Heat bluing clock hands with heat gun

Lightwater

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The hands on my Vienna Concordia were a bit rusty. They had been blued originally, but just with rough edges and covered in scratches from the milled steel sheet. So thought I would polish them properly and try bluing them.

So I did a quick test with a heat gun to see if that would work. Firstly on some screws, that was easy. The minute hand was also easy but pretty uneven. I had some brass wool so tried that to even out the heat. It worked reasonably well. The hour hand in the photo even though it looks polished was still a long way off from a perfect surface. Still about 4 more hours of sanding.

I sanded the hands starting with 800 wet and dry, then 1000, 1200, 1500, 2000, 2500, 3000 and finally 5000. Then some Brasso. Cleaned with detergent and finishing off with acetone, trying extremely hard to not touch the metal which is absolutely critical.

There were a few minor scratches on one hand looking through a Peak scale 10x loupe, use a magnifying glass of some description, so decided to go back to 1500 wet and dry and repeat. I was not happy as it was going to be another 3 hours. In the end I am glad I redid the sanding and polishing, as even the tiniest scratch ruins the finished result.

The bluing is not perfect by any means, but considering the minute hand is 130mm long and varying widths of steel which was difficult to control the rate of heating, I think it is a pretty good effort. The bluing differences show up more in the photos than in real life. So I will live with it.

Key things I have learnt on this first go at bluing is next time I would use a brass shavings bed and a thick base of metal to even out the heat a lot more. Precook the shavings to burn off any impurities or dust.

The heat gun was a Bosch which goes up to 630°C accordingly to the LCD display. I used it at 630°C but on the lower speed fan. There was more than enough heat.

Using a heat gun as it blows air I would vacuum the room better than I did as it does blow dust around, you do not want any dust on the polished surface. Maybe better to set up in a bathroom as it is an easier space to remove dust and clear the room of towels and any other dust sources. It is that critical.

I think I would also use some 7000 wet and dry after the 5000, I was just getting a bit stingy buying this far more expensive paper.

So you can see the bluing process changing colour you need an area light (defused) so you would see the light as if the hands were a mirror, which they should be! So if looking at the hand almost square on, then the light should be the same angle to be seen in the reflection. A white translucent shopping bag over the light will do to defuse light. I had a desk light but it was not good enough as is. Also used a torch but because it is a point light source it didn't really help seeing the changing colour easily.

So final notes, polish out every last scratch, it took me 2 days. Clean clock hands and room as if doing heart surgery. With tweezers drop hands is motor oil straight after bluing to cool. I used some 10W-30

The dark blue photo is with point lighting and the light blue hands is with a small area light. I did also polish the back of the hands as it was often easier to sandwich the hand inside a folded piece of wet and dry when I couldn't sand anymore on one side as my fingers were a bit raw.

_MG_0285_052349.jpg IMG_0295_051415.jpg _MG_036603_052045.jpg _MG_036903_052040.jpg _MG_0314_060420.jpg _MG_0332_104940.jpg
 

JTD

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It was a lot of work but you seem to have achieved an excellent result. Congratulations!

JTD
 

Martin G

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Excellent technique!

I use the tempering color of iron quite a bit in determining temperature in heat treating various parts, and of bluing gun parts. To achieve the darkest blue, the critical temperature range can be just a few degrees. I like your heat gun approach. Very intuitive. I have seen forced air tempering ovens where a stiring fan was hung inside the box to even out the temperature by bulk mass movement.

Using the same principle, I wonder if a setup with a heat gun could be made starting with an air filter of some sort on the gun intake to eliminate dust, and with the hot air pointing into a glass bottle. This way, dust would be eliminated from the envelope, and being pressurized from the inside with clean air, prevent any from getting in. The parts could be placed on a tray to be surrounded from all sides with the hot moving air. The glass bottle would provide some thermal insulation, and would also permit viewing the color achieved.

The last trick would be to toggle up the air temperature by the lowest controller increment, with enough time to saturate the envelope to the new set point. We blue parts in the heat treat oven at 565F (296.1C) If a person started at 500F, and ramped up by 5 degrees every 5 minutes, then the run of color would be very controllable. The onlt issue would be how to get the parts into the oil...

Mind the hot glass bottle! Do not shock the hot glass or burn yourself! Wear safety glasses at all times!

I am going to try this and let you know how it works.

Martin
 

bwclock

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Feb 17, 2015
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The hands on my Vienna Concordia were a bit rusty. They had been blued originally, but just with rough edges and covered in scratches from the milled steel sheet. So thought I would polish them properly and try bluing them.

