Drilling flat bottom holes

MSC has a 7/8 end mill 1/2 inch shank #01727486 for $11.92 in my catolog [1999] but you will have to grind the ends flat. And it will probably cut oversize. If size is important Msc has a 3/4 end mill with a 1/2 inch shank and if you grind the end flat and use it as a first cut the 7/8 will cut closer to size. Jim
Reply to
jim sehr
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I have to drill a number of flat bottom holes, 7/8" diameter and 1/10"
(.1") deep in some 2/10" (.2") thick aluminum. Is there a source for
flat bottom drill bits of this size that will fit in the 1/2" drill
chuck that's on my drill press? If there are no bits of this size with
a turned down 1/2" shank, can an adapter be purchased to go from the
7/8" bit to the 1/2" chuck? Thanks for any help. Marty
Reply to
Marty
Have you considered using an end-mill instead of a drill bit?
Perhaps W.L.Fuller can supply you with something that will help.
Reply to
random
If you can live with a small (say 1/4" dia) deeper hole in the middle of the 7/8 hole, you would probably have better luck with a piloted counterbore.
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It's not too difficult to grind a flat bottom drill, but unless you have a very rigid machine to run it, it's going to push the work all over the place. An end mill that large won't be much better.
Ned Simmons
Reply to
Ned Simmons
In a drill press? You're dreaming. You *could* make it happen, but the hassle to do it would be ridiculous. Mill.
michael
Reply to
michael
Bottom cutting plunge endmill, followed up by the correct drill bit for the screw shank hole. Or a ready made counter sink for the screw. Aint no other way to do it without it walking all over hell and gone.
Gunner
"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke
Reply to
Gunner
First, drill a 7/8" hole THROUGH a piece of steel plate, say 1/2" thick. Clamp the plate on top of the aluminum piece. Drill with an end mill or a flat bottom drill bit.
John Martin
Reply to
JMartin957
I like this. It's a drill jig. But the OP implies all he has is a drill press.
I'd take a 7/8 Forstner bit, and change to Mg plate instead of Al if I could get away with it. Then I'd use the method I developed the other day for reaming an 11/16 hole in mild steel to 3/4 with a shell reamer.
Apply a large disc to your drill press drive pulley. Fit the belt for maximum speed reduction. If you want, make the disc the same size as a PSA sandpaper you use. It can serve as a disc grinder. Glue the disc to the pulley with silicone, make sure it's on center, let it dry, and trim to center and smooth the edge while it's running, with a block plane and a file, then some sandpaper. The larg mass of the block plane will tend to catch the high sector and shave it down. Take very light cuts.
Then, modify your Forstner to have less than a 1/10 inch pip, preferable no more than 1/10 inch wide, as well.
Lay out your
with center marks, and find the center mark with the pip. CLAMP THE WORK. Remove the up-spring from your drill press's feed handle, with gloves on, and put it in backwards, so it automatically feeds down, as hard as possible.
Then you can rotate the disc by hand and if the spring pressure is sufficient, the Forstner will cut.
The proper setup for doing this, if a mill is available, is:
cutting speed 300 fpm diameter 7/8 inch cs * 4 / d = less than 1300 rpm cutting time: Let's say 3 sec depth: 1/10 inch cu inch: 0.72 / min HP: about 1 HP milling machine
The reason it's not working on your drill press is there's no way it's going to deliver 1HP at 1300 rpm. Also, at that speed and feed, a standard drill chuck will slip. At the hand speed, you can arrange things so it will not slip.
So you can save $10,000 on a new mill by doing these holes by hand, or give it to a machine shop and it'll be done in 5 sec + move time, times how many holes, billed at about $45 (at least ) per hour. If you're lucky you can be in and out in a quarter hour for $50 minimum. The reason they charge so much is that when the machine sits over two shifts at night, not being used, the interest on their loan really piles up, because interest is 24/7.
It's much easier with a disc, and preferable a finger hole in the disc, because the drive pulley is not made to be rotated by hand. Make everything on the disc smooth, it must never hurt someone. If needed, make up a guard for it, or remove it when done.
The problem I was faced with about a half a week ago was that while the HP and speed were OK, the stiffness was inadequate. As soon as I hear the chamfer on the reamer start to chatter and groan, I quit for the day. That shit scares me. With a fresh start later, I was able to start the chamfer and even proceed into the material a bit, then power up and ream right through it. Getting a 7/8 bit started in Al with a drill press is similar. You might get it started by hand, but the depth is so shallow, why not do the whole thing while staying in the safety zone.
CLAMP THE WORK.
UNPLUG THE MACHINE.
HAVE A NICE DAY.
Yours,
Doug Goncz (at aol dot com) Replikon Research
Replikon Research researches replikons, which are self-reproducing configurations of non-living matter in environments that support replication, analogous to organisms living in ecologies.
Reply to
Doug Goncz
Hi Marty,
Easy one if you can sharpen a drill by hand. It's called Zero Angle sharpening. I'll put the instructions and a couple of drawings on
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within the next couple of days.
