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'[EE]: Drilling a square tube??'
2001\10\15@110950 by Roman Black

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face
Hi, I know this is more of a mech engineering
question than an EE one, but here goes. :o)

I need to drill a square tube, hardened aluminium,
to make it as LIGHT as possible. The square tube
is 25mm across each edge, and used on a racing
motorcycle for a non-critical purpose, ie it's
not part of the drivechain!! It's about 1.2mm
thickness wall (25mm x 25mm x 1.2mm) if that
helps.

From my rather "fuzzy logic" examination of the
stucture the square tubing is not stressed under
flexion, but it will be exposed to compression
and expansion forces, so there is nothing to bend
it, but it needs good strength for compressing
and stretching forces... ;o)

I'm not after formulae as the problem is slightly
more complex than what I have posted, but any
general ground rules and "reasons why" will be
really appreciated.

Do we drill the tubing with large diameter
holes, or lots of small holes, and why/how
will each method give the BEST STRENGTH for
the MAX amount of weight lost???

Thanks guys! :o)
-Roman

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2001\10\15@113037 by Douglas Butler

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If the aluminum is tempered the edge of each hole will lose some of its
tempering when drilled.  That means each hole will have a ring of weak
soft aluminum around it.  This leans me towards fewer bigger holes.
Also drill slowly with a sharp drill.

Sherpa Doug

> {Original Message removed}

2001\10\15@115028 by Roman Black

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face
Thanks Doug, but the hardening is not at all
the problem here. The tubing can be re-hardened
at any time by heating and cooling at the correct
rate etc.

I'm more interested in finding out if it is better
to drill a lot of small holes, (like a honeycomb)
or a few larger ones, and what will give better
strength for the same final weight of tubing. :o)
-Roman


Douglas Butler wrote:
>
> If the aluminum is tempered the edge of each hole will lose some of its
> tempering when drilled.  That means each hole will have a ring of weak
> soft aluminum around it.  This leans me towards fewer bigger holes.
> Also drill slowly with a sharp drill.
>
> Sherpa Doug
>
> > {Original Message removed}

2001\10\15@122222 by Madhu Annapragada

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From a stress concentration point of view, the stresses around an aperture
are directly proportional to the circumference of the opening; so having
many small holes or a few large holes will end up with the same overall
stress concentration in the beam as long as the sum total of all the
circumferences is the same. Of course the more your stress concentration,
the more the chances of the member failing under long term fatigue. Now if
you want to spread your stress concentrations around then drill a lot of
small holes which will give you a lower stress at any one aperture (so you
spread your bets around).
Madhu
PS: If you really want to, call up an applications engineer at one of the
companies that make material test equipment like MTS (http://www.mts.com)
(Telephone: 952-937-4000). These guys do this sort of an analysis for living
and they will be able to tell you right off the bat which is better.

-----Oriinal Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of Roman Black
Sent: Monday, October 15, 2001 11:48 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: Re: [EE]: Drilling a square tube??


Thanks Doug, but the hardening is not at all
the problem here. The tubing can be re-hardened
at any time by heating and cooling at the correct
rate etc.

I'm more interested in finding out if it is better
to drill a lot of small holes, (like a honeycomb)
or a few larger ones, and what will give better
strength for the same final weight of tubing. :o)
-Roman


Douglas Butler wrote:
>
> If the aluminum is tempered the edge of each hole will lose some of its
> tempering when drilled.  That means each hole will have a ring of weak
> soft aluminum around it.  This leans me towards fewer bigger holes.
> Also drill slowly with a sharp drill.
>
> Sherpa Doug
>
> > {Original Message removed}

2001\10\15@122851 by Don Hyde

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Well, I have no idea how to optimize it, but I'm building an airplane from a
kit and have had to cut a bunch of lightening holes in aluminum.

They are always as large as possible, with the edges of the holes going to
within about 10-15% of the edge of the part, with similar amount of material
between the  holes.

As I understand it, the loss of hardness around the hole is a plus because
it helps to release stress concentrations.

The airplane instructions stress again and again that it is necessary to
make sure that the edges of all holes be very smooth, as any nicks, gouges
or sharp edges will create stress concentrations which can initiate
cracking.

> {Original Message removed}

2001\10\15@123447 by Bob Ammerman

picon face
Roman,

Since you are interested in compresion / extension and not bending or
torsional strength you might be better off with long slots than round holes.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

----- Original Message -----
From: "Roman Black" <fastvidspamKILLspamEZY.NET.AU>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Monday, October 15, 2001 11:47 AM
Subject: Re: [EE]: Drilling a square tube??


