Milling Square Corners

[cnckid]

I have a project to machine some cutouts in 3/8 x 2 6061 aluminum flat bar. The cutouts are various sizes from .600 x .900 to 1.25 x 1.25 but all require square corners for the electronic components to mount. Couldnt convince the customer to go with .06 radius so I could use a 1/8 endmill, so now I must square out the corners. If it was one or two I would file them, but I have 200 pcs with 3-4 cutouts in each so that's a lot of corners. I read somewhere a long time ago about the use of a square punch used in the CNC mill utilizing an M19 to lock the spindle and then programming a series of strokes over, down, back and out repeating mooving in a few thousandths each pass. Sounds feasable to me, was wondering if anyone out there has done this and would be willing to share the process, tooling resource and other points that might help.
Thanks,
Mike

[underthetire]

Iv'e seen it done. Guy used a small 1/4 HSS tool bit for a lathe. High speed spindles hate loads without turning though. Go small steps.

[Delw]

Originally Posted by cnckid I have a project to machine some cutouts in 3/8 x 2 6061 aluminum flat bar. The cutouts are various sizes from .600 x .900 to 1.25 x 1.25 but all require square corners for the electronic components to mount. Couldnt convince the customer to go with .06 radius so I could use a 1/8 endmill, so now I must square out the corners. If it was one or two I would file them, but I have 200 pcs with 3-4 cutouts in each so that's a lot of corners. I read somewhere a long time ago about the use of a square punch used in the CNC mill utilizing an M19 to lock the spindle and then programming a series of strokes over, down, back and out repeating mooving in a few thousandths each pass. Sounds feasable to me, was wondering if anyone out there has done this and would be willing to share the process, tooling resource and other points that might help. Thanks, Mike

a goo post on it in the haas forum about a week ago

yes to what he said
VVVVVVVVVVVVVVV

Originally Posted by underthetire Iv'e seen it done. Guy used a small 1/4 HSS tool bit for a lathe. High speed spindles hate loads without turning though. Go small steps.

[cnckid]

Thanks, I will go check that out now.
Mike

[Delw]

Theres also another way using the same method thats a tad easier.

drill the smallest hole you can in the corner, then take a TPG carbide insert and use that as the make believe broach. you would have to make the insert holder.
I think I would use a Square sandvik face milling insert for alum though and just relieve the sides a tad.
the reaon I mention the sandvik face mill inserts is the are cupped very nicely for something like that and sharp as hell
I was going to try it on some gun parts one of these days if I ever get the time.

Delw

[cnckid]

Hi Delw,
I was thinking along that same line. Taking a square face mill insert and making a holder to seat it in and write a program to nibble the corners. I looked for a post in the Hass forum on this but did not come up with anything. I'm thinking machine a small pocket to accept the back face of the insert so as to locate it securely, and relieve any holder material and the natural clearance angle on the insert should provide a clean cutting "nibble broach".
Thanks,
Mike

[kawazuki]

Nibble broaching seems a bit long winded? What size are the holes? could they be cut with a saw in an arbor - that'd give you square corners? Just a thought

[Delw]

Originally Posted by cnckid Hi Delw, I was thinking along that same line. Taking a square face mill insert and making a holder to seat it in and write a program to nibble the corners. I looked for a post in the Hass forum on this but did not come up with anything. I'm thinking machine a small pocket to accept the back face of the insert so as to locate it securely, and relieve any holder material and the natural clearance angle on the insert should provide a clean cutting "nibble broach". Thanks, Mike

Mike
I spoke before I looked, the square inserts have a 45º angle on the edges, at least mine do, so the corners wouldnt be sharp.

TPG would probally work much better, but the indexing to opposite corners would be a pain. but then you have indexing issues on the opposite side, I think "underthetire" idea would probally be best if you have more than one side to do.

Sorry about that.

Delw

[cnckid]

Here is one of the panels. .375 thick aluminum. Square corners or .020 radius max allowed. I will have to look but if I can't find a square insert I will have to make or purchase a hardened square bit and go that route. I thought maybe by uploading the part it may jog an idea or two. The other panel has only two cutouts but still needs square corners.

[HuFlungDung]

.020" radius is somewhat better than a square corner. You could drill the corners with a 1mm drill. The followup finish operations then don't have to cope with excessive material in the corners, which never wants to come out very well because of the collision of chips coming from two directions.

You can then mill up to the drilled corners, probably with a 3/32" endmill. You'll have some slight scallops to remove. I would consider making a punch to finish shaving the corner areas. Make a pilot on the punch that matches the machined hole, and clears the scallops, followed by the finish rectangle that performs the final shaving. Press the punch through with an arbor press. This punch would basically serve as a single tooth broach. You could get fancier and add an additional stage or two to the punch to make incremental cutting possible.

[Perfect Circle]

Is a wire EDM an option to cut out the windows?
Then you can do the rest of the mill work.
I know its added time and cost but that can get you the results your after.
Good Luck~!

[cnckid]

I have been thinking of making a punch like mentioned. I like the idea of drilling the corners so as not to put so much work on the punch since I would be doing that by hand arbor press. I have contacted a friend that has a waterjet and we discussed putting all of the other holes in the parts and locating off of those and use the waterjet to do the squares. Will probably take a couple of pcs to get dialed in, at $2.00 per cutout.