Metal bluing parts of the lathe

[Danny M2ZParticipant @dannym2z]

Brownells cold blue is excellent if one follows the instructions. **LINK** Degeasing is the secret.

This stuff is is also great to prevent rust and the MX3 makes a very good aluminium cutting lubricant. **LINK**

The grease seems to work well for gear boxes and slideways.

Have you ever seen a rusty sheep?

* Danny M *

[Douglas JohnstonParticipant @douglasjohnston98463]

Posted by Emgee on 22/12/2016 15:15:42:

Posted by Douglas Johnston on 22/12/2016 14:31:33:

Rapeseed oil (cooking oil from the supermarket ) works well for heat blacking, but not a good idea for hardened objects. ..

Douglas, do you mean use rapeseed oil for quenching the heated part ?

Emgee

Yes Emgee, I heat the part to dull red and dunk it into a container of cheap "own brand " rapeseed oil. I have never tried coating the part with oil then heating if that is what you were wondering. The oil would probably just burn off and not blacken the surface but might be worth a try.

Doug

[JAParticipant @ja]

This thread on bluing has come a bit early for me.

In about a months time I will have more than100 special small nuts and bolts to black. The blacking is for show and must be permanent. I have given this much thought and have come to the conclusion that the hot caustic process will give by far the best results. I am trying to get a good recipe for this process and have started searching the internet. I am fully aware of the dangers of hot caustic soda.

I would like to hear of anyone's experiences with the process or be told of any firms offering such a service.

JA

[MWParticipant @mw27036]

So I just looked up what this is a few moments ago, the only bluing I've ever known of in engineering was the layout ink and micrometer blue! A passivating process, to protect metal..

This must be more well known among the gun community that's here.

Michael W

[Stuart BridgerParticipant @stuartbridger82290]

All my steel apprentice pieces from 1980 were phosphated. I don't remember the details of the process or whether it is practical in a home shop, but not a spot of rust on any of them

[Harry WilkesParticipant @harrywilkes58467]

Posted by Mike on 22/12/2016 14:21:28:

Harry, this looks like oil blacking, which does work on steel. Motor oil doesn't seem to work very well, probably because of its composition these days. I've oil blacked lots of gun screws, and have found cheap supermarket own-brand margarine to be very effective, although it does make the workshop smell like a fire in a chip shop!

Mike never tried oil but saw it done on a youtube vid once and the guy demonstrated the process but he did it with used motor oil !

H

[MikeParticipant @mike89748]

Harry, it probably depends on the grade of motor oil – there are so many nowadays, including mineral and synthetic. Also, well-used oil probably contains tiny carbon particles, which might help. I must confess the only motor oil I have tried is fresh Castrol GTX. Maybe I've taken two clean an approach!

[Rik ShawParticipant @rikshaw]

I only tried bluing once when I did the cylinder lagging sheet for a stationary steamer. I used thinnish shim smeared with some oil I had laying around at the time and then waved the bow torch over it till I got a nice deep blue. Very easy to do and looks good on the engine. —– Rik

[Gareth TParticipant @garetht]

Picked up some of this at the local Gun shop, I will let you know how it goes with photos.

Edited By Gareth T on 24/12/2016 22:09:23

[Neil WyattModerator @neilwyatt]

I use rapeseed oil, in an empty Golden Syrup Tin for small parts, I pop the lid on if the fumes catch fire.

Over repeated use it gets very thick, but melts when the hot part hits it, this doesn't seem to affect the process.

Neil

[Glyn DaviesParticipant @glyndavies49417]

In reply to JA's post about the hot caustic blacking. You can make up the salts yourself – they are all available on ebay. The recipe is 65 parts sodium hydroxide, 25 parts potassium nitrate and 10 parts sodium nitrite. Or you can buy commercial black oxide salts but the minimum quantity is usually 25kg.

Mix the ingredients in a suitable steel container and add an equal mass of water. Very carefully bring to a rolling boil (it can spit while heating and hot caustic salts will cause very bad burns to unprotected skin or eyes, full IPE is essential). You need to adjust the salts/water ratio so that the rolling boil occurs at between 134 and 139 deg C. Then immerse the degreased steel components into the solution for three to four minutes (or until black), then fish out the components and drop them into a jug of cold water.

The hot salts will devour aluminium before your very eyes and do not keep well – once cooled, they will absorb atmospheric moisture and grow out of their container. So once the job is done, you probably need to carefully dispose of the solution.

For the toolpost parts, a rust blueing process is less hazardous, will give a very durable finish, only needs the parts heating to 100 deg C and the cost of chemicals is much less.

[mechman48Participant @mechman48]

Posted by Bob Rodgerson on 22/12/2016 15:27:28:

Russel, I rub Barrier Cream into my hands and don't have a rust problem either.

Me too.

George.

[David George 1Participant @davidgeorge1]

In my apprentice I used to do alcoline hot caustic bath blacking and it was just a case of dipping the parts suspended from wire in a ceramic bath of caustic soda heated from below with gas burners below then putting them in a wash bath of water and then a bath of lanolin oil. We had to wear full face head guard, a rubber apron and full length heavy rubber gloves. It is still done by some engineering firms perhaps you could find someone in your area that dose it.

David

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