I got myself a keyboard arm for my desk and instead of paying $100 for their molded ABS tray I thought I'd make an aluminum one.

I want it to be 12" deep by 32" wide. The mounting surface on the arm is 5 3/4" x 5 1/2" and it would mount in the center back of the tray.

I'd like it to be reasonably rigid, but I'm not going to be leaning on it with my upper body weight. I'd like to put a 1/4" - 3/8" bend in the back to stop the keyboard/mouse from sliding off so that should help give it some structure.

I'm not crazy about putting any other bracing on the bottom, as I want the top surface to be as close to my legs as possible.

1. What grade+thickness of al? I'd like to keep it at max 1/8" if possible.
2. I was thinking of getting it anodized for a finish, but I'm not set on that.
3. I'd like to tap holes (they can go the whole way through) and mount from underneath to have a flat surface, but countersunk bolts would work.

Or if anyone knows a better forum for this, please let me know.

On Sat, 29 Sep 2012 03:12:44 +0000, KEYBOTRAY
wrote:


I got myself a 'keyboard arm' (http://tinyurl.com/chtfdey) for my desk
and instead of paying $100 for their 'molded ABS tray'
(http://tinyurl.com/9hecxvz) I thought I'd make an aluminum one.

I want it to be 12" deep by 32" wide. The mounting surface on the arm is
5 3/4" x 5 1/2" and it would mount in the center back of the tray.

I'd like it to be reasonably rigid, but I'm not going to be leaning on
it with my upper body weight. I'd like to put a 1/4" - 3/8" bend in the
back to stop the keyboard/mouse from sliding off so that should help
give it some structure.

I'm not crazy about putting any other bracing on the bottom, as I want
the top surface to be as close to my legs as possible.


- What grade+thickness of al? I'd like to keep it at max 1/8" if
possible.

6061T6. With a bent lip at each edge 1/16" would be more than
adequate.
- I was thinking of getting it anodized for a finish, but I'm not set
on that.
- I'd like to tap holes (they can go the whole way through) and mount
from underneath to have a flat surface, but countersunk bolts would
work.
Countersunk bolts would be my recommendation. With Stover nuts on the
bottom, or acorns and locktite.

A few basic concepts to start with. One, all aluminum is about the same
stiffness (force required to flex it a little but not so much it doesn't
return to the original shape when you let go), the differences are in
weldability, yield strength, and bend radius. 6061 is the most common,
welds nicely, has a good yield strength (how much force is needed to
permanently bend it), but the minimum bend radius is at least 5 or 6 times
the sheet thickness to avoid cracking. The common alloy to bend is 5052,
which has the same stiffness, about half (depends on exact spec) the yield
strength, also welds nicely, and has a minimum bend radius of about 1.5-2
times the sheet thickness so you can make nice tight bends.

Next, given the material the final stiffness is determined by the shape, and
here height perpendicular to the direction of bending is everything. The
stiffness goes as the height * height * height, or height cubed, so twice as
tall is 8 times as stiff. If you have a keyboard sized sheet of aluminum
you can either keep making the material thicker and thicker until it gets
stiff enough for you (it generally works out that stiffness requirements
result in designs that have way more than enough yield strength, which is
why I'm focusing on stiffness), or you can take a sheet of thinner material
and turn the edges up to make a three sided box (rear and sides turned up,
front open so there's no edge sticking up to hit your hands on). Using
thinner material and turning up the edges results in a much stiffer and
lighter tray. You can turn the edges up or down but since you wanted to
minimize the overall height I'd use some 5052 that is roughly 1/16" thick
and turn the back and sides up so that they are at least 1" tall. Remember
that height cubed? Turning the edge up 1" versus only 1/4" is a difference
in stiffness of (1/.25)^3=64, and the tray still is only as tall as the
keyboard. Only thing left is to mount it, and that's left as an exercise
for the student :-) :-) (actually I can't remember your description of how
you wanted it mounted, sorry).

-----
Regards,
Carl Ijames
"KEYBOTRAY" wrote in message ...


Or if anyone knows a better forum for this, please let me know.




