How to machine a circle when it isn't

[devils4ever]

I'm working on making a panel to mount Aviation-style connectors for my CNC mill conversion.

The ideal cutout would be a circle with two flats on it on opposite sides. See pic.

How do I do this on a manual mill?

 

[Technical Ted]

I suggest you buy a hand punch.

Ted

 

[RYAN S]

A rotary table would work.

 

[RobertB]

You don't show what size these need to be. There are double-d panel punches available in many sizes, but they are pretty expensive. You could make your own though. I made a new electrical panel in my boat that need double-d holes and I just drilled a hole and then filed them to shape. Only took a couple of hours and I had to do 20 of them. Was better than spending a couple of hundred dollars on a punch.

 

[cathead]

View media item 96743
If you have a vise with a rotatable feature, you can do the rounded milling by rotating the vise and using a small end mill. You can clamp the work
to a short piece of 2x6. I like to drill a 1/4 inch hole in the center of the work and also use several clamps as I rotate the work. Mounting the 1/4 inch
pin at the exact center of rotation makes for a very handy jig for many applications. I mounted a steel flat on the end of the 2x6 for instant repeatability
as far as centering the pin. The flat sides of your piece could easily be done using the X axis crank all in one set up. I can't count how many times I
have used this jig.

Edit: As I study your post, I think the shape you are making is an inside hole. You could conceivably use the above method by first
marking off the center of the connector holes and drilling a 1/4 inch hole. then rotate the work for the rounded part and run X axis for the flat part.
I think you are making connector holes in a plate.

 

[devils4ever]

Yeah, I'd rather not buy a hand punch since I only need it for 4 holes and they are expensive.

I don't have a rotary table and my Kurt vise is not rotatable. Maybe, I'll mill a circle of the smaller diameter (between the flats) and file to shape. Or, I can just forget the flats and just make it round!

 

[cathead]

You could clamp down a piece of plywood to the mill table and install a 1/4 inch pin in the plywood and rotate the work
around the pin. It would be the same principle as in my previous post.

 

[mmcmdl]

Make something temporary that would hold the desired connectors and when the cnc mill is completed , mill some permanent ones .

 

[Karl_T]

There is also manual CNC. You do need a DRO.

Just find a point on your curve every 1/4" or so. Not a big job with an excel spreadsheet.

turn both handles at same time to next point.

I've faked in a lot of curves this way, just file it a bit after machining and it looks perfect.

 

[Chewy]

Scribe the exact hole on the metal. Using the X & Y, mill to almost touching the scribe line. Make sure your straight sides are in alignment with either X or Y to make life simple. A couple of hand files and or large carbide rotary burr will then smooth the sides. I did this a couple of yeras ago on a drill press with HF XY vise to make electrical plates for duplex outlets. It worked really well and you can't tell mine from commercial ones. The vise didn't have backlash, but slop all over. Had to use bungee cords and clamps to reduce movement, but still got good results. Used 3/16 endmill. With a real mill it would be a piece of cake. Seems to me I remember about 5 minutes a hole.