3-d corner rounding mannually?

B

Bill Kahn

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I am making a set of dice. (Efron non-transitive numbering). Would like them to actually roll and not be obviously unfair/unsymmetric.

They are 1". I am using a 1/4" radius corner rounding end mill to round over .2" (not .25) of each of the 12 edges. (Leaves me with .6"x.6" on each face to place the pips. Seems to be plenty of space.)

This edge rounding process leaves a sort of sharp pointy bit at each of the 8 corners.

Yes, I can file or belt sand. But I start to lose machining precision then.

Is there a bit/tool/holder/sequence of manual operations that will symmetrically round the 8 cube corners?

Thanks.

-Bill
 
Just a quick guess, get a .2 radius tool. That might solve the problem, as I said, just a guess.
 
You could try putting it on a rotary table, preferably a small vice mounted on a rotary table. Center the dice up on the rotary, set the radius bit at the right distance, and turn through 360 degrees. Repeat for each of the 6 faces of the dice. It wouldn't perfectly round the corners, but it would knock the corners off.

If you wanted to do it perfectly, you could set up each corner on the rotary, with the two vertical faces each 0.2" off center if I'm picturing it right in my head, really should sketch it out, cutter diameters and all that. That would be painfully many corners since you'd end up doing 4 corners times 6 faces. With the right vise stop it might not be too bad ....
 
With practice hand operations can be much more accurate than mechanical ones. That is why scraping by hand or machine is way more accurate than surface grinding, for instance.

I would choose a piece of flat, resilient material like soft polyurethane or hard rubber, and put (for instance) 600 grit emery paper on it. I would visually half the resultant angle and choose the same pressure and number of strokes ( one or 2 will suffice) to break the edge corner. The difference would be hard to measure - even on very sensitive equipment.. If the finish of the corner is more critical, I'd use a higher grit, 800 or 1000.

Use lots of lube, I use low odour kerosine for things like that. Water with a hint of dishwashing detergent can work fine, as well as ammonia spray cleaner.
 
I just discovered this, and this is what would do what you want. It has triggered my TAS so bad.

 
C-Bag said:
I just discovered this, and this is what would do what you want. It has triggered my TAS so bad.
Click to expand...

Another couple options.
A benchtop machine like @darkzero has:
https://www.hobby-machinist.com/threads/metal-working-files-which.57471/post-472520

or a shop built one like this:
https://www.hobby-machinist.com/threads/beveling-and-deburring.57517/post-473020

There was another one, but I can't remember who posted it.
It used an electric die grinder. Hopefully I saved some info somewhere, because I wanted to build one too!

-brino
 
Yeah Robin Rinzetti made one too. I like that little handheld because it's the only one I've seen so far that can get into really tight places. I wonder if anybody sells that type of carbide insert cutter with a 1/4" shank.....
 
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