{Quote hidden}

> > > {Original Message removed}

2001\10\15@130209 by Roman Black

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face
Bob Ammerman wrote:
>
> Roman,
>
> Since you are interested in compresion / extension and not bending or
> torsional strength you might be better off with long slots than round holes.


Bob, thanks for the input, but how the heck
are we supposed to drill elongated slots??
We have lots of time and labour, but very
limited equipment and budget.
:o)
-Roman

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2001\10\15@131433 by Stephen Webb

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> Bob, thanks for the input, but how the heck
> are we supposed to drill elongated slots??
> We have lots of time and labour, but very
> limited equipment and budget.
> :o)
> -Roman

Not sure how it applies to working with metal, but in woodworking it is
common to drill two holes at the ends, and thread a saw blade (scroll saw,
for instance) through the holes, and start cutting.  A fence helps make
the lines straight.

Maybe a "sabre saw" would work?  Clean up the edges with a file?

Build a PIC controlled laser cutter? :)

-Steve

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2001\10\15@131847 by Batchellor, Gary

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There is a tool commonly called a nibbler, they come in air powered,
electric and hand. They fit through a hole and cut square edges in sheet
metal. Don't know the price exactly but here in U.S. they cost around $60 or
so for hand ones, $200 and up for powered. I'm in Wichita and this is
aircraft central so this are fairly easy to find here. (commonly used in
aircraft construction, instrument panels, etc.). You may have to find an
industrial supply house to find one near you.

{Original Message removed}

2001\10\15@133152 by Bob Ammerman

picon face
On a milling machine, of course ;-)

But, you can approximate the effect by the arrangement of your holes,
perhaps something like this:

* * * * *    * * * * *   * * * * *   * * * * *
* * * * *    * * * * *   * * * * *   * * * * *

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\10\15@134021 by Roman Black

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face
Batchellor, Gary wrote:
>
> There is a tool commonly called a nibbler, they come in air powered,
> electric and hand. They fit through a hole and cut square edges in sheet
> metal. Don't know the price exactly but here in U.S. they cost around $60 or
> so for hand ones, $200 and up for powered. I'm in Wichita and this is
> aircraft central so this are fairly easy to find here. (commonly used in
> aircraft construction, instrument panels, etc.). You may have to find an
> industrial supply house to find one near you.


Thanks Gary, and also to Steve Webb, I do own a
nibbler but this is not the issue. The square tubing
is a fair size, 25mm x 25mm (x 1.2mm wall) by many
linear inches in the motorcycle's rear subframe.

It will be fairly easy to DRILL full of holes
with the equipment we have, and what I really
am asking is the best way to drill it for max
weight savings and max retained strength, in the
compression and tension axes.

Do we drill for a few large holes, nearing the
size of the tube, or a lot of small holes, like
"honeycombing" each flat wall of the square tube??
-Roman

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2001\10\15@134555 by Roman Black

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Bob Ammerman wrote:
>
> On a milling machine, of course ;-)
>
> But, you can approximate the effect by the arrangement of your holes,
> perhaps something like this:
>
> * * * * *    * * * * *   * * * * *   * * * * *
> * * * * *    * * * * *   * * * * *   * * * * *


Thanks Bob, now we are getting somewhere. :o)

Using my "very fuzzy logic" brain, what you
are proposing is a hole structure with minimised
walls between holes in the left-right direction.
So it doesn't matter whether we have groups of
5 holes (as you drew) or just reduced the distance
left-right between each hole, you are suggesting
that the tension/compression strengths remain
similar??

In some other commercially drilled members i've
seen something like this:

---------------------------
* * * * * * * * * * * * * *
* * * * * * * * * * * * *
---------------------------

on each side wall of the square tubing, which
makes sense to me for a number of reasons.
Any suggestions?
-Roman

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2001\10\15@135028 by Douglas Butler

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Can you beg, borrow, or steal a carpentry router?  You should be able to
cut thin aluminum with a carbide carpentry bit.

I still think big holes are the way to go if only because that is what I
have seen on aircraft.

Sherpa Doug

> {Original Message removed}

2001\10\15@141758 by Josh Koffman

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face
Why not drill a bunch of holes the same diameter of the slot, right next
to each other, then using a dremel with a cutting wheel connect the
holds into a big slot. Then switch your dremel to a grinding wheel and
clean up the edges?

