Drilling Stainless Tube

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ctwo
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Drilling Stainless Tube

Post by ctwo »

Hi All,

Been out of season for a while so just wanted to get a calibration. A family friend dropped off some stainless tube for ~1/16" holes. Looks like typical brushed tube you would see for handrails in bathrooms or hospitals, and he wants to use it for handrails on outside entrances - not a lot of wall thickness. He also provided a typical looking silver wood screw for fastening, like the cheap HD junk...

He's tried various drill bits, cobalt and brands like Irwin/DeWalt, but can't get through it. He has punch marks with divots that look like they have molten metal flowering out. IIRC, SS work hardens and that's probably the issue? My cheap drills won't have a chance at this?

Is heating to anneal the metal in order? Like a propane torch and then slow cool with some foil or other insulator over it? Then go at it with my drill?

What is a better fastening choice?

Thanks.
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rklopp
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Re: Drilling Stainless Tube

Post by rklopp »

Hand drill, drill press, or mill? If the latter two, you should be able to drill it. Get the speed down to 50 ft/min, for one. For a 1/4” drill, that’s 750 RPM. Next, feed it hard enough to make a continuous chip, and don’t stop until you’re through. You may not be able to push hard enough with a hand drill. Use a high quality drill.


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Steggy
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Re: Drilling Stainless Tube

Post by Steggy »

rklopp wrote: Tue Sep 21, 2021 10:51 pm Hand drill, drill press, or mill? If the latter two, you should be able to drill it. Get the speed down to 50 ft/min, for one. For a 1/4” drill, that’s 750 RPM. Next, feed it hard enough to make a continuous chip, and don’t stop until you’re through. You may not be able to push hard enough with a hand drill. Use a high quality drill.

...and don't forget the cutting lubricant. My go-to formulation for stainless is lard cutting oil mixed with mineral spirits in a 90:10 mixture (oil:spirits).
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Harold_V
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Re: Drilling Stainless Tube

Post by Harold_V »

Unless the material in question is 303, 302 or 416 (and I strongly suspect it is none of them), I highly recommend that the speed be drastically reduced. The description tendered leads me to determine that the speed being used is totally unreasonable.

Stainless, unless it's free machining, tends to be unwilling to cut, especially by hand. Do NOT attempt to drill with a drill that displays even a hint of dullness. The drill should be dead sharp and never allowed to spin in contact with the tubing without cutting.

I heartily agree with those who suggest hand drilling be abandoned, assuming that's what has been tried. The vast majority of hand drills offer too great of a speed to be useful, plus it's exceedingly difficult to apply the necessary pressure to get the drill cutting, especially if there is no pilot hole that is at leas as large as the web of the drill in use.

A tip in regards to drilling stainless. If the drill doesn't cut without squealing and chattering, it's just a matter of a very short time before it ceases to cut at all. If your speed is slow enough and feed heavy enough, stainless will drill quietly. I just enjoyed success that I described when drilling through a 2-1/8" long piece of 304 stainless, opening the hole to 1" in three drilling steps. Secret to success was slow spindle speed and sharp drills.

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Rich_Carlstedt
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Re: Drilling Stainless Tube

Post by Rich_Carlstedt »

Just what Harold said,
Drill press Only ( Or Mill )
1/16 th running under 2,000 ( 20 FPM )
New drill, prefer a Short or screw machine drill ( for strength )
Place drill bit on part, exert pressure, then start drill press
Can also use a carbide drill, BUT the part must be clamped

Rich
pete
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Re: Drilling Stainless Tube

Post by pete »

After a quick check on Google it seems that 304 stainless is the most common grade used for pipe. That's the bad news. I'd also assume that hand rail material was from one of the big box stores and an off shore producer so no way to be sure what it really is. I'd still assume the worst and it's now seriously work hardened 304. I've drilled a fair amount of 304 on DP's and mills with just decent but sharp HSS drills, but not after it was butchered. It needs to be approached exactly like others have already said. Very sharp tools, keep the feed up, speed down, no rubbing at all, and a good lube that helps keep the heat down and the tool cutting. Using a small carbide end mill or burr might get you through it now. (Maybe). Got a milling machine? Because I think your going to need one or start over with a new piece that isn't hardened. Even with a new piece I wouldn't ever try drilling it without at least a DP and a known good quality drill that's new and sharp. I'm really unsure about trying to anneal it, and hot enough to do so will discolor the surface finish. And with just a hand held torch I'm not even sure just how successful you might be. But there's then zero chance of removing that discoloration without screwing up it's brushed finish unless you redid the whole piece.

Not enough information for fastener choice though, a rough drawing of sizes, what he's doing, attaching to and how it's being attached and even what exact indoor or outdoor environment it's meant to be used in would help. But a 1/16th fastener diameter meant to hold something that might be used as a hand rail? No way no how will that survive it's first use. For anything like a hand rail I'd want a safety factor of at least 5 times the load it might see just in case. And that goes for the attachment and then possible high working loads that would need spreading out on what I'll assume is fairly thin wall pipe.
ChipMaker4130
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Re: Drilling Stainless Tube

Post by ChipMaker4130 »

You will not be successful trying to anneal 304. I work with it regularly in tube and solid form, turning, milling, threading and drilling. It just isn't a problem unless drilling deep. If the holes are within a couple of inches of the end, see if you can borrow a small punch, like a Roper/Whitney No. 5jr. A 1/16 punch will have severe thickness limits in 304, but most handrail tube is very thin.

I'm not sure where the 'wood screw' comes in, but if it needs to engage thread in the SS tube, that won't work either. If its just going through a hole and into wood, maybe, but they are notoriously weak. To pursue drilling go with the above mentioned slow speed and consistent feed. You can peck if you need to, but the in/out engagement/disengagement must be quick. Personally, I do not agree with putting pressure on the drill before starting it turning.
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Re: Drilling Stainless Tube

Post by Rich_Carlstedt »

ChipMaker4130 wrote: Wed Sep 22, 2021 6:48 pm.......................................
Personally, I do not agree with putting pressure on the drill before starting it turning.
I agree with you Chipmaker 100 % .
My "pre" pressure related comment only relates to a center punched spot which the poster mentioned--my bad for not stating it .
It is not for normal drilling as the drill will walk without that concave guidance
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ctwo
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Re: Drilling Stainless Tube

Post by ctwo »

Thanks All! It went like butter. I asked for his drill bits and rubbed them on my diamond hone. Then just pushed it through on my cheap drill press. I deburred with a larger drill bit. His last suggestion about fastening was a rivet. I did not inquire about that.

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Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...
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