Circle Cutting Jig

Cutting circles using a bandsaw is easy with a jig designed for the task. There are commercial jigs available and many variations of home made jigs can be found on the Internet. As far as I can tell, my jig is unique in the way it is constructed and uses materials commonly found in lumber and hardware stores. The idea behind all circle cutting jigs is to position the work on a pin at the center of the circle and slide the jig parallel to the cutting blade so that the pin is aligned with the front of the bandsaw teeth. Once in position, the jig must be secured in place and then the work is rotated around the pin until the cut is complete. By adjusting the pin to blade distance, different radii can be cut.  Dimensions for the jig are determined by your bandsaw table.  My jig uses the miter slot in the table.  If your table does not have a miter slot, add left and right side rails to hold the jig parallel to the cutting blade when sliding the jig into position.

Materials for my circle cutting jig are:

  • 3/4″ particle board for the table
  • 3/4″ x 3/8″ plastic miter track insert for table guide
  • T-track for the sliding pin holder
  • T-bolt and thru knob to hold the sliding bar in position
  • Threaded insert and mating knob with bolt to clamp table in position
  • 3/8″ bolt used for adjustable stop when positioning table
  • Misc pieces of hardwood to make stop/clamp assembly
  • 1/8″ diameter steel rod for circle pivot point

 

Jig Overview

This is a view of the circle cutting jig in position to make a cut. The work must be in place and the bandsaw running before sliding the jig to this position.

Circle

Starting with a square blank, the entry cut can be seen on the upper left. Once the jig is in position and secured in place, the work is rotated to complete the circle. The T-bolt used to hold the T-track securely in the dado slot is shown next to the work.

Pin-Blade Position

A dado is cut in the top side of the jig table to accept a T-track held by a T-bolt from the underside. Note that the pin is exactly in line with the front of the teeth when the table is slid into position.

Dado and T-track

A piece of hardwood was cut for a press fit into the end of the T-track. An undersized hole was drilled through the T-track and wood to accept a pin that was also press fit.

Stop clamp assembly

A hardwood block slightly less than the cast iron table thickness was glued and screwed to the jig table. This block was drilled and tapped to accept a 3/8″ bolt that can be adjusted to hit the table for positioning the pin relative to the blade. A hardwood clamp is held to the block using a tapped insert screwed into the block bottom. Note also the plastic piece that rides in the bandsaw table miter slot. It was positioned in a shallow dado and secured in position using countersunk flat head screws from above.

Underside view

This view shows the clamp block assembly in it’s final position. The slight gap between the block and the table is the 3/8″ bolt butting up against the table for fine adjustment.

Underside view 2

Another view of the underside of the jig showing holes drilled in the exact center of the top dado slot allowing the pin to be positioned without any “dead” spots.

Jig in action

My first project for the circle cutting jig was for a semi-circular shelf. This view show the work supported with auxiliary roller stands because the cut had a radius of 20″, far exceeding my bandsaw table.

Completed cut

To be on the safe side, I enlisted the help of Jerry, my neighbor and friend. Jerry helped insure that the work stayed on the pin and that the scrap didn’t hang up on anything as the cut was being made. I think that I can cut these large pieces by myself in the future but it’s always best to be on the safe side when attempting any tricky shop operation especially the first time.