Lots of good info Acheda. Thanks!

Steve

 

Many people think stainless is harder than regular steel, which isn't true of most S.S., but it is very tough to machine. Low RPM and a lot of pressure are required. It's the high chromium content that makes it so tough (and rust resistant). Soft metals have their own set of problems- try drilling copper or lead. Using a little oil helps, and use WD-40 when drilling aluminum. Also, when you sharpen a bit, if you discolor it by overheating, that part of the bit is shot. You would then need to slowly grind away the discolored part. Same goes for a bit burned up in use. Keep a pot of water on your grinder and use it frequently. Acheda and I can bore you guys into the ground with this stuff!

 

Stainless is nasty to machine. I about lost a finger to some stainless that I could not get a chip to break on. Some types of stainless seem to have some work hardening properties. Let up on that pressure while drilling just for a split second and you were done...

 

With a reference like that, how can I resist? I'll fill in the theory (just a little).

Many non-ferrous (=not iron/steel) and some of the "stainless" steels exhibit a property called "work-hardening" in the shop. To give you a non-drilling example from daily life, I am sure you have all had to make a wire coat-hanger into a straight piece of wire (say to get into the car when your keys were locked in). You may have noticed that it was very difficult to get the original bend straight without getting bends right next to it. This is because the "worked" part of the metal is actually stronger, so the nearby areas bend easier. Work hardening is one reason wrought forms of metal are preferred when strength or hardness is desired. This is one of the ways that metals can be made harder & stonger AND tougher - usually you have to give up toughness (ability to absorb shock loads) to gaine strength/hardness.

BACK TO DRILLING: As FLgargoyle states, some soft metals fool you. When you are drilling along successfully and ease up a little to take a breath, all of a sudden a thin layer just ahead of the drill is work-hardened by the slight deformations caused by the cutting action. This layer is very thin, but hard enough to totally DESTROY your drill bit. (I'm talking about red heat, friction welding the drill bit in the hole, and snapping off the drill bit. (You were not holding that piece in your hand, were you - ouch!)

PREVENTION: Always make a serious chip. (You should be anyway or you are wasting your time and dulling your drill bits faster than necessary.) If you need to take a break from continuously applying thrust to that drill, pull back a little. Actually it is a good idea to pull the drill repeatedly out of a deep hole to clear the chips - this is called "peck drilling" and most NC machines are programmed to do it (they never get tired).

RECOVERY: If you fall asleep and end up noticing that the hole seems to be pushing back at the drill, PULL BACK IMMEDIATELY. If the end of drill is dull, get another one. (Do not test the cutting edge by touching it - it will be HOT. Ask me how I know.) Then take a deep breath and break through the thin layer aggressively. With some extreme work-hardening alloys you may be stuck - the hard layer may be thicker and harder than the drill bit. Now some people (in a machine shop) will say: "Just change over to a solid carbide drill." This might save your butt, but carbide is brittle and if it breaks in the hole, you are "up the creek". (Ask me how I know.)

P.S.: Speaking of "stainless" steel, I can tell you more than you want to know about that subject - if encouraged, I'll start a new thread.

 

A desirable quality, no doubt!

The age-old question..........
Only learned by experience.


Sorry, someone was going to do it sooner or later any way.

 

I thought about this thread today in my shop while I drilled out about four dozen spot welds in my now "convertable" '61 F-100. PLUG: The Eastman spot weld drilling tool works very well. I can drill every spot weld from the side I am throwing away and leave the panel I am going to use in pretty good shape. I am putting another roof on it and, YES, I am taking pictures and will do a thread or article unless someone has already done it.