"Drilling" with an end mill?

We've done this for years with brass with no problems. We make a 3/8 diameter hole that is about 3/8 deep.

Plunge milling like that is fine, just don't try to hold extreme tolerances for diameter.

Jim

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It is probably the most frequent procedure used to do this. The only exception might be to drill a slightly smaller hole and plunge through that if you want a prettier finish at the entry point.... otherwise, go for it....

It might walk a bit and probly will go oversize on your hole diameter a bit.

In aluminum this is likely to cause clogging if there isnt a nice deep relief and gullet for the generated chip to follow.

Shallow holes are less of a problem in this regard.

So from this brief discussion I take it that an end cutting endmill could be used in a drill press to make a land for a cap screw. I have looked at the counterbore drills (the ones that are sized by machine screw, i.e. a "10-24" counterbore), and they are fairly expensive IMO. An appropriate sized twist drill for the hole, followed by a touch with a larger endmill always seemed to me a reasonable way to make a nice land or counterbored hole. Now I'll have to give it a try !

Dave

No. A drill press does not have the ability (as a general rule) to cope with the side forces that an end mill will impose on the spindle. You run a real risk of unseating a taper-mounted chuck by doing this, unless there is a drawbar to hold it in.

Jim

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Generally speaking this can be done.

The shank on an endmill might slip as these are generally harder than your garden variety drill.

And an endmill has "dish" ground into the end teeth typically at around 2 dergees off horizontal--what this means is your counterbore will not be perfectly flat, instead the bolt will bear against the bolt head only at a small area nearest the threaded portion............

Usually not a problem, but with Aluminum or softer materials the area will often deform and a burr will appear, and be forced around the bolt threads, making subsequent accurate removal re-assembly difficult.

Do I do this ???

Yes, unfortunately all too often..........and all too often it causes me grief--like when changing out soft vise jaws when setting up for production work, indicating aluminum tooling fictures on the table, ect........

Can't use a punch mark to locate the hole, and it can walk a bit before it starts to cut, but otherwise no reason not to use an end mill.

They will walk. Remember, the lips are ground high on the outside.

John Martin

I think he was talking about using an endmill in a drillpress to make a flat spot for a screw to bear against. This would be a plunge only operation. That shouldn't put any more side load on the taper than drilling. In this case, and this case only, I think endmills and drillpresses are compatable.

Otherwise, I will agree with you.

-- Joe

-- Joseph M. Krzeszewski Mechanical Engineering and stuff snipped-for-privacy@wpi.edu Jack of All Trades, Master of None... Yet

Many people do this, but you should be aware that the 'counterbore' leaves a radius on the smaller diameter. Why be aware? I once disassembled some parts where the clearance hole was held close to screw size, and the c-bore made with an end mill. The cap screws produced a slight burr when tightened and effectively locked themselves into the c-bore. The radius would have prevented the burr.

Thanks, that's an interesting bit of information. As a habit now, after I drill to tap size, but before I run the tap in, I countersink the hole a tiny bit. This helps me get the tap started nicely. Then, after I tap, I again run the countersink into the tapped hole (I just 'debur' the entry with a countersink held in my hand, Aluminum remember). This helps the start the screw. My guess is that the countersink bevel would serve the same purpose as the radius on the counterbore. But again, thanks for the tip (I love this group :)

Dave

Depending on the size of the spotface, and the nature of the raw surface the endmill is cutting on, it can indeed produce some rather suprsing effects if the tool holder in the spindle is not proof against side forces.

Unless the drill press were far oversized for the task, I would say simply buy the counterbore and do it right.

Jim

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Been there, done that, got the surprise. With wood and a 5/8 router cutter used as a counterbore. Luckily I wasn't injured and I did find the chuck after it landed. In a mill or lathe with a drawbar or other positive tool holding, slot drills make excellent counterbores. With a drill press you need a counterbore with a pilot.

Mark Rand RTFM

I've done this for years... on holes that aren't really critical as for dimension. Saves a lot of time. Use a little lube, WD-40 or Kero, as occasionally you will end up trying to pick out aluminum that has "welded" to the end mill flutes. Not really welded, but I'm sure you get the idea.

Jim Kovar Vulcan, Mi

I'd certainly recommend you don't. A drill press typically lacks the type of rigidity that is required for cutting with an end mill, and end mills don't respond well to being held in drill chucks. Drill chucks are intended to slightly indent the item being held, which provides the necessary friction to drive the cutter without slipping. End mills shanks are hardened beyond 60Rc, so the jaws can't get a good bite on the shank. When you couple the flimsy design of a drill press with a cutter that has the periphery sharpened so it cuts there, unlike a drill, when you get the slightest load on one side of the cutter it starts winging, chewing out the hole. It not only screws up your part, but it's quite dangerous because the end mill can hook the part easily.

If you are hell bent on trying to use your drill press for any kind of milling operation, be certain to clamp everything down. At least that way you won't hurt your hands.

If you're interested in counterbores for SHCS's, it's a lot smarter to hand grind a flat bottom drill. To use it with good results, start the counterbore with a pointed drill, drilling until you have the full diameter deep enough for the flat bottom drill to use as a pilot. At that point, switch to the flat bottomed drill and take your c'bore to depth. Works great, and it's cheap. You have the added benefit of being able to sharpen them by hand when they get dull, unlike proper counterbores. Use a small square to check the end as you grind it flat, so you keep both flutes the same height.

Harold

Counterbores don't leave a radius. They are ground flat, and are able to accept pilots of various sizes, making it impossible for the counterbore to do as you say unless one uses a counterbore that is ground specifically for the job at hand, with an integral pilot. The only thing magic a counterbore does is prevent a burr from forming because the pilot fills the hole. The end result is a sharp corner on the hole. When you find counterbores with a break of the hole edge, it's usually a second operation.

Harold

An endmill may exert enough downwards pull to pull a chuck off of a cheap drill press. Ive seen it happen more than once, simply doing a plunge.

Gunner "A vote for Kerry is a de facto vote for bin Laden." Strider

I have used that type (*with* an integral pilot) on many occasions, and they do indeed break that edge. They work great in that regard.

Jim

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I use serrated belleville lock washers to provide a hardened seat for socket heads on soft materials. They're sized to match the head OD so will fit in a counterbore.

McMaster's p/n for 1/2" is 93501A033.

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