Milling Steel Tubing

[kizmit99]

Greetings all,
I have a question about the proper way to setup steel tubing for milling. I was trying to mill some quarter inch slots into a steel tube (1.5" dia x .058 wall) the other day and discovered that it is apparently more difficult that I would expected... The tube is 4130 steel and has an adhesive backed paper layout stencil applied to the outer surface. For my setup I tried first just clamping the tube in my mill vise (so I was applying clamping force across the diameter of the tube). I didn't crank the vise down too tight because I didn't want to deform the tube. The first slot worked basically ok, but on the second slot the tube started rotating in the vise (not enough clamping force I assume), but cranking the vise tighter just deforms the tube (not crushed, but a noticeable amount)... So, I tried slipping a properly sized piece of solid aluminum rod into the tube. This lets me crank the vise tight without deforming the tube, but I still experience slippage. This time it was lateral movement. I clamped some 1-2-3 blocks to the table on either end to stop that, but then it just started rotating in the vise again. On inspection it turns out the that paper label would just tear and allow the tube to slip...

So - what would be the "proper" way to setup for this type of milling operation? 3-jaw on a rotary table flipped to 90*, with a center tail stock? Since the tube is fairly thin I would think I'd need a chunk of the aluminum rod inside on the chuck end to avoid crushing? But also something on the tail end for the center to ride in? Not sure I see how that could be held in place (without pins or something like that)...

Is there some other setup I'm missing? Let me know how I should be doing this!
Thanks!

PS: assume the tube is only about a foot long, and it's a G0704 mill...

 

[JimDawson]

Clamp the tube right down on the table, right over the center T-slot. Sometimes I use a piece of shafting through the tube as part of the clamping system.

 

[pstemari]

And position clamps or blocks around it so it can't move in x or y.

Are you milling through the welded seam?

Sent from my Nexus 6 using Tapatalk

 

[David VanNorman]

If you are cutting a long slot put a piece of stock the same size as you are cutting. It will hold your slot open and give your clamps a better hold. your tube won't collapse and slip.

 

[Ebel440]

You can make a jaw for the vise with a 45 degree angle down the length to hold the tube better. It can actually be any angle as long as it gives enough clearance to the bottom of the angle. Or it can be a radius but the radius has to be sized for the tube. Or try the setup you used with the plug in the tube but put a piece of paper between the jaws and the tube. It may give you enough grip to get it done

 

[brino]

...how about a sacrificial rod of aluminum inside the tube. Something with a fairly tight fit, machine right thru it, then remove after your done. It will enable better clamping without distorting the tube, and support any free edges around your slot from collapsing.

-brino

 

[blaser.306]

Depending on the length of your work piece( and size of your vice of course ) , clamp it with the square cut ends as the clamped surface. You may have to re orient the vice to suit . Just a thought ( all that before coffee even )!!! This should give higher clamping force and less chance of distorting the work.

 

[Charles Spencer]

When I cut round stock or pipe on my band saw I put a small notch where I intend to cut. I have a cutoff wheel on a mini bench grinder that I use for this purpose. Of course this is not as accurate as you might need to get on a milling project.

For holding round stock in a mill I usually use v blocks against the movable jaw and a 3x5 index card folded over the fixed jaw.

 

[rmack898]

Vee blocks against the movable jaw of the vise so that you have 3 points of clamping contact on the tube.

 

[RJSakowski]

Greetings all,
I have a question about the proper way to setup steel tubing for milling.

Clamping thin wall tubing is always problematic because you can't get enough clamping pressure to hold the work securely without severe distortion. Turning a plug to fit the tube will enable you to apply greater clamping force. Another method would be to support the tube externally full circle as with a collet. At 1.5" you won't have a collet but you can make a clamp fairly easily. Machine two rectangular blocks so when they are placed together, they make a square slightly larger than your tube O.D. Clamp them together in your vise and bore a hole the same diameter as your O.D. Now you have some custom jaws which will fully support your tubing. If the tubing slips, you can shave a few thousandths off the mating surface of the clamp to allow full clamping pressure.

Bob