[T i m]

Hi All,

I am trying to make a lift_and_slide_away storage system for my
Daughters 88 key MIDI keyboard.

So you can get an idea re the bigger picture I'll try to describe what
I have so far the best I can.

It's based around a 2' length of 3/8" diameter SS bar, held solidly by
two sailing dinghy rudder fitting (gudgeon) at either end ..

http://marinestore.co.uk/page/mrst/P...ings/PLB42519/

... to the underside of the front right hand edge of her workbench (so
it looks like a towel rail, sorta like this but with a SS bar g).

http://direct.tesco.com/q/R.100-4259.aspx

We then have a keyboard sized piece of MDF (so ~ 9" x 4'), also with a
pair of gudgeon fittings on the (left hand) end and these are also
threaded onto the same bar (forming a long pivot / 'sliding hinge'
assembly).

With the keyboard base in the horizontal position, one end joined to
her bench on this pivot / bar the other end on a stand (yet decided)
the keyboard is then placed on top, secured with Velcro so it can be
taken away if needed elsewhere.

If she then sits at her desk the keyboard is at the same level as the
desk and running down the right hand side of her (and her room) now
looking like a mini music studio. ;-)

When she is finished using the keyboard the idea is she lifts up the
right hand end of the keyboard (+ it's base, like a public bar door
top) till the keyboard is nearly in the vertical position, then slides
it back along the 'hinge' until it gets to the wall where it will rest
in a suitable stop / support (design yet to be finalised).

I have currently got this all clamped up for testing but have found
the 3/8" SS bar is quite 'springy', allowing the fairly heavy keyboard
+ base assembly to wobble / bounce about a bit whilst it's being slid
back (but it's ok when in the 'play' position).

But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?

Also, if not stainless is there anything else that could be used that
would make a nice sliding 'hinge' do you think please (and I don't
really want to re-design it all. e.g. silver steel, would that go
rusty?) ;-(

I *might* be able to open the nylon inserts up in the ends of the
gudgeons and use a larger diameter rod / bar (I would drill / bore
them out in pairs to maintain concentricity).

All the best and thanks for your time ..

T i m

[Ian Stirling]

T i m wrote:
Hi All,

Beeeg snip

Of the same material, exterior dimensions, and conditioning - no.
For the same weight, given the above, yes.

An important thing to know is that all steels have the same amount of
springyness - pretty much, up to a limit, depending on the alloying, and
heat treatment.
Once it gets past this limit for mild steel, it starts to bend
permenantly.
The key to better steels is that they will bend permenantly only at
higher loads.

[Guy King]

The message
from T i m contains these words:

But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?

No. Tube is stiffer per weight, but not stiffer per diameter. The only
way to make it stiffer is to use a stiffer metal or a larger diameter or
a different geometry.

--
Skipweasel
Pay no attention to that man behind the curtain.

[T i m]

On Tue, 28 Nov 2006 21:14:14 GMT, Guy King
wrote:

The message
from T i m contains these words:

But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?

No. Tube is stiffer per weight, but not stiffer per diameter. The only
way to make it stiffer is to use a stiffer metal or a larger diameter or
a different geometry.

Hmm, thanks 'guys' g and that makes sense (now I think about it).

Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube (I'm guessing it would still be a
function of the overall x sectional area)? This probably sounds like a
perpetual motion question ;-)

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

All the best ..

T i m

[Autolycus]

"T i m" wrote in message
...

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

Stiffness is proportional to the fourth power of diameter for a round
beam in bending, so 3/8 to 1/2 inch is a factor of 4^4/3^4, or 256/81,
or 3 and a bit, as we engineers say (or pi, or root 10).


--
Kevin Poole
**Use current month and year to reply (e.g. )***

[Guy King]

The message
from T i m contains these words:

Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube

Better, but still not as stiff as solid.

--
Skipweasel
Pay no attention to that man behind the curtain.

[Tony Bryer]

On Tue, 28 Nov 2006 22:02:41 GMT T i m wrote :
Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube (I'm guessing it would still be a
function of the overall x sectional area)? This probably sounds like a
perpetual motion question ;-)

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

For a solid bar, stiffness is proportional to D^4, bending strength (in
simple terms) to D^3 and weight to D^2. For a tube substitute D^x -d^x
where D is the OD and d the ID.

