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Drilling 1/2" holes in 1/4" HRS plate

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ACHiPo

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#1
Feeling like I'm making this harder than it needs to be, but it's taken me 2 hours to drill 4 1/2" holes and 8 3/8" holes in 1/4" plate (actually 24"-long angle).

I center-punched the locations, pilot-drilled using Bosch TiN coated drills (3/16" until it broke, then 7/32). The 3/8" holes weren't too bad using my 18V cordless drill, but I needed to pull out my Bosch 1/2" corded drill for the 1/2" holes. The first one went fine, the second one grabbed the bit when it broke through and took me for a bit of a ride (now icing--externally and internally ;))

After deciding that I wanted to keep my thumb, wrist, and shoulder attached, I decided to move to the drill press. The Bosch 1/2" bit is dinged up a bit from the last break throught. Chucking it into the drill press I can see that it's running about 0.020" TIR, so I swapped in an old HSS 1/2" bit. With the angle firmly clamped, I was able to punch through a couple holes using oil and mineral spirits as lubricant, but the last two holes I drilled were more dramatic than I'd like--the drill seized several times, lots of smoke, etc.

I still have a few more of these to drill. What am I doing wrong?

TIA!
 

jlsmithseven

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#2
Maybe the drill bit is getting dull, did you try sharpening it after cutting a few holes? If you're pushing really hard, it's probably due to a dull drill bit. Try letting the drill bit cool down between holes as well, it's probably pretty hot...not sure if that would make a difference or not, just trying to give my experience and process.

Also, for the 1/2" holes, try drilling with a 3/8" drill bit first and then go in with the 1/2". It might just be that it's too much material at one time for ya! Good luck!
 

terrywerm

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#3
It sounds like your bit might not be as sharp as it should be. A sharp bit consumes less power and will cut through a 1/4" plate like it's made of butter - with or without lubricant.

Your pilot holes are properly sized, so they should not be a problem. jlsmithseven mentioned that you could step up to a 3/8" hole before drilling the 1/2" hole. It's not a bad idea, but this puts more pressure on the outer ends of the cutting edges on the bit, making it more likely to chip the cutting edges if you apply too much pressure.

As you are drilling in the drill press, start easing up on the pressure as the bit starts to break through the bottom of the work. Keep a little bit of pressure on the bit as you start to drill through the bottom, but not too much. Too much pressure allows the bit to take too big of a bite as it breaks through, resulting in the problems you experienced. You might also want to place a piece of scrap material under your work piece when drilling so that the drill is still cutting into something other than a shrinking cross section of your work piece. This would also help to reduce the problem of jamming up as you break through.
 

mikey

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#4
I still have a few more of these to drill. What am I doing wrong?
I agree with Justin - a pilot hole will make this go much easier. You only need a drill the size of the web of your 1/2" drill and drill through. For both drills, I suggest slowing your speed to the slowest your drill press will go and use a high enough feed pressure to produce a continuous chip. Use coolant or cutting oil. When doing holes like this, I can usually do so with very little heat produced. The fact that your drills are hot is a tip off that your speed is too high.

I do agree with you that clamping the work down when drilling holes is the safest approach. Hope your hand gets better soon!
 

RJSakowski

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#5
It takes a bit of pressure to push a 1/2" drill bit through steel. The drill press is the way to go. You don't realize how much of a mechanical advantage the rack and pinon create but it can create a lot pf pressure. Use a sharp drill and keep the pressure up to the point of breaking through. As you feel it cutting faster, lighten up on the pressure to avoid the break-through grab.

If you go too slowly, the drill will skate over the work and quickly go dull.
 

darkzero

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#6
Just a thought to add. HR mill scale can be tough on HSS. It could be dulling your drills if the sacle hasn't been removed. Maybe try spot drilling with carbide to break through the scale & follow with the HSS drills.
 

ACHiPo

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#7
Wow once again amazed at the helpful folks here! Thank you! I have a nearly new set of cobalt drills and will try one tomorrow to finish the rest of the holes. Will definitely use the drill press, as that Bosch hand drill has more torque than is comfortable!:faint:

Will post updates tomorrow.
 