So I did a quick test with a heat gun to see if that would work. Firstly on some screws, that was easy. The minute hand was also easy but pretty uneven. I had some brass wool so tried that to even out the heat. It worked reasonably well. The hour hand in the photo even though it looks polished was still a long way off from a perfect surface. Still about 4 more hours of sanding.

I sanded the hands starting with 800 wet and dry, then 1000, 1200, 1500, 2000, 2500, 3000 and finally 5000. Then some Brasso. Cleaned with detergent and finishing off with acetone, trying extremely hard to not touch the metal which is absolutely critical.

There were a few minor scratches on one hand looking through a Peak scale 10x loupe, use a magnifying glass of some description, so decided to go back to 1500 wet and dry and repeat. I was not happy as it was going to be another 3 hours. In the end I am glad I redid the sanding and polishing, as even the tiniest scratch ruins the finished result.

The bluing is not perfect by any means, but considering the minute hand is 130mm long and varying widths of steel which was difficult to control the rate of heating, I think it is a pretty good effort. The bluing differences show up more in the photos than in real life. So I will live with it.

Key things I have learnt on this first go at bluing is next time I would use a brass shavings bed and a thick base of metal to even out the heat a lot more. Precook the shavings to burn off any impurities or dust.

The heat gun was a Bosch which goes up to 630°C accordingly to the LCD display. I used it at 630°C but on the lower speed fan. There was more than enough heat.

Using a heat gun as it blows air I would vacuum the room better than I did as it does blow dust around, you do not want any dust on the polished surface. Maybe better to set up in a bathroom as it is an easier space to remove dust and clear the room of towels and any other dust sources. It is that critical.

I think I would also use some 7000 wet and dry after the 5000, I was just getting a bit stingy buying this far more expensive paper.

So you can see the bluing process changing colour you need an area light (defused) so you would see the light as if the hands were a mirror, which they should be! So if looking at the hand almost square on, then the light should be the same angle to be seen in the reflection. A white translucent shopping bag over the light will do to defuse light. I had a desk light but it was not good enough as is. Also used a torch but because it is a point light source it didn't really help seeing the changing colour easily.

So final notes, polish out every last scratch, it took me 2 days. Clean clock hands and room as if doing heart surgery. With tweezers drop hands is motor oil straight after bluing to cool. I used some 10W-30

The dark blue photo is with point lighting and the light blue hands is with a small area light. I did also polish the back of the hands as it was often easier to sandwich the hand inside a folded piece of wet and dry when I couldn't sand anymore on one side as my fingers were a bit raw.

View attachment 711245 View attachment 711246 View attachment 711249 View attachment 711250 View attachment 711251 View attachment 711252
Thanks for posting you experience. Your excellent photos are appreciated.
Bruce
 

Kevin W.

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Thanks for posting this. Your clock hands look great.
 

Lightwater

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Thank you for the comments. I was sure people would expand on my experience, as I did searching on the internet on other peoples' experiences. I only stumbled across one comment on using a heat gun for bluing hands, but there were no photos. The brass wool, even though it was not ideal, was from a soldering iron tip cleaning kit which I had. I only used the clean wool and first burnt of impurities.

I love the various ideas to create a clean room. I often see cheap clear Pyrex oven bowls in charity shops. One could adapt one or two to at least create a semi enclosed work space to control heating. One just needs to work out how to hold everything carefully.

It would be a lot easier with a high temperature professional oven which you can control to a single degree, but most of us like and or need to use the tools we have at hand.

Agree with safety glasses, it's not worth the risk. Probably a bucket of water nearby just in case you burn your hand, even though we are all extremely careful, accidents can happen even with the best process.

P.S. I have used the heat gun for soldering 1awg cable for jumper leads onto Anderson plugs.
 

Lightwater

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A close up photo of the tale end of the minute hand. It shows that one can't do too much sanding. A bit more time with 3000 and 5000 and also with more random directions. Plus some 7000 would help.

Lighting was window light bounced of a white surface which you can see in the brass reflection.

_MG_04170_034830.jpg
 
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Martin G

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A close up photo of the tale end of the minute hand. It shows that one can't do too much sanding. A bit more time with 3000 and 5000 and also with more random directions. Plus some 7000 would help.

Lighting was window light bounced of a white surface which you can see in the brass reflection.

View attachment 711334
The infinite beauty of craft transcends time. You have crafted a breathtaking example of it for us to admire. Thank you.

Good call on making that gorgeous blue beacon your vignette!

Martin
 

Lightwater

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Thank you for the comment. The photo was a crop from a much larger image. The primary task was actually to show the scratches but I did shoot it to look aesthetically pleasing.

Attached is a cropped photo but not scaled down. So a bit more detail for those interested.

