about 1/2 the long length. The larger the sample size, the better the results (at least 5 parts at each length).
- Accurately measure and record the length of each part.
- Calculate the average measured length for both samples.