Drilling metals

[Shoalcove]

I have just aquired a complete set of high quality HSS machinist's drill bits ( at an auction at a severe discount) and would like to get some advise on drilling aluminum and Stainless properly without ruining them. I have a reasonably good Delta drill press but don't know much about proper speeds or cutting oils etc. I tend to burn up bits and realize there must be a better way. Thanks, David

[catamount]

Stainless - rotate the bit as slow as you can possibly go, but apply a lot of pressure and keep on cutting (don't let the bit spin on the metal, you'll end up hardening it). Lubricate a lot. Cobalt bits may be better than HSS bits. When everything is right, it cuts like butter, which is truly amazing.

Aluminum is generally much less of an issue, it's so much softer and eaiser to cut. You want to keep your bit clear - don't let it get clogged up with cuttings.

That's been my experience, but I'm hardly an expert.

Tim A.

[Zach]

For stainless, you really can't go slow enough... or put enough pressure or oil on it. When the chips go blue, stop and take a break for X seconds out of every minute. Somewhere around here the cutter will smoke the oil off.

With aluminum the chips get sticky, and melt if you put to much pressure and speed on it. Not real cool because a gummed up cutter is as good as dull, which makes more heat. Oil a lot... and break the chips.

When you are countersinking, go even slower. It sounds like you are grinding rocks, and that chatter gives scallops to the surface. The softer the material the deeper the gouge.

Always clamp the work, even if its a small job/hole. Drill presses like to throw stuff, and hands move the work. Center the work under the bit, lower the quill so the bit is where you want it (machine off) on your center punched mark. Then clamp it. Vices are really really nice to have. You will want some precision machined stock, and a couple of big C-clamps, so your hole remains perpendicular to the surface of the part you are machining... if your cutter is bigger than the hole in the table (Hole saws...)

For precision, when you clamp the bit in the chuck tighten it down, start the motor and flip it back off. Get up close eye level as its slowing down and you will see the side to side play where it is not centered. This is important as the tip will wander around as the hole starts, and the hole will wander. Loosen up, rotate the bit a touch and tighten the chuck, look at it again. (Cheap chucks can be quite bad...)

Use the shortest bit that will get the job done. Shorter = less flex. Less flex means a straighter hole and less wear and tear on the bearings.

Buy a good center punch, the spring loaded ones are nice.
Centering bits don't technically require a centerpunch on a drill press, BUT you will need the center punched mark to get things situated on the table and clamped down. Use a centering bit prior to the start of any hole you want perfect, then switch over to a twist drill. Trying to start a regular twist drill without a center punch wears out the tip, and a worn tip wanders... and without a centering drilled hole the flexing of the bit bores an angled hole. If precision is required consider drilling with a smaller bit, and then reaming the hole to correct size for as close to perfect as your going to get from a drill press.

For laying out lines, a sharpie works. Rough guess where you want color... then I use my dial calipers to scribe the line through the markers ink, instead of scribing the surface.

Slow with a lot of pressure is best. Break your chips by letting off on the pressure until the cutter cuts the chip. Make short spirals, these chips carry heat away from the cutter. If you have shop air, all the better... If not a chip brush works too. Clear them out as they start piling up. When you get deep into a hole, the chips back in the flutes of the bit, and trap heat. Pull back out, blow off... oil, and keep on going.

I like Rapid Tap for a lube and cooling oil, its good for tapping too. Use lots of oil. If you are making smoke, break your chips pull out and hang for a few seconds till things cool down. Go back down, and repeat. This is called pecking. Its not only easier on the bit, but it gives a more precise hole that wanders less.

If your cutting tip has blued, you have lost the heat treat and will have a very dull cutter. If it is smoking, squeaking, and otherwise protesting stop and oil it down, give it a few seconds or a minute before continuing.

(Resist the urge to put a pipe on that lever... drill presses really aren't meant for hogging out big deep holes. Check to see the rating on the motor while you are at it... a lot of them aren't rated continuous duty, that % rating is the % out of an hour you have to work with. The rest of those minutes the machine needs a break, by design. Go slow! Stuff lasts longer that way.

Your dull bits aren't dead, they can be resharpened. Just have to get ground past the metal that has lost the heat treat.

Good luck. A machinist handbook has a lot of suggested RPM's... but on a drill press I think its best to just play with the belt on the first hole until you find a zen moment. Drilling stainless leads to those... or at least gives you a lot of time to ponder the meaning of life!

[Rachel]

Vices are really really nice to have.

That's what I always say ;)

Kidding aside, wow, there are a lot of good tips in there!