--
KEYBOTRAY

"KEYBOTRAY" wrote in message
...

I got myself a 'keyboard arm' (http://tinyurl.com/chtfdey) for my
desk
and instead of paying $100 for their 'molded ABS tray'
(http://tinyurl.com/9hecxvz) I thought I'd make an aluminum one.

I want it to be 12" deep by 32" wide. The mounting surface on the
arm is
5 3/4" x 5 1/2" and it would mount in the center back of the tray.

I'd like it to be reasonably rigid, but I'm not going to be leaning
on
it with my upper body weight. I'd like to put a 1/4" - 3/8" bend in
the
back to stop the keyboard/mouse from sliding off so that should help
give it some structure.

I'm not crazy about putting any other bracing on the bottom, as I
want
the top surface to be as close to my legs as possible.


- What grade+thickness of al? I'd like to keep it at max 1/8" if
possible.
- I was thinking of getting it anodized for a finish, but I'm not
set
on that.
- I'd like to tap holes (they can go the whole way through) and
mount
from underneath to have a flat surface, but countersunk bolts would
work.
KEYBOTRAY

1/16" 6061 should be fine, but making a 32" long bend in it without
warping it will be very difficult without expensive tools or
experience. I would bend 1" or larger aluminum angle into a U frame
and screw or rivet a flat sheet to it. Then the metal's strength and
stiffness will continue around the corners. If you bend up flanges the
discontinuous corners will flex.

Practice notching and bending the angle with short pieces to see how
big a gap and radius you need to keep it from cracking.

The pan will be substantially stiffer if you put shallow diagonal
creases across it. Look at large panels in a commercial air ducting
system.
http://www.cadalyst.com/files/cadaly...CrossBrake.jpg

jsw

On 9/29/2012 7:19 PM, Jim Wilkins wrote:

1/16" 6061 should be fine, but making a 32" long bend in it without
warping it will be very difficult without expensive tools or
experience. I would bend 1" or larger aluminum angle into a U frame
and screw or rivet a flat sheet to it. Then the metal's strength and
stiffness will continue around the corners. If you bend up flanges the
discontinuous corners will flex.

Practice notching and bending the angle with short pieces to see how
big a gap and radius you need to keep it from cracking.

The pan will be substantially stiffer if you put shallow diagonal
creases across it. Look at large panels in a commercial air ducting
system.
http://www.cadalyst.com/files/cadaly...CrossBrake.jpg

jsw



I'd go the other way. Maybe a little thicker - .080?
Make form blocks and deep form the lip by hand.

I've done instrument panels that way up to 3/4" deep flange.

It takes repeated annealing to work 6061 that deep. but it works
well and looks really good.

"Richard" wrote in message
m...
On 9/29/2012 7:19 PM, Jim Wilkins wrote:

I'd go the other way. Maybe a little thicker - .080?
Make form blocks and deep form the lip by hand.

I've done instrument panels that way up to 3/4" deep flange.

It takes repeated annealing to work 6061 that deep. but it works
well and looks really good.

You and I know how from experience, but what did your first attempt
look like?
jsw

On 9/29/2012 8:00 PM, Jim Wilkins wrote:
wrote in message
m...
On 9/29/2012 7:19 PM, Jim Wilkins wrote:

I'd go the other way. Maybe a little thicker - .080?
Make form blocks and deep form the lip by hand.

I've done instrument panels that way up to 3/4" deep flange.

It takes repeated annealing to work 6061 that deep. but it works
well and looks really good.

You and I know how from experience, but what did your first attempt
look like?
jsw



This was my first attempt - the gas tank.

http://www.home.earthlink.net/~cave-2/

I think it came out pretty nice.

Truth is, a bit of patience works wonders.

Richard

"Richard" wrote in message
m...
On 9/29/2012 8:00 PM, Jim Wilkins wrote:

You and I know how from experience, but what did your first attempt
look like?
jsw

This was my first attempt - the gas tank.
http://www.home.earthlink.net/~cave-2/
I think it came out pretty nice.
Truth is, a bit of patience works wonders.
Richard

It DID come out nice, and the photo sequence is much more helpful than
a brief text description.