So if your tubes are of 1/16" material the numbers are (work in 1/16" for
ease of calculation)

3/8: Stiffness 6^4-4^4: 1040 Weight 20 Stiffness/weight 50.2
1/2: Stiffness 8^4-6^4: 2800 Weight 28 Stiffness/weight 100.0

But it's not quite as simple as just making it as big and thin as
possible as you reach a point where the tube buckles before its
theoretical strength is reached.

Note that no reliance should be placed on any calculations done at this
time of night g

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

[T i m]

On Tue, 28 Nov 2006 22:49:39 -0000, "Autolycus"
wrote:


"T i m" wrote in message
.. .

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

Stiffness is proportional to the fourth power of diameter for a round
beam in bending, so 3/8 to 1/2 inch is a factor of 4^4/3^4, or 256/81,
or 3 and a bit, as we engineers say (or pi, or root 10).

Ah, cheers!

So (just to make sure understand your results) the 1/2" bar will be
~3x stiffer than the 3/8" one ??

All the best ..

T i m

[T i m]

On Tue, 28 Nov 2006 22:51:05 GMT, Guy King
wrote:

The message
from T i m contains these words:

Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube

Better, but still not as stiff as solid.

Doh! ;-)

All the best and thanks (again) ..

T i m

[T i m]

On Tue, 28 Nov 2006 23:05:52 GMT, Tony Bryer
wrote:

On Tue, 28 Nov 2006 22:02:41 GMT T i m wrote :
Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube (I'm guessing it would still be a
function of the overall x sectional area)? This probably sounds like a
perpetual motion question ;-)

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

For a solid bar, stiffness is proportional to D^4, bending strength (in
simple terms) to D^3 and weight to D^2. For a tube substitute D^x -d^x
where D is the OD and d the ID.

So if your tubes are of 1/16" material the numbers are (work in 1/16" for
ease of calculation)

3/8: Stiffness 6^4-4^4: 1040 Weight 20 Stiffness/weight 50.2
1/2: Stiffness 8^4-6^4: 2800 Weight 28 Stiffness/weight 100.0

But it's not quite as simple as just making it as big and thin as
possible as you reach a point where the tube buckles before its
theoretical strength is reached.

Note that no reliance should be placed on any calculations done at this
time of night g

lol.

Thanks and all the best ..

T i m

[Guy King]

The message
from "Autolycus" contains these words:

Stiffness is proportional to the fourth power of diameter for a round
beam in bending, so 3/8 to 1/2 inch is a factor of 4^4/3^4, or 256/81,
or 3 and a bit, as we engineers say (or pi, or root 10).

In other words - make the tube a bit fatter and it'll be a /lot/ stiffer.

--
Skipweasel
Pay no attention to that man behind the curtain.

[Weatherlawyer]

Tony Bryer wrote:

work in 1/16" for ease of calculation.

I wonder if the imperial system is the reason why the British used to
seem so much more inventive than dago/gerry types.

I'm convinced that the love of the game fluxed out once metric became
the norm. I supposed it was just me getting older and jaded.

It would explain the inertia in the mature tradesmen when the switch
occurred. It wasn't just reluctance to change but revulsion at the
digitalising what has always been an analogue sport.

It might also explain why there is so much acceptance of dodgy
materials and techniques these days. This may seem kook territory to
some but there is a lot to it I feel.

With the imperial system you could think in terms of volume at the same
time as you were considering lengths and breadths.

[raden]

In message , Guy King
writes
The message
from T i m contains these words:

Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube

Better, but still not as stiff as solid.

But a lot lighter

and as for stiffness


--
geoff

[Guy King]

The message
from raden contains these words:

Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube

Better, but still not as stiff as solid.

But a lot lighter

True, but in this application it doesn't sound like weight matters much.

--
Skipweasel
Pay no attention to that man behind the curtain.

[Robert Laws]

Autolycus wrote:
"T i m" wrote in message
...

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

Stiffness is proportional to the fourth power of diameter for a round
beam in bending, so 3/8 to 1/2 inch is a factor of 4^4/3^4, or 256/81,
or 3 and a bit, as we engineers say (or pi, or root 10).


