Drilling metal, very novice questions

[Joel OF]

Two very novice questions about drilling metal with an electric hand drill folks...

 

What sort of drill bits are best for regular drilling? I had to drill a 8mm hole in some 10mm plate the other day and was recommended HSS bits but they only got into the metal a few mil and wouldn't go any further. I gave up and punched it in the end.

 

Is there any particular type of hole saw I should look out for if I want to drill a 2 inch hole in some steel pipe that's about 3mm thick and a piece of plate that's 6mm thick?

 

Cheers

[Rich Hale]

If you are trying to drill steel that has been heat treated you will dull more bits than you wish to buy,.There is information in the forums about annealing and how to tell if steel needs that,  Will take you a while to find everything you need to know but its worth it.

[Laertius]

I do not want to hijack this thread, but do have one question:  I was making a punch/drift plate out of 1/2 leaf spring steel (2005 ford ranger bottom leaf -- its what I had).  without any annealing / normalizing, I was able to lay out all the holes and drill pilot holes  with a 1/8 hss bit -- with the gold carbide coating.

 

So all went well, until I went to bump up the size of the holes (1/4, 5/16, 3/8 etc).  The drill just skated (drill press on lowest setting).  I then tried to anneal (heated to non magnetic and left to cool in dying out forge.  There seemed to be no appreciable difference in the hardness of the steel, and I am still stuck with a plate with a lot of 1/8th holes in it!

 

SO my question is:  Why can I drill a 1/8 hole no problem, but a brand new 5/16 bit, on the same drill press, using same lube and speed just skates and dulls!??  I have drilled many holes is mild steel....and never encountered this......  And yes Rich, I understand I am using unknown steel, and I have read the stickies etc.  What I am asking is why 1/8 holes drill like butter, but as soon as I try to bump it up it is impossible!

 

Thanks ......and please forgive any thread jacking lol!

[ciladog]

First, that gold coating is not a carbide coating it is either a titanium coated drill or if a dull gold, it could be a cobalt drill bit. 

 

Cobalt drill bits are not made of pure cobalt.  They are made of a steel alloy with 5 to 8 percent cobalt. The 5-percent alloy is known as M35 grade, and the 8-percent alloy is M42.

 

The cobalt increases the strength of the steel and makes it more heat-resistant.  Some cobalt drills will withstand temps up to 1,100 degrees F. 

 

Cobalt drill bit will drill in much harder material than will HHS, you can apply greater pressure, and will withstand the heat.

 

So you didn't say if your 5/16 drill bit was HHS, titanium coated, or Cobalt. 

[John B]

A good quality HSS drill bit should work fine for most steels in their normalised or as bought condition.

 

You can purchase Carbide tipped, cobolt or stellite drills for harder materials,

 

A lot of the problems are because the drill's speed is too fast, and overheats the HSS drill bits thus dulling them, the smaller the drill, the more rpms you need, there are charts you can source (eg http://www.google.co.uk/search?q=drill+speed+and+feed+chart&hl=en&rls=com.microsoft:en-gb:IE-SearchBox&rlz=1I7ADRA_enGB434&tbm=isch&tbo=u&source=univ&sa=X&ei=jMJQUYblM-Kc0AXGuIHgCw&ved=0CDAQsAQ&biw=1024&bih=556) for speeds for diameter and materials to be cut, but bear in mind these are usually for pillar drill or other industrial drilling machines.

 

Another is incorrect drill point grinding/angles, and specifically rakes, negative rakes rub and do not cut, lipping or grinding the edge reduces the tendency for the drill to grab upon exit, and is useful when drilling brass or cast iron.

 

Once they are cutting, steady pressure is required, and constant amounts of lubrication can assist in keeping the tips cool.(except in the case of stellite drills where the heat generated assists cutting)

 

Drilling has been well covered before on the site, try a search.

 

With regard to hole saws, they again need to be of a good quality and suitable for using on steel, and speed and lubrication/cooling again is a critical factor in their use. In the UK these are readily available try RS components or Buck and Hickman, Enox used to be the most recommended, BUT make sure they are rated for metal.

 

Trepanners can be sourced or made for cutting large holes in sheet or plate, but are best used in pillar drilling machines as opposed to hand held units, clamping of the sheet is also essential for safety , place plate to be cut on top of a piece of timber so as not to go into machine's table.

