How is it done? I drilled two holes in a piece of .200 stainless steel and the metal seemed to be 'soft'. The bit dug in and made long beautiful curls of metal. The third hole, the bit chattered extremely bad and only made a few small chips and I gave up. On the fourth hole, the same bit dug in and easily made long curls, so its not the bit. Then when I tried to tap the holes, using Tap Magic, resistance was so bad I knew it would break the tap and Yes, the hole was the right size for the tap. I welcome any advice.
i've been successful in the past using cobalt-type(not brand) drill bits and lots 'o wd40. don't know much 'bout tappin' though.
Sounds like you might have "work hardened" the third hole. It's all about speeds & feeds. If your drill bit speed was good, and your feed rate (how much pressure is applied) was too much or too little, stainless will work harden and you will have a really hard time drilling through the hardened metal. Usually wipes out the bit too. look at the cutting edges of the drill tip and see if they still look sharp. If the cutting edges look shiny and reflect light, it's dull. If you think it might be dull, try another bit. If you are using a drill press, you can check what the right speed should be for that size drill bit with stainless, and set it. You'll have to guess with a hand drill. After a while you get a feel for the right speed/feed when drilling stainless. Shane
Not really enough info as to size of bit and speed of spindle. When tapping stainless you need a tapping lubricant that is high in sulfur or Moly D. Also believe it or not, bacon grease or plain old lard work well. Drill speed needs to be about 50-60 feet per minute, feed firmly enough that you don't EVER LET THE BIT RUB. If it's a small hole and you're worried about twisting off the bit, then use a "pecking" action, but DON'T LET IT RUB!!!! This comes from an old hot rodder who earned his pay as a machinist the last 40 -50 years in the trade. Dave
Not sure if this will work in S.S. like it does in Aluminum but I found a tip that said to drill the hole a few thousandths larger that the tap drill chart says. I always thought that you needed as much of the full thread engagement that you could get in Aluminum, and that a slightly tighter hole would give this. Does not seem to be so, as the slightly larger bore gives me a nicer finished thread. Another strange tip that seemed to work for me. K
Most tap drill sizes are calulated to do a 75% thread. You can get away with a 60% thread which is very nearly as strong by drilling 1/64th oversize on your tap drill and the hole will be much easier to tap. I do it all the time on the CNC machine at work, where I typically tap at 200-700 rpm and don't want to risk breaking the tap. Haven't had one come back yet for lack of thread strength.
Are you using a center drill or spotting drill? Those help a whole lot, even on a drill press. The drill point stays sharper and drills a straighter hole where you want it. Do you have an idea of what alloy stainless you have? It is probably in the 300 series, 302 or 304 for plate and sheet stock. Treat it like a high alloy to be safe. For RPM, I use this formula. RPM =[CS (cutting speed) x 4]/ Tool diameter or [cs x 4]/D Figure on a cutting speed of 60 and a 1/4" drill, as an example. RPM = [60 x 4]/.250 = 960 RPM. This will keep you from burning up a drill bit. I prefer cobalt or TiN coated drills, but HSS is ok for few holes. If I'm not doing something that has to be inspected, I always go a few thou over the recommended tap drill size in stainless. I like Moly D for stainless tapping, or water soluble in a thick mix. Anything around will work, Vaseline, 90 weight gear lube, be creative. Back off the tap every 1/4 turn or so to break the chip. Need a quick tap drill formula? Use this: Tap Drill = Nominal thread size - [1/TPI (threads per inch)] Example for a 1/4-20 thread: TD = .250 - [1/20] = .200 or use a #7 drill, or a #6 which is .204 diameter. 13/64 is the same in fractionals. Bob
You need real top quality taps...very sharp, 2 flute is best, and I agree with larger holes. I work with stainless daily, and for the past 12 years or so. Go slow and steady, plenty of cutting fluid. If the tap is dull, get ready to extract the broken piece!!!
I've used the bargain ba*****t MSC HSS taps with success, but for a production run, I go with good name brand ones. The rule of thumb for power tapping is 1/2 the RPM of the tap drill. I do them all the time in the Bridgeport, but use back gears as slow as possible. CNC rigid tapping is another story, not applicable to what is happening here. At home, I use a Tap Matic tapping head for everything I tap, if it will fit on a drill press or Bridgeport mill. For hand tapping I recommend a tap handle and a tapping block that keeps the tap straight. They can be made from phenolic, fibergl*** or aluminum which I use here. This cuts down on messing up a hole or breaking a tap. Bob
stainless is really some temperamental stuff. been drilling and tapping the stuff for 20+ years and it does what it wants and usually wins. top quality drill bits sharp as hell and lots of luck.
Stainless isn't that bad to deal with. I started out with it 28 years ago and my first job was in 410 aloy stainless, tough stuff! Run of the "mill" alloys like 303, 304 aren't bad. 316 which is great for marine use has hard spots in it and is often used for casting, this stuff is brutal. 416 (mainly supplied in round stock) machines very well and is heat treatable. Any of the 400 series can be hardened. The higher end alloys like 174PH, 15-4PH and the 13-8 alloys are pretty good in the annealed state and worse as the hardness increases, which is the way they are supplied for structural aircraft work as forgings. I just did a job in 17-4 that was annealed and it cut very nicely. Good quality name brand tools are key for production work. I like Sossner, OSG as well as other brands of taps. TiN coatings and other coatings extend the life of the tooling. Since I deal with them extensively, stainless steels are pretty predictable and experience tells me how many drills and taps I'll need for a specific job. Bob
Slow speed Fast feed is the stainless steel rule of life. JAX cutting oil is the best I've ever used for stainless, but any sulphur based will work.
I didn't see what size tap/drill your are working with, but stainless steel kind of closes in on the tool as you cut it. So using a drill a few thousands bigger than the recommended tap drill is a good idea. I figure in material that is only .200 tk. you must be using a tap smaller than 1/4". So this tells me that you will be using the "number" set of drills, there is usually a bit that is only a few thousands larger in that set. Don't turn it to fast, use some kind of coolant on it. Then the most important part is to use what is called a [spiral point tap] this is the only tap I use on anything, it can be used by hand or in the machine under power. Make you use the tap magic or some kind of tapping/cutting fluid. Don't worry you wont drown it. Sometimes when I have to tap deep into a tuff grade of stainless or ***anium I will grind some relief on the tailing edge of the tap to give more clearance because of the closing in of material that I mentioned before. here is a pic of a spiral point tap and a pic of one that I have ground some relief on. Always remember when working with metal,"HAST MAKES WASTE" These pics should help JC Note, all 3 of the flutes should be ground not just one.
This is true, if you putz around with it, the material work hardens and causes trouble for tapping. Also strive for a nice surface finish which aids the tap life. We used to use that horrid fish oil years back. But it worked well on turret lathes. I like Moly D (now made by Castrol) or Anchor Lube, which can be thinned with water. For CNC use, Valcool and Hangstefers have great water soluble coolants. Bob
I use Blaser Swisslube in our Haas and really like it. The last stuff we used was called Rustlick and when rigid tapping, the tap actually squeeked as it cut, which to me indicated the tap was getting ready to become two-piece (or more). Since we switched to Swisslube, I can tap at twice the rpm and the taps last much longer.
Just Sharpen your drills. That's what I do...use a bench grinder and point gage. I sharpen the my drills every 2nd hole if many. lotsa oil/coolant/ whatever cools your tip when drilling...Stainless Steel ruins center drills... My 2 cents...
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