[REVS]

Hi All-

I will be making a run of large 12' x 7' frames made from the aforementioned 2" x 2" x 3/16" 5053 aluminum angle. They are to be mitered, welded, ground down and powder coated. There may be some kind 'strainer' to keep it rigid for transport and painting.

I've done some aluminum in the past (http://itisaprocess.tumblr.com/post/852 ... o-pictures), but nothing where squareness is critical. Anyone have tips / pointers as to how to get a nice square fit up / weld on this stock?

My plan is to cut the stock on my steel max dry cut chop saw (with a new aluminum blade), then touch up the cut with a bench sander if necessary so as to get it dead on square / 45 deg. I may grind some bevels in. Then I'm going to fit the whole thing up in corner clamps on my assembly table and tack it up. Then I will weld from the outside of the corner in, in 1" stitches.

I've done a few prototypes and they seem to come out acute. obviously, if they are not dead square, then it will torque out the frame, no matter how flat my assemble table is. It would seem that the aluminum pulls the joint closed more than steel would. My solution would be to cut them a little fat of 45 to compensate for this, but I would rather have a welding technique that did not necessitate it in the first place.

Any pointers appreciated,

-Rev

[weldin mike 27]

Nothing wrong with pre setting weld joints. It's the smart way to work. The trick is, welding each one the same so you can be assured that your preset will work every time.

[Braehill]

Personally I don't like changing my miter cut, I just leave a little more gap on the side where my weld will terminate. On angle I usually start on the open edge and weld towards the heel with the open ends touching and a gap at the heel. How much gap is dependant on how long and how heavy the material. It's a guessing game and how good you guess is how good it turns out some days.

Len

[REVS]

Thanks for the pointers. I'll go TIG up a few more samples and see if I can't get that consistent dead 90 degree miter before I go cutting up 12' lengths.

[Rick_H]

Personally I don't like changing my miter cut, I just leave a little more gap on the side where my weld will terminate. On angle I usually start on the open edge and weld towards the heel with the open ends touching and a gap at the heel. How much gap is dependant on how long and how heavy the material. It's a guessing game and how good you guess is how good it turns out some days.

Len

That is the way I do it as well, sometimes I'll add a little thin stock under the center section to back bend it slightly if it wants to pull. I clamp it to the acorn table tight.

Last time I used the spool gun on the Mig, less heat input...

[Bill Beauregard]

Preheating the joint will cause the whole thing to expand. Then it will all shrink at once. It should reduce distortion.

[REVS]

About what temp would you preheat this too? Also, does anyone use a coped joint for this application? More cutting obviously but intuition tells me there is less opportunity for warpage.

[Braehill]

Revs,
I would think more cuts translates into more welds that translates into more warpage.

Len

[REVS]

Yes, I would too! But from what I've read it seems that since all the welds are rectilinear to the frame the warpage is minimized. The miter has the potential to magnify warp because it has the possibility of creating more radial movement.

[Braehill]

Revs,
Check out this video that Jody did awhile back and you'll get a good idea how your metal moves while welding. Just because your welds are in line with the piece being welded doesn't mean they move in that line while being welded.

http://welding-tv.com/2014/05/07/weldin ... damentals/

Len

[Rick_H]

How'd it work out?

[REVS]

Coming along well. I'm taking some time to dial this in before I really start production so as to avoid the SNAFU possibility.
I built myself a quick table for this job as I mentioned previously in the thread. http://itisaprocess.tumblr.com/post/111 ... r-upcoming
Its dead flat should help out a lot. I am still having trouble dialing my Chinese SteelMax saw to dead 90 / 45, which is a bummer cause I just bought a new blade for it. As some of you have probably experienced with shitty saws, the table isn't flat or perpendicular to the blade / parallel to the substrate its sitting on. I did a lot of shiming and what not to get it as close as possible but even that is not good enough for these purposes. I am going to use my woodworker shop partners Festool Kapex miter saw next week and see if I can't get better tolerances with that. We built a good table for it so it should cut at a perfect 45, and I'll clamp it sufficiently so it won't pull into the cut.

I am thinking that a gusset of some sort would help with movement.

More pics to come next week.

-REV

[dave powelson]

Coming along well. I'm taking some time to dial this in before I really start production so as to avoid the SNAFU possibility.