 

this is the last time I edit your posts, Please stop using itallics all the time its annoying and very hard for some to read

[Laertius]

thanks,  i will check what the coating is--- they are the mastercraft maximum bits from canadian tire

[Joel OF]

Cheers John. I've now seen a few YouTube videos of people using your low speed and lubrication method and drilling with ease, I was definitely taking the wrong approach. You're right I should have done a search, it didn't cross my mind to do a search because I thought I was being incompetent and no one else would have encountered this problem (or have admitted to it) so I'm glad that others have asked similar questions!

[Dale M.]

One thing I did not seem mentioned, is emphasis on procedure.... After locating hole with center punch, first drill a pilot hole  of about 1/8 inch or less... Then step up to larger size drills (maybe 2-3 sizes)  till you reach desired size.... The point of any drill in not really a point but a sort of chisel shape and if its to broad it will not penetrate and actual cutting edges of bits will not be able to remove metal.... Result will be a "cooked" drill bit....

 

 

 

A drill bit with proper pressure applies should  produce spiral shavings... A drill bit with not enough pressure will just over heat drill bit point....

 

 

And small drill bits need high speeds to drill properly, and larger drill bits need slower speeds to cut properly....    So as hole sizes increases reduce drill motors speed....

 

A dull drill bit is not your friend.... Once you have takes cutting edges off bit or damaged point (over heating) its next to useless..... A drill sharpening tool can be your best friend...

 

Dale

[Dale M.]

thanks,  i will check what the coating is--- they are the mastercraft maximum bits from canadian tire

 

Not the very best of quality (Chinese) but workable if use properly....

 

Dale

[evfreek]

When I was just beginning, I received a lesson in drilling at our blacksmith conference's workshop.  We were drilling holes in a spatula handle that we had just forged.  The drill just spun.  It was in a drill press, and someone before me had just successfully drilled a hole.  The instructor asked me if I had quenched my piece.  I said yes, but mild steel doesn't harden.  He replied, either it does, or that isn't mild steel.  He said this could be a teachable moment, and asked me to heat the bar to critical and just let it cool in the air.  This worked just fine.  I still have the spatula.  Then, he gave a few explanations that I won't bore everyone with here.

 

As for the leaf spring, I noticed that even cooling in ashes can be too fast.  This stuff can air harden.  Someone on this forum or another suggested a subcritical anneal.  Heat to below critical, for example, dull red.  Then allow to air cool.  This will leave the somewhat red hard steel about RC 20-30 or so, and you can just drill it with a decent drill.

 

Some steels work harden.  I have had trouble even with mild steel (really, hot rolled A36, which is probably not mild steel).  Drill these with lube before they work harden.  If you are broke, use Crisco.  If you are really broke, use fat skimmed from a stew.  A little goes a long way.  Edible oils really outperform used motor oil, so much it is not worth trying the motor oil.  If you already work hardened the piece, there are tricks that you can search for on this forum, so I won't bore everyone here.

[ptree]

To drill leaf spring, my friend who is the 3rd generation owner/operator of a Truck spring shop offers the following:

All of the Triangle brand springs he buys are preheattreated, and are 5160.

He uses a big old camelback drill press, that his Grandfather bought, and runs 90 rpm max, with industrial quality HSS drill bits, keeping the feed steady by using the feed on the machine.

He does not predrill a pilot hole for a hole of say 5/16" just centerpops the location and drills, using black oil.

 

I buy virgin spring stock for him and on the ones for my power hammer, I drill holes just as he does with no issues.

I cut the spring stock as recieved from him in a 4x6 bandsaw using a bi-metal blade with no issues other than a little slow to cut.

[Rich Hale]

This really a great thread,,however let me offer another thing.

Anything we cut,,wood metal. plastic wotever has needs that we must meet to do that. Surface feet per minute is the key. Each tool has a speed that works best for a specific item it is used on. In this case each drill bit has a speed it will do its best work in wot we are drilling. Your hand drill met that speed correctly for the small bit,,,,when you changed to the larger bit you exeeded that bits ability to cut the same metal as the little one did. There are charts that give you the speed in revolutions per minute for drill sizes used for metal. If you look at one of the charts you will see that as the  drill diameter increases the speed in rpm's is lessened. You can do that with a variable speed hand drill alittle bit by guess...simply keep the drill bit turning as slow as the drill will go. That is really tough for me to do, as soon as I get started I have an urge to give it more speed.

