Bosch router large circle jig

This simple and sturdy jig is designed for creating large circles (Ø 125mm and larger) with a Bosch router. Although I made it specifically for my Bosch POF 1400 ACE, it is likely compatible with other Bosch models as well. Step files are included in case anyone wants to modify the model.

To use the jig, place the router on the base and secure it with a couple of 8mm rods. I opted for 1m threaded rods due to their availability and affordability. These rods can be joined with a coupling to extend their length, enabling the creation of even larger circles. However, most 8mm rods should work just fine.

The thumb screws are made using an M5x20 screw with a hex head and an M5 hex nut pressed into the block. The printed thumb screw is designed to be a very tight fit for the M5 screw and must be either pressed in place or gently hammered. For optimal results, heat the M5 screw sufficiently to melt it into place.

To use the jig:

1. Position the Router
  - Place the router on the base.
  - Insert two rods through the holes in the base and secure them to the router using the thumb screws on the router.

2. Attach the Block
  - Slide the block onto the other end of the rods, ensuring the arrow on the block points toward the router.
  - Fasten the block at the center of the circle by inserting a 5mm screw through the hole in the middle of the block.

3. Measure the Desired Radius
  - Use a folding ruler to measure the desired radius of the circle.
  - Place the end of the ruler in the notch on the base and measure the distance to the beginning of the block. Note: The notch itself adds 5mm, so don't measure from the edge of the base.

4. Fix the center block
 - When the desired distance is measured, fasten the block to the rods using the thumb screws.

Use the following formula to calculate the radius of the outer edge of the cut:

Radius = <Router bit radius> + 100mm + <Measured ruler length> + 15mm
 

Example: To create a Ø 100cm circle using a 20mm router bit, the measured distance on the ruler should read 375mm.

You will need:
2 pcs. Ø 8mm rods of suitable length
2 pcs. M5x20 screws with a hex head
2 pcs. M5 hex nut
 

Printed in PLA, but any type of plastic will do. Use support for the 8mm holes in the base. Print the center block on it's side (8mm hole up) for easier print, but you might want to use supports for the 6mm holes for the thumb screws.