Drilling through stainless 3/8" steel bolt

[Deodiaus]

I am trying to drill though a stainless 3/8" steel bolt (grade 6) on a poo l pump. How long should it take to go 1/2 inch? I think after an hour, I managed to get through 1/8 inch using oil as a lubricant. I am using a 1/4 Dewalt Cobolt bit from Lowls (listed for stainless steel). Is this better than the Irwin titanium bits? I have some diamond bits from Harbor Frei ght tools, but it seems as if the diamond dust was scraped off very quickly . Any suggestions on what else to do, i.e. take it to a mechanic who will cha rge $50 an hour. Are there any suggested drill bits made from industrial di amonds or are they overpriced?

[Deodiaus]

drill a pilot hole. Black Oxide bits

[Ed Pawlowski]

With a good bit you should be through it in about 10 minutes. When we work on molds at work, my maintenance guys do it easily on 10 mm bolts. Get a good bit at an industrial supply house. Check

for the right type.

[philo]

Sheesh

Do not start out at the full size, use a smaller bit first... maybe 1/8" or even smaller

[clare]

The secret when drilling stainless is NEVER let the bit "skate". Keep a constant pressure on the bit at all times. MAKE the drill cut. If it skates and heats, the stainless hardens like glass, and NOTHING will drill it. Start over with a fresh bolt. Clamp it in a drill press vice. Run as slow as possible (or even slower) and keep pressure on the drill at all times. A power feed press works best - cuts fresh stainless like butter.

[notbob]

!?!?!?!?

Using what? A hand drill?

nb

[Terry Coombs]

For a quarter inch hole ? I 've never had a problem unless I let the bit rub and work-harden the SS . Heavy pressure and a low speed are key .

[notbob]

True dat!

By "skate", Clare means "not cutting". IOW, if chips are not coming off the work, it's "not cutting" and will harden the SS. Make sure "chips" are being created and the drill bit is not merely spinning in place. If the chips are dark blue/purple, you are feeding the drill with too much pressure. Back off until the chips are jes bluish.

nb

[notbob]

I disagree.

I think the poster claimed he was using a 1/4" drill bit. I'd start the hole with a no. 2-3 "center drill"[1] and finish with a 1/4" HSS twist drill turning at about 750 rpm[2].

[1] [2]

[philo]

Yes...as he said it was stainless steel...otherwise a pilot hole would probably not be needed.

[philo]

A pilot hole is never a bad idea no matter what.

Many years ago I got a good laugh when I saw my boss trying to drill a

1" hole through an i beam with no pilot.

I was not really paying attention to what he was doing until I came back into the shop an hour later and saw him still trying to drill.

He might have been stupid but at least he was no one to give up.

[clare]

Recommended speed (RPM) to get the proper cutting speed for stainless with a 1/4" drill is 1280 RPM, but I find that still too fast usually (Speed in sfpmX4/ decimal inch diameter of drill - in this case80X4=320 devided by 0 .25= 1280 rpm) I like 600- 750 - or closer to 500 RPM for a .5 inch hole. If I'm drilling on the lathe I'l use

300-ish and use the power feed set to about 20 threads per inch

Back up the exit with hardwood or aluminum, or even mild steel so the bit doesn't catch coming out the bottom.

[Deodiaus]

My bit must have been too worn. I was giving thought to sharpening it using a grindstone. Well, it just got worse. I got a new bit and drilled a 1/8 pilot hole. The guy at HD talked me into getting a screw extractor. Well, shit, the screw extractor snapped off the tip and is now lodged in my pilot hole!! I guess I am going to have to drill 3 holes around the extractor bit in order to pull it out. One of my friends was doing the same thing, and said that even after he got the flange bolts out, the metals had rusted together. Apparently this is a big problem with pool water pumps. The back housing that I am trying to salvage sells for about $100. Almost wondering if it is worth trying. Never thought that this would be as difficult.

[Deodiaus]

Yes, I am using a hand drill. THere isn't enough clearance to get it on a drill press.

[19lord62]

ive used a hand drill with a good cobalt drill bit and a coolant paste start small and work up use the right drill speed TTP Hard Drills are the brand we use see

[Shade Tree Guy]

Oh yeah. The old "Easy Out" (talk about false advertising) They're never easy and usually won't get it out On steel bolts, I've taken to using reverse cobalt drill buts. If yur lucky, only takes about one per frozen/broken bolt & ya gotta drill dead center thru the bolt. (not that easy)

[DerbyDad03]

Maybe even harder now that there's part of screw extractor stuck in the bolt.

[TimR]

Time to give up on the drill and use a popper.

[Micky]

When I see hand drill, I think that it's one you crank.

Is that it, or is it a hand-held electric drill that is meant?

[Shade Tree Guy]

Haven't seen a "hand powered" drill since cleaning out my deceased parents garage years ago.