View Full Version : why not steel?

09-28-2003, 03:44 AM
Why don't we see (m)any CNC routers made out of steel? I've seen lots made from aluminum and/or wood, but nobody seems to use steel for anything else than a stand.

Here are they reasons that immediately popped into my head for this:
1. Aluminum is stiff enough
2. Aluminum is easier to machine than steel
3. Aluminum is lighter weight.
4. Aluminum will only lightly corrode, but not "rust"

I'm guessing that for most wood cutting, aluminum machines provide enough stiffness and accuracy.

being the standard "tougher is better" advocate that I am, I have been debating aluminum vs. steel for some times. I'm leaning towards making my router out of steel, but have some doubts.

1. An all-steel router of any good size is going to be UBER-heavy!

2. It will be more stiff. May allow heavier cuts without loss of accuracy?

3. Steel is cheaper than aluminum

4. It might rust if not well maintained.

I'm not really sure what I'll eventually decide, so fill me in on any insight y'all have.

High Seas
09-28-2003, 08:11 AM
I'm real new at this - but my thoughts for picking AL are the ones you mentioned.

A big concern I gather, is excess weight in the gantry (if moving gantry mill).

Plus - I don't weld - would have to get it done - I'd want the unit square - so would need a welder I'd trust (and make sure they had a frame/chasiss jig to keep it that way).

I also like the "tinker-toy aspect" of aluminium frames!

:cheers: Jim

09-28-2003, 09:41 AM
Plus you can cut and machine aluminum with woodworking tools.


09-28-2003, 01:07 PM
Originally posted by ger21
Plus you can cut and machine aluminum with woodworking tools.


A buddy made an all steel machine, mostly from angle iron. It works very well. He painted it. I think steel is a great material if you have the tools to work with it. I like aluminum because it so nice and shiney. :)


09-28-2003, 05:23 PM
Well guys,

I guess i am one of the few then, making mine for 90% out of solid and 3mm sheet steel. Sheet steel tends to vibrate / bend more than solid materials, so i had to add angles and bent edges for more stiffness. The weight is within fair limits and welding and folding is no problem for me.

Aluminium is lighter, more expensive and no corrosion / rusting problems occur. The price is for me the biggest argument not to use aluminium. And i cannot weld aluminium. Too bad i have to paint or oil my sheet steel. It rusts in seconds :mad:

The remaining 10% are made up by stainless steel for the sliding bars and brass for the sliding blocks.

In future i plan to post some pics. The machine is not finished, not just yet :D


09-29-2003, 12:53 AM
I am making mine out of steel angle. I'm using 2 x 2 x 1/4. And still it flexes. The amount is acceptable for what I plan to use it for. As far as weight? I've added concrete to remove a fair amount of flex. It weighed 150 before and now weighs about 500. Still can move it with an engine hoist, and will...

Welded steel frames produce their own problems. At first I was going to use a laser level to set up the THK rails. I ended up using a Machinist Level. Great investment. Took me a full day to do the first axis. The time was well spent. I found that I had to be systematic about setting the shims. (I made sure to tighten all the cap screws in the same order every time I changed shims.)

I couldn't afford making a machine out of aluminum that has the same characteristics that I'm after. Check out:


and the photos I've left. Hope this helps.


09-10-2004, 06:14 AM
Hi guys,

Too bad that this thread ended in a broken link. I really thought that this thread was going the right direction.

My first machine is practically finished now. You could say "Been there, done it and made some major designing mistakes". Now that i learned a bit more about bearings, steppers, materials and my own mistakes, i'm ready to built my second machine.

I will continue to use the first one though, just for practising G-codes and so on. I even consider on mounting a pen or pencil in the Z-axys, just to learn a bit more about 2D G-codes. Just think about it, having a very delicate pen mounted on your Z-axys, suspended in some kind of mechanism to prevent it from being destroyed when plunging downwards :p (I don't want to engrave anything with my Rotring pens :p )

Some ideas for upcoming colder months. It keeps me off the street i guess :D

Maybe somebody could fix the broken link in the message above? Tnx!


09-10-2004, 07:48 AM
Hello Mr. Ed,

Glad to hear you have kept at it! Like you, I clamped a pen in mine to do tests and I still have a bunch of blunt felt tipped pens in a can in my shop :rolleyes: I hope you get a chance to cut something with yours, soon.

