I am 7/8" spade drilling some A514 3" thick burned plate. I am doing this in a 15 hp cnc mill.
I spot the part first, and then drill.
I have a part, that has an unusually hard spot at the bottom of the hole.
It has eaten 3 super cobalt tips already, just in making 2 holes! I have to finish this part, and have another 8 behind it. This is a repeat job. This is the first time in maybe 50 parts that I have run into this.
My thinking was to order 1, or 2 carbide inserts fro this part. Then go back to super cobalt Tin coated (unless you all think I should do otherwise)
What grade carbide should I order? C2, C3, or C5?
i would assume that even carbide can't make it
i would drill a pilot hole and see how the metal behaves
some of the stuff is simply not machinable, like when they cut titanium forgings with oxy-acetylin
from my personal experiecnes I have concluded that we get sabotaged, willful interference by someone to end our industrial age, it could be anyone
with that in mind, you may not feel its allways and only you that is lacking
send the metal back, and don't thinks its only stupidity that causes interference
A514 is also known as T-1 alloy plate. The problem I've run into a couple times in the past with what was supposed to be heavy T-1 plate is that I'm pretty sure some of it was AR instead. IIRC, AR also falls into the A514 spec. The difference between it and T-1 is that T-1 is produced to a specific minimum yield (100ksi I think) while AR is produced to a minimum hardness. I've always found true T-1 to be very consistent, but the AR, while it will meet the guaranteed minimum hardness, may be a bunch harder in some places than others. I hit a place in drilling some 2.5" AR400 once that was so hard you could hit it with a hammer and center punch, and the punch would flatten without even marking the place in the plate. If it was furnished as one of the AR grades, then that's just one of them things, but if it was furnished as a T-1 grade then it likely doesn't actually meet the T-1 spec. For that reason alone I'd be leery of furnishing it to the customer if the part is used at stress levels anywhere near those common for T-1 applications.
As far as carbide is concerned, the C-5 would be a steel cutting grade while the others are for non-ferrous use. The material itself is going to be in the Rc30 range, so you'd probably find the carbide spade inserts would work better all the way around. There's nothing I've ever noticed about any type of A514 that would make the term free-machining come to mind
I would assume carbide can do it. Carbide is what? around high 80s to mid 90s on the rockwell C scale. A cobalt tool is mid to high 60s.
i would assume that even carbide can't make it
As for grade of carbide, I've never really dealt with C2 and C5, though, if I remember right, one is hard, one is tough. Dealing with inserts and endmills a lot, I understand that well.
"Hard", stand up to abrasion very well, but is not very happy with being beat on (does not like abuse). On the lathe a "hard" insert would be a very good finisher. Holds size and doesn't wear. Good for non interupted cuts.
"tough" a little softer carbide, you can beat on it and abuse it and it will wear instead of break, great for roughing.
Saying that, I would go with the "tough" end of the carbide "c" scale since when you lost your cobalt bits you probably mucked up the bottom of the hole pretty bad, interrupted nasty cut.
Honestly, I wouldn't even return to a cobalt tip, especially if this appears to be a problem with this batch of material. The carbide will just chew on through, while the cobalt will die, and then you'll have to go to carbide anyway to clean up the mess.
You're going to do more damage to a carbide tip trying to eat through a damaged hole than if you just drilled 50 holes with the carbide (pulling fictional #s out of my butt, but, I hope you get the idea).
Going back to cobalt if this could happen again is a classic case of "penny wise and dollar foolish"
I will pass on a cheap trick for drilling hardened steel that I thought up years ago. Carbide masonry drills are much less expensive than die drills or carbide tipped drils designed for drilling steel. But masonry drills are rather dull when new, since they are meant for hammer drills and concrete. I have found that I can freehand grind a masonry drill, on my Baldor carbide grinder with a diamond wheel, to have a sharp edge with geometry suitable for steel drilling. The drill will then go through a blue tempered flat steel spring which would have instantly dulled a HSS drill. Cutting fluid will not hurt.
Masonry drills are probably C2 carbide, but that does not keep them from doing the job on steel.
By the way, is your hole close to a burned edge? The flame cutting process will change the material properties in the heated zone along the cut.
