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02-26-2006, 05:41 AM #1
I know you gentlemen are professionals and this question will seem almost foolish but Machinists are far and few and you guys are my tutors... =) What is the best way to drill a 1 inch hole in Aluminum plate between 1/2" and 3/4"? Do I predrill with 3/16? Do I increase drill sizes until I reach the desired size? Do I slow down the drill speed as the bit gets larger? I drilled a few holes of this size and even with the work clamped tightly and slow speeds with lots of cutting fluid the big bits don't curl off the material, they seem to chip it off. Also there is a lot of shaking going on. I'm using regular twist bits and the 3/4 has a slightly reduced shank. Thanks much!
02-26-2006, 07:11 AM #2the big bits don't curl off the material, they seem to chip it off.
Drill a 1/4 hole, then a 1/2, and then the 1" at the slowest speed your press has should drop through like butter with nice curly chips, don't worry about cutting fluid, maybe a spray of WD-40 if you want. If the workpiece is clamped good, push that drill right through with heavy feed.
02-26-2006, 08:19 AM #3
First....I'm assuming that this is a drill press job. A 1" drill requires some torque to drive, even in AL. The workpiece must be clamped and/or blocked securely. You must have the rigidity in the machine to hold everything safely. You AIN'T gonna drill this hole on a $39 HF dp. If I was going to drill this on my big Barnes drill press, I'd devote more time to setting the job up safely than I would to drilling the actual hole.
As far as pilot drills....I'd drill a 5/16 or 3/8 pilot hole, then blast the 1" drill thru. When I try to step up to the size (1/4 to 1/2 to 3/4 to 1") I wind up with the drill snagging or rifling (climbing up the flutes of the drill). The pilot drill wants to be just bigger than the thickness of the web at the point. That allows you to keep enough thrust on the drill to hold the workpiece down and cut with full control.
And as far as the shaking: Probably a dull drill, could be a bent drill, could be chatter from excessive speed.
If you're drilling this on a milling machine, the same princeples apply.
Good luck, and WORK SAFE!!!
02-26-2006, 08:29 AM #4
" the big bits don't curl off the material, they seem to chip it off."
Hans is correct but it is also caused by not enough feed.You need alot more pressure to push a large bit.If you dont cant feed it fast enough then a pilot drill will do.But you still need to push it.Probably a feed of .012 to .018 per rev. on steel and more on aluminum.
02-26-2006, 08:35 AM #5
Use an annular cutter. Like a Rotobroach. It leaves a slug and doesen't turn all that material into chips. Like a very heavy duty hole saw. --Doozer
02-26-2006, 09:52 AM #6Drill a 1/4 hole, then a 1/2, and then the 1"
Also there is a lot of shaking going on
On a 1" drill, I would measure the web, and then just drill a pilot slightly larger, and then stuff the one inch in.
Do I increase drill sizes until I reach the desired size? Do I slow down the drill speed as the bit gets larger?
If your thinking I cut 'X' material at 1200 rpms and 'Y' material at 600 rpms, your going to eat a lot of mills/drills/inserts. If its stuck in your head 'X' material at 80sfm with HSS and 'Y' material at 600sfm with carbide, then your pretty far along the learning curve, and will save yourself a lot of headaches in the future.
By asking the question of "do i need to slow down as the bit gets larger" it seems that you have an understanding of whats going on, and yes, for the bigger drill you do need to slow the RPMs compared to the pilot drill.
As for the chips, all I can say is that big drills suck. Its not that often that you'll see two nice shiny curls come off of one. In my case part of it is probably that big drills are expensive so I buy buy the cheapest piece of crap I can find.
02-26-2006, 09:56 AM #7
Try drilling a pilot hole that is slightly smaller than the chisel edge, ie., the non-cutting point of the drill. Then, put the final size drill in and drill down with firm pressure until the drill has made a full diameter countersink. Then, if your machine lacks torque to continue, then you can use intermediate drills. The countersink at the top is important to steady the final drill. If you can prevent the chatter pattern from getting established, it should drill smoothly provided that the feed pressure is adequate.
Edit: sorry Bobw, you was a postin' while I was a typin'
02-26-2006, 10:14 AM #8
1) exactly how fast the one inch drill was
turning, in rpm,
2) how many hp the machine had,
3) what kind of cutting fluid were you using?
02-26-2006, 10:30 AM #9
No pro, but I have noticed that it is not uncommon for the drill to shake a bit until it gets into the hole all the way, depending on material, size etc and accuracy of sharpening.
I also would never step drill, that WILL cause all sorts of shaking. The drill does not want to establish its center when only the outer edges are "catching" any work. They almost certainly won't both hit at once exactly the same (especially if drill has ever been hand sharpened), and so there will be a bending and sideways force that will cause chatter.
Shouldn't need any larger pre-drill than the larger drill's web, if that much. If your drill press is heavy enough to drive the 1" drill, it probably is heavy enough to take the 1" directly from the solid with no pre-drill, but the location may be better if you use the pre-drill.
Something that hasn't (I think) been mentioned is that your 1/2" pieces are so thin that the cone of the 1" drill is hardly established into the work before it is poking through the other side. The 3/4 would be better.
That may make it similar to drilling sheet metal, and changes the problem a bit. Drilling thin material normally gives problems. With such relatively thin material you WILL have problems with step-drilling.
Any particular reason you cannot use a hole saw? Aluminum often works fine for me with a hole saw, if the DP can be slowed enough. I assume you have no access to rota-broaches (I don't either).
Also, what alloy aluminum ? Some alloys don't seem to make curls, just chips.
02-26-2006, 11:42 AM #10
Why not just use a hole saw?
