Drilling holes in thick metal

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I am going through my learning curve in using my small drill press and drilling in metal (latest project is to drill 1/2" holes in 1/2" plate).  Most of my drilling time has been spent in wood.  I bought some Dewalt cobalt drill bits that I will use to do this.Is there a set formula/rule-of-thumb about how much I should increase the size of the bits that I use to get to my desired size?  I think I am stepping up too slowly by using every other or every 3rd size bit.Also, how often do I want to use cutting oil?Any advice would be greatly appreciated.Thanks,Brian
Reply:The formula for figuring out RPM is: (SFM*12)/(D*3.1416) SFM is safe to calculate at 60 for most steels and D is the diameter of the tool. so in this case, 720/1.5708 = 458 or 450. If you do not have this option, use the next lowest speed closest to 450. Good cobalt drills are key to longlife and easy cuts.As for the step rule, you can safely start with 1/4 the jump to 7/16 then to 1/2. There is a rule, but i do not recall at the moment. How precise does the hole need to be? Also, remember to use a center drill before drilling the hole. This will prevent the drill from walking (wandering). If you have a big enough center drill, you could actually go ahead and just use the 1/2 if the size is not too critical. If you need to be exactly at 1/2, I would use a reamer.When i started out as a machinist, I bought a book called machinist's ready reference. It has been a godsend. I use it regularly, even after 17 years of machining. If you know anyone in the Navy, they have a book called machinery repairman course, or something like that. It is also a very good book. If you have any other questions, feel free to PM me or email me direct.Tony
Reply:SIR,i read your post on another website,and replied. (practicalmachinist)wlbrown
Reply:Originally Posted by wlbrownSIR,i read your post on another website,and replied. (practicalmachinist)wlbrown
Reply:You don't say what kind of metal you are drilling through. The best drill bits I ever used are the original bullet bits by black and decker. I don't think they are available anymore. I have one half inch bit left and have drilled over 100 holes through half inch 5456 aluminum plate. I do not use cobalt bit on anything except very hard steel. They are expensive and break very easily. Since time is a concern of mine I would use a quarter inch bit and then a half inch bit to drill a half inch hole in steel. The only draw back to the bullet bits was they can't be sharpened and you can not use a starter hole. They have there own starter tip built in. For big holes (anything over 3/4 inch) I use hole saws.
Reply:Dewalt sells those type bits (bullet). they will make quick work of 1/2" plate. As to the cutting oil, flow as much as you can afford. The cooler the bit stays the longer and sharper it will last. I built a recirculating coolant system for my d/p using a 110 pond pump and a catch pan. It makes cheap bits cut well.Millermatic 251Century 180 migSpectrum 625 Syncrowave 250DX
Reply:I've never found a bit from a hardware store that worked half as well as the cheap HSS bits that I purchase from a machinist supply regardless of what it says on a package.  Even the hardware store bits that are labeled as cobalt steel or TiN coated don't work as well as good HSS bits.  They should, but I think the labeling is false.  I've given up on bits from the hardware store and simply order stuff from Rutland Tool.-Heath
Reply:Halbritt Mentioned HSS bits... What are HSS bits?? I boldly ask...I also have I  have a new drill press and am looking to buy a GOOD set of bits...also does anyone have any niffty things you can make for a drill press??? clamps and such...Thanx.. Marty
Reply:High Speed SteelOwner of Welding Wiki,The free wiki based resource for weldor's around the world.http://www.weldingwiki.comWe have cookies!
Reply:HSS is high speed steel. On the shank it will have HS or HSS on them. Cleveland is a good brand. Try MSC. They usually have sets on sale and at reasonable prices.
Reply:thank you very much... now I can sleep...
Reply:Note that HSS bits should theoretically perform less well than cobalt or TiN coated bits.  My point was that even the premium hardware store bits don't work as well as the cheapest HSS ones from a decent tooling supply place.  I once had to drill a couple hundred holes in a thin (1/8") piece of stainless.  I believe the holes were 1/16 or 3/32.  In any case, I went through two or three "cobalt" bits from Home Depot with very little luck.  I was able to drill about 15 holes before the bits would become impossibly dull.  The following day I picked up a handful of HSS bits from Rutland Tool.  I believe they were about $.40 each.  I went back to my task and was able to finish drilling almost all the holes (>100) with a single bit before it got dull.For general purpose use on metal, a set of HSS bits would be desirable.  Learning to sharpen the larger ones is also a valuable skill.-Heath
Reply:Note that HSS bits should theoretically perform less well than cobalt or TiN coated bits. My point was that even the premium hardware store bits don't work as well as the cheapest HSS ones from a decent tooling supply place.
