A Question for the Machinists!

Professional Machinsts usually sharpen there own bits on a bench grinder.

Cobalt bits are good but not necessary for the run of the mill steel you would be working with. If you can't sharpen a drill bit, they might help for a time. The hardest thing on a drill is running too fast, followed by trying to force a dull bit into the work. A properly sharpened drill bit is a wonderful thing. Learn how to sharpen them and when to sharpen them and save yourself a lot of time. Pay for my plane ticket and I'll come and show you how to sharpen one. LOL

Well, agreed about fast but the hardest thing is getting them too hot, and high speed zooms up the temperature. They need to be run slow, and be generous with the cooling oil. Second big problem is almost always the bit pressure is too light to cut well and the associated bit chatter knocks the edges right off. Should have at least chips or preferably a pair of curls if things are completely right. A lot of factory bits will only cut a single curl though. And they should cut 50 holes without much change when treated well. 4 to 6 just means bad practice is at hand, and that can be remedied.

When I read the original post I thought I'd written it !!! Glad I'm NOT the only guy with dull bits.The old Dormer brand bits lasted forever,sigh. Yes, oil helps a lot, and I have 2 coffee cans FULL of dull bits. Hopefully Santa will bring me a drill doctor....

As stated before running to many RPM's is hard on them, pay attention to the chip it will tell everything, if you are running to fast they will be small and probally blue in color, you want a nice curl of both flutes, if you are only getting one chip it is only cutting on one side, make sure the cutting edges are the same length on both sides and that it is relieved (tapered down) from the cutting edge back. Also let off the pressure every few seconds to break the chip and you can't  use too much cutting oil.

Always remember speed kills with cutting tools. a constant force is needed and lots of oil. For the work you are doing a 135 degree split point works best. The drill doctor is a good machine. I have sold cutting tools for 30 years.

Formula for drill speed = 4 x cutting speed / diameter = RPM                                      We used 80 fpm for cutting speed using high speed steel tools.     For a 1/2" dia drill the formula would be............4 X 80  / 1/2=  320 / 1/2=  640 RPM.     If I remember correctly from class 35 yrs ago.

For those not inclined to get a calculator out to figure spindle RPMs a basic rule for any HSS cutting tool is to watch your chip color. Blue means tool is going bye bye in the next 5 seconds if you dont slow down. Gold means you have a couple more seconds to get it slowed down. Straw means your pushing your luck but you might get awat with it. No color is safe. With Colbalt your safe range goes into the straw color. Carbide is sparks, LOL.

speed kills cutting tools. also not all drill bits are a like. some have a 118 degree tip some are 135 and some 90. Try the 118 degree tip with not a lot of back rake (to much back rake will cause the bit to chip on steal) and use good cutting oil. When sharping the bit aline the grinding wheel with the flite and sharpen cutting edge to heal. The amount you take off the heal is called back rake the moke you take off the faster the bit cuts but it also weekens the cutting edge if too much is taken . on the bigger bit some guys will cut some of the back side of the cutting edge flite off to help chips remove with alot a heat

Edited by Dave A - 11 Nov 2010 at 6:50am

i have the drill press set about 400 RPM and nver change it. Been that way for 30 years. I have to get a small set up to 3/8 inch every 5-6 years due to breakage or kids using them.. My 1/2 inch to 1 inch drills have been there for 30 years. I sharpen each once or twice a year. You dont have to run fast to cut good. Cutting a little slow dont hurt. I seldom use oil unless the stuff is real hard. Pilot holes help when drilling 1-2 to 1 inch holes.

Actually giving "proper" speed, "proper" down pressure are only guide lines. Along with had sharpening drill bits on a bench grinder, which I have been doing for over 50 years, is something you have to learn a feel for.  I had to make a part out of pre hard steel yesterday that took three trips to the bench grinder with a high speed steel drill bit. I couldn't find a carbide in the correct size. You learn the amount of rake it takes for the different steels or you make extra trips to the bench grinder. I haven't seen a drill doctor that could figure the different rake for different drilling jobs.

The best set of drills I've found for us ordinary non machinist guys are Rodman brand. They have some sort of really hard inserted tip in them. I've found that I can use them to dress an ordinary grinder wheel. It takes a diamond wheel to sharpen them. As soon as i saw the guy selling them poke holes in a file, I figured that was a bit that would hold it's edge. Nice thing about them is they are life time guaranteed. Break them, knock the tip off, they replace them free. I do remember the guy saying a drill doctor would work well on them if it had a diamond wheel in it.

I use Mobil 1 for cutting oil,works great,bits stay sharp longer.

I've had really good luck with Oatey clear thread cutting oil. It's around 6 bucks a 16oz bottle at our local Menards, and is easy to apply at the point of the drill.

Are you using a drill press?   Drill bits in a drill press always seem to last longer for me then using them in a corded/cordless drill.   Keeps the bit straight and true.  On my D17, when I drilled out the rear hubs and put in wheel studs, I drilled by hand, and went through drill bits like crazy.   Sharpened them alot, but alot broke as I was drilling by hand.   I was almost tempted to take the time and take it all apart, drill in the drill press and then put back together.   Would have taken some time, but would have saved it clamping and drilling properly in the drill press.    I just drilled some 1/2" holes in 5/8" plate for some loader mounts and I did them in the drill press.   12 holes, did them in about 15 minutes.   Started with an 1/8" then 1/4" then the 1/2".   Same drill bit on all the holes.   I keep my drill press on the slowest setting all the time as well.   Just make sure you're material is clamped or secured properly.   I have a finger that the tip was sliced off  on my dad's drill press when I was about 12.   Tough lesson to learn but I never forgot it.  

Edited by ChuckLuedtkeSEWI - 11 Nov 2010 at 6:16pm