Question on drilling and cutting angle

who fast are you turning your drill bits? The 1/2 inch bit should be at several hundred RPM. Are you turning it faster? Are they good quality drill bits? Are you using cutting oil while drilling?

chuck

One way to cut slots is to drill a series of overlapping holes, and file the scalloped edge straight. You may need to experiment to find the amount of overlap that is best, too much and the drill will tend to veer off to the adjacent hole. (If you are making a longer slot consider drilling holes 1, 3, 5, etc., and then go back to drill holes 2 and 4, so that holes 2 and 4 have a hole on both sides, a more balanced arrangement.) If you have too little overlap, it will be hard to remove the excess metal.

For a 1/2 inch hole in steel, the maximum RPM should be around 400 RPM. If you use faster RPM, it will tend to burn up the bit. If you burned up the bit, it needs to be replaced or perhaps resharpened.

Richard

Rod wrote:

Wht speed are you spinning that bit and what is your feed rate? Also, what type of bit are you using: quality, material, sharpness, point angle?

For mild steel, you should be using a point angle of 118 deg, and a cutting speed of 60 to 80 surface feet per minute (~ 450 to 600 rpm). Your feed rate (downward pressure on the quill) will be higher than with smaller drills. Make sure you are using a good quality bit, either new or professionally re-sharpened, and proper cutting fluid.

The easiest way to do this is with a die grinder or a Dremel-type tool. Either use a carbide burr or abrasive point to grind out and elongate your holes, or use a small cut-off wheel to make connecting cuts between two or more holes.

Regards, Michael

It sounds as if your 1/2 inch drill needs to be sharpened. You can sharpen a 1/2 inch drill yourself on a bench grinder. Google on this use group to find lots of discussion on sharpening drills.

If I were making slots by hand, I would drill a hole at each end and another hole that slightly overlaps one of the end holes. Then I would use a hack saw to saw the slots. and a file to get the sides straight. A sawzall and a jig saw tend to bind and shake. At least when I try using them.

Dan

wrote: (clip) A sawzall and a jig saw tend to bind and shake. (clip) ^^^^^^^^^^^^ A good saber saw works fine for me. It's important to have the metal held firmly in a vise, and to keep good pressure between the sole plate of the saw and the angle iron, The better saws have a rotating balancing weight to eliminate vibration, and that is a HUGE help.

Check your drill bit. I recently had a 5/16 drill that I for the life of me could not drill a hole. I kept running it slower and slower. Finally pulled it out of the chuck and looked at it figuring it most be duller than a spoon(even though it was brand new).

Looking at it, when it was ground it must have slipped as one flute was all botched up. The relief had wiped out one cutting edge.

Maybe it got munged up when it was ground, or it's dull, or you running it too fast. Or a combination.

JW

For drilling 1/2": lower speed, more pressure and cutting fluid. But have a look at the drillbit. I recently tried to use a brand new

1/2" HSS drillbit from Home Depot with zero luck. Mild steel, new bit, WTF??? I stopped and inspected the drillbit. I found that the bit was ground backwards: the cutting lips weren't even touching the metal! It wouldn't have drilled cheese, much less steel. It worked fine after I reground it.

Thanks everyone for the suggestions. I have two 1/2" bits that I was alternating between and both seem to be fairly sharp. The newest bit I've tried is from an assortment type kit from Home Depot, Blue M-something. I do think the rpm's are definitely to high on my drill press. I even had a tough time drilling a 1/2" hole through 1/2" aluminum. I'll give it a shot at the lowest speed and see what happens. I think if I can get some 1/2" holes drilled then I should be good with making some slots with the jig saw or dremel even though the cutting torch is much more fun.

Now if I can just get my concept to work, this will be prototype #2 as prototype #1 was chain drive and the torque is too high for the roller clutches I was using and keeps ripping the insides out of em. Gonna possibly try direct drive on the new one. I can go into more detail on my project if anyone is interested in providing opinions.

Thanks,

Mark

I'll note along with the others that a 1/2" bit needs to have 4x the pressure as well as 1/4th the speed of a 1/4" bit. The little 1/4" bit will dig in very nicely with the pressure but the 1/2" bit will really need to have a lot more pressure in order to dig in properly. Also going too small in the steps of hole sizes does tend to dull the outer part of the cutting edges relative to the center. Drill a hole that is a little bit larger than the center part of the bit and then use the larger bit to do the hole. Finally, I'll note that with a 1/2" bit, the angle iron gets to be a bit thin so you have to start using thin metal techniques to drill such a hole otherwise the bit will grab the angle iron and spin it. A half inch unibit is probably going to work best in this application.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Just a couple of quick comments:

Go to an actual hardware store and request "High speed steel" drill bits. I have an Ace hardware close by which carries them.

If you must pilot drill, do it only once! Measure the web thickness of your

1/2 drill and pilot drill same size or slightly larger. It doesn't take much of a drill press to drill 1/2 dia. in mild steel.

Calculate RPM at which to run your tools. RPM=(cutting speed * 4) / dia. Cutting speed for mild steel using High speed steel is approximately 80 sfpm.

So 80*4/0.5 = 640 RPM for the 1/2 drill.

It's unlikely your drill press will match exactly, so select speed closest to what you have calculated. Better to start slightly slower if possible.

If a true do-it-yourselfer, you probably don't have any cutting oil. I have found WD-40 is a pretty good substitute and is readily available.

Good luck!

He would be better of buying some cutting oil at the hardware store too.

Or slower! See

last two may need to be pasted onto one line)

If you're going to be drilling this size hole a lot, it'll be a big help.

Depending on how long you need, you can get half decent slots using a 4-1/2" grinder, again drilling holes at each end and cleaning up with a file. HF has these grinders cheap, google on this group to get the model number of the "good" one.

--Glenn Lyford

This will teach him not to own a milling machine. :)

Measure the web of your half inch drill bit, and use a pilot drill no bigger than that web thickness, then drill the pilot, followed by the

1/2" drill. Or simply center punch and drill with the 1/2" using no pilots. Which is the preferred method.

Drill a series of holes, and clean up between them with a file, jigsaw etc.

Or buy a milling machine.

Gunner

"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke

Or...spring for one of the Irwin Step Bits. It is a TAD pricy, but, is a great way to drill larger holes in metal. Get a real one, though...as I am not sure how good a metal the clones use.

I would put a big thumbs up for the milling machine suggestion! After all, one of the "project rules" is that it should require a machine we don't have yet. That is why I am building a drum sander, after all...(*smile*).

However, I have had good luck with drilling a hole at each end of the slot, and cutting walls with a sabre saw. Of course, the length of the slots make a diffence too. For slots of an inch or so, I probably WOULD drill a series of holes and use a file/grinder to flatten the cusps down.

*snip*

regards Dave Mundt

I missed the staff meeting but the minutes show Gunner wrote back on Mon, 18 Apr 2005 07:12:08 GMT in rec.crafts.metalworking :

No doubt you have some suggestions as to where he could get a good deal, eh? :-)

I win the lottery tomorrow, I'll be in touch.

tschus pyotr

"I get up in the morning, and check to see if anyone won the lottery. If nobody has, then I open the want ads."

Absent a milling machine for the slots, drilling a series of holes(which is called chain drilling) and clearing them out would work, but is time consuming. However, I have done it fairly quickly without a file by using a so called " side cutting " drill. I know HF has a set of 3 for sale, however the largest size drill in the set is 3/8 inch which is smaller than the 1/2 inch you need. Nevertheless, you could try that, and clean up the resulting slot with a small die grinder or similar tool.