I have 1/4" x 1" bar stock that is 316 SS. I would like to use it to make a wrench to tighten/loosen the plug for my boat (boat used in salt water) - basically I need a 9/16" square hole in the bar stock. I was thinking of drilling, then filing/grinding a square hole, but then I thought I could just drift a square hole. My concerns: If I make a drift out of mild steel, will this be tough enough to drift a hole in the stainless, or will the drift be too soft? Also, will the 316 SS discolor when heating? Will I be able to passivate the 316 SS to remove iron contaminants from drifting a hole (I have citric acid)?

Thoughts/suggestions to make a square hole in 316 SS?

Thanks in advance...

Have you done a web search? I searched the terms, "316 stainless steel passivation at home." and got several pages of hits. Do you have good PPE for handling acids? KNOW how to use the PPE and know how to safely handle and dispose of acids?

Broaching 1/4" x 1" stainless, flattening it back out and passivating it will be time consuming and NO I don't believe mild steel will work very well unless you heat the blank silly HOT and then you might weld them together trying.

Citric acid will work eventually but a jug costs as much or more than a 9/16" SS wrench and don't forget proper disposal, you can NOT reuse it or it WILL deposit dissolved iron ions on whatever you're passivating or just cleaning. Same for Nitric acid, it's faster but way more dangerous to handle and expensive to dispose of. Just opening a jug WILL cause corrosion of everything metal in the same room in pretty short order. 

Another quick search for 9/16" stainless steel wrench also showed pages of hits though lots were hopeful marketing. I did see a number of stainless wrenches on Amazon for pretty reasonable though most are advertising 1/2 . . the guys writing the add don't seem to think inch, centimeter, yard, cubit, etc. matters. You'll want to look up the various company's web page or call one.

This is a case of spending way more to use something you have than it'll cost to buy one. Don't sweat it, we've all done that or we wouldn't be blacksmiths.

Frosty The Lucky.

I'm not the one to ask for passivating, but I would also tend to think mild might be too soft. As far as just making the hole, slitting or punching, then drifting might be easier than drilling. If you did drill, you can also do a square broach in a press, but if you're not already set up for it, it again might be more expensive than it's worth.

Either way, welcome to the site.

Why not buy a cheap chromed wrench from Harbor Freight, and put the wrench in a gallon Ziploc bag that also has a few paper towels drenched with WD-40?

Or are you one of those (us) buy it for $6 or build it for $600?   I understand that character flaw. 

I'm pretty sure I've successfully drifted stainless steel with a mild steel drift.  But it's easy enough to forge a drift from a piece of coil spring if you want to be safe.  I'd just drift slightly undersized (or use an on-size drift which will result in a slightly undersized hole when the material cools), then file to final size.  That should remove any mild steel from the drift.  You might consider punching instead of drilling, which would leave more material around the hole and make a stronger wrench.  

Of course, there still would be potential contamination from the file, and none of it would be passivated.  But you're making a wrench, not a through-hull, and it would probably be fine.  I forged a stainless pot handle a couple of years ago, and left the finish as forged.  It gets washed and air dried two or three times a week -- no trace of rust so far. 

I have a few drops from #5 (actually 16mm) stainless rebar, so I flattened an end, punched it, and drifted it to 5/8" square.  I used mild steel drifts I had on hand (I went to 3/4" round and then 5/8" square, since the 5/8 drift had a rather abrupt taper -- I think I made it to finish a tapered hole at some point).  In any event, the drifts worked fine with the piece at a nice yellow.

The rebar is a "duplex" alloy -- S32304 -- that's twice as strong as 316.  That's cold, of course, but at 23% chromium I doubt it's any easier to forge.

 

 

Nice and rebar makes such a nice grip though I prefer it after it's been softened a bit by a good brisk wire brushing or tumbling. SS brush of course and I use a cup brush in a right angle grinder. Just be REALLY careful with the grinder, they can throw things!

(wish I knew how to draw an emoji or that one would have something sticking out of it's eye)

Frosty The Lucky.

Just for the record, I only knocked that out to prove to myself I wasn't hallucinating about using mild drifts in stainless.  If I was making an actual wrench, I would have taken the time to make proper drifts.  Though looking at it again, it's about two heats shy of being a bottle opener . . .

It's a good point to make Mike, lots of new guys here deserve that kind of lesson and example.

Frosty The Lucky.