This surface feet per minute applies to sanders, grinders,,,just about anything we use to reduce size or makes holes in. Most drill presses, lathes and milling machines have a chart on them to show wot  the speed is in rpm's with each of the belt postions or machine settings. Those and a chart to translate to bit size needs or material sfm speeds.

[ThomasPowers]

Having drilled .5" (12.5 mm) holes in 1/2" (12.5 mm) steels with a hand cranked Cole drill before I can say *Speed*, *Pressure*, and *Quality* of drill bit makes all the difference!

 

Titanium Nitride does not necessarily indicate a high quality bit.  Lots of cheap trash bits have been so coated to make them sell.

[Joel OF]

Cheers for all the pointers folks. Thanks for the pics Dale, love the top one, it's like the drill bit version of the Vitruvian Man!

[ptree]

A Machineries manual has speeds and feeds for about every possible situation. I commend it to all.

[Chinobi]

Kurgan thank you for posing this question and everybody else thank you for the replies, i have googled this topic a few times myself because i am notorious for breaking my little drill bits (materials vary from sterling, to brass, to mild steel, bits come from HF, micromark.com, or elsewhere.  hard to find good quality drill bits that are really small).  looking at the replies i can see that i am running my drill press glacially slow relative to the size of the bit, but it seems counter intuitive to run it really fast with drill bits that are so tiny (0.04"-0.1" diameter, give or take).  but i will take a look through those charts and see if i can find a guideline, or just extrapolate a bit and test it out.

[Frosty]

Oye! Drilling holes properly is covered in metal shop I. . . Oh wait there isn't any metal shop classes any more are there. <sigh>

 

Drilling with a hand drill, sounds like you had too many rpms and not enough down pressure. Slow the drill speed and hog the pressure. How much to hog it is a learned skill, you're ears will tell you more than your eyes. A nice curl of cuttings is visual confirmation but is behind the cutting.

 

Piloting is an important skill and stepping 1/4"-5/16"-3/8" is sure to fail unless you're using really expensive bits. If you have a drill press 3/8" requires no pilot. heck, if you have a good press 1/2" requires no pilot. how good is good enough for a press? The worst two things to happen to a drill bit are: 1, too fast and 2, stalling. If the bit stalls the only way to remove it without damaging it is to stop the motor and reverse it by hand. If you just lift the feed handle you will break the edge and the bit's done till resharpened.

 

A proper pilot hole is no larger than necessary to allow the bit to rest on it's cutting edges AND cut just enough to prevent stalling. The general rule is NEVER less than half the cutting edge in contact. Soooooo, stepping from 1/4" to 5/16" has 1/16" of cutting edge in contact. What happens is either rolling the edge making it a friction drill so it gets HOT, the drill runs it's temper becoming soft while the stock gets work hardened. Failed process.

 

Another result of too close a step is simply stalling one edge snapping it so the bit only has one cutting edge so it stalls and now you have a non cutting bit. If you continue you have a friction drill, see above results.

 

Okay, too close steps is a prime way to stall bits but the most common is on break through. When you reach the far end of the hole the stock becomes thinner and the bit being pointed breaks through in the center first so the cutting edges are now contacting less and less of their length so it grabs (stalls). There is a sound change as the bit begins to penetrate the far side, let off the feed and let it just baby it's way through.

 

If you can find a beginning metal shop book all this stuff is covered. If we could get together in person I could run you through this faster than it takes you to read it, let alone me write it. Drilling, your most important organs are your ears, then the feel through your hands, THEN your eyes.

 

Sharpening drill bits is another lesson.

 

Frosty The Lucky.

[Dogsoldat]

Little rusty but the formula  for cutting speed I was taught was

 

  4 x cutting speed (100 give or take for HSS in mild) / Diameter = Rpm

 

therefore

 

4x100/ 5/16" = 1282rpm 

 

adjusted up or down dependant on feed rates, tool rigidity, work holding  chatter etc.

it gets you a  a pretty good ball park most of the time.  Hope it helps

[Dogsoldat]

Little rusty but the formula  for cutting speed I was taught was

 

  4 x cutting speed (100 give or take for HSS in mild) / Diameter = Rpm

 

therefore

 

4x100/ 5/16" = 1282rpm 

 

adjusted up or down dependant on feed rates, tool rigidity, work holding  chatter etc.

