Newbie question about drilling

[dbrandow]

I seem to be running into an inability to drill through my work after I've forged it. I'm not quenching it at any point, and I've tried annealling it before trying to drill through it, but that doesn't help. The bit is sharp enough, it works on other pieces I haven't been hammering on, nothing wrong with the drill press, either. Can anybody explain to me what I assume is the blatantly obvious thing I'm doing wrong?

[Paul42`]

I've been having the same problem... went through a lot of bits too...lol! I believe the steel needs to "normalize" (let it cool down slowly on its own - no quenching) before drilling. I've had good luck with this, but still have the occasional piece that gives me trouble (usually about half-way through ).

I bought a "cobalt" drill bit and this seems to be working without the normalizing. I think speed will be a factor too, but I'm sure others can better explain. :)

[MattBower]

What kind of steel are you working with?

[Dave Budd]

that's very odd. I've had problems with some very high carbon steel when its not normalized properly or the scale has been quite thick (scale is very hard so should be removed before drilling imo) but never a problem on mild. I got around some of the trouble by regrinding my drills to be a little more aggressive

[MattBower]

that's very odd. I've had problems with some very high carbon steel when its not normalized properly or the scale has been quite thick (scale is very hard so should be removed before drilling imo) but never a problem on mild. I got around some of the trouble by regrinding my drills to be a little more aggressive

He didn't actually say it was mild.

Again: what kind of steel are you using?

[son_of_bluegrass]

What steel are you using?
What speed are you drilling?
What size drill bit?
Are you using cutting fluid or lubricant?
If so what kind?
What kind of drill bit?
How much pressure on the drill?
Did you remove the scale?
What did you do to the steel after forging (anneal, normilize, clean scale etc)?

The more details you offer the better the answers you will receive.

ron

[dbrandow]

What steel are you using?
What speed are you drilling?
What size drill bit?
Are you using cutting fluid or lubricant?
If so what kind?
What kind of drill bit?
How much pressure on the drill?
Did you remove the scale?
What did you do to the steel after forging (anneal, normilize, clean scale etc)?

The more details you offer the better the answers you will receive.

ron

Thanks to everyone for the answers/guidance so far. In regards to these questions, the answers are:

Mild steel.
Not sure about the speed, I'll have a look at the drill press when I get home.
Drill bit size varies, 3/16 and up, typically.
I'm just using tapping oil.
I've tried titanium and black oxide, haven't tried cobalt yet.
I've tried varying the amount of pressure on the drill from a light touch to heavy pressure, doesn't appear to make much of a difference.
I'd like to think I did, but I'll be sure to make sure of that next time.
When I have a piece like this that I'm struggling with, I anneal it (raise it above critical point, stick in bucket of pearlite to cool overnight).

[MattBower]

Thanks to everyone for the answers/guidance so far. In regards to these questions, the answers are:

Mild steel.
Not sure about the speed, I'll have a look at the drill press when I get home.
Drill bit size varies, 3/16 and up, typically.
I'm just using tapping oil.
I've tried titanium and black oxide, haven't tried cobalt yet.
I've tried varying the amount of pressure on the drill from a light touch to heavy pressure, doesn't appear to make much of a difference.
I'd like to think I did, but I'll be sure to make sure of that next time.
When I have a piece like this that I'm struggling with, I anneal it (raise it above critical point, stick in bucket of pearlite to cool overnight).

Good answers. Very strange. The drill speed is a question mark, but you did say that you've had no trouble drilling mild in the past, so that's probably not the problem.

My best guess -- and it's just a guess -- is that this steel is made from remelted scrap, and there's some high alloy, air hardening stuff in there that didn't melt completely. I've heard of such things.

[pkrankow]

Work hardening of the surface is possible, especially if you start and stop, or let the bit turn without cutting in the dimple. Mix up some chalk, baking soda and oil, equal parts should be fine, should be a paste. Apply this and try drilling through it, the abrasive in the chalk and baking soda should break surface work hardening.

if you stop producing chip you will need to stop and reapply.

