Preventing steel rusting on diy CNC router?

[Goemon]

I went away for a week and just came back to find that some of the steel components on my CNC router build have started to rust. It's not major yet but I can't imagine that this sort of problem gets better with age.

Do you guys have any tips for preventing rust on your CNC machines? I am assuming that there must be a way or you guys wouldn't be using anything except stainless steel for your diy builds.

The environment in my work area is fairly humid and, realistically, there is nothing I can do about that any time soon. If I can't prevent further rust then I guess I'll have to start again using all aluminum for the metal components but I am hoping that won't be necessary....

My steel rails, bearings and ball-screws are all fine. It's just the steel frame components I bought.

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[Jim Dawson]

Painting the frame components might be the best option.

[Goemon]

Painting the frame components might be the best option.

Sounds simple enough. Does regular paint actually prevent rusting vs just hiding it?

what type of paint do you use?

[Jim Dawson]

Some Rustoleum paint products are good at preventing rust. I think Rustoleum has a paint product that they say can go on over rust and prevent further rusting. Check at your local hardware or home supply and look at the range of available products in the paint supplies. Normally any paint will prevent rust, some products are better than others. Best is paint that is designed for metal, and then properly prep and clean the metal before painting.

[wizard]

This is an interesting problem with many solutions. I will try to list some of them here.

1. Surface conversion is one approach often called blackening or bluing. It is similar to what is seen on firearms though you can get cold blackening systems these days. This is probably the least durable and the finish that ideally gets coat of rust preventive solution regularly (think gun oils / rust preventing solutions. I use this approach on some in-house made tooling at work and in this situation it works good enough.

2. Paint covers a wide range of materials. Rattle can paints from the local hardware store are probably the least effective, but I've gone that route for some stuff I built for home. for machine frames, guarding and such it is more common to go with a two part Epoxy or urethane paint that can be very effective at controlling rust.

3. Electroless nickle plate is very effective. The technique is used on "marine" grade shotguns and even some rifles. Done right this plating can make structural steel look like Stainless. Some clamp that it holds up better than stainless steels to weather. This could be true has stainless steels have their own corrosion problems. We use this method at work for places where stainless can't be justified but need a thin protective layer on a part.

4. Galvanizing is a good choice. You would need to prep the materials and find a local Galvanizing business. However it is extremely effective and protects steel in direct wether for many decades. Gavanizing does build up the surface a bit and frankly isn't much worse than a couple of good coats of paint. These guys: https://www.galvanizeit.org are the goto people for information about techniques and requirements.

5. There are many new coating techniques such a CERAKOTE that require thermal process to apply. This material has a large following in the weapons community due to durability. Like plating the thin coatings can be an advantage for certain parts of a machine. Interestingly it sounds like you may have suitable equipment to apply this material with your resin curing oven.

6. Lets not forget Powder Coating. Like Cerakote this requires a thermal conversion but you end up getting more of a plastic coating.



There are probably lots of techniques that I'm missing here. On automation tools we commonly use a variety of techniques all on one machine. Most of the frame gets painted with a two part paint, the base table top is often electroless nickel, parts of the machine may be stainless or anodized aluminum. In the end the solution used depends upon what you are trying to accomplish. Almost everything above is better than bare metal, the only real problems coming with some techniques is the heavy build ups making the approach unsuitable for things that need to go together precisely. In other words don't paint mating surfaces.

One thing to realize is that structural steels rust real easy compared to some other steels As such I will try to get them attended to as early as possible. If I'm welding up stuff I will spray the tube as soon as possible afterward. Usually that mean right after wire brushing and scraping of any splatter. Under the right conditions I've seen rust on the surface of structural steel in as little as a few minutes.

[wizard]

Sounds simple enough. Does regular paint actually prevent rusting vs just hiding it?

what type of paint do you use?

Any thing that keeps the combination of moisture and air from getting to a virgin steel surface will prevent rust. How well it will work long term is an open questions. I consider hardware store single component paints to be very low end. However they do work to some extent. How well that some is depends upon the local conditions and other metals in the area.

