Drilling Inco 718 with HSS?

Anyone here do it? I do believe it's the one material I've come across where I always break down and buy a carbide drill. I had to drill a 5/16 hole for a 3/8-16 tap. We started with 135 degree Cobalt drill at 10 sfm and .004 cpr. It wasn't having it. Switched to good ol' fashioned HSS Clevland drill. No dice. CAM said it was gonna take 10 minutes to drill. Got an MA Ford Carbide Twist, and popped them in 1 minute at very conservative feeds and speeds.

Anyway, just wondering if anyone here drills 718 with something other than carbide? I don't LOVE dropping $80 on a drill to put a hole in 3 parts, so if there's a cheaper though much slower alternative, I'm all for it.

I've never bothered to even try drilling that stuff with anything but carbide. I'm sure it can be done, but I'm thinking 10fpm is about it. I'm rather surprised that you couldn't get it done at that speed. What was the failure mode of the HSS-Co drills? Did you get any work-hardening when the non-carbide drills stopped working?

Product Detail

Part Number: 0.3125" DIA 1520H 5/16
Product ID: GT 77631
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Price: $29.01


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PixMan said:

I've never bothered to even try drilling that stuff with anything but carbide. I'm sure it can be done, but I'm thinking 10fpm is about it. I'm rather surprised that you couldn't get it done at that speed. What was the failure mode of the HSS-Co drills? Did you get any work-hardening when the non-carbide drills stopped working?

Click to expand...

Don't think I was in long enough to have work hardening. Basically within the first .100" the drill started snap, cracklin', and poppin' so I just ejected. Tried it with a couple different drills and then just ordered the carbide jobbie.

I drill a lot of inco and I have never done it with anything other than carbide. Tried milling it one time with HSS because I had no carbide that size on hand and it blew out the corners in seconds. Put another new one in and that blew as well. Got the carbide in and it cut like butter. Well the tuff kind of butter.

If you occasionally drill this stuff you could look at some indexable drill tips. They are a bit cheaper to buy instead of the drill but you will have to take the hit on the drill body at first. This would also give you some flexibility if you have a different size to drill and the different tip size fits the same body.

Stevo

I use HSS on the tough alloys, hastelloy, a-286, and some other lovely stuff, rarely see regular inco unless its just turning, but even a solid manual machine won't make carbide hold up in that stuff. A CNC gets away with a lot more, so much more mass and rigidity. So for me its HSS, slow speed, cutting oil, much tougher edge and doesn't chip like carbide.
Main reason hss dies is too high a SFM, unless you get into the higher rockwell hardness that only carbide manages to cut.

Drilled lots in Inco-718 with HSS or cobalt, 30 years worth, go slow it works. Have to watch that you don't work harden the mat'l. Carbide is too fragile unless your machine is rock hard. Also too expensive and hard to resharpen.

Carbide drills are anything but fragile these days, IF you buy the right ones. Get some "this week's special", expect garbage. Buy a Mitsubishi, Titex, Coromant or Kennametal drill made for the application and you can expect performance.

The very first Inco 718 job I had to do required a Ø3/16" x 1.375" deep hole. I got a Mitsubishi MWS drill for the job. I made 40+ pieces with ONE drill, no resharpening during the process. By contrast, I went through a turning insert edge for every other piece. I've since learned a LOT more about turning, and wouldn't have that problem again, but I digress.

If you have more than a couple of holes to drill and a controllable process, carbide drills are the first choice. The cost-per-hole is lowest, reliability is highest.