How did you seal the joints and rivet holes?

I bought an open-topped stainless tank of similar riveted construction
with soldered joints that had failed all around, then were puttied
with some goop that also leaked. I finally cut it up to make
stovepipe:
https://picasaweb.google.com/KB1DAL/...71642404646402
The narrow hammered flange under the clamps determines its roundness
and the fit into unyielding double-wall Class A chimney pipe. I don't
think I could properly explain how I fine-tuned the snug fit here in
text. It comes down to learning the difference between a blow that
bends the metal and one that also stretches it.

jsw

On Sun, 30 Sep 2012 06:38:18 -0400, "Jim Wilkins"
wrote:


"Richard" wrote in message
om...
On 9/29/2012 8:00 PM, Jim Wilkins wrote:

You and I know how from experience, but what did your first attempt
look like?
jsw

This was my first attempt - the gas tank.
http://www.home.earthlink.net/~cave-2/
I think it came out pretty nice.
Truth is, a bit of patience works wonders.
Richard

It DID come out nice, and the photo sequence is much more helpful than
a brief text description.

How did you seal the joints and rivet holes?

I bought an open-topped stainless tank of similar riveted construction
with soldered joints that had failed all around, then were puttied
with some goop that also leaked. I finally cut it up to make
stovepipe:
https://picasaweb.google.com/KB1DAL/...71642404646402
The narrow hammered flange under the clamps determines its roundness
and the fit into unyielding double-wall Class A chimney pipe. I don't
think I could properly explain how I fine-tuned the snug fit here in
text. It comes down to learning the difference between a blow that
bends the metal and one that also stretches it.

I think you defined it just fine. That knowledge is the "art" portion
of "skill."

your Ranger dust shield, Revere Ware Rides Again!

--
Never trouble another for what you can do for yourself.
-- Thomas Jefferson

On 9/30/2012 5:38 AM, Jim Wilkins wrote:

wrote in message
m...
On 9/29/2012 8:00 PM, Jim Wilkins wrote:

You and I know how from experience, but what did your first attempt
look like?
jsw

This was my first attempt - the gas tank.
http://www.home.earthlink.net/~cave-2/
I think it came out pretty nice.
Truth is, a bit of patience works wonders.
Richard

It DID come out nice, and the photo sequence is much more helpful than
a brief text description.

How did you seal the joints and rivet holes?

Thank you, Jim.

A friend welded it for me. I can weld steel,
But aluminum is a whole 'nother thing...


It comes down to learning the difference between a blow that
bends the metal and one that also stretches it.


That's it in a nutshell.

On 2012-09-29, KEYBOTRAY wrote:

I got myself a 'keyboard arm' (http://tinyurl.com/chtfdey) for my desk
and instead of paying $100 for their 'molded ABS tray'
(http://tinyurl.com/9hecxvz) I thought I'd make an aluminum one.

I want it to be 12" deep by 32" wide. The mounting surface on the arm is
5 3/4" x 5 1/2" and it would mount in the center back of the tray.

I'd like it to be reasonably rigid, but I'm not going to be leaning on
it with my upper body weight. I'd like to put a 1/4" - 3/8" bend in the
back to stop the keyboard/mouse from sliding off so that should help
give it some structure.

I'm not crazy about putting any other bracing on the bottom, as I want
the top surface to be as close to my legs as possible.

Hmm ... for fairly thin metal, you want a bend down about 1/4"
in the front to add to the rigidity, and to keep it from cutting into
your legs, you want another inch or two bent back parallel to the top.
Also, bend down about a quarter inch on each side to keep it from
bending just from the weight of your hands on the keyboard. (You
reality should have a wrist support designed into it to minimize carpal
tunnel syndrome. And you also want it rigid enough to handle the weight
of the hand on the mouse off to the side of the keyboard.

- What grade+thickness of al? I'd like to keep it at max 1/8" if
possible.

I would suggest 1/16" instead, with the additional bends I have
suggested. This will still be lighter than the 1/8" aluminum.