For example many people have pools, and thus a selection of pool chemicals stored in a garage. Some of those chemical can cause very rapid rusting that spreads quickly if it can find raw metal. I use paint myself so I can't really knock it too much, however it isn't the best outdoors. Frankly some of the metal stuff I've built for outdoor use requires yearly touch ups. You can get additional protection with more coats, clear coats and even wax. Think about pickup or car maintenance.

[NIC 77]

Steel rusts very easily. Often new steel has a thin layer of gray covering on it from the foundry, I'm guessing left over from the manufacturing process. This prevents rust a bit, but if you put new steel outside in a rainstorm, it will be red the next day. Obviously I'm not talking about stainless.

Don't worry about a little bit of rust. It's easy to clean off. Build your machine. When you are done, you take an angle grinder with a sandpaper flapper disk and you clean off that thin layer from the foundry and any rust that has started, really well, then you spray it with paint.

Any two part industrial or high quality paint should work fine. Duracoat doesn't need to be heated, but would be pricey for such a large area. Endura is one that works well, and there are many more brand names. You need to go to a proper paint or industrial supply store, and not the local big box hardware store, for good two part spray paint. Anything industrial with two parts that mix together is ideal. A cheap spray gun can be had for around $30 and for inexpensive compressors, check the local classifieds. Just make sure to check the CFM for the compressor, some are just made for nail guns with low CFM.

If you don't want to do that, then perhaps go to your local hardware store and get the paint that is typically used on concrete floors and put it on with a roller. That stuff takes a while to dry but is pretty durable. Typical spray can stuff is not very durable in my opinion. The one exception perhaps, is krylon paint, that works well on fiberglass and plastics and is quite good for those applications, not on steel though.

For now, don't worry about it, you'll clean any rust and paint it when you're done.

[NIC 77]

Also, I believe that the rustoleum products, correct me if I'm wrong, but I believe those are made more for the person who doesn't want to do the prep work to remove the rust, like on an old steel drum for a BBQ or something like that, or for something that has already been painted and has a bit of rust showing through and you don't want to do the work of stripping off all the paint and taking it down to bare metal. I don't know, BBQ's, lawn mowers, steel chair legs, that kind of stuff, where you just want it to look nice for a few more years. For your purposes, put in the prep work, an angle grinder with a sandpaper flapper disk is all you need. If you had a sandblaster, it would be less work but the result is the same.

For the insides of tubes, if you can't get it reasonably cleaned out inside or spray the insides because they are long tubes then you can either weld on caps or even glue in some caps made of plastic or wood covered in epoxy to prevent any new moisture and humidity from getting inside the tubes. This should prevent it from rusting out from he inside.

I wouldn't worry about it too much, what you are seeing is normal. This isn't a car made of thin sheet metal that you drive through salt saturated water. Once it is finished and painted it will be fine.

[64dodge]

I use ospho on bare steel. It etches and coats the metal for prime or paint. It also helps keep it from rusting.
I have had bare treated steel for up to a year in my shop in the hot humid Bama summers and cold damp winters
in an uninsulated building without rusting. You can find it at almost any hardware store.
Tim

[A_Camera]

Sounds simple enough. Does regular paint actually prevent rusting vs just hiding it?

You must of course clean the surface before painting otherwise you just hiding and may make it worse.

[ger21]

Also, I believe that the rustoleum products, correct me if I'm wrong, but I believe those are made more for the person who doesn't want to do the prep work to remove the rust, like on an old steel drum for a BBQ or something like that, or for something that has already been painted and has a bit of rust showing through and you don't want to do the work of stripping off all the paint and taking it down to bare metal.

Rustoleum makes about 20 types (or more) of paint. They do (or used to) make paints for covering lightly rusted surface.

But as others have said, you should sand off the rust, clean, prime, and paint. A painted steel machine frame should never rust.