With Zero angle sharpening I,ve drilled hundreds of 1/2" holes in 26 gauge material, no burrs. Your only problem may be getting the 7/8" drill with a turned down shank check out
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Glenn
Reply to
Glenn Cramond
You want a slot drill, not an end mill. Slot drills look like endmills but have one or two teeth that extend to the centre. They're used for cutting keyways in shafts, or slots in flat stock; they'll drill through vertically then can be run sideways like an endmill. But it will take a really good, heavy drill press to keep it from walking around. Better to use it to clean out and bottom a previously-drilled, slightly undersize hole. Dan
Reply to
Dan Thomas
If this hasn't been suggested then you could try the following: Grind a drill flat on the end that's the same size as the hole. This can be done by grinding, by hand, the end of the drill square. Then, also by hand, grind each flute so there is relief back from the cutting edge, Use a wheel with sharp corners. When close to the edge and center finish with a hand stone. Drill hole with regular drill and remove point with flat ground drill. I do this from time to time. I am always grabbing the flat bottom drill out of the drawer even though there's a bunch of regular drill in there. ERS
Reply to
Eric R Snow
Do a quick search for reduced shank drills at the top of the page.
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Glenn Cram> > I have to drill a number of flat bottom holes, 7/8" diameter and 1/10"
Reply to
Wayne Harris
Marty Drill your 7/8 hole with a regular drill to the proper depth. Then uses a reground 7/8 drill with flat bottom. It will need a relief gash in the center to enable it to cut properly and I would put a small radius on the corners of the drill to prevent chipping. at this url the second pic from the bopttom shows a bottom drill
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I have to drill a number of flat bottom holes, 7/8" diameter and 1/10"
Reply to
James P Crombie
Sadly, while your suggestion is a good one, one that I have used for the bulk of my years in the shop, it won't work in his case. The size of the hole versus the depth won't allow for it.
Harold
Reply to
Harold & Susan Vordos
Hi Folks,
Gotta agree with Harold here! I had the mill set up for some other tasks and needed a quick and dirty counterbore a few nights ago. Had the work clamped well on the table, used a nice US made 3/8 inch 2 flute endmill - fresh out of the tube. Around 500 RPM, kerosene, and 6061 with a clearance hole already in it. Lined it up with the drill bit used to poke the clearance hole, clamped down, verified no deflection of the bit going in and out of the hole. In short, did everything as right as I could for a half assed work around. I just couldn't control the feed finely enough with the drill press spider. Grabbed, wandered a bit, chatter out the wazoo... In short, a mess. Now my drill is just a JET 17 incher, not an industrial grade machine. I tried playing the mill on this drill press game years ago, accepted that it doesn't work well, and saved up for a mill drill. Still not as heavy a machine as I'd like, but the kids want to eat and there's only so much room and money available.
Finished the previous work on the mill, then did the job using the same endmill on the mill and knocked out the counterbore just fine, so at least I didn't booger a fresh end mill. A piloted counterbore would do just fine for this application in a drill press, but as I understand it the desired result is really a round pocket, not a counterbore.
I really should finish up the counterbores I roughed out a while back for these sorts of tasks, just haven't gotten to it. Don't counterbore often enough to justify the cost of US made commercial ones, and avoid PRC stuff whenever I can.
Cheers, Stan
Reply to
Stan Stocker
Perhaps I was misunderstood, I was soliciting your opinion to understand why you felt it wouldn't work, not to suggest you were wrong.
My
Thanks, as much as I like being right I enjoy understanding why I was wrong even more.
Reply to
Roger Shoaf
Opps, didn't see the depth criteria in the original message. The only other thing I can think of short of a milling machine and endmill is a spur type bit or what B&D calls their bullet drill bits(I think) and that will leave a small hole in the middle, and they would have to be modified a bit to give you a flat bottom. You may be able to get away with a 4 flute endmill by using a drill bushing in a jig, but that could get a little costly and you might be better off subconstracting it out.
Harold & Susan Vordos wrote:
Reply to
James P Crombie
Plus there's a good chance that the end mill will come uncorked out of the chuck - as you say, drill chucks are not designed for this use!
Even running a horizontal milling machine with an end mill in the spindle, where the setups are pretty rigid, one can still not depend on the hole being any particular size when plunging. I don't do this unless I'm just spot facing something.
Jim
================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================
Reply to
jim rozen
|Marty | Drill your 7/8 hole with a regular drill to the proper depth.
Hard to do that when the hole is only 1/10 inch deep.
| Then |uses a reground 7/8 drill with flat bottom. It will need a relief gash |in the center to enable it to cut properly and I would put a small |radius on the corners of the drill to prevent chipping. |at this url the second pic from the bopttom shows a bottom drill |
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|> I have to drill a number of flat bottom holes, 7/8" diameter and 1/10" |> (.1") deep in some 2/10" (.2") thick aluminum. Is there a source for |> flat bottom drill bits of this size that will fit in the 1/2" drill |> chuck that's on my drill press? If there are no bits of this size with |> a turned down 1/2" shank, can an adapter be purchased to go from the |> 7/8" bit to the 1/2" chuck? Thanks for any help. Marty |> | |-- |-------------------------------------------------------------------------- | |James P Crombie | |Summerside Machinist |Prince Edward Island Amateur Astronomer |Canada 3D Designer | |E-mail snipped-for-privacy@pei.eastlink.ca |Astronomy webpage
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|Rhinoceros 3D webpage
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|Mirror Grinder page
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|-------------------------------------------------------------------------- |
Rex in Fort Worth
Reply to
Rex B
What the
Well unlike the bozo's that build tract houses, I bet you have a firm grasp on the concepts of level, plum, and square.
Reply to
Roger Shoaf

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