02-26-2006, 12:17 PM #11
DOOZER nailed- annular cutter is the way to go, with either Cool Tool or stick wax for lube.
It takes a big drill press to run a 1" silver and deming bit- anything that cost under $3500 new is not gonna cut it.
A big old Clausing, or one of the made in USA powermatics, or a bridgeport.
Anything smaller, including Mike C.s $1000 chinese wilton, will just twist the chuck out of its taper, when you put those kinds of loads on it, unless you go so slow its not worth it.
Bite the bullet, buy a Jancy or Rotobroach annualar bit in the size you need, and zip thru those holes.
02-26-2006, 12:20 PM #12As for the chips, all I can say is that big drills suck. Its not that often that you'll see two nice shiny curls come off of one. In my case part of it is probably that big drills are expensive so I buy buy the cheapest piece of crap I can find.
02-26-2006, 12:29 PM #13
I'd simplet set it up in my (fairly husky) drill press pilot drill about 5/32" and follow with the size dril.
About 2/3 of the thrust it takes to make the drill penetrate is used to force the chisel edge (the web) into the work. Thus for most materials you really don't need to step out in fine increments unless your drilling machine is short on power or rigidity. Stepping out usually means you'll have a problem with lobing or chatter or both. If the chisel edge is forced to center by a slightly smaller pilot hole the drill steadies and is more likely to drill a clean hole.
You can drill a 1" hole in aluminum at about 1000 RPM but the chips might try to flog you to death. 500 RPM or so might be a less "dynamic" spindle speed to run a largish drill in aluminum.
If you have teouble with lobing and chatter drill through about 3/4" of wood first. The wood will act as a polit bearing.
One last thing, "back off" (stone a 1/64" wide flat) on the cutting edge so the edge angle is nearly parallel to the dirll's axis. This will make the drill a little harder to hand feed but much less likely to grab and spiral down following the helix on break-through.
02-26-2006, 01:38 PM #14
Ries is right. 1" hole in aluminum with a typical drill press?... ain't gonna be fun with anything less than a 5ft Fosdick radial or a good mill (and I mean at least a Bridgeport 2J or similar size). Make sure the bit is sharp, make sure everything is tight, run fast, feed hard.
Silver and Deming bits are kind of a cruel joke that way. You think because you can chuck that thing in your drill press, you can now bore big holes with ease. Maybe in balsa wood or styrofoam. Your press came with a 1/2 or 5/8" chuck for a reason. That is the minimum speed the spindle will run and it may not even have enough power to pull that size bit properly.
The problem is further compounded. Assuming the cheap Chinese chuck that came with it works at all, the drill is probably going to try to spin (unless the bit has flats, in which case it will probably spring the chuck). Chances are your #2 Morse taper drill press chuck is going to pop out if the bit chatters or grabs. Best bet for work like this is a Morse taper shank bit. I will NOT slip on you. They are available on Ebay for nearly nothing. You will, of course, have to have a sufficient spindle taper on the machine for that selected bit and a 1" will have at LEAST a MT3 shank.
As has been mentioned, you need a SERIOUSLY stiff machine to keep chatter at bay. You will also need to be running about 800 or more rpms for proper surface speed (300sfpm) to get a nice smooth hole. Without 3+hp on the spindle to pull a properly fed cut at that radius, this hole is not going to be any fun.
I agree with a clearance hole only large enough to prevent binding of the web. Step drilling will be a PITA. Reamers work great this way, but drills will grab and chatter.
I would not even consider a drill press for this job. This would be set up in either my Van Norman bridge mill at home or the big Van Norman 22L at work. 3/4" hole and a boring head would be a strong consideration, too.
You might try upping the speed and feeding enough to just keep from stalling. Just keep and eye on both the bit lip corners and the motor. This is likely to burn up either one. If the corners of the drill bit even begin to discolor, slow down. Put and hand on the motor about halfway through and see how it is going.
02-26-2006, 01:47 PM #15
Using the equipment you have now...
On the drill press clamp the aluminum between two pieces of steel that are at least 1/2 inch thick and step drill all three pieces at once. This way the steel acts like a guide and support. When finished drilling, the edges of the aluminum hole will be nice and crisp and may even need to be deburred!
02-26-2006, 02:05 PM #16
I have several large size 3-flute core drills and find them good for this type of task. The one in the picture is 25mm dia. on a 2MT shank, it gets used most on an ancient Myford ML7 lathe to open up holes to enable a boring bar to get in. They are very good for enlarging and finishing existing holes and I find they greatly reduce chatter and vibrations. The others I have are used on the BP, using a R8-3MT adaptor and running into about a 5/8" diameter hole.
02-26-2006, 04:40 PM #17You must be doing something wrong then, I have a pair of nice shiny curls come off all of my properly sharpened drills,
02-26-2006, 05:39 PM #18
here is how you determine proper rpm, or at least a good starting point in most cases.
sfm*3.82/diameter of cutter=rpm
for most aluminium with a 1 inch hss drill:
300*3.82 =1146/1=1146 rpm
for mild steel:
90*3.82=343/1= 343 rpm
write this down or memorize this formula. It will almost always work, unless you have a less than ideal setup.
02-26-2006, 05:43 PM #19
I drilled a 1" hole in 5/8 aluminum just last week. I drilled a 1/4 inch hole first then followed with a silver and deming 1 inch drill bit. I ran the drill press at 400 rpms and really put pressure on the down feed. Worked great and no it is not a huge drill press, just a Craftsman with a (supposely) 1 hp motor.
02-26-2006, 06:57 PM #20
One can trade off speed to reduce chatter on
a less-than rigid machine. For a light drill
press I would start somewhere around 100 rpm
or less if chatter were a problem.