Chipper5783

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#9
Forcing a dull drill will break down the land. When you sharpen the drill, you have to ensure the land is the full diameter of the bit, or else the bit will bind, heat up, require a lot of torque and generally give poor results.

Maybe you need to cut the bit back a good amount and repoint it?
 

Glenn Brooks

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#10
+1 for clamping, proper speeds and feeds, and a very sharp bit. Also drilling into scrap underneath your work will mitigate getting hung up on the bottom surface of the piece. After a sharp bit, maybe the scrap underneath is the best thing you can do to punch through your plates. Most home use drill presses don't have a large enuf motor to drill 1/2" holes in steel plate. So you will have to watch your feed and speeds closely at the end. Doesn't take much for the edge to grab the bit and stall it out with 1/2 HP or less...

If all else fails, I've found step drilling with several bit sizes helps immensely when drilling 1/2" and larger holes with my Delta 16 DP.

Glenn
 

Wreck™Wreck

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#11
1/2" is a small hole so no pilot drill is required.

1/4" drill depth is only .5 diameters so drill through in one shot, no pecks needed, this should take less then 30 seconds per hole of spindle time.

Do not be afraid to push the drill harder then you think safe, you want it to cut a thick chip at all times, if it just rubs the work it will dull quickly.

One of the problems when using a drill press with an uncontrolled spindle is the tool digging in upon exit so place a piece of scrap material underneath then drill through the part and into the backing material, this will not allow the spindle to jump.

Good Luck
 

ACHiPo

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#12
1/2" is a small hole so no pilot drill is required.

1/4" drill depth is only .5 diameters so drill through in one shot, no pecks needed, this should take less then 30 seconds per hole of spindle time.

Do not be afraid to push the drill harder then you think safe, you want it to cut a thick chip at all times, if it just rubs the work it will dull quickly.

One of the problems when using a drill press with an uncontrolled spindle is the tool digging in upon exit so place a piece of scrap material underneath then drill through the part and into the backing material, this will not allow the spindle to jump.

Good Luck
Wreck,
Thanks. I was wondering if I might not be pushing hard enough. Will try again with the cobalt drill today.

I don't have much in the way of scrap metal yet--would wood work to back up the part?

Also, given the relative low power and rigidity of my Atlas drill press, I'm assuming I need to drop the speed as low as it will go and feed as high as I can? Even though I don't need to pre-drill, might it better allow the drill motor to keep up with chip making?

Evan
 
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ACHiPo

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#13
Thanks to your advice, things went much faster today. The drill was definitely dull. The cobalt drills were too short (screw machine length), so ended up using a 9/16" Silver and Deming HSS bit and things went much better. Used scrap wood as backing and that helped a lot, although my belt kept slipping which limited how much feed I could give.

Need to get a Drill Doctor!
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The finished product--leveling casters for my lathe bench.
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IMG_0027.JPG
 

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Wreck™Wreck

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#14
Wreck,
Thanks. I was wondering if I might not be pushing hard enough. Will try again with the cobalt drill today.

I don't have much in the way of scrap metal yet--would wood work to back up the part?

Evan
Better then nothing, the goal is to control the feed of the drill when it goes through the far side, if a machine with an uncontrolled spindle is used for drilling at a rate that the drill will live through it will auger in like a wood screw when it passes through the now very thin far side. Anything that impedes the drills sudden uncontrolled progress is good.

I believe that you have just learned something, keep at it and it all make perfectly good sense in time.
 

ACHiPo

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#15
Better then nothing, the goal is to control the feed of the drill when it goes through the far side, if a machine with an uncontrolled spindle is used for drilling at a rate that the drill will live through it will auger in like a wood screw when it passes through the now very thin far side. Anything that impedes the drills sudden uncontrolled progress is good.

I believe that you have just learned something, keep at it and it all make perfectly good sense in time.
Wreck,
I learned quite a bit in the last two days. I've drilled countless holes in my life, never paying much attention. Now that I know a little bit about what's actually happening when the drill is cutting, it's pretty clear what was (or wasn't) happening.

