[LazyMan]

Steel rectangular tubing is never very flat or straight. How are you some of you guys building machines with steel tubing machining the surfaces flat to mount rails to?

The only way I can see it being done is only with access to large machinery.

[Geof]

Not exactly an answer to your question.

The sides of steel tube definitely are not flat, but if machine them flat you will likely finish up with them no longer straight. There are a lot of stresses inthe tube as a result of the manufacturing process and when they are released unevenly, such as by machining material off one side, how the tube will distort is not predictable. It is predictable that it will distort; take a piece of tube and slice it lengthwise, the two pieces curl away from each a surprising amount.

It is not just the flatness of the tube that has to be considered but additional distortion from welding, or bolting, a frame together. To get flat surfaces for mounting rails you need to either do a lot of shimming and/or bed the rails in an epoxy. If you so a search using 'moglice' or 'madvac' you will find more information.

[BobF]

Here are 2 builds using steel tubing and how they solved the problem. (same solution)
Haydn's build thread. Smaller than Madvac but similar construction methods. Steel tubing.
http://www.cnczone.com/forums/showthread.php?t=30751
Madvac CNC the inspiration
http://oneoceankayaks.com/madvac/madvac_index.htm

[jcc3inc]

Sir,

When I was in the business of making plasma and pxyfuel machines, we made our cross axis ways systems using steel tube. We chose to weld flats to the top and bottom edges of the tube, using care to keep it from twisting and keep it straight while welding. After the tube had cooled, we did flame straightening of the assembly, choosing 3 or more areas on the backside (opposite the welded flats) to heat lines up and down in these places. This was done with the tube assembly horizontal. After cooling, the straightness was rechecked and redone if needed. Next, we sent the assembly to the grinders where they Blanchard ground the mounting surface of the weldment (this would be the two welded-on flats). This procuced an excellent starting point as straightness and no twist were assured.

Regards,
Jack C.

[jcc3inc]

Just as an adjunct to the idea of bolting and epoxying many parts, the attached pix show my test bed machine made without the use of a welder. I used a 1/4 x 4" cold drawn flat as the main cross axis ways; is is bolted to a 2" sq tube. If I were making a small machine for routing, maybe the flat should be 1/2 x 6 bolted AND epoxied to a larger tube for better stiffness.

Regards,
Jack C.

[eloid]

Here are 2 builds using steel tubing and how they solved the problem. (same solution)
Haydn's build thread. Smaller than Madvac but similar construction methods. Steel tubing.
http://www.cnczone.com/forums/showthread.php?t=30751
Madvac CNC the inspiration
http://oneoceankayaks.com/madvac/madvac_index.htm

Is Madvac Inspiration posted only on that link or is there more
of build log here cnczone. please post a link if you have it i didnt come up with much with the search button here?

[BobF]

Is Madvac Inspiration posted only on that link or is there more
of build log here cnczone. please post a link if you have it i didnt come up with much with the search button here?

That is the only link I know of. There is a pretty complete build log on the site.

[Apples]

Jack,

Once the rails were ground. How do you stop them from rusting? Did you just hit it with a coat of paint? Becasue you can't really have the rollers/bearings running along on painted rails.

Peter

[jcc3inc]

The way we handled the rust problem was to spray the ground surfaces with LPS-3, an aeorsol spray of grease-like material. That seemed to help prevent rusting.

Regards,
Jack C.

[wcarrothers1]

LPS - 3 or that tephlon stuff.

How ever... If your exposed steel rails start rusting your not using your machine enough..hehe

b.

[toastydeath]

There's always the long way - scraping it.

[BobF]

Gun blue. Protects better than paint, and doesn't wear off easily.

[Apples]

Gun blue....

That stuff would be really thin wouldn't it, so that would not affect the thickness of the rail as pain would. yes?

[CarveOne]

Anything you put on the contact surfaces will quickly wear off. If you use your machine every few days the contact surfaces will stay relatively free of rust unless it is in a damp area.

Cold bluing won't stop rusting and the contact surfaces will soon have no bluing on them. Hot bluing done in a gunsmith's tanks is somewhat better but it will still rust eventually, and it wears off also.

Gun Kote spray finish on properly cleaned steel is pretty tough, but will soon wear off on the contact surfaces. It has to be baked.

You can use BoeShield T-9 or carnuba wax on the unpainted steel surfaces. These don't collect dust (which forms a wood paste). Woodworking supply sources have them both. These too will wear off of the contact surfaces.

CarveOne

[Cartierusm]

As a side note to those of you interested in building new machines. For years I just assumed that aluminum was "true". I guess it was because it was clean looking and came in a more uniform package. But as time worn on and I began measuring new stock and nothing is very "true". Always be sure to mill aluminum flat and always check everything with a precision straight edge and square.

[andy_ck87028]

Why does it need to be flat?

For example, if the material you are cutting is non rigid, then it will assume the bed it is laying on. If that bed has been pre-trued to be equi-distant from the combined top surface matrix of the X and Y rails, then it is not important to have a true surface.

I agree that it would be a problem if the material to be cut is rigid.

Furthermore, I have long held an argument that the larger the sheet to be cut, the less likelihood there is of needing full precision across the entire plane.

So, from a hobbiest perspective, design the rails for the material intended rather than creating a design criteria that cannot be met within the hobbiest budget.

Andy

[BobF]

Gun blue....

That stuff would be really thin wouldn't it, so that would not affect the thickness of the rail as pain would. yes?

Blueing is more a chemical reaction and not a coating. If you use Oxpho-Blue from Brownell's it will darken the metal and prevent most rust. It will likely wear off on a high contact surface, but it will help prevent rust. Once the metal is blued, you can coat it with any of the coatings suggested or any lubricant you like. There is no guarantee that anything will prevent rust, but this helps.
I have used it on hand tools and the ways of my wood lathe. I think it helps.

[Apples]

What about this Blanchard Grinding?

I think that is just a big diameter grinding machine?

Will grinding the steel stop the warpage or minimalise it compared to milling it?

Peter

[Apples]

What about milling that heavy C section steel flat, will it warp as much as the rhs???

I have some 75x150mm, 10mm and 8mm thick.

Peter

[toastydeath]

Blanchard grinding is vertical spindle grinding on a rotary table. If you have a 4' bar, which isn't unreasonable, you need 4' diameter swing on the blanchard, which is unreasonable for a DIY project. There are other grinding processes which require less expensive time on a smaller machine.

The core issue here is that there's a ton of surface stress in rolled steel tubing. No matter how you take material off, you are always upsetting the balance of stress, resulting in warp. Stress relieving it helps tremendously, both on the short term (keeping warp from developing during the machining process) and long term (stability as the part continues to stress relieve itself over the working life).

But the OP wants to know about how to machine it without machinery capable of handling the part. Scraping is how that was done originally, and that is how I would do it here.