[crane550]

Looking to buy 1/2-10 5 start in the next couple days. There is a price difference between the black oxide rod which is ~$44 a section and ~$28 for the plain steel.

Anyone have experience with either? Is it worth the extra $45?

Alex

[gjhammer]

I had the same dilemma when I purchased mine last year but I finally decided on plain steel finish 1/2"-10 5 start 6' rods from McMaster-Carr. They are still nice and shiny, no signs of rust, and they seem to twist smoothly and the machine seems to run smoothly. On McMaster-Carr for the 6' sections, the price difference is only $29 but for three rods I was purchasing that added up to $90 and if I ever had replace them to due to rust (or my own mistakes), I could replace them a lot cheaper.

It says the black-oxide finish "mild" rust resistance and a little extra lubricity but I'm not sure how much more. Hopefully someone with direct experience with both the plain finish and black-oxide finish will respond.

[microcarve]

Alex,

This is mostly an opinion still at this point...and I could be wrong, but
having been through a Lot of screws from several different places for
quite a while now, I've noticed that the black oxide coating tends to
create a lot more friction with plastic nuts. That makes the screw a lot
hotter and it softens the plastic a tiny bit.

Those black oxide coatings are...best that I understand it....meant to be
used with lubrication. The oxide layer is supposed to hold some of it and
make things slide smoother.

I don't like using lubricants on my machines if I don't have to....wood projects
are easily stained-up with it....and it does seem to find it's way to the wood
no matter how careful I am.

But, I'm just now beginning to go with screws that don't have the oxide when
I can. I may be wrong, but I'm convinced that extra friction makes the screw
run hotter.


John

[microcarve]

Oddly enough, I just mentioned oxide coatings a few weeks
ago with my experiments with ballscrews with cast plastic nuts...

http://www.cnczone.com/forums/881982-post436.html

I still haven't had time to actually try out the idea, but I sure will,
because I'm pretty sure it should work very well.

Ballscrew material isn't much more expensive than acme...it's the machining
and bearing holders that cost $$$$. I'll find some place that doesn't have
oxide coatings when I buy the next ones. The ball nut has lube in in so
it makes a little sense that some have the black coating. But some specifically
do not have the oxide coating.

And...the oxide can be different from different places. Some looks like paint...
though it isn't. And some is a nice matte finish. Hot or cold treatment I believe.

Just a few thoughts about it....


John

[leaveme]

I second John.

Oxide coating makes smoother finish however it creates trouble for plastic nuts in high speed move. It will melt the nut if not lubricated well.

[CarveOne]

Black oxide coating on steel is an alkaline process that by itself does not afford much protection from rust. The black oxide coated button head screws on my CNC machines now have a reddish look to them from the overnight freezing temps in my shop. I need to take then out and paint the heads to prevent having moisture from the air collect on them as the temps rise above the freezing point in the mornings. Once it has a light rust patina on the lead screws it will act as an abrasive compound, even if oiled. My ACME rods are the plain steel finish and I keep the dry teflon wax spray on them to protect from rust and make them more slippery in Delrin anti-backlash nuts. Any finish that uses a strong alkali or acid etching process is not as smooth as polished steel lead screw surfaces. It has micro-pitting on the surface. I see no advantages from using black oxide finished lead screws. Teflon coating as used on cook pots may work, but I doubt it would stay on the screws very long even with plastic nuts.

The black anodized finish you see on heat sinks is not the same as black oxide finish, as it is a somewhat specialized process for aluminum.

CarveOne