Need Help!- how to drill burr free holes in aluminum

[springlakecnc]

Hi,

I’m fishing for ideas on how to drill a “burr free” hole.

We have an aluminum extrusion with walls about .06 thick. The shape is about 5/8” wide and 2” tall, and 30 inches long. This is a high production part. It needs holes drilled through it, and can’t have any burrs on the outside or inside. The diameter size tolerance is fairly open, I think about +- .005. There are some approximately ¼” holes and some ½” holes. The customer don’t want any kind of chamfer either, because some of the holes have a plastic part that has a titty that pops up into the hole to hold it in place, and some have plastic plugs that need the square edge to grab onto, so that rules out those spring loaded hole de burr outfits, that you send through after the hole is drilled.

We thought about pushing it over a mandrel and stamping it, but we done this before and would like to do it another way, because it needs to have a full length curve, with changing radius, and its easier to first form it, then cut it to length and put the holes into it in one grab, vs putting the holes in first, sawing to length, then trying to bend it relevant to the holes.

Our idea that we are going to try first is, to get a 25000-rpm router head and put in a bottom cutting, carbide end mill. We may even have the bottom of the end mill changed so the outside cuts first, like they do naturally, but we would exaggerate the angle.

Another thought was maybe a .010 step so the mill first pops out the big part, and then skims .005 or .010 a side.

Yes, we feel its no problem if we circle interpolate the holes, but that adds about $50,000.00 to the machine, for servos and ball screws, etc., and of coarse, the man that signs the checks would rather have that in his pocket.

Any other ideas?

Thanks

[MFassler]

plunge the holes with a center cutting endmill and call it done.

[mc-motorsports]

Originally Posted by MFassler plunge the holes with a center cutting endmill and call it done.

that was my thought, 2 flute HSS.

[springlakecnc]

Thanks guys,

It sounds like there is no "miricle" way of doing it.

Some of the things you come up with, are amazing, so I thought I would ask.

[blackbeard52]

Try using a pilot drill.... the tip has a smaller diameter that is about 1/8 longer than the finished size. the concept is to drill a pilot hole then clean up the sides to size with the outer diameter. they are readily available at tool supplies or Home Depot ( dewalt brand ) for a tryout. The only drawback with a pilot point design is that it's virtually impossible to resharpen.

I use them on 29ga steel with very good results.

Bob

[RoboElvis]

I also agree with the center cutting end mill.

A way to reduce burrs is to make sure the part doesn't vibrate at all.

A way to clean up a burr without breaking the edge is to machine a cray-tex stick to the same dimension of your hole and use a relatively slow air tool to polish the burr. We do similar things with sealing surfaces on air regulators.

[Lugy]

Have you tried using PCB drills?

I find that they don't leave much in the way of a burr. The ones I use have approx 170 deg tip.