[Apples]

So assuming I'm going to use cold rolled flat or square for linear rails with bearings.

I have a couple of concerns about using cold rolled, mainly with the issue of rusting.

So,

1. If I get the cold rolled rail surface ground for tighter accuracy, will a surface ground rail rust more quickly than a non ground rail?


2. If I was to use the same cold rolled but this time it was hardened and ground. Would it resist the rust more?


3. How do I stop it from rusting? I can't paint it as it will have bearings running across it.

4. Can I get the steel coated with something to stop it from rusting? Chrome would be nice but $$$$.

5. What if I used stainless steel for a rail. Would it be okay to use as an unmachined length, or would it need surface grinding as well? Is it more parrallel and as straight as cold rolled steel or is it not as straight etc?

Cheers,
Peter

[Karl_T]

You don't say what environment. I've had cold rolled parts in my shop for years with only a film of oil for protection. I keep the shop dry, AC in summer, heat in winter.

There's an inexpensive electroless nickel chrome available from Caswell
http://www.caswellplating.com/
that you might consider.

Stainless steel would be a good choice for corrosive environment.

Karl

[Apples]

The environment would be just in a shed/garage. No snow, little rain each year.

Does get humid when hot.

Maybe use something like "dry glide" I think it is called. Where wd-40 is wet and will attract dust etc the dry glide stuff will not.


Are stainless steel flats and square, 1"x1" and say 1/2"x3" more dimentionaly accurate compared to cold roll of the same dimensions?

[CarbideBob]

Cold rolled steels are full of internal stresses. Over time they will warp and twist as the stresses relax.

They must be stress relived if you want any kind of long term dimensional stability. This is a really big problem if they are machined on one side or subject to uneven loading (read rollers loading two sides of the bar)

Won't you need a hardened surface for the rollers to ride on?

You could spray the thing down with WD-40 after every use but hard chroming then finish grinding is the best bet.
Bob

[Karl_T]

You'll get rusting with steel in your situation. A dry lube won't help much.

You can order most all materials with the tolerance you need for dimensions. Tighter tolerance = more $

Karl

[Apples]

Here is what the rail is for:

Will only be designing gantry as single side drive. Round figures,
gantry will be about 5ft wide, in shape of triangle. Bearings will be
mounted on a truck/carrage that is say 2ft long. Table size 4'x4'.
Will either use those concave type bearings or normal flat bearings.

Will be for a slow moving gas cutting table. No fast speeds.

Rails dimentions rough idea either square 1"x1" or flat 1/2"x3".


CarbideBob
Won't you need a hardened surface for the rollers to ride on?
Well I don't know. Looking at the torchmate machines all they reccommend is using cold rolled flat for rails.

I don't need cnc mill or router accuracy, for oxy fuel cut plate. I might have to ask some torchmate users how their cold rolled steel rails are holding up.

[CarbideBob]

Well take my advice with a grain of salt as the stuff I work on is bit different than most of the stuff here. High production equipment with million cycle warranties, so the advice from others here may be better suited than mine.. Myself, I would never even consider using cold roll in a machine structure without stress relief.

Want to stress relive it yourself? Put your steel in the bottom of a big campfire. Bury it in the cinders and let it cool gradually over a couple of days.
Or, if you live in Michigan just leave it outside through the summer and winter for 2 to 3 years. Before the days of just in time this is what Cadillac did to all their engine blocks.
Bob

[Karl_T]

For what you're doing, cold rolled is your best bet. Don't do any of that put it in the fire stuff. You'll screw it up. Cold roll will warp if you machine one side off on a long piece. Use full dimension, as ordered, material and you won't have trouble.

I'd be tempted to just spray paint your unit for protection. Keep the coating thin where it might effect accuracy.

Karl

[dertsap]

http://www.sherwin-automotive.com/pr...?product=40331

give a wet rag of rust mort to it , and it shouldn't rust ,if it ever does wipe it down again

[Apples]

Karl_T
I'd be tempted to just spray paint your unit for protection. Keep the coating thin where it might effect accuracy.

I think that the PlasmaCam machines are just cam followers onto painted steel, come to think of it.


dertsap
rust mort

Never used this stuff before. Have used some "rust inhibitor" on chassis of old landrover then painted over with paint.

Will the "rust mort", or should I say does it have to go onto a rust surface, or can it go on a new clean surface and protect it from rust?

[dertsap]

generally it's to go on a rusted surface but it will protect the surface as well
,
ive used it a fair bit on vehicles and stuff and it works great

[Dean Dreamer]

Hi All

I was asking similar questions in another post Bright steel square bar guide rails - CNCzone.com-The Largest Machinist Community on the net!

I have had some great feedback reagarding lapping of guide rails to make them flat.

my point for what its worth. Oxy cutting steel is messy as hell. so i would use old engine oil to keep the rust at bay. not pretty but works well and free..

[diyengineer]

if you develop rust, use a bath of food grade citric acid and water to remove it. If you check out my build, i brought all my steel rails back to perfect condition, and they were really scary looking.

Hi All

I was asking similar questions in another post Bright steel square bar guide rails - CNCzone.com-The Largest Machinist Community on the net!

I have had some great feedback reagarding lapping of guide rails to make them flat.

my point for what its worth. Oxy cutting steel is messy as hell. so i would use old engine oil to keep the rust at bay. not pretty but works well and free..

[harryn]

The challenge you face, is that CRS is just barely ok as a rail. Nominal 5-6 mm thick material (the width of a skate bearing) sounds pretty thick until you start mounting it, and then it just twists down to the mounting surface. This starts to make a person think that 12mm wide and 2 bearings is closer to reality.

CRS isn't very hard, but hard enough for hobby use. By hobby, I mean a few hours a week, not 10 hours a day.

As soon as you start to do anything to improve cold roll, the price goes up - a lot, even in the US. CRS vs ground CRS is at least 5X the price, and I have seen on-line prices of 10X as well.

At that point, you might as well buy a commercial rail system, because that is the price point you are at anyway.