Cold Bluing Parts

[DannyC]

I have never tried it before so I thought I would give it a try.
I had seen how awfully rusty the mild steel stand-off bosses I made for Paul's SA drum hubs had become after just a few months.
I made some "QR" sleeves for second hand SA drum hubs I bought off e-Bay and these too are just mild steel and without a finish to them are destined to go similarly brown and crusty.
I bought some Jenolite KoldBlak bluing liquid (£27 for 500ml) and gave it a go this afternoon.
I'm pretty "meh" with the result TBH and that may be because my preparation wasn't thorough enough; you do need to degreased the parts fully and after my first pass I thought the parts looked "spotty" on the threads, some of this was because of air bubbles trapped on the threads preventing the stuff from getting at the metal.
Warning: This stuff is pretty toxic as it is mainly phosphoric acid and other stuff that you dilute down with 3 amount of water per amount of Koldblak. There are lots of don't drink, don't breathe, don't touch, don't taste warnings all over the label.

Anyway, you immerse your cleaned & degreased parts in the solution, for 5..15 minutes then take them out and wash them for 30 seconds under running water (note: you are then sending a diluted toxic stream down to your sewer .. See warnings above). Then you dry the parts (I put mine in a barely warm fan oven for 10 minutes). Then you apply whatever topcoat you want (paraffin wax, lanolin or whatever). The ability to withstand "weather" is as yet untested.

Here are some before & after pictures.
Before:

After:

 

[undertoad]

They don't look too bad at all - At least as not so spotty-looking as some I've seen, and reasonably dark.
Don't bet the farm on rust resistance, though - I think it will help a little, but it ain't hot dip galvanizing .....
You can also blacken steel parts by heating to 600ºF or so (not really red hot), and dipping in motor oil (not synthetic), or veg oil (linseed, canola, etc.), and it will make a black-ish / brown-ish coating, that will likely be as rust resistant as the bluing.
It won't look quite as nice, depending on your perspective, of course, but is cheap to try

 

[Popshot]

As an avid shooter I'm quite familiar with cold bluing. It's widely regarded as a very poor relation to a proper hot bluing job. I once owned a gun blued by Purdey (the people who make 6 figure shotguns). The finish was flawless and deep and so much better than anybody-elses.

I'd suggest heavy grease and some greaseproof paper to keep parts rust free.

 

[DannyC]

I do understand the difference and this is indeed "the poor relation" of the two.
But it is better than nothing (just). I'm not expecting it to last forever, just be less instantly rusting as soon as you look at it.
An application of Cherry Blossom (Black) on top of the oxide layer aids in the appearance as well.
I shall do the other pair of them too,

 

[savarin]

I live in a very humid part of the world where bare steel rusts whilst you look at it.
I tried cold blueing on the QCTP nut on my lathe and rust started showing after 3 weeks.
Next I tried nickel plating, its very simple and easy to do.
I'm unsure if it will help on the bolts/threads but its worth a try.
So far in 70 to 80% humidity there is no sign of rusting after 4 months.
Full account here if interested

POTD- PROJECT OF THE DAY: What Did You Make In Your Shop Today?

Nothing complex today—faced off a cast iron 11” fixture plate for the lathe to true it up. It had a .007” wobble, but now it’s within a tenth. Rick “pic to come” Denney The fixture plate is 10”, not 11”, and was clearly made for my lathe with the threaded hub cast in and fitting the strange...

www.hobby-machinist.com

 

[DannyC]

I live in a very humid part of the world where bare steel rusts whilst you look at it.
I tried cold blueing on the QCTP nut on my lathe and rust started showing after 3 weeks.
Next I tried nickel plating, its very simple and easy to do.
I'm unsure if it will help on the bolts/threads but its worth a try.
So far in 70 to 80% humidity there is no sign of rusting after 4 months.
Full account here if interested

POTD- PROJECT OF THE DAY: What Did You Make In Your Shop Today?

Nothing complex today—faced off a cast iron 11” fixture plate for the lathe to true it up. It had a .007” wobble, but now it’s within a tenth. Rick “pic to come” Denney The fixture plate is 10”, not 11”, and was clearly made for my lathe with the threaded hub cast in and fitting the strange...

www.hobby-machinist.com

Hey Savarin, good to see you back on here mate!

