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Blued Screws and Hands

Kenny S.

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What techniques were used to achieve this? As a machinist, I know that certain steels will turn blue when heated, so I assume this process could have been used but there is also the chemical route used to blue firearms. Was this ever used in blueing screws and hands? Has anyone here done blueing?
 

Kenny S.

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So heat is definitely an option. Knowing that steel changes color with heat I decided to give it a try. The picture is crappy ( I hate my cell phone camera) but it is blue. It was my second attempt. The first attempt I cooked it too long and it returned to a silver color. I knew this could happen from my experience in machining, so this is all about time and temperature. Once it started to darken, I pulled it from the flame, and viola! A blued screw. Not the perfect color, but with some trial and error, I'll get there.

20210612_105123.jpg
 
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gmorse

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Hi Kenny,

There are two reasons for bluing steel parts, which sometimes overlap. They both result in a range of colours which are produced by the thickness of oxide films on the surface, the thickness of which depends on the temperature to which they're heated. The range of colours produced with increasing temperature goes from pale straw, through dark straw, red-brown, purple, deep blue, pale blue, ending up with practically white; all this is long before the material is hot enough to glow.

The first reason is purely cosmetic and doesn't necessarily require hardening beforehand, (although that does tend to produce better blues). It's also important that the item is properly polished and that it's entirely clean and free of grease, finger marks and any other contamination. This heating alone doesn't produce a change in the hardness, and even mild steel can be blued like this.

The second reason is related to the function of the part; springs need to be springy, screws need to retain their threads and their heads need to resist mangling by screwdrivers. To achieve this, the part must be made of a steel with enough carbon content to allow it to be hardened, typically around 1% to 1.5%, and hardening is a process of heating to a bright red (glowing) state, and then quenching to suddenly reduce the temperature. This alters the crystalline structure of the steel, can be in water, brine or oil, depending on the type of steel, and should result in a part which is hard enough to resist a normal steel file. In this state it's quite brittle but can take a good polish. Once polished and cleaned up as before, the tempering process, which produces the same range of colours as mentioned above, can be done. The use to which the part is to be put governs the appropriate tempering colour. Screws and springs can be tempered to blue, whereas cutters and screwdriver blades are usually left harder by only tempering to a straw colour. In horology, parts are mostly left blued, but for some applications they are polished again and left bright.

Hope this helps,

Graham
 

Kenny S.

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Thanks for your response Graham. Yes, I'm familiar with heat treating of steels. I was interested in the cosmetic side of it. I had a screw for a movement that had been replaced at some point with a standard one. I have a small collection of screws and only a small portion are blued and none matched, so I decided it was time to give it a go. Like I said, I was successful, but not to the degree that I am completely satisfied with. It doesn't have the same hue as the other screws, but it doesn't stick out as a blaring obvious replaced/stolen/lost screw either. It's a work in progress.
 

Brunod

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To have the same color for all screws, you can prepare them as said, then place all of them together on a brass plate and heat all at the same time. Using a brass plate gives time to react because of its thermic inertia.
Even for a single screw, it helps to control the heat color.
Here is a yoke spring heated. 1623527985462.png
 
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JeffG

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I recently had a pretty good success with bluing a set of hands on a bed of brass filings. I'll see if I can link the thread with pictures.

Here it is ---> click
 
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gmorse

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Hi Kenny,
It's a work in progress.
There are several threads on the forum dealing with this subject if you do a search, covering different strategies for securing an even and consistent blue. A common factor is the need to control the process, mostly by indirect heating methods such as the one JeffG has linked to.

Regards,

Graham
 
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S_Owsley

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I just watched a couple of videos on this very subject. I found them informative.


 

Harold Visser

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Yes, it is a 2" x1.5x1.5" brass block I had laying around. Drilled a series of holes in it for various screw sizes.
The plastic electrical box is from Home Depot. In it is a PID controller from Amazon. It is what sets and holds the desired temp.
120V in run through the toggle switch then to the PID, the two red wires are part of a 200watt cartridge heater from Ebay. The bundled silver colored wires are the thermocoupler that senses the temp .
I use a pin vice to hold screws then a dremel to polish, then wash in hot soapy water then dip in acetone to degrease.
Works great except the other day it seemed like it wouldn't come up to and hold temp very well, found that my ceiling fan was blowing a slight breeze across the block enough to keep the surface temp down. Easy fix.
Somewhere I have a wiring schematic, If I find it I will post a pic ....
 
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Kenny S.

NAWCC Member
Apr 12, 2020
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Yes, it is a 2" x1.5x1.5" brass block I had laying around. Drilled a series of holes in it for various screw sizes.
The plastic electrical box is from Home Depot. In it is a PID controller from Amazon. It is what sets and holds the desired temp.
120V in run through the toggle switch then to the PID, the two red wires are part of a 200watt cartridge heater from Ebay. The bundled silver colored wires are the thermocoupler that senses the temp .
I use a pin vice to hold screws then a dremel to polish, then wash in hot soapy water then dip in acetone to degrease.
Works great except the other day it seemed like it wouldn't come up to and hold temp very well, found that my ceiling fan was blowing a slight breeze across the block enough to keep the surface temp down. Easy fix.
Somewhere I have a wiring schematic, If I find it I will post a pic ....
Very Cool!! Now we're getting somewhere. Yes please. The more info, the better!
 
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