Plans for a radius fixture?

[GillMcLane]

I am looking for ideas or plans for some type of fixture/jig to mill a radius on parts in my milling machine (Bridgeport). I am starting a build on a Beam Engine and the plans call for various size radius on some of the parts- anywhere from 3/8" to 1" in alum, brass and steel. In the past I would free hand on the belt sander but that doesn't always give the best results.
Thanks,
Gill McLane
Navarre FL

[doctor demo]

Rotary Table works most of the time.

Steve

[lynnl]

If the part has a hole around which the radius is to be concentric I've found it works great to mount a vertical pivot, and swing the part by hand against the rotating cutter, while taking light cuts.
It sounds a little scary, but I was amazed at just how little force you feel during the cut.

(added) Obviously you'd want the part to be long enough to keep hands well away, AND so you'd have sufficient leverage to hold it. Try a few practice cuts on scrap first.

[Toolguy]

I have had great success for years using carbide blade woodworking router bits. Use them for straight line, on the rotary table or as lynnl suggests. Make sure not to climb cut.

[GillMcLane]

Lynnl's technique is what I am referring too.
I have seen fixtures built that allow you to change the size pin for different hole sizes.
Now that I want to build one I cant find it.
Rotary table is on the wish list, Santa couldn't afford it this year.
Gill

[dp]

Make sure not to climb cut.

And be sure you have a hard stop in case the work slips from your grip else it will climb cut whether you intend it to or not.

[winchman]

If the part has a hole around which the radius is to be concentric I've found it works great to mount a vertical pivot, and swing the part by hand against the rotating cutter, while taking light cuts.
It sounds a little scary, but I was amazed at just how little force you feel during the cut.

(added) Obviously you'd want the part to be long enough to keep hands well away, AND so you'd have sufficient leverage to hold it. Try a few practice cuts on scrap first.

Dang it, with that on my mind I'll never get back to sleep.

[lynnl]

I got the idea from an article by Rudy (Kouhoupt). Don't remember if it was in one of his Shop Wisdom books, ...probably so.
(Yeah, just looked, it's in the Vol 2 Shop Wisdom.)

I took a piece of approx 2.5" round x ~2.5-3" L, turned down a step to within, say one inch of the end, to a dia of about 2". That large step can then be clamped to the table using a plate with a hole of suitable size to fit around the turned down section ...as Rudy did it. Myself, I just milled the bottom (largest section flat on two sides for clamping (vertically) in the vise.

Then I turned a series of two or three progressively smaller steps to diameters I thought might be useful in the future. But I left the top step big enough to drill about a 3/8" hole in the top and provide for a set screw in the side. This permits clamping two-step 'arbors', that are turned down to 3/8" on one end and the desired size on other end to meet future needs.

(added)
I should've mentioned, unless you're using downward cutting (reverse helix) end mills, which I don't have, you'll need to maintain a downward pressure on the workpiece to keep it from lifting off of the arbor when cutting the radius. Doesn't take a lot of pressure, but you can feel the lifting tendency. So it's also a good idea to insure the arbor, or pivot, is taller than the thickness of the workpiece.

I guess for maximum security one could put threads on or in the top of the arbor and provide a washer, with screw or nut, over the top to contain the work in the vertical. But I've not found that necessary.

[Black Forest]

What would be the shortest length you would like to put a radius on the end?

[GillMcLane]

Thanks Lynnl, I found it in the Sept/Oct 1994 HSM- thats what I was looking for.
I also found another version I think I like better here-

http://www.schsm.com/html/marv_klotz_38.html

Gill