Evan
 

markba633csi

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#16
I've found that I get better hole placement accuracy when I use at least one and sometimes two pilot drills when drilling 3/8" and larger holes. And the center punch
dimple has to be right on target for a perfect hole.
Mark S.
 

tq60

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#17
As mentioned before the Web is what matters.

We had wrong information commonly given to step up drill sizes and this may have been likely due to under powered equipment being common.

If drilling through sheet stock or less than 1/16 thick a step drill can't be beat as it is a controlled cut.

Anything else the Web at the tip determines the pilot.

Use a stout center drill to spot your punch mark then through drill pilot size of web.

1/2 drill can go first but 1/8 will work fine as the Web does not cut well.

Sunday we drilled a 1 inch hole in steel with 1/4 pilot with the lathe and we gave it good pressure and it came out fine.

Most important is correct speed and slower better than faster and give it lots of pressure and it will come out fine.

If you need to be sure the hole stays centered on the pilot a step drill is self guiding and can be used to open the hole to size of final size.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

Downwindtracker2

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#18
Having drilled more than my share of holes in plate, by hand, it comes down to the drill's point. The best millwright I ever worked with taught me that. He was an excellent machinist ,too, but that was only one of his many skills. We would take a drill new out of the package and sharpen it. It made our life so much easier. You can achieve the same ease by using cobalt 135 degree split points stub drills. Don't bother with a drill doctor, the cheap General jig works better for the small stuff.
 
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Silverbullet

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#19
From what I read he has never sharpened a drill bit. The other is he kept using after it was dull. When a drill starts singing and jaming up its done or even ruined.
I have several of the cheap step drills from HF and I've drilled hundreds of holes with the set off hand drill press and mag drill. The set is at least ten years or more old. For the holes you drilled one of those bits would cut from punch dimple to the 1/2" with one bit . There good for up to the 1/4" or 3/8" metal . For my $8.00 they're better then many other brands. Just my opinion and I use angle iron hot plate steel and no grinding just center punch. Even galvanized steel .
 

JPigg55

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#20
I agree a sharper bit is in order.
Another thing you can try is putting a small piece of cloth between the bit and metal.
It's an old machinist trick I saw on YouTube somewhere. Helped prevent grabbing and made holes rounder on thin material.
 

682bear

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#21
I'm not familiar with your drill press, but I have an old Buffalo benchtop drill press that I use... the slowest RPM mine will turn is a little over 500 RPM if I'm remembering correctly.

It drills pretty well up to about 3/8 inch... and I have drilled quite a few 1/2 inch holes, but I end up sharpening the drill often... 500 RPM is simply too fast, IMO.

A while back, I tried a 5/8 drill in some 3/8 mild steel... I never did get the hole drilled, I ended up chucking the part in a 4 jaw chuck on my lathe to drill that hole...

So... now I'm keeping my eye on Craigslist for a floor model drill press (at a good price) that will turn a good bit slower than 500 RPM...

-Bear
 

Downwindtracker2

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#22
Your old Buffalo is likely a lot tighter than any new Chinese or Taiwanese DP. These DP have a secondary step down shaft, even then they are pretty fast. Maybe think about one for your Buffalo.
 

MarkM

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#23
3/8 to 1/2 inch shouldn t be that difficult. I wonder if the drills you are using or purchased have the proper clearance angles. Also once a drill has been heated the way you describe you may have taken what heat treatment the drill may have had. Thinning the web is crucial to relieve pressure. Do some peck drilling rather than just plunge. As things heat up it also becomes more difficult. Walk away for awhile it will help. As soon as your drill shows any sign that it has lost it s initial charm. Don t wait until it won t work anymore. Touch it up so there is lees grinding less heat and much easier for you to maintain proper geometry. Don t take for granted the drill was manufactured properly. I Always take the time to go over them before use and you will be surprised what you will find. Drill doctor junk. I have a Tormek t8 with the ds 22 jig for grinding drills. A four facet grind. Bar none better than any drill you can buy at your common store. People pay for that grind. Speeds and feeds!
 
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