Reply:I agree with Sandy.  And its infortunate because this end the end hurts the consumer.  That ontop of the fact they are trying to do everything as cheap as possible.  Its a never ending story and quality is just going down the shettir. IF it Catches...Let it Burn
Reply:I agree with sandy... people do buy cheapest rather than quality... I have bought a bunch of the $20.00 drill bit index's from home depot.. and I have hardly any good bits that I can use... I do have lots of cool plastic cases that work good for other things... some times I think we ( I ) buy the cheap ones just for the case you can never have enough of those laying around (kiddin).. I kinda consider the cheap bits as disposable... how much would a descent set of HSS bits cost?? also does anyone have a pic or info on building a cooling oil system?? (recirculating)  AZ..... I spent 25 yrs in AZ only miss it in the winter.. 3 years in the Verde valley Thx Marty
Reply:http://www1.mscdirect.com/CGI/NNSRIT...PMT4NO=3591470 a cobalt index from MSCMillermatic 251Century 180 migSpectrum 625 Syncrowave 250DX
Reply:Don't mind me, just adding this to my favorites list RE Drilling.  Originally Posted by orphan68The formula for figuring out RPM is: (SFM*12)/(D*3.1416) SFM is safe to calculate at 60 for most steels and D is the diameter of the tool. so in this case, 720/1.5708 = 458 or 450. If you do not have this option, use the next lowest speed closest to 450. Good cobalt drills are key to longlife and easy cuts.As for the step rule, you can safely start with 1/4 the jump to 7/16 then to 1/2. There is a rule, but i do not recall at the moment. How precise does the hole need to be? Also, remember to use a center drill before drilling the hole. This will prevent the drill from walking (wandering). If you have a big enough center drill, you could actually go ahead and just use the 1/2 if the size is not too critical. If you need to be exactly at 1/2, I would use a reamer.When i started out as a machinist, I bought a book called machinist's ready reference. It has been a godsend. I use it regularly, even after 17 years of machining. If you know anyone in the Navy, they have a book called machinery repairman course, or something like that. It is also a very good book. If you have any other questions, feel free to PM me or email me direct.Tony
Reply:I have a DeWalt drill index with a plastic case that I keep with my cordless drill.  The bits that came in it have long since been tossed.  I replaced 'em with cheap HSS bits from Rutland Tool.  Unfortunately, they don't have a retail outlet here anymore so I can't just run down and get a handful of bits on a whim.  The smaller bits really are quite cheap, even moreso than the hardware store stuff, but they still perform better.Rutland Tool currently has a sale on a 29 bit index in a metal case.  That's 1/16-1/2 in 64ths.  It's $8.95 and they say it's their "value line".  I've used their value line, which is imported, and I have to say that they do work well.  An equivalent set from Cleveland Twist Drill or Chicago-Latrobe would be $40-50.-Heath
Reply:Here's a couple pennies for you ........... You could drill those holes with one of these............ Attached ImagesWe need to protect Freedom of Speech, otherwise, how would we know who the A-holes (like me) are.
Reply:And end up with some of these!  Attached ImagesWe need to protect Freedom of Speech, otherwise, how would we know who the A-holes (like me) are.
Reply:BB  whats the black thing next to the drill bit looks like a coffee mug I think says chevrolet?IF it Catches...Let it Burn
Reply:Yup........  just figured I'd put somtingh there for perspective....We need to protect Freedom of Speech, otherwise, how would we know who the A-holes (like me) are.
Reply:boy oh boy   now thats a drilll     I dont guess you can put that sucker in a 1/2" drill motor lol   nice setup there BBIF it Catches...Let it Burn
Reply:TX...... I guess a guy could use one of these also, it cuts sideways too!!!    The machine that ran this endmill was awesome...and huge too. It makes a cool paperweight though! Attached ImagesWe need to protect Freedom of Speech, otherwise, how would we know who the A-holes (like me) are.
Reply:Holy cow!  Can you get more pics of that shop?What did they make?Owner of Welding Wiki,The free wiki based resource for weldor's around the world.http://www.weldingwiki.comWe have cookies!Got it at an machinery auction in Seattle..years back.   Not sure what they made, but they had horizontal milling machines that ran on 30 foot tracks in the floor and had stationary t-slot tables probly 12' square!   They had a radial arm drill that had a 20' square t-slot table in the floor, and a column that must have been   6 to 8 feet in dia.!!! I could go on and on!!!   I regret not taking any pics...  I just was walking around in awe!!We need to protect Freedom of Speech, otherwise, how would we know who the A-holes (like me) are.
Reply:Quality is better than Cheap!Your Welding and Fabricating Super Site!
Reply:I have a rule: no cutting tools from asia unless they'll only be used on wood...- "If ya can't be handsome, ya may as well be handy!"   HTP Invertig 201Lincoln Power Mig 255CLincoln SP125+Thermal Dynamics Cutmaster 38
Reply:Originally Posted by BBchevy396TX...... I guess a guy could use one of these also, it cuts sideways too!!!    The machine that ran this endmill was awesome...and huge too. It makes a cool paperweight though!