Or -- 1/4" aluminum with triangular pockets milled from the
bottom, leaving lots of stiffening ribs.

- I was thinking of getting it anodized for a finish, but I'm not set
on that.

Do so if it is not too expensive. It will protect it from
corrosion from wrist perspiration among other things.

- I'd like to tap holes (they can go the whole way through) and mount
from underneath to have a flat surface, but countersunk bolts would
work.

If you do the milled pockets, you can leave full thickness
"strong points" for the screws to thread into. Leave about a 1"
diameter circle for each screw to thread into.

I just put the keyboard in my lap as I lean back in a Lay-Z-Boy,
and have the monitor to my right on an arm. There is a pull-out shelf
(about 1/4" diameter chromed steel wire) to hold the keyboard when I am
not actually typing on it.

As far as the mouse goes, there is a Logitech Trackman trackball
which is Velcro mounted to the right arm of the chair.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Thanks everyone for the info!

I like the idea of 5052 for its tighter radius. My only concern with the reduced yield strength @ 1/16" would be accidental deformation in storage or use. I'm not a metal worker though (could you tell?) so maybe I'm worrying needlessly.

IIRC, a woodworker friend of mine said the shop next to his who he's on friendly terms with has a press brake, so I'll look into that.

Failing that, the idea of form bending it seems good to me but I can see the difficulty keeping it from warping. Richard - what were your forms made from? The resulting tank looks very nice but when the ends were done, they looked warped. In your case, they had the cylinder of the tank to flatten them, but I won't have any additional structure to rely on and I'd like the surface to be as flat as possible.

If I can't expect to get a flat surface from a form bend, I like Jim Wilkins' suggestion of getting angle stock, forming a U, and attaching it to the sheet.

On 10/3/2012 4:35 PM, KEYBOTRAY wrote:
Thanks everyone for the info!

I like the idea of 5052 for its tighter radius. My only concern with the
reduced yield strength @ 1/16" would be accidental deformation in
storage or use. I'm not a metal worker though (could you tell?) so maybe
I'm worrying needlessly.

IIRC, a woodworker friend of mine said the shop next to his who he's on
friendly terms with has a press brake, so I'll look into that.

Failing that, the idea of form bending it seems good to me but I can see
the difficulty keeping it from warping. Richard - what were your forms
made from? The resulting tank looks very nice but when the ends were
done, they looked warped. In your case, they had the cylinder of the
tank to flatten them, but I won't have any additional structure to rely
on and I'd like the surface to be as flat as possible.

Good eye.

The ends are bulged out just a bit to keep them from "oil canning" with
temperature changes. I rolled that in with a baseball.

The form blocks for the tank ends were simple 3/4" plywood.
One time tool. But they suffered a lot less damage than I had expected
and could have been used again - probably several times.

I believe that was because I was hammering on the aluminum block paddle
instead of the actual metal. That tends to spread the impact force out
over a much larger area that the hammer head.



If I can't expect to get a flat surface from a form bend, I like Jim
Wilkins' suggestion of getting angle stock, forming a U, and attaching
it to the sheet.



If you want this tray to remain flat, I'd suggest something heavier than
1/16". Maybe 1/8? Regardless of how you make the edges...

1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!

Okay, this is giving me confidence in forming it if the press doesn't pan out. If I went with a similar form of wood with a 2 * thickness radius (5052), how flat could I expect the resulting piece to be?

Yeah, that's what I figured from handling various metal objects in my life. Part of me just wants to get 1/2" plate and find a CNC machine and carve in ribs. Then the more wallet-y part of me punches that other part in the groin.

"Richard" wrote in message
m...

If you want this tray to remain flat, I'd suggest something heavier
than 1/16". Maybe 1/8? Regardless of how you make the edges...

1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!

I can't twist a 15" x 24" sheet of 0.093" Al significantly by hand. It
bends only a little when I imitate using it as a support to get up out
of the chair. The slides on my keyboard drawer aren't any stiffer.
jsw

KEYBOTRAY wrote:

'Richard[_9_ Wrote:
;2938093']Good eye.

