Upgraded Bandsaw Circle Cutter Jig

Way way back in the history of this blog (around Episode 6 if anyone cares) I did a video on a basic circle cutting jig for the bandsaw.  That jig was decommissioned and abandoned after a few years of service as part of the cleanup during the shed expansion, but it has taken from then until now for me to do something about replacing it.  I’ve had plans in my head for a new version for a long time, and finally I have realised those into a new jig (which is still a bit of a work-in-progress).

So let’s jump into what I have been working on.

I started by raiding the jig drawer, and found some useful components that looked like they would work with my mental image of the new jig.  My main thing I wanted to be able to do with the new one, was adjust the diameter of the circle without having to use the agricultural method of hammering in a nail and clipping off it’s head to form a point to mount the work on.  So a rail was needed.

The other ‘problem’ I wanted to solve was angled circle cuts, which have a different bandsaw blade path, and over time would end up with the jig rather chewed up.  Will still be working on this as the jig develops.

Jig Components

What we have here is some Incra Rule Track, the Incra Mitre Slot runner (not sure it’s real name), a mitre slot lock nut and some scale rule.

I wanted to use the mitre slot lock as the pivot point – setting its position along the track and it then locks down with a hex key. I needed to put a pivot point into it, and what I came up with was a threaded bolt through the track lock, which is then sharpened to a point to mount the workpiece.  As much as my shed is a woodworking shop, there is still a number of invaluable metal-working tools in there and one that is invaluable for jig building is a thread cutting set.

Metal Thread Cutting

It doesn’t have a large range, but there is enough in there for the sorts of small-scale jigs etc that I need to make.  Jigs are, after all, one of the most useful things in a workshop, so making a jig is an artform in itself. (Not that I’m particularly good at it, but I do recognise their value!)

Measuring Thread Size

First step was choosing a suitable bolt that I wanted to use, and then determining what thread size it was to cut the matching threaded hole in the Mitre Lock. There is a tool in the kit to determine the thread on a bolt, and in this case I was able to work out that it was M5 0.8 pitch.

Drilling the hole to be tapped

Next, using the pro drill press table’s advantages with the clamps etc, I was able to hold down (with the aid of some Vice-Grips) the small Mitre Lock to drill the hole to be tapped.  I used a 4mm bit for this, as it will be tapped out to 5mm by the thread cutter.

Cutting the thread

Using the correct thread cutters, I then tapped the hole, first with the least aggressive 5mm 0.8 cutter, and progressing through to the final cutter which produces the sharp crisp thread required.  Using one is pretty easy, and it is just a matter of taking it slow, backing the tool off every 1/4 turn to break off the swarf that is forming, then continuing deeper and deeper.  This is repeated for the next two thread taps until the thread is fully formed.

Formed Thread

Here is the final hole produced, and all tapped ready for use.  You can also see in this photo the grub screw (hex drive) that is used to lock the Mitre Lock into the track

Inserting the Bolt

The bolt is then threaded through, and with the aid of the Vice-Grips again, the head of the bolt was sanded right down on the linisher. Then, with a combination of metal files, the Triton Rotary Tool and the linisher, the bolt was shortened, and sharpened to a point.

Ripping the Jig

The body of the jig has been made out of this heavy ply I have held onto for years, waiting for a good use to put it to.  It happens to be the ply that is used around electrical cabinets etc, and is quite weather (and electrically) resistant.  It has a shiny, smooth side, perfect for jigs.  This is probably one of the first photos on here of me actually using my tablesaw, so have included it for that reason (I normally don’t remember to take a photo while ripping a board!)

Routing the Dado for the Track

I wanted a stopped dado for the track (in other words a slot that doesn’t extend the entire width of the board, so as much as I was hoping to use the dado blades on the tablesaw for a legitimate job, I still needed the router table for the task.  The Incra fence again came into its own, allowing me to accurately position the fence so the track was an exact fit. I did use the micro positioner to do a couple of final fitting runs, taking off about 3/1000″ each pass to get the fit perfect.

The end of the stopped dado has rounded corners as a legacy of being cut with a router bit, so I needed to either square those corners up, or round the track over to match.  I have a small tool I bought from Carb-i-tool years ago, perfect (and designed) for this task.

Corner Squaring Chisel

A few quick raps with my home-made redgum mallet, and the corner is cut square.  It is a cool design, and the tool has a rebate on two sides so it fits perfectly in the corner over the top of the round section that needs removing.

After testing with the track, I decided I wanted to set it a bit deeper, and rather than making more passes on the router table, I had the perfect tool for that job too…..

HNT Gordon Shoulder Plane

…..my HNT Gordon ebony shoulder plane.  Sometimes a hand tool is the perfect tool (and yes, I am sure there are many other there that would argue that a hand tool is ALWAYS the perfect tool, but I don’t mind murdering a few electrons on the way).  It can be set so fine to take of just a fine shaving, delicately thin.  You can’t beat the feeling of working with a fine tool.

Track in Position

The track and Mitre Stop is now in position, and the track is significantly longer than the jig so I can cut rather large circles if required.  The size of the base board was chosen to roughly correspond to the width of the bandsaw table (including the area between the blade and the riser (the throat)), so the workpiece has plenty of support.

Marking up slider position

Another tool getting actually used in a real job was the Woodpecker T Square, used here to find the track that the bandsaw blade will follow, and therefore where the slider needs to be located.  I’ve used the Incra slider here because it can be fine-tuned to fit in the mitre slot of the bandsaw table for a good, sliding fit which can be adjusted and finetuned while the jig is fitted to the table with a simple hex key.   It also means I can reposition the slider easily, if I want to use this same jig on another bandsaw.  In my case this is important, as I am designing this primarily for my Jet 14″, but will also want the jig for cutting circles on the Triton 12″ bandsaw when I run my toy-making courses at Holmesglen.

The first cut

Finally, we are ready for the very first cut, the one that the blade will follow for horizontal circle cuts.  This is done with the slider in position, but no table stop is yet fitted, as I have not determined its position.

I’ve then fitted a stop to the underside, which catches the edge of the table so the jig can’t pass through too far.  In this case I’ve used a bit of Incra rail which is a bit of a waste, but it was the perfect size, so sacrificed to “the cause”

All ready

The track is in position, the stop is in place, the initial cut is made, the jig is ready to go.

Initial cut

A board is located onto the pin set to the desired radius, then (with the bandsaw running obviously), the jig is slid forward until the stop on the underside connects with the table.

Cutting the Circle

The board is then rotated through the blade as it pivots on the pin until the circle is complete, and as seen here, breaks free of the outside stock.

Backing out of the cut

You then back the blade through the initial slot cut until the entire jig is free of the blade, and remove the cut circle.

Circle Cutting on the Bandsaw

Circle cutting on the bandsaw – a simple task that takes a lot less time than it took to write this article!