The Home Machinist!

I have a project that calls for drilling 1/2-3/4" holes through the side of solid aluminum round stock. I've already tried regular 2 and 4 flute end mills, as well as ball end mills, all work but are rather slow, and the vibration is pretty bad with my small mill, a Grizzly 0619. And I don't have any drills larger than 1/2" at the moment. I recently discovered the drill/mill, an end mill with a 90 degree point on it. What, if any, advantage would this have over using a regular drill bit of the same size? And are there any other pros or cons to them? Thanks, guys.

Dave

I've never advocated drilling with end mills. The problem comes from the periphery being ground with the intentions of cutting, unlike a drill, to say nothing of an end mill's limited ability to deal with chips when used as a drill. The web section is far too great in size, in spite of the end being ground to be center cutting. They simply do not handle chips well, in particular if the hole has considerable depth. The slightest disturbance causes the end mill to wing, enlarging the hole. The problem would most likely be exacerbated by a light duty machine, which isn't able to resist forces well, and would wing far greater than a more robust machine. I'd advise against it.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

I've seen those drill-mill combo bits you are talking about. Never used one, but my impression is that it would be a compromise that would be less than either of it's focused counterparts. If you had a production run where swapping tools hurt your margin, and the "job" required sinking a hole and cutting a slot quickly without close tolerance or tool changes, then it might be just the thing. But if you are just making rough tolerance holes, I would just get the drills. They will do a better job (of just making holes) faster, cost less money, AND you'll likely need them down the road anyway.

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Russ
Master Floor Sweeper

Dave,

If you have to, drill a hole as large as you can with the bits you have, then use your end mill to take it to size. Even with a light duty machine you should see pretty good results.

By clearing out the center the end mill has a better chance to clear the chips as it cuts. The bigger the center hole, the better it will work.

Not a perfect idea, but works when it has to.

Dave C.

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I learn something new every day! Problems is I forget two.

I have some drill/mill and used for champhering a small 45* edge. They are no good to cut a V groove because the center has near zero SFM.
Even if they worked as drills I would not used them for the simple reasons that are 5 to 10 time more expensive than a drill bit and I can resharpen a drill bit but not an end mill.

Suggestion:
Lock the non moving axes, most likely the cause of vibrations.
Progressive drilling such a 1/4; 1/2"; 3/4" let the mill groing suggest the steps.

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Mauro Gaetano
in Austin TX

Drill a center 1/4" hole, then drill that out with a 3/8" end mill (to straighten the hole) and then step-drill upwards from there.

Also depending on how accurate you need the hole size, you may have to drill/mill it up to 1/16" undersize and then bore it from there with a single-point tool. The smaller machines flex quite a lot and I have found that mine won't drill a perfectly-sized hole with any mill bit (I have the same machine as you). The boring head can get it within .001" if you work upwards carefully.