The ends are bulged out just a bit to keep them from "oil canning" with

temperature changes. I rolled that in with a baseball.

The form blocks for the tank ends were simple 3/4" plywood.
One time tool. But they suffered a lot less damage than I had expected
and could have been used again - probably several times.


Okay, this is giving me confidence in forming it if the press doesn't
pan out. If I went with a similar form of wood with a 2 * thickness
radius (5052), how flat could I expect the resulting piece to be?

'Richard[_9_ Wrote:
;2938093']
If you want this tray to remain flat, I'd suggest something heavier than

1/16". Maybe 1/8? Regardless of how you make the edges...

1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!

Yeah, that's what I figured from handling various metal objects in my
life. Part of me just wants to get 1/2" plate and find a CNC machine and
carve in ribs. Then the more wallet-y part of me punches that other part
in the groin.



How about modifying a heavy aluminum food service pan? This pan is
15" * 21" and is under $7.

http://www.samsclub.com/sams/artisan-metal-works-2-3-size-aluminum-sheet-pan/prod6070159.ip

On Wed, 03 Oct 2012 23:36:01 -0500, Richard
wrote:

On 10/3/2012 4:35 PM, KEYBOTRAY wrote:
Thanks everyone for the info!

I like the idea of 5052 for its tighter radius. My only concern with the
reduced yield strength @ 1/16" would be accidental deformation in
storage or use. I'm not a metal worker though (could you tell?) so maybe
I'm worrying needlessly.

IIRC, a woodworker friend of mine said the shop next to his who he's on
friendly terms with has a press brake, so I'll look into that.

Failing that, the idea of form bending it seems good to me but I can see
the difficulty keeping it from warping. Richard - what were your forms
made from? The resulting tank looks very nice but when the ends were
done, they looked warped. In your case, they had the cylinder of the
tank to flatten them, but I won't have any additional structure to rely
on and I'd like the surface to be as flat as possible.

Good eye.

The ends are bulged out just a bit to keep them from "oil canning" with
temperature changes. I rolled that in with a baseball.

The form blocks for the tank ends were simple 3/4" plywood.
One time tool. But they suffered a lot less damage than I had expected
and could have been used again - probably several times.

I believe that was because I was hammering on the aluminum block paddle
instead of the actual metal. That tends to spread the impact force out
over a much larger area that the hammer head.



If I can't expect to get a flat surface from a form bend, I like Jim
Wilkins' suggestion of getting angle stock, forming a U, and attaching
it to the sheet.



If you want this tray to remain flat, I'd suggest something heavier than
1/16". Maybe 1/8? Regardless of how you make the edges...

1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!


Not 6061T6

On Thu, 4 Oct 2012 09:06:47 +0000, KEYBOTRAY
wrote:


1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!

Yeah, that's what I figured from handling various metal objects in my
life. Part of me just wants to get 1/2" plate and find a CNC machine and
carve in ribs. Then the more wallet-y part of me punches that other part
in the groin.


Been there...done that...still have the curled over stagger

VBG

Gunner

--
You just opened the window for a glimpse at the liberal mindset. You
people think, for some unknown reason, that since you are infinitely
more "intelligient" than the "average" citizen then it's not only your
God given right, but a responsibilty to tell everyone else how they
should live, spend their money, what to eat, what to drive, how much
to eat and drink and what to set your thermostat to. Of course, those
same rules don't apply to you because you, being a highly educated
individual with a degree in the "arts", don't have to abide by those
same rules. Thank GOD you are in the minority.
"Robert Westergrom"

On 10/4/2012 4:16 PM, wrote:
On Wed, 03 Oct 2012 23:36:01 -0500,
wrote:

On 10/3/2012 4:35 PM, KEYBOTRAY wrote:
Thanks everyone for the info!

I like the idea of 5052 for its tighter radius. My only concern with the
reduced yield strength @ 1/16" would be accidental deformation in
storage or use. I'm not a metal worker though (could you tell?) so maybe
I'm worrying needlessly.

IIRC, a woodworker friend of mine said the shop next to his who he's on
friendly terms with has a press brake, so I'll look into that.