I've noticed a lot of the links in various posts don't work since the site was updated and posts moved. My post above has been moved to the Project Logs section and can be found at


Hope this helps.


09-10-2004, 07:08 PM
My router will be made from scrounged structural materials. I bought a frame made of square steel tubing that is going to be the basic structure. I'm a big fan of square steel tubing. Square tubing is much much stiffer than the equivalent weight of angle iron.

I have some hefty aluminum beams that are going to make up the gantry.

09-11-2004, 08:34 AM
A good question, "Why not steel"

I love steel, its cheap, its strong, and it doesnt lie.

Rust is not a problem, unless you leave your machine out in the rain. I sprayed my machine in fish oil and it shows no sign of rust.

I would much prefer to weld two pieces of steel together than bolt aluminium together.
As for speacial tools needed, I dont think you really need that much. A cutoff saw, and a welder, thats all. I would expect most hobiests here would have both those things.

My only concession for aluminium is that it looks nicer.

09-11-2004, 07:40 PM
Steel is no longer always cheaper than aluminum by the foot... yes by the pound it is far less expensive, but per stick of similar sized metal Al can come up cheaper. (For what it is worth, Al is almost exactly one third the weight of steel.)
I just bought a few uncut sticks of 2" x 1/8" square tubing in both metals, Al cost less. The seller was astounded at the new steel prices as was I; it has almost doubled in the last two years at the per tonne level so those of us stuck buying retail are paying dearly.

Here in the humid southeast U.S. steel rusts immediately, the mantra is grind and prime.

There is an aluminum "solder" ...use MAPP gas, not propane with a standard blowtorch...seems to work for lighter strength connections.

Welding steel does give a solid bond as compared to bolting Al, but steel can warp substantially from the process. It is a real disappointment to have things twist out of shape even after taking all the time to carefully set everything up and tack and true.

09-11-2004, 08:43 PM
Here is my story:
I was going to build a nice steel machine. I even went as far as having the steel delivered. But, I figured when all was said and done that my 4'x8' machine would weigh over 1000 lbs. 4' wide x 8' long x 4' tall at 1000 lbs. Essentially, a big unmovable car in my garage. Of course, I knew that when I ordered the steel. But once you start looking at it and see how absolutely big and heavy the stuff is....well, it was just different in person than it was on paper! LOL. So, I chickened out and gave the steel to a friend who is building a metal bridge (another story).
I then decided to go with T-slots aluminum. Easy to put together, take apart, and reconfigure if need be. Light, mobile, and doesn't cost that much when bought surplus. Did I mention that aluminum is much easier to work with? However, it's a trade off. Steel cnc routers have lots of weight so they don't bounce or shake at all. I would think you could have much better accuracy with a steel machine because of that. I think most of the professional machines are really pretty heavy (We ain't talking Shopbots here!)

In any case, I'm happy with my choice. I'll trade a little speed and accuracy for being mobile and able to reconfigure. It just depends on what your looking for. It all has to do with "Design Philosophy" and what suits your needs for the moment.


09-11-2004, 08:45 PM
I agree that steel prices are way up, but using steel is still cheaper than aluminum(assuming you have the tools for both). The problem is that you are comparing the same sized steel and aluminum pieces. Aluminum is 1/3 the weight of steel, but it also has 1/3 the modulus of elasticity(ie it is less rigid and bends easier). To get equivalent deflections, you need to use much thicker aluminum than you would with steel. Even a solid 2x2 bar of aluminum would deflect more than a 2x2x1/8 steel tube. To get the same rigidity in 1/8 aluminum, you would have to go to 3x3.

09-11-2004, 09:37 PM
Re strength of Al:
Excellent info, thanks...are there multipliers that can be used to convert steel's properties to Al? Beamboy seems to be a handy freebee stress deflection calculator but as far as I can tell it only calculates for steel. It would be real nice if there were a constant to change E and I by...

09-11-2004, 09:52 PM
The only thing you have to change is the modulus of elasticity "E". BeamBoy defaults to 30,000,000 psi for steel. Aluminum is around 10,000,000 psi or about 1/3 that of steel. The moment of inertia "I" only depends on the shape and thickness, not on the actual material, so it doesn't change for steel or aluminum. For the same size beam and loading, aluminum will deflect 3 times as far as steel.

09-11-2004, 10:14 PM
Wow, quick answer and easy solution.