 

[savarin]

Hi Danny, thanks for the welcome, I'm not really back I just got the notice that the new site was up so popped in for a looksie.
I've stopped building bikes as I cannot ride any more (really miss it) due to knees and hips.
I just looked at some old photos and realised my last build was in 2014, it was going to be a tilting delta trike with full suspension.
I got as far as the back end with a type of differential drive to each rear wheel and was just getting ready to make the front end when I stopped.
I've been trying to give it away but no takers.
Most of my building is astronomical telescopes now.
Polishing two 12" mirrors for my giant binocular at present.

 

[DannyC]

It has occured to me that I can avoid all "cold-bluing" performance issues by making those parts in Stainless steel.
So, I think I will buy some SS bar and do it all again.
TBH it is a relatively cheap way of adapting ordinary front/rear second-hand SA drum brake hubs to Single-sided operation for use on a trike/quad.

 

[undertoad]

If you're planning to machine it, you might want to look for a 400 series SS - It will machine much easier than the more common 300 stuff.
OTOH, 400 SS doesn't weld so great ........

 

[DannyC]

If you're planning to machine it, you might want to look for a 400 series SS - It will machine much easier than the more common 300 stuff.
OTOH, 400 SS doesn't weld so great ........

Luckily, there is no welding of the parts required.
I got a metre of 304 stainless 20mm bar which I think doesn't machine too badly.
The A2 Stainless steel M16 nuts I used with the mild steel variant of these tubes machined very easily with carbide inserts so I am hoping the 304 will machine as easily.

 

[Popshot]

The 304 I used on the tilter was a drill killer.

 

[DannyC]

The 304 I used on the tilter was a drill killer.

Ooo-err, I will let you know.

 

[Popshot]

Given you can buy parts made of stainless that have obviously been made on a lathe it must be possible. High end tooling is probably a necessity. Do you have a coolant system? The odd bit I've spun up got very hot but my lathe skills are almost non-existant and my efforts resemble butchery more than engineering. You are a lot further along the learning curve than me.

 

[undertoad]

The 304 I used on the tilter was a drill killer.

Drilling SS, I've found that you should have a really sharp bit, one that cuts good curls as you feed it.
If the bit starts to get dull, stop then, and get a new one.
Stainless work hardens really quickly with a dull bit, and so you need to keep the bit cutting fresh meat, as it were........
Once it hardens, it can be almost impossible to start in the same hole again.
People that do this a lot use carbide drills, and usually some kind of cutting lube with moly in it.

 

[savarin]

very sharp tools and slow the speeds down seems to work for me.

 

[DannyC]

I will let you all know, I reckon the correct SFM with carbide inserts will do the trick.
@undertoad yup, hardening and thread galling are a real pain with SS.

 

[hape03]

Them bolts looks awesome, anyway! If exposed maybe coldblueing the stainless ones aswell?

//hp

 

[Conrad_K]

Stainless steels generally don't take bluing; that's why they're "stainless."

In the American SAE nomenclature, 3xx stainless is non-magnetic and generally rustproof. 3xx is used for medical implants, pipe fittings, hand rails, etc. that need to be rustproof. 4xx stainless is generally stronger, but only "rust resistant". It is used for knives, gun parts, etc. It will stain or rust in some circumstances.

One usually-desirable feature of stainless steels is that they go from silvery to mirror-like depanding on the surface finish. As is often the case, the end users often want some color or black. There are various processes to blacken 4xx stainless, usually complex and expensive. Unless there's some specific reason to avoid it, the best solution for coloring stainless is paint. Which the paint industry likes to call "coating" nowadays...

 

[Popshot]

I found Dewalt Extreme 2 drills with a nose and flat profile worked far better than regular shaped drills.

 

[DannyC]

Stainless steels generally don't take bluing; that's why they're "stainless."

In the American SAE nomenclature, 3xx stainless is non-magnetic and generally rustproof. 3xx is used for medical implants, pipe fittings, hand rails, etc. that need to be rustproof. 4xx stainless is generally stronger, but only "rust resistant". It is used for knives, gun parts, etc. It will stain or rust in some circumstances.

One usually-desirable feature of stainless steels is that they go from silvery to mirror-like depanding on the surface finish. As is often the case, the end users often want some color or black. There are various processes to blacken 4xx stainless, usually complex and expensive. Unless there's some specific reason to avoid it, the best solution for coloring stainless is paint. Which the paint industry likes to call "coating" nowadays...

As I am advised that "cold bluing" is largely ineffective on the parts I have made out of mild-steel, the alternative is for me to make the parts in Stainless because then bluing is totally unnecessary (which is obviously why it is called stainless). Going to make the parts in Stainless as the alternative.