Failing that, the idea of form bending it seems good to me but I can see
the difficulty keeping it from warping. Richard - what were your forms
made from? The resulting tank looks very nice but when the ends were
done, they looked warped. In your case, they had the cylinder of the
tank to flatten them, but I won't have any additional structure to rely
on and I'd like the surface to be as flat as possible.

Good eye.

The ends are bulged out just a bit to keep them from "oil canning" with
temperature changes. I rolled that in with a baseball.

The form blocks for the tank ends were simple 3/4" plywood.
One time tool. But they suffered a lot less damage than I had expected
and could have been used again - probably several times.

I believe that was because I was hammering on the aluminum block paddle
instead of the actual metal. That tends to spread the impact force out
over a much larger area that the hammer head.



If I can't expect to get a flat surface from a form bend, I like Jim
Wilkins' suggestion of getting angle stock, forming a U, and attaching
it to the sheet.



If you want this tray to remain flat, I'd suggest something heavier than
1/16". Maybe 1/8? Regardless of how you make the edges...

1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!


Not 6061T6

Yeah, 6061 T6 even.
A piece that size can easily be twisted out of flat.

"Richard" wrote in message
m...
On 10/4/2012 4:16 PM, wrote:
On Wed, 03 Oct 2012 23:36:01 -0500,
wrote:

On 10/3/2012 4:35 PM, KEYBOTRAY wrote:
Thanks everyone for the info!


1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!

Not 6061T6

Yeah, 6061 T6 even.
A piece that size can easily be twisted out of flat.

1/16" Al diamond plate bends more easily than I'd want for an
unreinforced keyboard shelf, though it might be acceptable. Pressure
on the keyboard will transfer to the plate at the feet under the ends
where the plate is better supported by end flanges.

I would first determine the maximum length and gauge that the brake
can bend, then see what thickness of aluminum is available in cut
pieces at what price. You can adjust the stiffness in the design. The
fuselage ribs of a B-17 bomber are only 0.040" thick.
jsw

On Thu, 04 Oct 2012 17:45:47 -0500, Richard
wrote:

On 10/4/2012 4:16 PM, wrote:
On Wed, 03 Oct 2012 23:36:01 -0500,
wrote:

On 10/3/2012 4:35 PM, KEYBOTRAY wrote:
Thanks everyone for the info!

I like the idea of 5052 for its tighter radius. My only concern with the
reduced yield strength @ 1/16" would be accidental deformation in
storage or use. I'm not a metal worker though (could you tell?) so maybe
I'm worrying needlessly.

IIRC, a woodworker friend of mine said the shop next to his who he's on
friendly terms with has a press brake, so I'll look into that.

Failing that, the idea of form bending it seems good to me but I can see
the difficulty keeping it from warping. Richard - what were your forms
made from? The resulting tank looks very nice but when the ends were
done, they looked warped. In your case, they had the cylinder of the
tank to flatten them, but I won't have any additional structure to rely
on and I'd like the surface to be as flat as possible.

Good eye.

The ends are bulged out just a bit to keep them from "oil canning" with
temperature changes. I rolled that in with a baseball.

The form blocks for the tank ends were simple 3/4" plywood.
One time tool. But they suffered a lot less damage than I had expected
and could have been used again - probably several times.

I believe that was because I was hammering on the aluminum block paddle
instead of the actual metal. That tends to spread the impact force out
over a much larger area that the hammer head.



If I can't expect to get a flat surface from a form bend, I like Jim
Wilkins' suggestion of getting angle stock, forming a U, and attaching
it to the sheet.



If you want this tray to remain flat, I'd suggest something heavier than
1/16". Maybe 1/8? Regardless of how you make the edges...

1/16" thick that size can easily be twisted out of flat by hand.
Even with flanges!


Not 6061T6

Yeah, 6061 T6 even.
A piece that size can easily be twisted out of flat.
With any kind of a bend on the 4 sides, 1/16 is plenty. I used 1/8
inch as a skid pan on the rallye car, and it never got even a DENT in
it. - lots of scrapes though.