Did not the state of Kentucky once legislate that pi=3?.

Robert

[Guy King]

The message . com
from "Robert Laws" contains these words:

Did not the state of Kentucky once legislate that pi=3?.

In 1897, the Indiana General Assembly passed a bill from which it could
deduced that pi was equal to 3.2 or other incorrect values. The Indiana
Senate postponed the bill indefinitely, preventing it from becoming law.

--
Skipweasel
Pay no attention to that man behind the curtain.

[The Natural Philosopher]

T i m wrote:
Hi All,

I am trying to make a lift_and_slide_away storage system for my
Daughters 88 key MIDI keyboard.

So you can get an idea re the bigger picture I'll try to describe what
I have so far the best I can.

It's based around a 2' length of 3/8" diameter SS bar, held solidly by
two sailing dinghy rudder fitting (gudgeon) at either end ..

http://marinestore.co.uk/page/mrst/P...ings/PLB42519/

.. to the underside of the front right hand edge of her workbench (so
it looks like a towel rail, sorta like this but with a SS bar g).

http://direct.tesco.com/q/R.100-4259.aspx

We then have a keyboard sized piece of MDF (so ~ 9" x 4'), also with a
pair of gudgeon fittings on the (left hand) end and these are also
threaded onto the same bar (forming a long pivot / 'sliding hinge'
assembly).

With the keyboard base in the horizontal position, one end joined to
her bench on this pivot / bar the other end on a stand (yet decided)
the keyboard is then placed on top, secured with Velcro so it can be
taken away if needed elsewhere.

If she then sits at her desk the keyboard is at the same level as the
desk and running down the right hand side of her (and her room) now
looking like a mini music studio. ;-)

When she is finished using the keyboard the idea is she lifts up the
right hand end of the keyboard (+ it's base, like a public bar door
top) till the keyboard is nearly in the vertical position, then slides
it back along the 'hinge' until it gets to the wall where it will rest
in a suitable stop / support (design yet to be finalised).

I have currently got this all clamped up for testing but have found
the 3/8" SS bar is quite 'springy', allowing the fairly heavy keyboard
+ base assembly to wobble / bounce about a bit whilst it's being slid
back (but it's ok when in the 'play' position).

But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?


No. A tube is really just a rod with the heavy and low stressed material
removed.

Also, if not stainless is there anything else that could be used that
would make a nice sliding 'hinge' do you think please (and I don't
really want to re-design it all. e.g. silver steel, would that go
rusty?) ;-(


You MIGHT find a carbon fibre tube is a bit stiffer..3/8" is 10mm give
or take

Try here..

However its not a good bearing surface.

There are custom keyboard sliding mounts and the like made for 19" rack
use..

There are radio keyaboards...


For a cantilever, I'd be thinking more in terms of 1/2"-3/4" steel...

I *might* be able to open the nylon inserts up in the ends of the
gudgeons and use a larger diameter rod / bar (I would drill / bore
them out in pairs to maintain concentricity).

All the best and thanks for your time ..

T i m

[The Natural Philosopher]

T i m wrote:
On Tue, 28 Nov 2006 21:14:14 GMT, Guy King
wrote:

The message
from T i m contains these words:
But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?
No. Tube is stiffer per weight, but not stiffer per diameter. The only
way to make it stiffer is to use a stiffer metal or a larger diameter or
a different geometry.

Hmm, thanks 'guys' g and that makes sense (now I think about it).

Ok, on the geometry then (and this is probably a stupid thought) what
about a 'X' section inside a tube (I'm guessing it would still be a
function of the overall x sectional area)? This probably sounds like a
perpetual motion question ;-)

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

Think its broadly proportional to diameter squared..
I.e. the load ends up at a greater diameter spread over a greater area..

Hard steel drill shaft is the least resistant to bending..usually
stainlesl too.

And a total pig to cut. No saw will dio it - needs a grinder.

All the best ..

T i m

[T i m]

On Wed, 29 Nov 2006 13:38:26 +0000, The Natural Philosopher
wrote:


Think its broadly proportional to diameter squared..
I.e. the load ends up at a greater diameter spread over a greater area..