Rachel

[CharlieJ]

From a LONG time ago ex-machinest, I agree- he pretty well nailed it.

[feetup]

Yeah, I would have to agree.
I've made my living in a stainless fab shop for quite a few years now, and Zach pretty much got it as it is.

Perhaps one note on center punching, since stainless work hardens badly, don't strike your center punch more than once. You can prick punch to help you locate the center punch, but then use a good heavy hammer and wallop the punch once. If you hit multiple times you end up with a hard spot right in the middle of where you want the hole to be and even a center drill will want to wander.

I also am a fan of Rapid Tap for stainless. Lots of it!

Tim J

[Shoalcove]

Thanks for all the good advice. I'll print off the tips and put them in my shop. I'm no machinist but there are times that I drill metal and I'm tired of ruining bits. I'll get some Rapid Tap and a center punch.
I've used Cobalt drill bits before. Some of the nicest bits I've ever ruined.
The new set is some HSS unobtainium alloy donated to a fundraising auction by a specialty industrial supply house. There is a pretty good selection of bits 1-60, A-Z, 1/16-1/2" in the set. They are a rather funky deep blue color that I'll try not to turn bright red!
Best regards,
David

[Zach]

Thanks guys... Gotta try and pull my weight around here!

David,

Don't leave out the Center drill!

If memory serves I used to use #4 center drills with a 60 degree countersink.

Zach

[Shoalcove]

Thanks Zach, sadly I've never heard of a center drill. Is that a specific style or just a smaller drill to start the hole? It's grand to display my ignorance yet again...
Best regards,
David

[Quetzalsailor]

Perhaps a sage will tell us what the difference is between cutting oil and WD40 or motor oil for the purpose of lubricating cutting tools. I recall dad's cutting oil would sort of foam when sprayed.

Using cutting or, as I do, any oil that comes to hand (even dipstick oil(!)) certainly makes drilling easier, faster and less likely to ruin the bits. Ditto for sawing; I roughed out a new partners trim ring in 3/8" aluminum, spraying WD40 every 1/2" or so. Failing to spray was rewarded by chatter, filling the blade with aluminum, and no progress.

I've taken to buying the gold-colored bits which are touted to be harder and longer lasting. Even after gross overheating in stainless, it was still adequately sharp. Many of these are shaped with a second step which aides in getting the hole started where intended.

[Summersdawn]

I beleive cutting oil is oil/water emulsification. The oil lubrictes, and the water cools, which would explain the foaming.

Any oil is going to be better than no oil, so if you don't have cutting oil, but WD40, I say go for it.

[Zach]

A center drill is very stiff very short cutting bit.

Mcmaster Carr #2925A56

If you notice, it is a double ended tool. In addition to that, each end has 2 cutting surfaces. The first is at the point, the second is a countersink. On a milling machine you can dial in the diameter of the countersink using the scale on the quill. A drill press, you just have to go slow. Countersinks have different angles, and in a production setting can either be used to deburr the part... prior to the hole being drilled! Or, if you want a flush fastener... or will be driving in dowel pins.

A spotting drill is used for starting holes too. Very short and very stiff. No countersink, and only one end has a cutter. I don't think many guys use spotting drills anymore.

As far as cutting oils go, I like Rapidtap. WD40 will work, so will kerosene, and motor oil. About all you want to cut dry is bronze and most plastics, something... anything... is better than nothing on everything else. Really low durometer plastics (gooey urethanes) like a water and dish soap mix. Stay away from aersols, and use oil cans or brushes. Less gets in the air and in your lungs... makes it a lot easier if you ever want to paint something in the shop too.

If you mix in enough soap you can dry off the table with shop air, and the phosphates in the soap will keep your tools from rusting till you get some oil on them. So long as the humidity isn't high, and the part is out of the rain... straight dish soap will keep them from rusting. CHEAP Toilet bowl cleaner with phosphoric acid is also the easiest way to remove light surface rust. (But its gotta be the purple, that is a color that doesn't exist in nature its so purple.... Grin!)

Emulsions and liquid flood cooling are overkill for a drill press in my opinion. If you are removing enough material to need them, the drill press isn't going to last long. Until you get through the part, its spinning a bit in a bath tub, slinging all over. (Enclosed CNC is a NICE thing.) I've used both, but for manual machining my preference is an airline an can of cutting oil. Bonus if it has a plastic spout as you can touch it to the spinning bit and hose it off.

[Shoalcove]

Thanks Zach,
I'll look for one of those to add to my tool kit. I'll likely pass on the CNC machinery; I struggle with a drill press!
I appreciate all your help.
Best regards,
David