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02-25-2006, 10:30 AM #1
When you use an end mill to "drill" holes, how much do you adjust your feeds and speeds from what is given in the book? Is it best to always rough the hole with a smaller drill first? I need a 9/16 hole 2" deep with a ball end mill profile at the bottom and good finish on the sides in 1020 Carbon Steel.
02-25-2006, 10:38 AM #2
As always, a lighter cut tends to produce a better finish.
I always lock the X and Y axes on the mill before drilling with an endmill.
Also, the knee is desirable over the quill for smooth even feeding to a predictable depth.
I recommend making some test holes in a piece of scrap material to test your setup. On the lathe, single-point turning one can fool around with tool geometries and finishes during roughing cuts...when making holes you don't often get a second chance.
02-25-2006, 10:53 AM #3
What Matt said and if driling the hole on an angled surface, a ball end mill will work.
02-25-2006, 11:45 AM #4I need a 9/16 hole 2" deep with a ball end mill profile at the bottom and good finish on the sides in 1020 Carbon Steel.
..Drill with 17/32 to within .030 of final depth. Make sure the drill point is right.
..Grind the OD of a ball nose endmill to .530 Dia behind the ball nose so the flutes never touch the reamed hole.
..Finish the bottom to depth.
ohh...and End mills are END MILLS NOT drills. Ok to plunge in to minimal depth with an End Mill, but NOT this deep.
02-25-2006, 01:19 PM #5
I've used end mills to "move" holes that are slightly out of the required location.
It helps if the hole is undersized, but it's easy enough to sleeve it once it's in the right place. Of course, there are lots of situations when it's not appropriate to do this.
02-25-2006, 01:37 PM #6
Hey Scott, you wouldn't be making something neat to add to the benchresting world, would you? I sure enjoyed testing that rest and was VERY sorry to have to pass it on to DWS. Did you get to read the finished article?
Charlie the Frog * [img]tongue.gif[/img] *
02-25-2006, 02:09 PM #7
End mills are sometimes used as drills in a process called 'plunge milling'. These articles will give you an idea how it works:
However interesting these artices are, none really address what you're trying to do.
IMO, the easiest way to generate a half circle at the bottom of a hole is to drill / bore the hole to the depth of the straight section. Then mill the bottom profile using either an inserted cutter or a solid carbile ball profile cutter and a rotary table.
Choose a tool with a reduced neck and a diameter less than 9/16. Center the rotary table on the mill, indicate the 9/16 hole to center, and figure the tool offset need to generate the hole. Raise the knee .100" and take the first 360* cut. Continue raising the knee on each cut while bringing the cutter closer to centerline. This will rough out the hole and allow you to finish with a 9/16 ball end mill that only has to bring the rough shape to final form.
02-26-2006, 07:33 PM #8
I drilled the hole with a 1/2" drill fist then went behind it with the 9/16" ball mill and the holes turned out good.
02-26-2006, 09:02 PM #9
I use end mills for sizing holes very often.
A hole pattern that calls for a counterbore.
Drill the holes, locate a proper size end mill for the c-bore (preferably a four flute) and have at it.
Multi- flute end mills are your friends but, they must be center cutting unless a pilot hole is in place.
02-26-2006, 10:57 PM #10Also, the knee is desirable over the quill for smooth even feeding to a predictable depth.
I agree with your post except for this statement.
When you unlock the knee to feed vertically, the knee shifts away from the column by an unpredictable amount and in an unpredictable direction. So your tool axis is no longer colinear with the axis of the hole in the workpiece. And the workpiece may shift position unpredictably as you feed the knee up, because the mating surface of the knee can shift on the column. Add to this the fact that you're applying rotational torque to the knee from the feed screw, and motion from your hand on the feed handle pulling the knee back and forth.
02-27-2006, 02:54 AM #11
Last weekend I drilled some holes in steel with a 3/16" two-flute center-cutting endmill and ended up with oversized and taperd holes. The oversize was on the order of .015. The holes were about 3/8" deep. I think what happened was that the endmill was not stiff enough. As evidenced by the "crunch" noise I heard once in a while, I think chips were getting caught under the lands and driving the endmill off axis. Since, unlike a drill, the lands of an endmill will cut, the off-center endmill ended up shaving the hole larger. Bending stiffness goes as the 3rd power of the size scale (scaling both diameter and length equally), so an endmill twice as big would be 8X as stiff. Hence, I'd expect the bigger the endmill, the greater chance of success.
02-27-2006, 10:08 AM #12
I have not tried this, but I see no reason you could not grind a "D" bit reamer to do this, as long as you could tolerate a small defect at the very bottom of the hole- and can drill the depth close enough. You would want to start the hole with a regular reamer.
How to shape the D reamer? If you tolerances allow a freehand grind would be the fastest. An alternative would be a form tool to establish the shape, then some careful grinding.
02-27-2006, 12:34 PM #13
Though not hole "milling" I have read somewhere that plunge milling is efficient when removing large amounts of material. Apparently this elliminates the side loading of the cutter reducing breakage. Use this to rough in, then mill in the conventional manner.