Machining Steel Tubing Flat

[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.
My First Router, Built in Steel
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]

Originally Posted by 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. My First Router, Built in Steel 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]

Originally Posted by eloid 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.