How To Put A Satin Finish On New Large Dials?

[woodchucker]

I am making large dials for my southbend 9a. I am going to mark 200 marks, and do a direct reading dial, what I don't know is how to get a satin finish on aluminum. I was thinking of glass beading them. I don't think scotchbrite will give me the satin look. I'll be testing on a scrap dial, but looking for a jump start from someone who has done it.

Thanks.

 

[dlane]

Glass bead first -mabey clear powder coat after

 

[MozamPete]

I put aluminium in a caustic soda (lye) solution - like you would do when preparing the part for anodising. The caustic soda will etch the aluminium surface leaving a matt finish. The caustic soda reacts with the aluminium so you need to watch it and not leave it in too long.

Have a look at the bottom of http://www.hobby-machinist.com/threads/brushed-finish-on-aluminum.38572/#post-331493 for an example.

 

[TOOLMASTER]

sand it, blast it, brush it,, throw it in the dishwasher

 

[RJSakowski]

I put aluminium in a caustic soda (lye) solution - like you would do when preparing the part for anodising. The caustic soda will etch the aluminium surface leaving a matt finish. The caustic soda reacts with the aluminium so you need to watch it and not leave it in too long.

Have a look at the bottom of http://www.hobby-machinist.com/threads/brushed-finish-on-aluminum.38572/#post-331493 for an example.

+1 on the caustic, aka soda lye, sodium hydroxide.

Make up about a 10% solution by weight, adding pellets slowly to water, not the other way around. The solution dissolves flesh! Wear personal protective gear; eye protection, or better yet, face shield, and rubber or nitrile gloves. Rinse any splashes or spills immediately. It is also a good idea to wear old clothes, preferrably cotton or synthetic. It eats wool.

After the parts are etched, rinsed, and dried, I like to spray with a clear acrylic spray like automotive top coat. It prevents oil or grease from discoloring the finish. But that's a personal preference.

 

[woodchucker]

Glass bead first -mabey clear powder coat after

I put aluminium in a caustic soda (lye) solution - like you would do when preparing the part for anodising. The caustic soda will etch the aluminium surface leaving a matt finish. The caustic soda reacts with the aluminium so you need to watch it and not leave it in too long.

Have a look at the bottom of http://www.hobby-machinist.com/threads/brushed-finish-on-aluminum.38572/#post-331493 for an example.

I like that, the finish is exactly what I am looking for. I probably will leave the hole for the shaft rough, and ream after then to get a smooth finish on the hole.
Now to figure out how to topcoat protect from staining w/o losing that look. Was thinking satin ruler, and your solution looks like a satin ruler.

 

[Bradrock]

What is your setup for scribing the lines? Is your project already posted here? I'd like large dials for my SB 405 9"er

Thanks, Brad

 

[woodchucker]

I'll take pics. Still working on building the tooling right now. Maybe some video.

 

[MozamPete]

I like that, the finish is exactly what I am looking for. I probably will leave the hole for the shaft rough, and ream after then to get a smooth finish on the hole.

I wouldn't think that was necessary - I don't believe you are dissolving enough of the aluminium to change the tolerance on the fit, I think it is almost a microscopic etching to get the dull finish (although I will admit I have never mic'ed a piece before and after to check, and it you left it in looooooong enough you would dissolve the aluminum). You will know it's working as it is quite a active reaction - lots of bubbling.

Just keep taking it out to checking and pop it back in for a bit longer it you want. Keep the parts hanging or at least moving around frequently so you get an even attack on all surfaces and ideally rinse them, dry them and spray them with clear lacquer before you touch them (the etched surface is great for lacquer or paint to key into so ideally spray them before you handle the piece and get oils back on it).

I've had good results on all purchased aluminum stock I've used so I don't think the grade matters - but experiment with a sample of whatever you are using. I did have a disaster trying it on some home cast aluminium I had machined - well it resulted in a very different finish anyway.
http://www.hobby-machinist.com/threads/another-igaging-touchdro-install.39060/#post-338478

 

[RJSakowski]

I've had good results on all purchased aluminum stock I've used so I don't think the grade matters - but experiment with a sample of whatever you are using. I did have a disaster trying it on some home cast aluminium I had machined - well it resulted in a very different finish anyway.
http://www.hobby-machinist.com/threads/another-igaging-touchdro-install.39060/#post-338478

It has been my experience that home cast aluminum tends to be porous. Controlling the porosity can be difficult in a home foundry. Hot aluminum tends to react with water to form hydrogen gas and hydrogen is fairly soluble in molten aluminum. It comes out of solution when the aluminum solidifies forming small bubbles. When a casting is machined, the pores are exposed, creating a surface that is hard to finish.