Drilling metal, very novice questions

[Gundog48]

It's probably been said, but I used to have the same problem. Make sure the piece is quite low so you can apply loads of pressure and drill at a low speed. You can use oil to lubricate and keep the bit cool.

[Gundog48]

DP.

[Gundog48]

Triple post, a new record! Posted from my mobile and it kept returning an error!

[Ten Hammers]

I (yesterday) drilled four 9/16 holes in a piece of 3/4 plate while talking to a friend on the phone ( bluetooth ).  I used a Cole Drill and I had located the center punch marks about 1/8 deep with a small bit just to get an accurate placement.  This was a mount for a pintle hitch.  I SHOULD have ground the mill scale off the plate since it is the stuff that dulls bits but the bit is still sharp.  I started and stopped on each hole.  As Thomas stated, drill speed and feed rate/down hole pressure are the tickets.  The friend didn't even know what I was doing until I told him (I dropped the bottle of cutting fluid and he heard me stretch to the floor).

 

I learned a long time ago that as long as the drill is turning and cutting ( power drill ) don't stop and you will have success.  Good cutting fluid of course is important.  Slow speed works.  I have no drill press that goes slow enough for anything more than 5/16 bits, hence the use of the cole drill.  I have hand drills but they only have 3/8 chucks.

 

Proper sharpening is of course the key.  I only have HSS bits and have broken maybe one bit on 10 years.

[OldCrusty]

Although this thread is pretty old I thought I would tell Laertius why he could drill ok with 1/8 bit but the 1/4 inch one just skated. 

Let's assume with the 1/8 bit your drill was turning at 500 rpm. The outer edge of the bit would be moving at 196 inches per minute (500*3.14*1/8). At the same rpm the outer edge of the 1/4 bit would be turning 392 inches per minute. So, to get the same cut you would need to slow the rpm down to 250 for the larger bit. 

If you understand the principle it's easy to adjust the cut speeds. If you have trouble just think of the drill bits like wheels on a bike. The bigger the wheel the slower it needs to rotate to cover the same ground as a smaller wheel in the same amount of time.

[Anachronist58]

I like your analogy. One COULD increase feed pressure, but your approach is better standard shop practice.

Bicycle wheels

Robert Taylor

[Irondragon Forge ClayWorks]

2 hours ago, OldCrusty said:

I would tell Laertius

Welcome to IFI... I always suggest reading this to get the best out of the forum. READ THIS FIRST

I doubt Laertius will see this as he hasn't been on in a couple of years. The information you posted is excellent for all of us who have struggled with speeds on our drill presses though.

[Kozzy]

It's pretty easy to estimate proper RPM.  For a 1" dia twist drill in most mild steel, you should normally be running between 250 and 350 RPM...so for convenience pick 300 and permanently park that in some dusty corner of your head.  That means a 1/2" drill needs to run twice as fast (to achieve the required surface feet per minute at the edge of the cutting tips)..or 600 RPM; a quarter inch 4 times as fast, 1200 rpm etc.  Harder steels: reduce the starting figure to 200 or so.  Stuff you know is dead soft can be bumped toward 400 as the stating point.

Most people's drill presses won't go high enough speed to actually meet the needs of small bits so you are stuck running under speed anyway.  And a 1" bit at even 300 RPM feels like it is really flying...to the point of being too fast...so most people choose to run a little slower so their heart doesn't skip a beat or twelve.  Nothing wrong with going a little slower RPM as long as you adjust your feed accordingly.

Feed pressure is where most people go wrong.  You need to keep a pretty good pressure on 100% of the time so the bit keeps cutting. It's generally way more pressure than you think.  Rubbing instead of cutting will dull a bit faster than anything and in some steels, cause work hardening of the material so that continuing to drill will be nearly impossible.

[Frosty]

1 hour ago, Kozzy said:

Feed pressure is where most people go wrong.

Ayup and another way folk go wrong with feed pressure is by lifting up if/when the bit catches. This tends to break or roll the bit's cutting edges and is ALWAYS A BAD MOVE. 

If your bit jams hold it in place while you turn the motor off or let go of the trigger. Then reverse the rotation direction BY HAND to let it slip out from under the bur it made when it jammed. You'll feel it lift the feed handle on a drill press if you pay attention. 

Drill bits tend to jam most often as they "break through" unless you have a no nonsense powerful drill press. I counter by easing off the feed as it goes through and let it nibble through the last little bit. You can hear when the bit begins to break through if you're listening and the shop isn't making your ears ring it's so loud. After a while you learn to feel it.

Frosty The Lucky.

[DuEulear]

If you have work hardend your steel it was to hot. If you cannot anneal it your only option is to continue cutting with something harder than what you are drilling 

 

it never hurts to have a few carbide bits in common ( to your work ) sizes for the occational drilling emergency. 

Save them for when you really need them and treat them well you will find they are really expensive. dont forget carbide can be used hot and dry or cold and flooded with coolant never inbetween if you tempature shock it you will shatter it!!!  And then you need a new one . 

Speeds and feeds for any material can be found in the bible of good shop practice ( machenery’s handbook)  surface foot per minute is how many feet the cutting edge must travel through the material in its given cutting path. 

Because of the circular path of a drill the smaller the drill the higher the rpm as the circumfrence of the cut is smaller. Bigger drill longer cut path per revaloution  to get the same surface foot per minute .

 

the material you are cutting and the material the tool is made from  will change your speed and feed.  as a general rule  high speed steal will need to run slower and be colder so you dont retemper your bit. Carbide will let you run faster and harder but you will pay $$$ so you can. However the tool will last long enough if used properly that the extra cost will pay for it in longer life. That is why we use carbide in about every modern metal shop. A good hss bit used properly should run 100 to 1000 holes in mild steel at least or you are probably doing something wrong. 

Machenerys handbook can be had at amazon you will find that new is expensive but older editions will have almost all the same info for a lower price which is more than you need for tge home shop. I just recieved a reproduction of the first edition 1912 for xmas it has all the blacksmithing info in it too!!!!

 

enjoy 

Susan

 

 

 

[anvil]

Nice xmas gift!

[DuEulear]

True my mother is amasing 

[ThomasPowers]

Work hardening is NOT a "too hot" thing; it is the  presence of dislocations in the crystalline structure.  What you get with "too hot" is localized self quenching and that hardening the piece in that location.  Two different things causing similar problems.  Feed is often too slow with work hardening as you need to cut under the WH face.

To remove work hardening from a piece you need to heat it above the dislocation climb temp and let cool slowly; aka normalization.