Circle jigs

[DIY Stew]

I need a jig to either cut or sand as near a perfect circle as possible, the smallest diameter being about 50mm (2"), I don't want any marks on the faces so using a centre point is out of the question.
I will be using different hardwoods approx 4mm - 8mm thick.
Does anyone have any idea for a jig, or am I asking too much?

TIA

Stew

 

[paulm]

I would turn them to diameter as a longer dowel and then cut the discs off as slices on the bandsaw, but then you might well not have either so that might not help !

The kind of jigs I can think of do tend to involve a centre pin as a pivot point for use with a disc or belt sander or bandsaw, but needn't be a large pin, just a sharp point. Would it be possible to use a fine and shallow point and then sand the resulting mark off the face after ?

Or maybe use a base piece to take the pin and attach the workpiece on top temporarily with double sided tape ?

Cheers, Paul

 

[marcros]

could you double sided tape a sacrificial piece to use a centre point on?

alternatively, can you not turn (or have somebody turn) a cylinder to size, and just take slices off. a jig to hold the cylinder on a bandsaw is pribably easier to make.

 

[marcros]

sorry, typing at the same time as Paul.

 

[mseries]

woodgears.ca has a small circle router jig where the router sits stationary above the workpiece and the workpeice rotates on a turntable underneath. The workpiece is stuck to the turntable with double sided tape. <- that's what I'd do.

 

[Eric The Viking]

Double-sided tape is a good idea.

I was designing a router table jig a couple of years ago, as I needed some pulley wheels, and throat-plate inserts for my Bandsaw table.

Vanity suggested I made one that didn't need a centre hole, and I succeeded, but it didn't really work well, and I haven't had time to revisit it.

Basically, it used coarse sandpaper to grip the workpiece for rotation against the cutter. It was guarded and safe, insofar as it was hard to hurt yourself with it, but it was very easy to chew up the workpiece and careful technique was necessary to get half-reasonable results. A double-sided tape hold-down (or hold-up!) would be a much better bet for a one-off job.

 

[Steve Maskery]

I think a centre pin is pretty much essential really. But it does not need to be in the workpiece itself.
The circle jig I use on my bandsaw uses a centre pin, but if I did not want a hole in my workpiece I would simply use a sacrificial piece of MDF and use DS carpet tape. You don't need much. Bandsaw setup is critical though if you are to avoid cutting spirals. Don't forget, you also have to find a way of getting from the edge of the board to the circumference of the circle in the first place.
After sawing, and with the pin still attached, I mount it on a V-table on my sanding disk. The pin nestles in the V and the job is rotated until it is smooth.
After sanding, you could then remove the sacrificial MDF and re-use it on the next piece.
HTH
S

 

[DIY Stew]

Thanks guys, off to the carpet shop for double sided tape!

Stew