it gets you a  a pretty good ball park most of the time.  Hope it helps

[Daniel.85]

I have a big drill press(1.5hp), I understand the pilot hole and web size of the bit concept but any pilot hole just gives me crazy vibration and had damaged a couple bits, I did tests on all sizes and I use lots of cutting oil, good pressure and proper speeds. So I don't do pilot holes anymore, I can sharpen the bits fairly easy anyway and even drilling up to 1" holes I get nice long curls coming out of the hole. Pilot holes can XXXX XX XXXXX

[Chinobi]

thanks for the lesson frosty! looking forward to the sharpening class :)

 

with regard to matching your RPM to the task/tools/materials at hand, if you are not so blessed to have a drill press with a robust transmission or speed control, is it better to round up or down to the next nearest RPM setting?

 

my HF 8" press just has a 6 tiered ratio transmission, so i can only get so close to the prescribed RPM setting.

[ptree]

I do not pilot drill when in a good rigid drill press. If you thin the web a bit then even a big dril like 1" or better will make a good hole. If you have chatter when pilot drill then bigger drill then something is NOT rigid. Either the quill is loose or the work is loose.

[Frosty]

thanks for the lesson frosty! looking forward to the sharpening class :)

 

with regard to matching your RPM to the task/tools/materials at hand, if you are not so blessed to have a drill press with a robust transmission or speed control, is it better to round up or down to the next nearest RPM setting?

 

my HF 8" press just has a 6 tiered ratio transmission, so i can only get so close to the prescribed RPM setting.

 

If in doubt, slower is safer. Slower also develops more torque at the drill bit and is less likely to stall.

 

If I can find my video cam I may take a lash at a sharpening how to. All I need to do is remember longer than it takes to write a note. . . Eh, what's this about again?

 

Frosty The Lucky.

[Frosty]

Chinobi: Going back through earlier posts I see you're having problems with non-ferrous and small drill bits. Welcome to the club. Drilling copper alloys can be a bear, MOTHER BEAR actually. The basic rules of drilling steels will usually lead to failure drilling copper alloys. (CUa)

 

There are a couple basic CUa tricks. Slow rpm. hog the feed. CUas work harden quickly and being good conductors friction heat is taken on by the base metal so it hardens even faster. Hogging the feed causes the chip to part from the parent stock quickly taking the friction heat with it so the parent stock does not harden as quickly. It's also cutting below the surface layer that WAS hardened by the last pass of a cutting edge.

 

Low RPM and hogging the feed will give better results for steels for the same reasons but copper alloys will NOT cut you any slack.

 

Never pilot CUa unless absolutely necessary, if you must use the absolutely smallest pilot you can get the finish bit to start in and still be strong enough to survive. Trying to ream a hole slightly larger is almost impossible, I use torch tip files.

 

Now for the "secret" tip and this was indeed a secret Dad forbade me from passing along till he discovered my Heavy Metal Shop class instructor Mr. Harding was telling everybody. When you sharpen a bit for cutting copper do NOT steepen the pitch, either one, keep them to the gauge. Then comes the secret finish on the sharpening stone, a fine grain Arkansas oil stone, is prime, you should have one in a safe place in your shop. When you finish a bit for steel on the oil stone you remove any wire edge and put a razor dress on the edges. For copper alloys remove the wire edge and with a gentle brush, blunt the edges.

 

Copper alloys tear under a sharp tool, a slightly blunted one parts the shaving cleanly, leaves a clean finish and doesn't break bits as readily.

 

Okay, got it? Hog  the feed, Avoid piloting if at all possible, dress your bits with a blunting kiss. AND I do mean KISS, a bare touch is all it takes. The kiss of bluntness applies to all cutters used on copper alloys, be they drill bits, lathe bits, mill bits, broaches, boring bits, deburring tools, etc.

 

About your problems with Silver alloys. Do they contain any copper? See above, Sterling works a LOT like brass in most any respect.

 

Frosty The Lucky.

[Chinobi]

Thank you Frosty!  thats maddeningly counterintuitive, so very good to know! ill add a fine arkansas stone to my list of stuff to aquire as well, only proper sharpening stone i have is a coarse/fine (325/750 grit) Smith's DCS4, and i dont think that will do well for a drill bit.

 

then again, at the rate they have been shredding themselves sharpening was never an issue! :D