I am trying to make a series of parts with rounded edges. The aluminum raw stock is screwed to a fixture plate. The raw stock is contoured once with 1/2 end mill and then with a 1/16" radius corner rounding end mill. Then the four parts are flipped over and another pass with the corner rounding end mill is made. The difficulty, of course, is getting the parts into exactly the same location after flipping. Sometimes it works fine other times there is a lot of filing to do afterward. I really have two questions.

How can one maintain alignment after flipping in general? I assume dowel pins would need to be added to the fixture plate.

Instead of rounding the edges on the mill would it be reasonable to finish the edges by hand using a router mounted on a router table with a corner router bit?

Thanks

if you mounting the second op on the plate as well what i would suggest is to mill pockets to fit the part into , just pocket by .001 or .002 over the part size
you ll have to keep a process control on the part size

dowel pins would work as well but may leave room for operator error

how are you clamping?

Oh, sorry - I hold a 1/4 fixture plate in a vise and then bolt by stock to that with small cap screws. After milling all that I can on the first side, the screws come out, the parts are flipped, and the second side is milled. You have a good idea of making a recess on the fixture plate. I will have to think about how the would work with rounded edges but with square edges that sounds like a great idea.

I was wonder if one of these might work well for corner rounding.

http://www.grizzly.com/products/G8693

Basically a small router attached to a table. I would remove the fence and insert a small radius round over bit

http://www.grizzly.com/products/G8693

and route the edge of the part along the bit. Would this work fine or will I not be able to hold on to the part well?

Thanks

Wildcat, is this the fan cover you showed?

Consider custom soft jaws for that. You'd put 2 vises on your table. Mill the "top" as you describe. Flip it over 2 the second vise, which has softjaws milled in the "negative image" of your part. It drops right in and tightens up. Set it up to leave enough vertical access to do your finish work.

Alternatively, here is a custom jig that is similar to what you could use to ensure a precise flip if you can register against the stops:

http://www.cnccookbook.com/img/OthersProjects/DominoJig.jpg

Best,

BW

Bob - that's a really neat setup you have in the picture. I'll have to give it more thought. I was hoping to find some easy way to do edge rounding - hence wondering about the mini-sharpener. The most recent need for this was while making some wrenches. It would be nice to round the edges a bit other than lots of filling and polishing. Rounding, then flipping, and rounding again just has not been very satisfying. Thanks for the advice.


Wildcat, is this the fan cover you showed?

Consider custom soft jaws for that. You'd put 2 vises on your table. Mill the "top" as you describe. Flip it over 2 the second vise, which has softjaws milled in the "negative image" of your part. It drops right in and tightens up. Set it up to leave enough vertical access to do your finish work.

One more thought. I wonder if you couldn't make up a custom fly cutter that would round top and bottom edges in one operation. The cutter is basically a form tool.

You'd need to make your fixture so the edge of the part plate is exposed enough to gain access to the bottom edge. Then, you'd just run the fly cutter all the way around the outside and both edges are cut at once, ensuring their proper alignment to one another. If it saves you the flip and re-registration, it might be well worth it.

Best,

BW

You can mount a router to a table from underneath facing up like you mentioned. I have rounded over aluminum like that. It should work fine with a 1/16 radius. If you can put a stop around the tool leaving
just enough of the tool exposed for what your cutting too run against. Also firmly hold the part down and keep your fingers away from the pull of the router. If you try this be careful it can be very dangerous.

I round over edges with a trim router by hand, I do it all the time...works very well and gives me something to do while the next part is running. The bit I use is a 1/16 round over carbide

Thanks guys. I tried this out with a hole saw (HF knockoff of a Rotozip) and a round-over bit. Works fantastically! Takes less time to round the edges by hand than it does to change the tool out in the mill. Definitely will be getting a router and router table in the near future.