Metal fabrication- pipe bending, drill presses

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Metal fabrication- pipe bending, drill presses

Postby rodiponer » Fri Apr 08, 2011 6:44 pm

Hi Guys,
I need to put a slight bend in 1" square aluminum tubing. 24" lengths need a mellow bend so that the center is about 2" off from a straight line. What is the best tool or way to do this? Harbor Freight has 'pipe benders', hydraulic benders, and floor mounted things, and a thing with a wheel. What would work best?

I'd also like to be able to do tight 90 degree bends in 3/4" to 1" round aluminum and thin walled steel tubing. The kind of bends you'd see on a kids bike trailer or wheelchair.

My second question is about drill presses.The bit on my drill press wanders about 1/8" as soon as it presses down into the steel. I believe this is called run out.

I have the least expensive drill press that Harbor Freight sells. Is there a way to fix this, or should I just not have bought such a cheap drill press? How much does one have to spend, or how big does a drill press have to be, to not do that? I am just drilling 3/8 or 1/2" holes in aluminum and steel tubing. How do I tell at the store if the drill press is going to do that? I've been using my milling machine to drill holes that can't have a wandering bit, but it's a pain in the butt since it's CNC, so I can't feel the amount of pressure on the bit and have to write a little program in that cryptic language to get it to go the right speed and peck. I'd rather just drill these holes by hand...

Thanks everyone. I'm still surprised that I was able to make Aluminipede, given how little I know.
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Postby ygmir » Fri Apr 08, 2011 6:52 pm

two blocks of wood and stand in the middle?
if you set it up, to account for "spring back" you can get pretty accurate.
even if you have to jump up and down a little.

sometimes, "center punching" where you want the drill to start helps.
give the punch a good whack, to make a nice size dimple.
Just a thought, that's worked for me.

a conduit bender will help with tight bends, but, be careful. Those thin walls can easily collapse.

good luck
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Postby Elorrum » Fri Apr 08, 2011 7:10 pm

a bender with squared up sides instead of a round channel like a conduit bender might help support the sides from blowing out.
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Postby Sic Pup » Fri Apr 08, 2011 7:49 pm

I'm not sure how portable this method might be but you may be able to adapt the concept to your specific needs.

I did some work with Growing Power out of Milwaukee teaching folk in food deserts how to build hoop houses out of readily available, inexpensive material. We used standard chainlink fence pipe as the support for the plastic sheeting(I believe it was 1 3/8"). We built a jig on a sheet of plywood with 2 7' lengthes of 1"x3", some trapezoidal shaped pieces of 2"x4" some wood glue, screws and 2 firring strips.

First we secured one 1"x3" perpendicular to the plywood with a couple of screws.

We screwed the second 1"x3" into the far end (not attached to the plywood) of the first piece so it would swivel the arc across the length of the plywood. Once the arc was drawn they can be removed.

Glue and screw the pieces of 2"x4" along the length of the arc.

Glue and screw the firing strips into the blocks thereby creating the arc.

Glue and screw a longer section of 2"x4" along the far end spaced so that the object to be bended just fits in the gap.

Insert the pipe in between the longer 2"x4" and the first trapazoid of 2"x4" and slowly pull the pipe down until it hits the arc, slowly move the pipe up and continually bend the pipe down towards the arc.

Voila, you're left with identical pieces of bent pipe.

Caveats:
The arc we worked with was more severe than what you're describing (essentially a half circle) but if you can get the bend you want down once this method will allow you to duplicate it.

We were working with 31' lengths of round pipe and it really helped to have a second set of hands to hold the pipe flat against the plywood .

Slow and steady will prevent the pipe from crimping (I don't know how this will work with square pipe)

Here's proof that I don't have an artistic bone in my body:

Image

I hope this helps.

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Postby Drawingablank » Fri Apr 08, 2011 7:50 pm

Bending square tubing is a real PITA, but for shallow bends I have had moderate success with the following:

[list=]Cut a block of wood in the shape of the bend with a bandsaw (save both sides of the cut[/list]
[list=]Position the tubing between the 2 pieces of wood[/list]
[list=]Squeeze the blocks together. On small tubing a vise or large C clamp may work for this. For 1" you will probably have to adapt this to a press or lacking that a heavy duty comealong rigged up properly may do the trick.[/list]

1/8" of runout seems excessive - even for cheap import stuff. I assume you have checked the bit for straightness (or tried a different bit). Give the chuck a once over. A sticky spring in the chuck could cause this as could uneven machining on the jaws. My experience with HF stuff is that the weak link is their chucks. If you can borrow a chuck from someone to test this, it may simply be a matter of just buying a quality chuck for the machine.

Measuring runout in a store requires some tools (dial indicator and a way to attach it), and will almost certainly vary from one machine to the next anyway. When shopping for most rotating stationary tools runout is a basic spec and you may be able to find it on the manufacturer's web site even if they don't have the specs at the store.
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Postby LeChatNoir » Fri Apr 08, 2011 10:22 pm

Rodiponer,

Drawingablank may be right. Check your jaws by closing the chuck all the way with no drill in it and see if the tips of the jaws line up. And you might need a new chuck for the drill, which may cost you as much or more than the cheap drill press. I finally replaced the cheapo jacobs-copy chuck on my large drill press with a nice keyless one and it's working very well.

Regarding bending the tubing, Sic Pup's idea is pretty much on for what you're needing. Though for your lengths, I think you could cut yourself a semi-circle out of wood that's slightly smaller than the radius you need to allow for the tubing springing back. If you were bending tighter radii, then you'd probably need a square slotted bending fixture and a square slotted guide to follow the tubing around the radius. But I suspect it'll be ok without it for what you're doing. Try to do it with longer pieces of tubing, cut off the length you need, then advance and keep bending. Better leverage this way. Or you could use some sort of cheater.

As to the tighter bends, those are ordinarily done on a bending machine or dedicated fixture that controls the collapse of the tubing in a way that it strengthens it and they do have slots the size of the tubing to help it retain it's shape.
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Re: Metal fabrication- pipe bending, drill presses

Postby LeChatNoir » Fri Apr 08, 2011 10:35 pm

rodiponer wrote:My second question is about drill presses.The bit on my drill press wanders about 1/8" as soon as it presses down into the steel. I believe this is called run out.


Wait, I just re-read this. Run out is actual eccentricity in the spindle of a machine tool. What you are experiencing sounds like your drill is wandering due to, as ygmir pointed out, lack of a center punch mark or similar. Split point drills can help alleviate this... very light pressure and let it make is mark, then proceed with normal pressure. Make sure your table is perpendicular to your drill axis, too. Even very slight sideways deflection will make it wander. And a center punch is a good idea.

There is also a type of drill that is sort of a center drill/jobbers drill combined (jobbers drills are what you normally think of as a drill bit) so that it starts itself on location, but I'll have to remember what they're called and then I can post a link.
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