Reply:Originally Posted by GarauldI have a rule: no cutting tools from asia unless they'll only be used on wood...
Reply:Originally Posted by ReggiewolfQuality is better than Cheap!
Reply:Originally Posted by BBchevy396An old wise feller, once told me.....  "Quality is remembered, long after price is forgotten".Chinese Drill bit set = $3.99  Actually being able to drill a hole = priceless
Reply:In my personal experience, I have found that the Chinese-made drill bits aren't universally bad.  Every drill bit I've ever purchased from a hardware store has sucked, regardless of where it was made.  Most HF bits also suck, but I've seen a few from there that are decent.  The "value brand" bits that I've gotten from Rutland tool have all been great.-Heath
Reply:Honestly, the large   .... 136 piece....or some such number set I bought has served me fairly well. I run my press slow. 150 RPM-ish. I try my best to keep oil on the bit and use good sense with the downfeed.   .....the HF set has my vote."I need this parade like I need a hole in the head"~John F.Kennedy
Reply:I also have some "offshore" bits, and various tools. Yes.... some suck, but some of them work suprisingly well. It seems that the method in which they are used/abused makes the most difference.  Cracker, yes, I also run my bits on the lower end of the rpm scale. And I always tell my guys... Cutting oil is cheaper than drill bits! use it. Hey this leads my thoughts to another thread!!!   Cutting oil!We need to protect Freedom of Speech, otherwise, how would we know who the A-holes (like me) are.
Reply:I can't resist adding my opinion to this thread.Costly experience tells me that it is an utter waste of money to buy unbranded or imported drill bits, no matter what the claimed metallurgy is.  I have (or, rather, had) a full fractional set of unbranded chinese drill bits advertised and marked "HSS," but have never been able to complete a hole in mild steel or even sheet metal cabinets with one of the bits.  They all go dull on the first contact with mild steel - they do not break - indicating soft metal.   Either they are simply lying about the HSS label or they are terrible metallurgists.Sure, there must be some good chinese drill bits made (after all, they fabricated the giant cranes shipped into the Port of Oakland last year), but the quality stuff is not what is exported to the U.S.HSS (High Speed Steel) is not necessarily harder than properly heat-treated carbon steel for cutting tools.  The high speed designation indicates steel with metallurgy (primarily tungsten, molybdenum, cobalt, and/or chromium, I think) that retains its initial designed hardness to much higher temperatures than carbon steel.  Dulling occurs when the heat generated by the cutting action can't be conducted away fast enough to limit the temperature at the cutting edge to below the temperature that draws the temper of the metal.  As a result, a carbon steel bit can perform excellently and durably if used under perfectly controlled, low-speed conditions.  Unfortunately, perfect conditions are very difficult to maintain and it only takes a momentary loss of coolant or excessive speed to instantly draw the temper and ruin the bit (as all of us have experienced many times in our careers).HSS is much more tolerant of high temperatures at the cutting edge than carbon steel, in addition to superior deep hardening and some other advantages, but does not necessarily have better initial hardness or a keener cutting edge.  This is the reason you don't normally see hand tools like chisels made of HSS.  It is not necessarily a better low temperature, low speed cutting edge than properly heat-treated carbon steel.Because the designation HSS covers an extremely wide range of alloys, I suppose it is possible that the TERRIBLE, USELESS chinese drill bits I was sucker enough to buy really are HSS, but I doubt it.  My advice is to save up your money long enough to buy the best quality drills made by a highly reputed U.S. manufacturer, and use them below the speeds recommended in handbooks with plenty of lubricant.I second the recommendation that name brand drill bits be purchased from a competent industrial supply distributor who knows what they are selling and has a reputation to maintain.  And be prepared to pay for the quality you will be getting.  You will save money and your temper in the long run.awright.Last edited by awright; 01-23-2006 at 03:15 AM.
Reply:Again, I'll reiterate, I've had good luck with some imported bits on difficult materials.  I suspect that the cheap drill indexes are just that.  In one instance I was able to drill a couple hundred 1/16" holes in a 1/8" plate of stainless.  I believe that I made it through all but three holes before the bit got too dull to use any longer.  In another instance, I had to drill out a 1-1/4" axle and bought the $20 import bit rather than the $40 US made bit because I was cheap.  It worked well for the purpose but did need resharpening afterwards.  I'm the most likely person that I know that will spend a lot of money on a good tool if it will save me anger and frustration.  This is why I don't use HF angle grinders.  However, I'll keep using Rutland's imported "value brand" bits until I actually get annoyed with them.  I just haven't yet.-Heath
Reply:It's not the cost of the bit that counts, it's the cost of the hole.