Ok ..

Hard steel drill shaft is the least resistant to bending..usually
stainlesl too.

And a total pig to cut. No saw will dio it - needs a grinder.

Tool steel or Stainless (I cut the 3/8 ss bar with a blunt hacksaw in
about 8 strokes?)?

All the best ..

T i m

[T i m]

On Wed, 29 Nov 2006 13:35:40 +0000, The Natural Philosopher
wrote:


But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?


No. A tube is really just a rod with the heavy and low stressed material
removed.

Nice description ;-)

Also, if not stainless is there anything else that could be used that
would make a nice sliding 'hinge' do you think please (and I don't
really want to re-design it all. e.g. silver steel, would that go
rusty?) ;-(


You MIGHT find a carbon fibre tube is a bit stiffer..3/8" is 10mm give
or take

I did think of carbon ..

Try here..

looks about Where? ;-)

However its not a good bearing surface.

I thought of that too. How about CF rod in a SS tube! ;-)

There are custom keyboard sliding mounts and the like made for 19" rack
use..

Yeah, I bought a couple of heavy roller draw slides for the MK1
version but the keyboard needs to be quite a long way out into her
room (so they would probably need to be multistage / telescopic and
I'd have to build something to mount them on etc .. (too many bits in
the room to do that easily) ;-(

There are radio keyaboards...

And there are smaller keyboards! The idea of getting this particular
instrument:

http://www.maudio.co.uk/products/en_...88sx-main.html

is because it has it's own built in voices and audio output (so can be
played live with just an amp) and USB / MIDI for connecting to a PC /
Mac. 88 full sized semi weighted keys mean you can play it like a real
piano (without running out of notes) ;-) But it's quite long so needed
to be 'hinged' away to fit in her packed box-room (or lifted away but
I wanted to keep it plugged in and ready for use).!


For a cantilever, I'd be thinking more in terms of 1/2"-3/4" steel...

Well this 3/8" is *ok* (as in work but not perfect) and if 1/2" is 3
times stiffer (if I understood things correctly?) then that should be
sufficient. 3/4" would probably be best of course (or even 5/8") but
possibly a bit over engineered and probably would require a complete
re-work. ;-(

All the best ..

T i m

[raden]

In message . com,
Robert Laws writes

Autolycus wrote:
"T i m" wrote in message
...

So, failing a 'yes' to the above, is there a simple formula (rule of
thumb) for how much 'stiffer' any particular steel would be for a
percentage increase in diameter please?

Say I go from 3/8 to 1/2" for example, would it be 25% or 33% or
something else stiffer?

Stiffness is proportional to the fourth power of diameter for a round
beam in bending, so 3/8 to 1/2 inch is a factor of 4^4/3^4, or 256/81,
or 3 and a bit, as we engineers say (or pi, or root 10).


Did not the state of Kentucky once legislate that pi=3?.

I think we're venturing into the realm of urban myth here IIRC

--
geoff

[The Natural Philosopher]

T i m wrote:
On Wed, 29 Nov 2006 13:35:40 +0000, The Natural Philosopher
wrote:


But it all works (so far) but I wondered if I could replace the SS bar
with *tube* (of the same diameter) and would that better / (stiffer)?

No. A tube is really just a rod with the heavy and low stressed material
removed.

Nice description ;-)
Also, if not stainless is there anything else that could be used that
would make a nice sliding 'hinge' do you think please (and I don't
really want to re-design it all. e.g. silver steel, would that go
rusty?) ;-(

You MIGHT find a carbon fibre tube is a bit stiffer..3/8" is 10mm give
or take

I did think of carbon ..
Try here..

looks about Where? ;-)

www.fibertechcgb.co.uk

[Aidan Karley]

In article , Raden wrote:

Did not the state of Kentucky once legislate that pi=3?.

I think we're venturing into the realm of urban myth here IIRC

Illinois, I thought, and the bill got to it's second reading
before someone with a trace of technical education heard the relevant
clauses and blew the gaff.

--
Aidan
Aberdeen, Scotland
Written at Thu, 30 Nov 2006 22:31 GMT, but posted later.