[JimBar]

It's an old woodworkers trick, rub it all down with a coat of Johnson's paste wax.


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[ger21]

That works better on cast iron than steel, and still needs to be redone from time to time. Not what I'd want to be doing on a machine frame.

[wizard]

I use ospho on bare steel. It etches and coats the metal for prime or paint. It also helps keep it from rusting.
I have had bare treated steel for up to a year in my shop in the hot humid Bama summers and cold damp winters
in an uninsulated building without rusting. You can find it at almost any hardware store.
Tim

Funny thing here is that I've heard of ospho before but have never found it at the local hardware store. It comes highly recommended though.

On a side note when it comes to paints at your local hardware store I've had mixed results. Generally it relates to chipping or high temp failures. Mainstream Rustoleum for example seems to fail at relatively low temps. In one case i addressed that by using auto store paint rated to 500 degrees. However that paint seems to chip or flake easily.

So even though i use them, (I'm cheap at times) the home owner paints leave a lot to be desired in my mind. There are somethings one can do to improve results though. As already mentioned clean bare metal is a must!! Also allowing plenty of time for curing is very important, when possible i leave freshly painted objects outside in direct sunlight for at least a week. The cans may say usable in 48 hours but I'm not convinced the film is completely durable in that time.

Even after all of the fiddling you still aren't getting the results one would get from better grade paints, especially two part solutions. It comes back to how you spend your money and how durable of a finish you need.

[wizard]

That works better on cast iron than steel, and still needs to be redone from time to time. Not what I'd want to be doing on a machine frame.

Not to mention that when it comes time to actually paint or coat the surface you need to get all of the wax off the surface. That isn't as easy as some might think.

My tendency these days is to keep a can of primer handy to flash recently exposed or welded surfaces. I was lucky enough to pick up some used steel tubing, heavily painted of course, and used this technique to keep exposed surfaces from rusting until the whole frame could be addressed.

[wizard]

One thing worth pointing out here is that if you can completely seal off a steel tube it won't rust after the moisture and o2 sealed inside does its thing. The seal has to be 100% though.

A tube with exposed ends or other entry points, though really needs to be coated inside out. The more aggressive local conditions are for rusting the more important an internal coating will be on an open tube. So often the easy way to address these issues is to cap the tubes for a 100% seal.

[ger21]

I'm trying some new paint I stumbled across the other day.
Tractor, Truck, & Implement - Majic Paints
It's $30 a gallon, plus $15 for the hardener to go with it, from Tractor Supply.

[Goemon]

I have spraying gear here already as I use it for clear coating my carbon fiber parts. Spraying the outsides should be simple enough after using the right degreaser. Doing the insides of the tubes seems impossible with my current skill and equipment.

my two largest steel components are a pair of 2" x 6" x 48" rectangle tubes with 3/8" walls. Thease are part of my gantry risers and frame. I can seal off the ends easily enough but I have no way of fixing any internal rust that has already occurred.

The other components that concern me is a pair of 3" x 48" flat bars of tooling steel which I had planned to partially embed in my epoxy granite base to attach my rails to. These have the worst rust and I was planning on leaving them exposed as they are perfectly flat. I'll have to make sure I don't overdo the paint thickness on these.

Another suggestion I have been given is "Top Secret" (that's the name of the product and not me saying I can't tell you what it is). Apparently it's a mix of silicone and epoxy which acts as a heat resistant clear paint.

[ger21]

The inside of the tubes isn't really an issue. They won't ever get more than light surface rust on them.
I wouldn't paint the flat bars if you plan on embedding them in epoxy. Just scrub them with steel wool and wd40, then wipe them with a light oil and wrap them in paper. Clean thoroughly when you are ready to use them.
When the machine is finished, you can then coat the exposed portions with wax, or a light oil periodically.

[64dodge]

Funny thing here is that I've heard of ospho before but have never found it at the local hardware store. It comes highly recommended though.

I get at ACE

Its them same acid used in etching primer.
Most paints wont bond to bare steel.