adjustable bandsaw circle cutting jig

[frances-ho]

Lookin to build a jig to cut 20" circles but would like to make it ajustable any ideas? has to be bang on when I'm done as I use will be using it to cut frames for glass art work.

ok ? do you know what is known as trammel points?
if not ? it is a beam compass, that can be adjusted to any size you need?
you would need at least 2 blocks of wood like 2" x 2" x 3" and a strip of 1/4" thick plywood, once you know how big the circle has to be?
you would also need at least 2 pieces of 24" square sheet of 3/4" thick plywood, you can create the 20" inch outside circle from one square to trace a circle to the second 24" square though you would cut out the inner circle and sand smooth the circlee with a drum sander.
for the trammel you can affix a glass cutter to one end of one block then make sure your cutter is at zero, and you can affix the second block so that a center pin would be at the 10" mark to become a center for the 20" circle.

[GregTheAgapanthus]

If the table of your bandsaw is too small or not stable enough to hold a jig such as the BritBoxMaher's wonderful fixture, remember that you can rough out the circle on the bandsaw and then do a fine finishing cut with a similar jig on your tablesaw, which, if cast iron, will be a lot more robust.

Good luck.

[Thelt]

On pg. 70 in the Woodsmith-Jigs & Tool Add-Ons book is a very nice circle cutting jig for the band saw. I haven't built it yet but it's on my "to do" list, which keeps getting pushed back with "honey do's".

I forgot to mention the book is online at Amazon.com.

[majnun]

I can't improve upon the posted suggestions. All I know is that the center of the circle has to be 90o from the front edge of the circle. The trick is starting the cut. You can't mount the board to be cut on the center pivot until the blade is exactly where the cut is to begin. Since you are cutting down an oversized board to begin with, you'll have to cut freehand from the edge to where the circle begins and THEN set it in the center pin. I may be wrong since I'm theorizing at this point, not having cut circles this way. I've cut 42" diameter table tops from 5/4 maple using a router and an arm (like a compass) screwed into the bottom of the table. I get a finished edge that way.




























THEN

[Thelt]

If accuracy is really critical my suggestion would be to cut the circle an eight inch or so larger and sand it to the "line". Or, better yet, use a router and trammel to the desired radius after cutting it oversize on the band saw. I actually would prefer the latter because 1) cutting the circle an eight inch or so larger then coming back with the router and trammel would be much less time consuming than the idea above. And, 2) way less time consuming with the router and trammel to cut the circle without the band saw. Wish you all the luck with whatever you decide.