Overhead Circle Cutting Jig

[MikeDingas]

This jig appears in Rosario Capotosto's book 200 Original Shop Aids & Jigs for Woodworkers. To avoid copyright issues, I've drawn a similar jig and attached it. I didn't have a suitable drafting program so my drawing is limited to that of Powerpoint. Use a hardwood for the jig. Explanations follow...

The jig attaches via the 1/2 " threaded rod to your scrollsaw. I have a Craftsman 16" saw which provides a clamp on the left side for a hold down. Like most, the hold down was removed as being pretty useless but the clamping mechanism will work for this jig. Adjust the plans to utilize whatever clamping is provided on your saw.

The pivot needs to be ground to a point. The A and B dimensions need to be adjusted to your saw. I would imagine that the pivot point and the front cutting edge of the blade should be parallel and in very close alignment.

This jig should be able to cut up to 18" circles but I don't know the minimum diameter possible. Also, my saw table probably needs an extension of some sort as the pivot likely needs support from underneath to support the wood.

I've omitted parts lists and cutting/assembly details for brevity. If I need to clarify anything, please let me know.

[Rivari]

Thanks for posting that Mike.

The drawing was helpful and the reference to that book is great as well. I beleive that book could be quite an asset to have around a shop...do you know of the availability of it.

I would sure like to see firsthand someone using that jig, I can read a book and only get so much from it, however if I see something done firsthand I am all over it.

[CanadianScroller]

That is awesome Mike.
I have made circle jigs before but I like the overhead approach here.
I did find that cutting the circles one direction resulted in a spiral and the other direction a perfect circle. I think it was to do with the bias of the blade. I am not sure but I don't think a spiral blade would have the same bias.

[workin for wood]

eventually that spiral has to end with a snap and a bonk to the head.

[MikeDingas]

Todd, The book is available from Amazon.com but I may have gotten it at a local BooksAMillion store

Carl, I a bit concerned about the direction of cut, too. My saw would require the jig to be mounted on the left. I usually rotate my wood so I'm cutting the pattern towards the left. Is that CCW? Anyway, you can see how the wood would feed from the left in the jig. Do you think blade bias would be a problem? I suppose I could modify the design so the pivot is still on the right.

[CanadianScroller]

easy solution that everyone will scream at me for suggesting....if the blade bias is on the wrong side turn the blade upside down.
Yes it works. Yes you have to hold the wood down.

[BirdOasis]

Have you guys tried putting a sharpening stone or file against the blade to get rid of any burs. I've seen photos but I'm just not brave enough to try that yet. I don't care about the blade, I just don't want to hurt my sharpening block. It has four sides, each side has a differant grit, but I use each side for differant tools. Especally when turnning. Gotta keep those chisels sharp you know.

[MikeDingas]

Well, I couldn't resist trying to make the circle jig. The pics show my first attempt. At first, the resulting circles were okay but slightly oval. My test was to put the cut out back into the outer waste and try to rotate it. I was not happy with the first few trys.

What I discovered was that my assumption about blade and pivot point alignment was correct. If this alignment is off, expect poor results. So, I put slots into the mounting arm to help me line things up. Once the alignment was corrected, near perfect circles resulted. I'll likely build another and try to make more accurate measurements.

You may notice that I modified the design to keep the pivot on the right side of the saw. This, I had hoped, would avoid the problem Carl mentioned. Also, I made use of the hold-down mechanism that came with the saw. This may not have been the best move since it has some play in it. Lastly, I didn't have the right bolt to make the pivot so what you see in the pic is temporary.

The circle cutting on the saw was my fifth try. It still comes out with a slight bump where the blade comes full circle and wants to wander to the left. This I simply filed down. My test showed a pretty darn good circle. To the naked eye, it looks near perfect.

The other two pics show the overhead vertical drilling jig I made. Not my design, of course. I mentioned this in another post and thought I'd show it as well.

[CanadianScroller]

Most excellent! Thanks for posting the pics!