-REV

I'm confused. What are these frames 7' x 12' for? They have no gusseting or inner bracing?
You're fixated on corners being square, but for fit and function-what's the inside/outside tolerance of the width & length?
......and the tolerances are measured at 70˚F? ......and you're furnishing these to outside party whose method of
inspecting the frames is exactly what your inspection criteria is?

On most frame fitups using mitered joints with bevel groove weld on the outer corners and flat outsides of the joint, 90˚ open corner joint on vertical outside corner; and using match cut lengths, multiple location checks on width and length to get those 'close', then measure the diagonals--which tells much as to the true squareness of the assembly, then checking each joint squareness for confirmation of what the diagonal measurements showed, then making adjustments to get the needed width/length to tolerance. Pay more attention to the diagonal measurements than what the square sez slapped up to one corner.
IOW--it's a balancing act, since in these large sizes, the mill stock variances do show up.
The most important feature--length or width is established with some trade-offs in squareness or diagonal measurement.
Mill stock in 2x2x3/16 angle, can and will have some twist, camber, bow, bend, warp--as furnished.
A frame this size will be wholly flimsy without any additional members and could distort just from handling.
Is this angle stock with normal radiused feet and radiused inside?....or sharp cornered....or 'architectural' grade?

From past and present experience with p-coaters:
-etch the frames and rinse with phosphoric acid--then white glove handle-ideally
-design, build and furnish a stout steel frame for appropriate hanging for the coater to use. AL can and will
distort and sag--quite nicely and permanently, if allowed to.
-verify your and others handling methods by running a test frame
-coater must have accurate oven controls and verify frame temp before bake cycle
-how/what/where the coater handles the frames before, during and after processing is important

-how you handle the frames is equally important
This sounds like the job from Hell.

[REVS]

Dave-

All good points you make. I feel that the potential problems that you point out with this type of job(from hell?! Lol) are mostly solved by a flat assemble table and square welds, consistent distributed heat input. It's when one of your joints opens up and /or one of the corners pulls out of 90 that problems start to arise, no?

I think I mentioned previously that these frames will need a strainer of sorts for transport. They are to be mounted on an existing painting stretcher so any type of gusset, brace etc will be hidden.

I am still designing the construction.

For the gusset I was thinking 3/16" x 2" flat bar, though I am also considering a 3/16" plate if nec.

If this is indeed the job from hell then my feeling at this point is that hell ain't all that bad.

[REVS]

Revs,
Check out this video that Jody did awhile back and you'll get a good idea how your metal moves while welding. Just because your welds are in line with the piece being welded doesn't mean they move in that line while being welded.

http://welding-tv.com/2014/05/07/weldin ... damentals/

Len

Thanks Len,

I knew about this in theory and practice. But I never quite saw it demo'd like this...direction of travel-- makes so much sense. You (and Jody) just made me that much of a better welder.

Thank you very much,

-revs

[REVS]

Here are some pics of a sample I TIG'd up today. I think I am going to pull the trigger on this next week.

it came out pretty durn square, after a few prototypes. I've done a few at this point, and think I've got my tacking order such that it comes out square and not obtuse or acute. I would be very curious if anyone has any recs about the order in which they would tack this up. I found that if I start on the vertical outside corner, it ends up obtuse, so I'm starting on the horizontal top section toward the outside corner, then the vertical outside corner, then the underside.

200A, 60% penetration, 4043 filler, 3/32" lanthanated electrode. I found that 5053 filler has a tendency to crack more. My imagination?

I cut my vertical bevels on the chop saw, and am grinding my horizontal bevels by hand with a wheel. I don't like the burr it leaves though/ flap disc? Or clean up with file...

[Braehill]

Revs,
I would use 4043 for the reason you stated, cracks less.

For bevels on Aluminum I use a trim router, I finally found a 30* chamfer bit for it, I used to use a 45* bit. It's very fast and clean. The chips go everywhere so wear glasses and plan on a mess.

Len


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[REVS]

Thats a great idea-

One would need both an over and an under-mounted bearing for doing the 45 degree part of the angle, or perhaps something like this: http://www.toolstoday.com/p-5004-double ... embly.aspx

I just cleaned all of the aluminum chips out of my shop last friday, but it looks like that may have to happen again...