Technical: Canon 5D2 300mm + 1.4 tele extender + 12mm extension tube, ISO 400, 1 second, tripod, cable release. I wanted the second hand moving but the minute hand moves as well so 1 second exposure was the maximum. Camera was mounted as close as it would focus, roughly a metre. The depth of field is next to nothing even at f14 the sharpest before diffraction starts to set in. I didn't use a light to illuminate the hands as this wasn't showing up the scratches as well as a white surface to bounce light. In LAB doubled image size, sharpened L channel, small blur AB channels, halved image size. Then crop etc.

Anyway, next time I might look at telescope mirror polishing techniques.

_MG_041701_021410.jpg
 

Jeff Salmon

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Apr 11, 2002
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Well done!
Very timely for me as I have a couple of projects to do: The first is a set of hands for a 3 weight Vienna clock I am restoring for a client. These hands are pitted, however, and I don't think I can get the level of quality you did. I have made a bluing tray, but am going to make another one that is more substantial. The other project is to blue some screw heads for a bracket clock I am restoring.
 

Lightwater

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Preparation of the hands is not difficult, it's just patience... plenty of it. I don't think anyone would be prepared to pay an hourly rate for the time required.


Today stopped by a scrap metal place, not actually planned. They didn't have any brass swarf, but I a bought a length of brass angle for au$5.00 740 grams. So I will bolt a tray together.

Enough to make a tray plus plenty to drill enough swarf. Preparation for when I next do maintenance on the clock.

Brass is easy to drill but has horribly sharp edges which give nasty cuts. Always use a drill bit with the cutting edge squared off a whisker. Stops the drill bit from biting into the brass. Keep these drill bits seperate from the ones you drill steel or you will get very frustrated.
 

Lightwater

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Make sure you really heat up the brass swarf to burn off any impurities as there is often cutting fluid. Even dust on the brass if it has been sitting around is an issue.
 
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Jeff Salmon

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I haven't had any success with my bluing project. The large cheese head screws that I want to blue, I tried to heat them up and wait for the color change and got nothing satisfactory. No blue, boo-hoo. I am not even sure what kind of metal the screws are made of. They are old and look like steel, but perhaps they are an alloy of some kind. They look beautiful when polished however, so I may leave them like that. The bluing was just an experiment. I have several to practice on. I used a torch with MAPP gas and the heads got orange-red, but no blue.
 
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shutterbug

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The first thing is the red color. Let that cool, then reheat for the color you want. Stop when you see it.
 

gmorse

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Hi Jeff,

Just to be clear, the colours we see when bluing are due to the thickness of the oxide film on the surface of the steel, the steel doesn't get hot enough to emit light, as it sounds as though yours did. When hardening, the steel is certainly heated enough to glow bright red before quenching, but tempering happens at far lower temperatures. Typically, steel is hardened first and then cleaned and heated much more gently so that the surface colours run from pale straw, through dark straw, reddish brown, purple and then blue, which is where we mostly stop.

Regards,

Graham
 
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Jeff Salmon

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Hi Jeff,

Just to be clear, the colours we see when bluing are due to the thickness of the oxide film on the surface of the steel, the steel doesn't get hot enough to emit light, as it sounds as though yours did. When hardening, the steel is certainly heated enough to glow bright red before quenching, but tempering happens at far lower temperatures. Typically, steel is hardened first and then cleaned and heated much more gently so that the surface colours run from pale straw, through dark straw, reddish brown, purple and then blue, which is where we mostly stop.

Regards,

Graham
Thanks. Never done this before. These screw heads are about 10mm in diameter and 5mm high. I'll keep working on my technique.
 

gmorse

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Hi Jeff,

Using a direct flame to blue steel items is possible but it demands very fine control and it's usually much easier to control the process by placing the screw on a bed of brass filings or fine dry sand which absorbs the heat and allows the colour changes to happen more slowly. An alternative is to drill some holes in a brass block and heat that. Once you get to purple it's time to stop heating and let the colour develop to the required blue. For larger items such as your screws it's worth dropping them in oil to halt the process, but for smaller items just drop them on a metal plate or tin lid which should be cold enough.

Regards,

Graham
 
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Jeff Salmon

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Hi Jeff,

Using a direct flame to blue steel items is possible but it demands very fine control and it's usually much easier to control the process by placing the screw on a bed of brass filings or fine dry sand which absorbs the heat and allows the colour changes to happen more slowly. An alternative is to drill some holes in a brass block and heat that. Once you get to purple it's time to stop heating and let the colour develop to the required blue. For larger items such as your screws it's worth dropping them in oil to halt the process, but for smaller items just drop them on a metal plate or tin lid which should be cold enough.