Josh Koffman

Stephen Webb wrote:
{Quote hidden}

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2001\10\15@142358 by Bob Ammerman

picon face
I think that you can space the holes very close together in the right-left
direction, if you leave occasional stronger areas (as represented by the
spaces in my drawing below) to make sure that the remaining thin strips
don't bend out of shape under a compression load.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\10\15@142611 by John Ferrell

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face
I would think that the distribution of the stress vectors would dictate the
size of the holes.

I would guess it is not the holes that are important, it is the
size/location of what ever is left?

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



{Original Message removed}

2001\10\15@145521 by Roman Black

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John Ferrell wrote:
>
> I would think that the distribution of the stress vectors would dictate the
> size of the holes.
>
> I would guess it is not the holes that are important, it is the
> size/location of what ever is left?


Hi John, please explain, we are fairly smart
at most stuff but drilling holes in our expensive
race motorcycles is a bit intimidating. :o}

I understand that the bit left over is the
important bit, so if you were to personally drill
holes in your expensive motorcycle's subframe,
would you drill a lot of small holes or a few
larger holes??

Assuming all the members are square tubing that
is exposed to compression/extension forces, and
you have to drill the holes yourself in a fairly
expensive frame, what are the basic guidelines??

Do you drill mainly in the "middle" of the
sidewall, leaving the corners of the extruded
square tube for strength, or drill right to the
edges of the square tubing for max weight loss??

I've appreciated everyone's input, but really
we're the poor fools that have to drill the heck
out of something that we then have to ride at
260kph... :o)
-Roman

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2001\10\15@145736 by Dave King

picon face
>It will be fairly easy to DRILL full of holes
>with the equipment we have, and what I really
>am asking is the best way to drill it for max
>weight savings and max retained strength, in the
>compression and tension axes.
>
>Do we drill for a few large holes, nearing the
>size of the tube, or a lot of small holes, like
>"honeycombing" each flat wall of the square tube??
>-Roman

You want round holes drilled along the longitudinal axis
of each face of the tubing. ie down the middle. You don't
want them any bigger  than about about 2/3-3/4 of the
face width. You also want them 1/2 to 1.5 dia apart.
If you can chamfer the edges that will help. Make sure
there are no nicks or notches around the holes (stress risers)
and you won't have problems.

If you knew the loads you can figure out how swiss
cheesy you can get away with. Without that and the calcs
you can drill the holes and then watch the part. If it deflects
or you can put a straight edge on it and its bent you
made it too cheesey. On square tubing the load paths
are in the corners (roughly) depending on the total load.

Dave

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2001\10\15@150807 by Olin Lathrop

face picon face
> Bob, thanks for the input, but how the heck
> are we supposed to drill elongated slots??

With elongated drill bits ;-)


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, EraseMEolinspam_OUTspamTakeThisOuTembedinc.com, http://www.embedinc.com

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2001\10\15@151430 by hard Prosser

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For My 2c worth! I'd go along with John.

The tensile strength is going to be that of the smallest cross section area
left after you've cut away the holes. Therefore, in order to minimise the
weight you need to work out how much tensile strength you are going to need
(with a safety factor)  and remove metal leaving only as much as is
required. (The strength of a chain theorem). To maximise the metal removed,
a combination of large holes or slots and some small holes may be optimal.
If you are also worried about compression, smaller holes may be preferable
to slots  (or larger holes ?) to minimise the possibility of any  lateral
forces causing buckling.


Richard P




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I would think that the distribution of the stress vectors would dictate the
size of the holes.

I would guess it is not the holes that are important, it is the
size/location of what ever is left?

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



{Original Message removed}

2001\10\15@152217 by Andrew Warren

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Roman Black <KILLspamPICLISTKILLspamspammitvma.mit.edu> wrote:

> we're the poor fools that have to drill the heck out of something
> that we then have to ride at 260kph... :o)

Roman:

Here's my input.  Your aluminum tube weighs about 1 pound per foot of
length; assuming that it's 3 feet long, even removing HALF of its
weight will only save about 2 pounds. Hell, even removing ALL of it
will only save THREE pounds.

Seems to me that it'd be much easier (and safer) to take three pounds
off the hero riding the bike than to take weight off this presumably-
important (else it wouldn't even be on the bike) component.

Have your rider drink one less pint of water before the race --
that's a pound.  Spend a couple-hundred dollars more for a lighter
helmet/boots/armor -- that's another pound or two.  Don't fill the
tank all the way if you don't need to.

