Advice needed on ideal large-diameter drills for 304 SS

keeena

keeena

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I need to do a bunch of drilling ops in 304 and 303 SS round stock in a lathe. Yes, these alloys are different from a machinability standpoint; I'm hoping what works for 304 would work for 303. My drill chuck max capacity is 5/8", so would need a reduced shank bit or a 3MT tabbed shank drill. I will be using the drill to rough out the ID to 3/4" diameter; will bore to final diameter. About all I know for sure is that I should be looking for a 135 degree drill point angle and a good grade HSS minimum. That's where I get a little stuck - all the HSS on McMaster is 118 degree. Being a hobbyist: cost is also factor. Full carbide drills at $275+ on McMaster is not happening. :)

I'm looking for 3/4" because i can't take big bites with a boring bar on my particular machine. GIven the amount of drilling: worth getting 3/4" vs. using my 1/2" drills (I've also managed to smoke a couple of these 1/2" drills and my re-sharpening skills require...sharpening).

So...what's your favorite flavor of drill for this sort of thing? And while we're here - suggested S&F?
 
Are you in need of the drill ? I have a few ………………………...thousand . :)
 
Thoroughly confused! If that was a joke: r/woooosh
 
Do you need 3/4 inch drills ?
 
If you're going to drill that big I would suggest you spot it, then use a cobalt pilot drill, then use a morse taper drill at low speed to rough it to size, then bore it. How deep are you going and what kind/size of boring bar do you have?
 
Drilling 303 is not a problem with 118 deg drills, nothing special is called for, it can be machined at speeds not much less than CRS, especially if coolant is used; 304 is another story entirely. There is no reason not to use 303, its only shortcoming is in welding; with TIG, it tends to undercut.
For 304, I'd pick a cobalt HSS drill.
 
Regarding cobalt (in general): yes, I've found 5-8% cobalt HSS parting blades to work much better than straight HSS. If they use that recipe for drills: I'll look for it. Coolant not an option at this point (cutting/tapping fluid yes, but don't have a coolant system)

@mikey - what is "low" speed? :) And yes - i always spot and then drill a small-ish (1/4, 3/16) initial hole before attacking with a larger bit.

@mmcmdl - at the time it crossed my mind that you might be a vendor (?) but didn't think it was likely. Or your a tool collecting habit is worse than mine. Joke is on me! Yes, I do need a 3/4" drill for 304SS. Whatcha got?
 
keeena said:
- what is "low" speed? :) And yes - i always spot and then drill a small-ish (1/4, 3/16) initial hole before attacking with a larger bit.
Click to expand...

Most austenitic SS (300 series) will work harden, especially 304/316, so you want sharp tools and a continuous feed that allows you to keep the drill cutting. Big drills need to run slower. While the cutting speed for SS is near 100 SFM (SS is not that hard), I find that too fast because SS tends to hold the heat in the part instead of transferring it to the chip like other materials and this leads to work hardening if you don't keep the drill cutting or if you dwell.

Personally, I usually run at 60 SFM for drills up to 1/2" in SS and then slow it even more for bigger drills. I typically use a cobalt pilot and then go straight to my main drill; I usually don't step it up on sizes because it isn't necessary if you can run the lathe slow enough. The main thing is to use a sharp drill and keep up with the feed. Coolant also helps - Anchorlube works well, as does sulfur-bearing tapping/cutting fluids.

Note also that drills above 1/2" generate a LOT of torque so I prefer MT-shanked drills instead of trying to hold a drill in a drill chuck.
 
keeena said:
@mmcmdl - at the time it crossed my mind that you might be a vendor (?) but didn't think it was likely. Or your a tool collecting habit is worse than mine. Joke is on me! Yes, I do need a 3/4" drill for 304SS. Whatcha got?
Click to expand...

A vendor ? :grin: Maybe I should be , but I'm just an owner/hoarder over the years that is downsizing . I've got drills . As Jim says , you want split points .
 
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