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?
On Mon, 13 Jul 2015 01:02:49 -0700 (PDT), Deodiaus
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
www.mcmaster.com for the right type.
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.
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.
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" and finish with a 1/4" HSS twist drill
turning at about 750 rpm.
Do NOT heed the previous advice to drill "slow". The bit may "catch"
on the material and snap the drill bit. Drill at the recommended
drill/feed speeds (the smaller, the faster). Special purpose drills like
carbide, diamond, etc, are unnecessary, as a properly sharpened std
HSS twist drill will work just fine. If you have or plan to purchase
"center drills", make sure you run them faster or as fast as the
recommended twist drill speeds. ALWAYS use a lubricant. Serously,
dirty oil off yer car's dipstick is better than nothing. ;)
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.
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
case80X420 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.
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.
On Monday, July 13, 2015 at 10:00:09 PM UTC-7, Deodiaus wrote:
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)
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