Flycutting a Saddle

For flycutting a saddle I’m using the example of the cylinder saddle for the miniature traction engine. The saddle was flycut on a manual milling machine (Sieg SX2.7) with a flycutter. The flycutter doesn’t have any fine adjustment, it just has grub screws to hold the tool in place. Here I will show you my approach to cutting an accurate radius that will then sit on a cylindrical barrel.

distance measurement

The basic approach is simple:

  1. set the flycutter to approximately the correct diameter
  2. start flycutting so that you have a reference surface
  3. stop the machine and measure the tool tip to surface distance – you need the maximum distance and so rotate the tool to opposite the surface
  4. move the head half the difference in diameter
    1. towards the surface if the diameter is too big
    2. away from the surface if the diameter is too small
adjust the tool to the correct distance
  1. Loosen the tool in the flycutter
  2. rotate the tool back to the surface
  3. push the tool tip up to the surface and tighten the tool
  4. make further cuts
  5. repeat the distance measurement

This video shows me making a cut and making the measurements.

The flycutting itself is quite aggressive and can really thump. Also, depending on the material it’s likely you will need to sharper the cutting edge more than once. When you refit the tool, once again use the technique of pushing the cutting tip up to the surface being cut whilst tightening. It is also worth re-checking the dimensions afterwards.

Hopefully you can adapt this technique to your own equipment so that you can try flycutting a saddle.

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