Pass me another drill bit this one's dull

[PineRidge]

Pass me another drill bit this one\'s dull

I was going to start a small project today. While rooting around in my metal scrap bin I found an old draw-bar that would have fit the bill for my steel needs. My project required that I drill a single 1/2 hole in the steel so I grabbed a quarter inch bit figuring it would be easy to start small and work my way up to a half inch bit. When I stepped up to the drill press and muscled down on the draw-bar with the quarter inch bit it appeared that my first bit was really dull. I grabbed a second and finally a third bit with exactly the same results. No way did I have 3 dull drill bits in a row, especially with a Drill Doctor in the house. I always figured that the strength of any draw-bar was in the extra thickness and sheer bulk of the metal itself, never even considered that the blasted thing would be treated to a hardness that would make drilling it next to impossible.

Well tomorrow I guess its off to Summit Equipment & Supply once again for some steel that I can work with.

 

[markct]

Re: Pass me another drill bit this one\'s dull

your drawbar most likely can be drilled, it will take a slow rpm and steady pressure, and plenty of cutting oil and maybe a sharpening a few times to get thru, or you could use a carbide drill, stuff like drawbars are usualy tempered to be tough rather than hard like a wear surface would be, and it may just be case hardened, just two days ago i drilled holes thru some old hyd cylinder rod, it was tough and case hardened but a slow speed and heavy pressure got thru the case hardening and then it didnt drill too bad with some oil, but i did have to resharpen the center drill when i tried to do the second one it wouldnt cut into it, but once it was resharpened it went ok

 

[Syncro]

Re: Pass me another drill bit this one\'s dull

For what its worth, I was told once a long time ago never to drill in two passes, in other words use a 1/2" drill to drill a 1/2" hole in one shot as using a smaller hole first will dull the bit. Funny, just last week I did the same thing in mild steel, but the smaller holes were already there, and I dulled a couple real nice bits. That was soft steel and those bits I had should not have dulled.
I wonder if anybody out there really knows the straight scoop on this.

 

[EddieWalker]

Re: Pass me another drill bit this one\'s dull

I used to always drill a pilot hole first and work my way up, but I also sharpened my drill bits on a grinder.

After I bought my Drill Doctor, I use the drill bit the size of the hole I want.

Takes less time only drilling it once.

 

[ZJ_HR]

Re: Pass me another drill bit this one\'s dull

I'm 90% with you. I do the same in most cases. Drill small 2-3mm pilot hole, and in next step final hole.
In rest of 10 % cases, I sharpen drill in special way, that it hasn't dull middle and bore direct with bigger drill (if you haven't idea how it looks like, I can make a picture).
Bigger means over 8 and up to 22mm dia. This way is particularly used when is necessary to "copy" holes from one part to another.

 

[ZJ_HR]

Re: Pass me another drill bit this one\'s dull

Try with drill for stainless steel.
Just an idea /forums/images/graemlins/wink.gif

 

[markct]

Re: Pass me another drill bit this one\'s dull

</font><font color="blue" class="small">( For what its worth, I was told once a long time ago never to drill in two passes, in other words use a 1/2" drill to drill a 1/2" hole in one shot as using a smaller hole first will dull the bit. )</font>

if you let the bit chatter in the hole then yes it will dull or chip the bit, but as long as you have a good setup and proper rpm then it should work just fine with no harm to the drill at all, and it will cut a more accurate hole in two passes rather than forcing it thru in one shot, think about it, a drill is not much different than an end mill, and with an end mill you only cut with a small portion of the cutter on one side usualy, or you can even plunge thru half of a hole or offcentered on the hole. and another point about drilling with multiple size drills is that if you were drilling by hand and tried to feed a 7/8 bit into steel you wouldnt have much luck, but with stepping up bits and a slow drill you can do it just fine

 

[have_blue]

Re: Pass me another drill bit this one\'s dull

It's most likely not that hard. Your drill press RPM is probably set too high, and the drill is burning. Try 500-800 RPM with the 1/2" bit. Use a few drops of oil. No pilot hole needed.

The first drill may have burned or "work-hardened" the metal. Get a sharp 1/2" (carbide spade) masonary drill, and go real slow with lots of oil and don't force it. If you see smoke, stop and peck at it until you get a few normal chips. Then go back to the M2 HSS drill.

If the drawbar is case hardened or really that dang hard, buy a 1/2" cobalt drill. They are a little spendy, but they will last forever if you touch it up occasionally with the Drill Doctor.

 

[PineRidge]

Re: Pass me another drill bit this one\'s dull

Hmmm, I'm going to have to rethink this project and head for the drill press again today and see how it comes out. I admit that I was spinning my bit pretty fast and it never even occurred to me that a slower speed might be better.

Thanks for all the input, I'll let you know how it pans out.

 

[markct]

Re: Pass me another drill bit this one\'s dull

a masonary drill wont do anything unless you regrind it, a normal masonary drill is made to be used in a hammer drill so it doesnt have a cutting edge like a regular bit, instead it has a blunt point on the cutting lips that is angled both ways to allow it to chip at the concrete like a chisel or jackhammer would, they do sell carbide bits tho for drilling metal and they will cut some very hard stuff, altho with proper technique you can even drill a car axle shaft with a high speed steel drill bit