You can also use only the baking soda with enough oil to stick, less fuss at least.

It doesn't take much, so mix up about a baby food jar amount, it will last a long time.

Matt's suggestion is quite possible too. If you lack success then a full anneal is needed.

Phil

[Don A]

Double check the scale.

Ususally, a good shot with the center-punch will break the scale sufficiently.

If not, hit it with a Dremel stone or a file or something to expose bight steel.

I've been suprised at how resistant thick forge scale can be at times.

Don

[John B]

Back to basics, Centre punch, Check the drill is sharp, and rotating in correct direction, slow down the rpm to the lowest speed and try it at that.

Good luck with it

[BIGGUNDOCTOR]

Number one get a good drill. A lot of whiz bang "coatings" are used to sell a crappy drill. Coatings help, when applied to a quality drill.

I have run into hard spots in various pieces before, but nothing that I couldn't drill through. Use plenty of oil/cutting fluid, and a sharp bit. Make sure the bit is ground correctly, if not it can drag causing cutting problems.

For speed try 110 x 4 divided by the diameter of the drill. Example 110 x 4 divided by .500 (1/2") - 440 divided by .500 = 880 rpm. Start there then slow up if needed.Too slow is just as bad as too fast.

[John B]

Number one get a good drill. A lot of whiz bang "coatings" are used to sell a crappy drill. Coatings help, when applied to a quality drill.

I have run into hard spots in various pieces before, but nothing that I couldn't drill through. Use plenty of oil/cutting fluid, and a sharp bit. Make sure the bit is ground correctly, if not it can drag causing cutting problems.

For speed try 110 x 4 divided by the diameter of the drill. Example 110 x 4 divided by .500 (1/2") - 440 divided by .500 = 880 rpm. Start there then slow up if needed.Too slow is just as bad as too fast.

I am intrigued where this 110 x 4 or (440) divided by drill diameter comes from as in my experience the resulting recomendations seem a tad faster than what I would use on a general mild steel.

General rule of thumb I was shown was smaller drill diameters, faster the RPM, particularly on drills under 1/16" diameter as not only is peripheral speed akin with cutting ratios in ft per min, the speed also imparts rigidity to the drill and it is less likely to bend or break so long as a reasonable feed rate is applied.

For details of different 'recommended' drilling speeds for different materials try this site

http://www.ollivier.nl/html/drillspeedchart.htm

Suitable lubricants in adequate quantities also usually help when drilling (or machining) metals

[Spears]

I am intrigued where this 110 x 4 or (440) divided by drill diameter comes from as in my experience the resulting recomendations seem a tad faster than what I would use on a general mild steel.

I came across this post and since I’m a machine shop teacher “has been” I figured maybe this question hasn’t been answered yet.

4 X CS / dia is a beautiful simple derivative of the more specific formula 12 x CS / PI x DIA. The number “twelve” is there because that’s how many inches there are in a foot. Hence, many scientific documented cutting speeds are in “feet per minute”. Twelve divided by PI is 3.8 so for most drilling applications (forgiving as they are) the number “4” works fine in the formula. The cutting speed number in surface feet per min is not a “constant” and will go up with certain conditions like “flood coolant” when CNC drilling and may go down with conditions like dry drilling by hand. Hope this helps someone else if the answer was pre-obtained. Spears.

[John B]

Thanks for that

[AndrewOC]

I've found guides like these helpful;
http://autospeed.com.au/cms/title_Sharpening-Drill-Bits/A_110814/article.html

Did a google image search 'drill''angles'.

Difficultly drilling porbably sounds like no clearance angle.

regs
AndrewOC

[TonyD]

Most of the time mild steel is fine as long as it is not quenched. However, due to all of the recycling you will find some pieces or even sections in the same piece will, in fact, harden sufficiently to stop drilling, usually about 1/3rd through. If the bit starts ‘clicking’ stop as it will break the bit. On these pieces it is necessary to full anneal by leaving in hot forge overnight for super slow cool. I have also found that using Black & Decker, point tip, titanium coated bits at low speed 300-500rpm cut thru like butter.