Drilling deep holes in cast iron

[DruMor]

In the very near future I will be machining grey iron castings that have 25/32 dia holes drilled 5.5" deep thru the part. I have been machining these parts for the past 3 years without TSC and have to make many small pecks to get the iron out and it takes forever. The machine has just been equipped with TSC, installed by Haas. What kind of feed/speed increases are possible since I now have TSC? Any ideas on if I will still have to peck drill with larger pecks or if I can drill straight thru?

Machining will be with a VF-4 and HSS TSC drills.

[HuFlungDung]

Question: in your previous drilling operation, why the many small pecks? That is a pretty fair sized drill and you should be able to use one of the Haas drilling cycles to drill the first 2.5 inches without a peck, then about a 1" peck after that. It should not take forever. You should be feeding the drill at about .02" per revolution to keep a fluffy swarf that doesn't pack into the flutes too much, but instead augers up well. You might want to temporarily adjust the peck return height parameter if you do a lot of this, so that your drill doesn't come back down hard onto a few chips in the bottom of the hole. Just make sure your peck depth is longer than the peck return height or you'll be there forever

There may also be some benefit to grinding the sharp edge off the drill lips, turning it into a neutral rake tool, instead of positive rake (following the helix angle of the flutes). Grind a flat as wide as your feed in IPR.

With TSC, I suppose you can drill non-stop, that is the whole idea of it.

[DruMor]

I kept the pecks small because it seemed like if I made them deeper I started to have problems with the drill slamming into chips on the way back into the hole. Also I wanted to make sure I kept the end of the drill cool. In the G83 drill cycle, I had a I1. J.187 K.6 for my peck depths. Sounds like between the peck depth and FPT I wasnt pushing it hard enough before. Right or wrong, I usually seem to start way slow with feed/speed and sneak up slowly because the only thing I hate worse than scraping a part is tearing something up.

My boss and I did discuss this morning possibly changing the peck return parameter you mentioned. Our thinking was it would give the coolant a little more time to flush out the hole.

[HuFlungDung]

Too light of a feed in cast iron will make too much powdery swarf, such that the drill flutes are not able to auger them out of the hole. That is why you need to push the feed to make a heavier chip that will come up. But with TSC, it is really a moot point.

I would still 'doctor' the cutting edges as I describe above. The drill will be less apt to hog in on heavy feed, and the neutral rake edge will last far longer than a conventional drill tip, giving you much less headache so far as premature seizing of the drill in the hole, due to dull corners.

I cannot say I'd like machining cast iron wet because of the sludge it makes, but I'd suspect that poor sludge handling may be a result of poor sump design. The old mills with a sump in the base, of course had no ready method of cleaning the crap out, so cast iron was machined dry to keep the sump clean.

[DruMor]

I know exactly what you mean about wet cast being nasty to clean out. I try to get the coolant drain hosed and scraped out well every night after I run iron so it doent turn into a concrete blob in the coolant drain shoot. Lying on my back digging the crap out of there isnt fun

I know we have had a drill ground before like what you describe for a manual drilling operation in this same part. A normal drill liked to grab real bad.

Thanks for your advice!

[Cmailco]

Using a drill specifically designed for cast iron will save you a lot of grief. I have a client who I've totally sold on the Guhring RT100R, getting roughly 25% better tool life than with the previous tooling in SG cast iron automotive components.

You really need a good setup for these drills though. Less than .001 TIR, and at a minimum, soluble oil through the tool. The 'best' method is in using neat oil, like Blaser Vascomill, but at a minimum, 10% mixture soluble. We're running these drills at ~230-300 sfm in SG, depending on the depth. .012-.024 inch/rev depending on drill size. Consult specifics with Guhring if you decide to go that route.

Best regards,
Chuck