Regards,

Graham
Thanks. I do have a pile of brass shavings and am making a bluing tray. Does any oil work? When I did this the other day, the dipping in the oil made a smoke bomb in my shop. As these are clock screws, should I use clock oil?:D
 

gmorse

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Hi Jeff,

Was the smoke when you had the steel red-hot? That's quenching, not tempering, it doesn't get that hot when you're just tempering it, so you shouldn't get any smoke then.

The sequence is, heat to glowing red and quench; if you don't want the smoke, use water, or if you need it really glass-hard, salt water. If it doesn't need to be completely hard, (and very brittle), the tempering then has to happen. Next step, clean up part or all of the surface so that you can see bright metal. This allows you to judge what colours you're getting when tempering, for which you can use a bed of brass filings or whatever, (as per post #22), and gently raise the temperature until you begin to see colour changes on the surface of the steel; this isn't the steel glowing, it's a thin film of oxide altering how the steel reflects light. For hardening, keep the lights dim, but for tempering the light over your bench should be bright.

If you're cooling the items to keep the desired colour after tempering, any light oil will do, you just need its cooling properties, not its lubrication. Water would be just as effective, but that way lies rust, so it's not such a good idea.

Regards,

Graham
 
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Lightwater

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If you can melt a small lead fishing weight you are too hot, 327°C. Bluing is about 290°C.

If your item is red hot the steel is around 700°C. After dropping it in oil or water it will be brittle, so you will need to do it again to around 290°C and cool it. Then polish it for bluing, then 290°C again.

A direct flame would be virtually impossible to control the heat as it is about 1990°C.

I used some Honda badge engineered 4 stroke oil, ironically it was the cheapest for a litre.

For the few seconds picking up the item with tweezers it then cools so much that there is virtually no reaction in the oil. Just a little bit of heat convection within the oil.

A heat gun is more than adequate. The only issue with the heat gun is that it obviously blows air, so if your working environment is not like a surgery you will more than likely blow dust onto the component. There is more dust in the air than we can easily see.
 

Lightwater

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I tried to heat them up and wait for the color change
You do not heat them up and wait for the change.

As you heat them up the colour changes to straw > brown > purple (aim to stop heating) > blue > grey.

It goes very quickly from blue to grey. Then it is back to polishing again.

You have to stop at the end of the purple colour, it changes very quickly. A cold fan in the other hand at a nano seconds notice would stop further heating if you have a heavy mass of brass under the component.
 

Lightwater

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Another perspective on temperature. I make up various brackets out of 316 stainless steel, usually 3 x 20mm flat bar, which I cut with a Bosch 10.8v angle grinder (great tool).

If I don't dip the steel in the water often enough the end starts going blue. You really don't need vast amounts of very high temperature heat for bluing.
 

gmorse

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Hi Jeff,

Tempering Colours of Steel.jpg

Remember, these are surface colours produced by the thin oxide film, and the surface has to be clean in order to see them properly.

You can buy hot air soldering machines, (aka 'rework stations'), quite cheaply, which have much more precise temperature controls than paint stripping guns.

Regards,

Graham
 

Jeff Salmon

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Apr 11, 2002
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Hi Jeff,

View attachment 716317

Remember, these are surface colours produced by the thin oxide film, and the surface has to be clean in order to see them properly.

You can buy hot air soldering machines, (aka 'rework stations'), quite cheaply, which have much more precise temperature controls than paint stripping guns.

Regards,

Graham
Thanks, Graham. I really appreciate the picture of the different colors. I have about 10 of these large screws that I will want to do, and I have extras to practice on. I think one of my problems is that I am trying to just blue the head and the body of the screw is about 1/4" in diameter and 1 1/2" long (6.35mm by 38mm. I am extensively modifying the length of the screw and making it smaller for my particular needs.
 

Lightwater

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I only had 2 screws to do but still only did one at a time sitting on the brass wool. With such a basic setup one screw at a time is really about all I could do with controlling heat. I poked the screw vertically into the brass wool so the head was facing up. You need really good lighting which covers a broad area. Diffuse lighting.

Not to forget that for the best blue effect the screw head need to be highly polished and perfectly clean. My two screws were pretty ordinary so I had to spend a far bit of time on them. It wasn't difficult but just time consuming for such a little thing. Also they became a little curved and the corners polished down. So technically now not a perfectly dimensioned shaped head. But the bluing came up really well and from normal viewing distance the screw heads dimensionally look ok.
 

everydaycats

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Thanks. Very informative. I have a very small sub-second hand I would like to blue, but I don't like the thought of all the hassle. This seems like it may be the easiest bluing process I have found so far.
 

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