The risk you're taking by weakening this component of your bike seems
WAY out of proportion to the potential benefit.

Just my opinion, I could be wrong.

-Andy


=== Andrew Warren -- RemoveMEaiwTakeThisOuTspamcypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2001\10\15@153749 by Roman Black

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Thanks Andy, everyone is already on a diet! :o)

But motorcycle weight is like financial planning,
every few grams seems totally stupid by itself
but when added up at the end of the day makes a
major and important change in the balance of
performance.

Going by your input we would have a steel frame
and aluminium wheels, because heck, the rider can
just drink less... ;o)

Really, we already have magnesium wheels, mag
(and some plastic) engine covers, hardened alloy
chain sprockets, a few grams removed from everything
we possibly can, this frame section holds the
rider's weight, so the forces are fairly safe and
predictable, how can we drill the heck out of it
to remove the most possible grams of wasted
aluminium??? :o)
-Roman


Andrew Warren wrote:
{Quote hidden}

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2001\10\15@160155 by David P. Harris

picon face
Hi-
Sounds like a solved engineering problem.  I will ask a friend for you.  If
the circumference thing was right, this would suggest large holes, as the
area goes up by the square, while the circumference goes up linearly.
David

Roman Black wrote:

{Quote hidden}

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2001\10\15@164454 by Andrew Warren

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Roman Black <RemoveMEPICLISTspamTakeThisOuTmitvma.mit.edu> wrote:

> motorcycle weight is like financial planning, every few grams seems
> totally stupid by itself but when added up at the end of the day
> makes a major and important change in the balance of performance.
>
> how can we drill the heck out of it to remove the most possible
> grams of wasted aluminium???

Roman:

Ok, if you really ARE at the point where a) every few grams will make
a difference, and b) you've removed all the weight you can from other
areas of the bike/rider, then I'd advise getting an FEA (finite
element analysis) program and using it to decide what you need and
what you can cut away... At this point, everything that's still on
the bike is there for a reason, and it would be foolish to start
cutting and drilling without doing some real analysis first.

I was kinda lucky when I was doing this sort of thing -- the Nissan
IMSA GTP team was just down the road from my house, so there were
people nearby who were willing to run my simple pieces through their
high-powered FEA systems for free -- but you can do what you need
with a relatively low-priced PC-based FEA package.  Algor's FEA
programs, for instance, are quite good.

If you can't afford Algor, your local university may have an FEA
setup that you can use; one of the engineers with whom I worked on an
SCCA car enrolled in a mechanical-engineering class at UCLA just so
he could use the computers in their lab.

-Andrew

P.S.  If you haven't already, read Carroll Smith's "Tune to Win",
     "Prepare to Win", and "Engineer to Win" (and his "Nuts, Bolts,
     and Fasteners Handbook", aka "Screw to Win").  They're written
     with auto racing in mind, but the information within them
     applies to all forms of motorsport.  Truly EXCELLENT books
     that, along with Keith Code's "Twist of the Wrist" series,
     should be required reading for all racers.


=== Andrew Warren -- aiwEraseMEspam.....cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2001\10\15@173940 by Anthony Bussan

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I have often seen woodworking routers and other tools used to cut aluninum.
By the way, a brave soul can cut 2 inch aluninum plate with a hand held
circular saw.

Tony

{Original Message removed}

2001\10\15@183606 by Dave King

picon face
At 04:29 PM 10/15/01 -0500, you wrote:
>I have often seen woodworking routers and other tools used to cut aluninum.
>By the way, a brave soul can cut 2 inch aluninum plate with a hand held
>circular saw.
>
>Tony
We cut up to about 3/4" 7075 and 6061-T6 plate with a table saw and a
good carbide blade. The only thing you have to watch for is the feed rate.
Once you get that down this leaves a surface that take a few swipes of a
file to debur. As long as you use carbide tipped tools you can get away
with using woodworking tools.

Dave

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2001\10\15@232700 by Bob Ammerman

picon face
Do you worry about the chips getting into the bearings, etc of the tools?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\10\16@011130 by Anthony Bussan

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It's never been an issue so far :)  My assumtion is that the motor is
designed to avoid consuming too much dust, so it doesn't suck in too much
aluminum either.  I've even run storm windows that were 1/16" too long
across the jointer.

Tony

{Original Message removed}

2001\10\16@032101 by Roman Black

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Andrew Warren wrote:
{Quote hidden}

Excellent help, thanks Andrew! :o)
I'll look for a FEA type program.
-Roman

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