I use C1 carbide for roughing hard scale on hot rolled. It's used for chipper blades that chew up trees, rocks and all. Tough as old boots and cuts well. Very hard to grind though. It has extremely high abrasion resistance and toughness.
Metal, I always thought that A514, and T-1 were interchangable...guess not. Thanks.
This material is supplied to me from the customer as a weldment. I have to slab mill, side mill, face mill, drill c-bore, and slot....
Yea for me! :rolleyes:
I ordered some 2 ea. C-5 inserts earier, b/c that was all they had. I also ordere 5 cobalts one to get thru the job. (hopefully)
If the carbide does not give up its cutting life in the first two holes, and it does as well as I hope, then cobalt will be a thnig of the past.
Now if I could only figure a way to quit going thru all the ADKT's that these welded nightmares chew up then I will have REALLY figured something out!
BTW Carbide Concepts on ebay sells ADKT1505's for $6.00 ea. just in case anybody esle has to buy in bulk, like I do.
If the customer supplied the material give it back to him and tell him it's to hard to machine and to get you a different piece. If you are dead set on machining it then use cobalt drills starting with maybe 1/4" and go up in 1/4" steps. Use a slow speed, maybe 25rpm, with a spray mist and manually feed it at a rate to cut heavy but not get a blue chip. Slow speed, heavy feed, cool tool and work. You can drill a truck spring with a HSS drill bit if you turn it slow and use the right pressure and I have done it.
I've done what L Vanice suggested with masonary drills as well. They are cheap enough that you don't cry if they get trashed The OD might require touching up the side of the carbide as well.
In the bad holes you have to finish, maybe use the cheap masonary bit solution and save your carbide drills for the new holes.
It might even be an idea to turn the part over to finish drilling the bad holes from the other side.
I would drill dry with the masonary drill. Its a cheap grade of carbide, and coolant flow will be intermittent, which is hard on the tip.
These are the tradtional "C" grades.
8. Tungsten Carbide Grades
There is no comprehensive comparison of tungsten carbide between and among tungsten carbide suppliers. A big part of the problem is the huge number of suppliers, grades and trade names. There are at least 5,000 different grades of tungsten carbide sold under more than 1,500 different trade names by more than 1,500 different companies.
There is no true standard. The US "C" designation, The ISO designation and other designations are not necessarily relevant. Tungsten carbide from two different manufacturers may have identical designation but vary widely in almost every imaginable way including performance.
The original concept was to rate tungsten carbides according to the job that they had to do. If you had a particular job you would specify a "C" grade of tungsten carbide and you could buy from anybody. This has lead to a situation where a C-7 tungsten carbide can be almost anything as long as it does C-7 style work. According to Machinery's Handbook it can range from 0 - 75% tungsten carbide, 8 to 80% titanium tungsten carbide, 0 - 10% Cobalt and 0 - 15% Nickel. The problem is that two C-7 tips from two manufacturers will almost certainly work very differently in two different applications.
A common misconception is that there is a straight progression from C-1 to C-14 or wherever. A common view is that each higher grade has less cobalt in the binder and is therefore harder and more likely to break. Following this line of thought is belief that the higher C number is harder and better for wear resistance. This is like classifying automobiles by size from a moped to an eighteen-wheel semi. This is clear and handy but unfortunately it is not true.
C grades classification
C-1 to C-4 are general grades for cast iron, non-ferrous and non-metallic materials
C-2 General Purpose
Steel and steel alloys - these grades resist pitting and deformation
C-6 General Purpose
C-9 No shock
C-10 Light shock
C-11 Heavy shock
C-15 Light cut, hot flash weld removal
C-15A Heavy cut, hot flash weld removal
C-16 Rock bits
C-17 Cold header dies
C-18 Wear at elevated temperatures and/or resistance to chemical reactions
C-19 Radioactive shielding, counter balances and kinetic applications
Every task using tungsten carbide is different. Northern sawmills know that the cutting varies with the temperature. Identical knotty pine cuts differently frozen in December than it does warm in July. Boeing machinists can often tell the difference in different lots of Aluminum that are supposedly identical. Each and every cutting job needs a different set of factors to be successful.